FE Power Forums
FE Power Forums => FE Technical Forum => Topic started by: Autoholic on July 29, 2015, 04:00:49 PM
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Looking through my collection of SOHC related stuff, I found an image of an article I once saved. It's rather hard to read at times (requires you to zoom in on the picture) but it is interesting. I will try to transcribe it in the next hour or so.
(https://lh3.googleusercontent.com/-8uLAcr38i2E/Vbk-OUVrJII/AAAAAAAABZk/rjaZ2hvPhAk/s576-Ic42/3970992719_e9e6e66da2_z.jpg)
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Here is the text from the article...
Despite the fact that both early and late Chrysler-powered cars have surpassed the SOHC Ford supremacy in dragster ranks, and that FoMoCo itself has all but abandoned their overhaed cammer in favor of their new 429 "Shotgun Motor", Pete Robinson is single-handedly waging a campaign to save the SOHC engine from obsolescence and extinction. This winter, Pete conducted an extensive independent research program on the SOHC Ford engine (in the supercharged fueler form). Utilizing the NASA-like dynamometer facility at Crane Engineering in Hallandale, Florida, Pete paced his blown 427 cammer (on alcohol) through 10 fact-finding "runups", and came up with lots of discovery data.
For some time Pete has felt that the long chain which drives the Ford's camshafts might be the culprit responsible for the SOHC's strange internal antics (i.e., one bank runs hotter than the other, one bank detonates before the other, different size port nozzles are required on different banks, etc.). However, just thinking that this might be the cause of the problem is not enough to justify the cost of building a non-flexing gear drive for the SOHC. This is one of the major reasons he went to Crane's, to examine the inherent problems in the valve timing characteristics of the chain-driven camshaft engine. The 'dyno-flog" at Crane Engineering seemed to substantiate his thoughts.
The manner in which the timing chain study was accomplished is quite ingenious, yet simple. Pete extended a shaft from each cam forward through the front of the valve covers, and a degree wheel to the front of each shaft. As the cams rotated, so did the degree wheels, and by utilizing a common strobe light, the advance and retard characteristics of the camshafts could be observed. Tests were conducted at three different rpm levels: 2000, 4000, and 6000 rpms; and within that span no less than eight degrees of variation was noted. This was attributed to a variable standing harmonic wave in the chain which differed with rpm, taking the cam from a dour degree advanced position to that of four degrees retarded. maximum rpm and maximum power outputs were not desired, so rpm was limited to 6000. However, since the SOHC engine in the AA/FD application operates between 5000 and 9000 rpm, Pete and the boys at Crane surmised that the camshaft timing variation could easily exceed eight degrees at these higher rpms, affecting the operation and horsepower output of the engine.
The standard "stock" chain -driven SOHC Ford has another odd idiosyncrasy in that, because the cams are rotated in the same direction, the cam lobes on one bank approach the intake rocker from below and the exhaust rocker from above, while on the opposite bank of the engine the cam lobes approach the intake rocker from above and the exhaust rocker arm from below. At first this may sound confusing, but the important thing is that the very same camshaft profile produces....
That's it on this image, it continues on another page that I don't have yet. This is from Car Craft, July 1969. I do not have the rest of this story and I'm rather interested in it, so I've purchased the issue. When I get it, I shall post the whole article up with high quality scans.
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"Sneaky Pete" was a pretty sharp guy, that's for sure. Here are a couple larger examples.
(http://i12.photobucket.com/albums/a232/jaredaebly/Mobile%20Uploads/3813287348_7394f72413_z_zpswzs1moxw.jpeg) (http://s12.photobucket.com/user/jaredaebly/media/Mobile%20Uploads/3813287348_7394f72413_z_zpswzs1moxw.jpeg.html)
(http://i12.photobucket.com/albums/a232/jaredaebly/Mobile%20Uploads/tinker-toy-dragster-engine_zpsvjfabamo.jpeg) (http://s12.photobucket.com/user/jaredaebly/media/Mobile%20Uploads/tinker-toy-dragster-engine_zpsvjfabamo.jpeg.html)
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I bought the issue and when I get it, I'll upload scans of it. I'm particularly interested in a SOHC gear drive. I only know of two designs, Pete's and another that was done like 10 years ago. I'm currently working on my own design that hopefully one day I'll be able to do when I build my own SOHC. My design would allow you to run it under the stock timing cover. It uses double helical gears for consistent, accurate timing combined with reliability and strength over a spur gear design, without having thrust loads normally seen in helical gears. Ball bearings would also prevent thrust loads and minimal friction in the idle gears. I've already worked out the size and some of the specs for the crank gear, large stub cam gear, small stub cam gear, cam gears and a pair of idle gears connecting the crank to the stub cam (Pete's uses 1 idle gear for this). The large and small stub cam gear would be one solid gear. I also know that my design would need a total of 12 gears. Just like with Pete's design, I would reverse the direction of one of the cams so this would mean custom cams. The reasons why I would go for this mainly rest on reliable cam timing (no chain stretch), no risk of the chain breaking since there isn't one, higher RPM stability and lastly, personal OCD issues of having the cams rotating the same direction when they should be opposed for a SOHC layout. With DOHC, it doesn't matter as you do not have rockers.
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So yours will have bearings like this one? And helical of course.
(http://i12.photobucket.com/albums/a232/jaredaebly/Gear%20Drive%20SOHC_zpsvbyqf8yd.jpeg) (http://s12.photobucket.com/user/jaredaebly/media/Gear%20Drive%20SOHC_zpsvbyqf8yd.jpeg.html)
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Pretty much, but my design reverses the direction of one of the cams. This should make the two banks equal, as Pete noted there were issues with heat and detonation. I look forward to reading the rest of the article to find out what Pete was able to solve. The gear drive that replaces the short chain in that pic is actually a production part and is the basis for what I have done so far. I believe that by adding another idle gear here will help deal with torque transfer as well as serving as a fail safe. It may be overkill but then again, some would say a gear drive by nature is overkill. I see it as a way of bullet proofing a $40-50k engine. Only thing I'd worry a little bit about is trying to get some oil splashed around on the gears, I don't know how much oil spray actually makes it up front. I would opt for permanently lubricated and sealed ball bearings, instead of open ones. Then I don't need to worry about the oil lubricating the bearings, just helping decrease friction in the gears rubbing together. Oh and one more reason for double helical over spur is quieter operation, however hearing a gear drive over the sound of 7 litres of American V8 with side pipes is pretty hard.
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With the new chains available, the long chain drive might be less of an issue than it's been said to have been in the past. Some of the guys that have dyno'd these engines recently may have some data to share on this.
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I can share a little bit of info on this. First of all, the original Ford cams, and the newest Comp Cams, have slightly different lobe profiles for the left and right cams. This was to address the differences in the valve train geometry from side to side, so that the valve action was identical on both sides of the engine. Barry at Survival and I worked with Billy Godbold at Comp Cams to get this done a few years ago. Back in the day, when Crane was doing SOHC cams, they made them the same side to side, which led to the problems already mentioned, so that's why Pete Robinson's gear drive reverses the direction of the right cam. Nobody racing these engines back then was running stock cams, of course. Reversing the direction of one of the cams is not necessary if you are running factory Ford cams, or the latest Comp profiles (Comp 8500 series).
On the chain stretch thing, I did extensive experiments on that back in about 2006, using magnetic sensors on the crank and both cams to see how the cam phasing with respect to the crank changed at various engine speeds. On that engine, from 3000-7000 RPM, I found that the right cam retarded about 3 degrees, but the left cam actually advanced a couple of degrees. This was not an expected result, of course, but it was repeatable on that engine.
Fast forward to one year ago, when I upgraded to the MS3X EFI system on my big SOHC. This EFI system has provisions for an engine with variable valve timing, so it has inputs for multiple cam sensors. So, since I needed a crank and cam sensor anyway to run full sequential EFI, I added a second cam sensor on the second cam, and logged the data. I was surprised to find that this engine behaved quite a bit differently than the engine I built in 2006. Rather than having the right cam retard and the left cam advance from 3000-7000 RPM, I found both cams retarding, the right cam by about 7 degrees, and the left cam by about 4 degrees. Also, in my testing in 2006 I was not able to get data from idle to 3000 RPM, but with the MS3X I could do that. I was again very surprised to see that both cams retarded another 3-4 degrees between idle and 3000 RPM! Basically I got a total of about 10-11 degrees of retard on the right cam, and 7-8 degrees of retard on the left cam.
The difference on this engine, compared to the one I did in 2006, was a much more radical cam profile, and much heavier valvesprings, something like 280 on the seat and 660 open for this engine. The engine in 2006 had much less pressure, if I recall correctly around 170 on the seat and 450 open. I think this is probably the reason for the different results.
On the current engine I ended up degreeing the right cam at about 104, and the left cam at about 107, in order to make maximum power. The LSA of the cams is 114, which puts them nearly straight up, or maybe a little retarded, to get peak power. Which kind of makes sense, based on how cams work.
Bottom line on this is that I think a gear drive would be a great option for an SOHC, to help control all this variation in cam timing. But, as long as you know its happening, at least with the variable timing position built into the SOHC sprockets, you can compensate for this issue.
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Jay, thanks for all of that info. I remember you had done some testing and my memory told me you had one cam advance 4 degrees and another retard 4 degrees or something along those lines. Probably came from reading about your 2006 testing. Your most recent testing though confirms the need for a gear drive or a dynamic chain tensioner, not just a bolt to tension the idle gear. Without conducting specific testing, there is no way to know what is going on with your timing and that is not something you want when building an engine. It would be better to proactively tackle the issue than to react and respond to the issue through testing. The cheapest solution would be to design a chain tensioner that uses oil pressure and a spring to constantly tension the chain, similar to what is already used in modern vehicles. The more expensive yet far more reliable solution would be the gear drive. There are many good reasons why Formula 1 doesn't use timing chains or belts anymore. I believe F1 uses spur gears though, however they also inspect their engines on a regular basis.
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Only thing I'd worry a little bit about is trying to get some oil splashed around on the gears, I don't know how much oil spray actually makes it up front. I would opt for permanently lubricated and sealed ball bearings, instead of open ones. Then I don't need to worry about the oil lubricating the bearings, just helping decrease friction in the gears rubbing together.
I think a simple solution to the lubrication of the bearings and gear teeth would be to use something like 3/16" brake line tubing or similar and drill .020-.025" holes in it and bend it and direct the flow to wherever it is needed. If you play your cards right, you may be able to get by with one long piece of tubing or two pieces with a t fitting. I would prefer this method because I don't think sealed bearings seem to live very long in general and exposed to excessive heat would surely shorten it's life span I'm sure. Plus the ease of maintenance, not having to pull the front of the engine apart to replace them and worry about bumping the timing accidentally. The oil method "should" be reliable if done correctly. Set it and forget it. :)
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Where would you plumb it from? The holes in the sides of the heads or up from the oil pump?
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Where would you plumb it from? The holes in the sides of the heads or up from the oil pump?
Right from the heads like Jay did on his build here.
(http://i12.photobucket.com/albums/a232/jaredaebly/headinstall_zps4vxxzn5w.jpeg) (http://s12.photobucket.com/user/jaredaebly/media/headinstall_zps4vxxzn5w.jpeg.html)
(http://i12.photobucket.com/albums/a232/jaredaebly/readyforfrontcover_zpstwuzwuhc.jpeg) (http://s12.photobucket.com/user/jaredaebly/media/readyforfrontcover_zpstwuzwuhc.jpeg.html)
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Is that what that boss is for? I love it when I learn something new about this engine. Thanks :)
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Is that what that boss is for? I love it when I learn something new about this engine. Thanks :)
No problem. As far as the boss, it is just there for the main oil passage to the cam, but is convenient to tap into for something like this.
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It's the small details like this, that would make for an awesome book. Going over the testing and the tricks various builders have done to improve the engine. Each chapter could be about a specific builder / racer and what he did with the engine, various memorable races both good and bad.
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I forgot to add scans of the article, that can be read easily. So forgive the thread resurrection, I'm sure many will like to see the whole article.
(https://lh3.googleusercontent.com/9_-Hbjt1bO9Xk7o_jYDNsCkGjdXxndIRyRj_EV9cgT6wxORZdW3N8azt-KpbIfdCKBiE1NrnK9e2UuD8engrkAgiJlMr9j0ozAtdq54WzG26tIbrqYCjbQRmRZWPsPMh_Nzhc6qr3aFNupM3ioYurfZzcfQZFbcWSdEvQzSEXI1bd8tmEd5nnMIQxKbGXONVINIqia_VA3q-E-Es8MayccH2V5kcP9dB7NggUiurJAL-MOCG9KC3qFyMkc0BQHea05ay2lcC-GXaN5R2j9k1iW8B7OWxVoBbXEFO5F2l0xa0Re9qbS8mBJd9DN1S4DE1mr8Qw-WxVYHtCmHsCk7p1wy9OPuIqr0nniH2bFPw1TV6c4kdespDd4RLQKbeMrv0xmQ3aCMmuMFA7saainhDDu8BqGQFrRanI_ZtRWPT4CdxnRWI06MnY0GJ5cPI67Jh2ufSJfcofp6RgbRy2dJPF9e1_ePtkDxL1xG14o3ZASnfTtPBeds43ddHDlq2TB_VTecWMPKvzmVpvhAxl4ulu_2C_Ose1mD6zeifusjnBJqyC4KeSbS4ApLY6AUyCD2qr4d_IQRVxo2MqhwCQsJ7TcO-QT2PDxFmUuskVBYbJOalOyC2=w590-h783-no)
(https://lh3.googleusercontent.com/XShRd3dLvC6QGCdef02g7pQH1iZN8oweOdKZlqHcbmQdWGbgGIgAAxxrN4AcDo6GaNunkLBBha8D3BMtQoPTSHyEBiJWPn2RmFXAKclh0uL-6-JOQ9uDoK026mLg0JnJpVEFVjvLn4KQO9T3ZG3MDU-zTegNAyE6ph8GyPZaGUKaZ5jc_g2tITnV6DVHCdeqsFb6iJKGtRojlpmuIY2lOa32JklFoHw9v6GHyfdVgkXWvzQsPTQBG3EwNJAD7useZavxKpjHkH9Zq8ymF2jAt0B4jK5F7nKlSwVN6ZGE6Tb4hDtIZ22uJRVywdkAXg0L5dP2GokM-lhQjOGAW9VPUi8mL8xKPPSKTdiu78wGjbnvapoQXlbIKfzKsRGpkpkvLclHOX_7vlnSG0rvtRWijff5AC3Vs90flLaRRL5_JVAgjqKW0rfhIhoZcko-4XNf0AVAeyE60_BzdA55p3FS7-RArLdH-kpHe-5k9JuYvUxOdj7_mted0_D0bNslq1aEWLx4qt16Q_y2olSv00yvimNOpKf9QMEVqYeLaM637TtNLKH7E6XsEBAcY9XONHIvexowsini1Q5gDi4dhTZm7_kootS9AWt4zrZf-KU7XZ2KJN56=w590-h783-no)
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Connie get under your skin Joe. ;)
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A little, how can anyone who knows the SOHC be that ignorant to say that chain stretch doesn't exist? The tiny chain on your regular OHV will stretch a little, a 6 ft timing chain most definitely will.
Then again, I have an engineering degree and Connie only graduated HS. He knows business, but engineering problems? I bet he thinks steel doesn't stretch, or know that there is elastic and plastic deformation.
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I did extensive experiments on that back in about 2006
Bloody hell! Seems like yesterday!!
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The most recent stretch info Jay has is intuitive in that the stretch is load over the unsupported link count on the chains. The "lead" chain and cam are carrying the full load from both heads, while straight shot from the driver side to the passenger side only carry one head's spring load. They should be different. I degree the driver side first, then once that's locked in I go and degree the passenger side - treat it like two four cylinders. I do not have the tuning history Jay does, so I target the cam card data for setup.
I would be willing to wager that old Conrad has dealt with an engineer or two over his 50 years of drag racing at the highest level. I would be pretty leery of getting into an argument with a self made millionaire with literally hundreds of fuel wins. He absolutely knows about chain stretch, he also enjoys ripping on old competitors every chance he gets.
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Then he should know better than to lie in an interview that would be published, just to lash out at someone who actually builds engines for a living.
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At this point in his career Connie can do and say anything he wants. To anyone he wants to. Actually he never had a problem doing that. In person. His reputation for being a brawler exceeds his reputation as a businessman and a drag racer. He knows exactly what he's doing and who he is talking to. You do not have to like the man (few do) but you probably should respect him. I bet Pinkie reads that interview and says something along the lines of "that #$%^&*^!er"...
He probably has a few dozen degreed engineers working for him at any given time.
Despite the positive attributes I do not believe that either the belt drive nor the gear drive notched any wins....
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The gear drive I think came a little late in the game and Sneaky Pete died not too long after creating it. It most likely is one development on the Cammer that didn't get to show its full potential. Improved and more reliable timing will always provide better, more consistent power.
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After running my initial tests back in 2006, I've learned a lot more about the chain stretch phenomenon. Better chains, like the 0.250" pin full roller chains (like the ones Munro and Robert Pond sell), don't stretch anywhere near as much as the factory type, 0.222" pin non-roller chain that I tested in 2006. On the other hand, bigger valve springs will make the chain stretch more. Kind of makes sense. Also, there is an initial stretch to the chain after the first run-in, and then the stretching starts to decrease somewhat, so that you don't have to monitor the chain tension as often. After I replaced the cams at Drag Week in September I ran the engine another 400 miles to finish the event, then checked the chain tension at home, and hardly had to adjust it at all.
One thing I like about the chain stretch at speed is that the cams retard. At high RPM, this is what you want. I normally time the cams way advanced, and with my springs see the right cam retarding about 6-8 degrees by 7000 RPM, and the left cam retarding about 3 degrees less (assuming I can trust the log data from my cam sensors). So, by about 7000 RPM the cams are timed straight up, but with less RPM they are advanced, which is good of course for mid range torque. Right now, I don't think I'd run a gear drive if I could; I'll stick with my variable valve timing due to chain stretch ;D ;D
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Trying to put this as politely as possible, I'll take experience over a degree sitting behind a desk any day. Being someone who works on equipment day in and day out, you quickly learn the shortcomings of engineers who have no field experience.
Connie Kallita knew a thing or two about a thing or two. His propensity for 'stretching' the truth, or outright lieing, is pretty common among top racers.
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No offense taken, and you have to be an engineer that thinks about how something would be operated and maintained, to be a good engineer. One of the funniest memes I've ever seen about this...
(https://pics.onsizzle.com/why-mechanics-hate-engineers-damn-thats-a-tight-spot-lol-3967616.png)
I get it. What makes the perfect spot to put something can also be the worst place to put it in order to service the device. You have to be an engineer with common sense and have grown up using your hands, as I did. Whenever I designed something, I'd think about how it has to be constructed, used and maintained. Often KISS was the method used. German engineers have a reputation of designing nightmares.
As for Connie, I figured you'd have to have some gall to say that. I'll take a difficult engineer over an asshole trying to one up everyone all the time.
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If this long chain is such an issue why not put two short chains on it , it looks like it would be a lot less headache than gear drive, the gear drive gear mesh from the head to the idler gear looks to me like a problem the gasket thickness would be critical, if you plain the head to straiten it the gear mesh will change, maybe I am missing something here. Leny Mason
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One of the problems we have to deal with---highlighted here---is the propensity for taking anecdotal information from fifty years ago and acting as if it were equally true today.
For today, gear drive for the cams on an SOHC Ford engine are a solution looking for a problem.
Go back and read carefully what Jay said just above.
Better chains and the experience that now exists have zeroed-out what was once a real problem. Which doesn't mean you put-'em-in-and-forget-'em. But it does move such things solidly into the realm of routine maintenance.
KS
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One of the problems we have to deal with---highlighted here---is the propensity for taking anecdotal information from fifty years ago and acting as if it were equally true today.
For today, gear drive for the cams on an SOHC Ford engine are a solution looking for a problem.
Go back and read carefully what Jay said just above.
Better chains and the experience that now exists have zeroed-out what was once a real problem. Which doesn't mean you put-'em-in-and-forget-'em. But it does move such things solidly into the realm of routine maintenance.
KS
Fair enough, and often hammers mistakenly try to find nails without a reason, but you don't have to have a failure to want an improvement.
Although power per $ is why I don't spend on a cammer, (better way to say it is I am a cheapo LOL) the other reason is that I think the front of the engine is overly complicated and rockers still seem to be more of an issue than I ever would expect) Keep in mind this is from what I read, not experience, I have never laid a hand on a cammer. But, I do think the design could be improved. I'll also add that it likely would be improved if it was a mainstream engine, but even with the incredible (and welcome and WAY cool) new interest, I wouldn't think the demand warrants any significant engineering cost unless guys like Jay personally want to improve it.
I think the dynamic cam retard is good, but remember, harmonics do funny things, you may find that chain does a lot of different things as the rpm rises and does different things based on cam and spring design.
That being said, the engines are still cool as cool can be, and I respect anyone who is willing to spend the time and money to play.
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My 2 cents says.....Jay hit on the #1 limitation of the SOHC engine. It's the rocker/cam design that severely limits the lift one can achieve. Heck, many all-out pushrod race engines are at, near or over 1" of lift, a number the OEM stock cammer can't even approach. Fix that and then maybe the gear drive is #2 on the list. JMO!
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Leny,
That is a valid point. Decking the engine and gasket thickness could be an issue. The design of the gear drive would have to allow some play at the cam gears. Decking the engine could be recovered with a thicker head gasket, but ultimately you would have to have a relatively precise target for deck thickness and gasket thickness. Another solution would be to have the cam gears cut after knowing specific distances, and there are companies that specialize in 1 off gears. No matter what, a gear drive is a more expensive option. If you're trying to build a SOHC on a budget however, that doesn't really work. No one says I'm building a $40,000+ engine on a budget. You would have to decide if the extra cost is worth it for you however. A gear drive is more about overkill than a necessity.
If timing chains were predictable, Formula 1 would be using them. The reality is that a timing chain will be subject to a harmonic wave, that changes as RPM changes. So Formula 1 uses gear drives, it is the only way to have flawless timing. What Jay has said about having done recent testing is very interesting however, and I was aware of the work Comp Cams has done to eliminate problems with rotational direction acting on the rockers.
The main problem with the 6 foot long chain, is that the tension mechanism is static, not dynamic. Jay, have you ever given serious thought to a spring loaded, oil pressure driven tensioner? There are some simple designs out there that could be adapted for use on the SOHC.
A simple spring loaded bolt design, that uses oil pressure...
(http://c1552172.r72.cf0.rackcdn.com/233083_x600.jpg)
Or a ratcheting design, that uses a spring and oil pressure...
(http://image.superstreetonline.com/f/24774259+w640+h427+q80+re0+cr1/modp_0910_01_o%2bhybrid_racing_honda_k_series_chain_tensioner%2bchain_tensioner_cross_section.jpg)
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The Cammer is a great, fun, engine. I got the Ford/nitro bug watching the all conquering blue Mickey Thompson Mustang as a 9-year-old fence rat. Still the greatest race car ever...for me at least.
A couple things:
The SOHC 427 is a neat kit. I had the privilege of working with FE Forum member SOHCLane building his blown '63 Fairlane. I'm sure it was REALLY advanced in 1965, but 50 years later not-so-much. Realize that it IS a kit, and was not a "clean sheet of paper" engine. The parts are well made and the motor is quite reliable at the 5-600 horsepower level.
My first "real job" was as an apprentice tech for Mercedes Benz in 1980. I was amazed by the 6 foot+ timing chains on those V8's when I started. At 60 thousand miles it was normal maintenance to roll a new chain in. Remove one valve cover, undo the masterlink and hook the new chain on, keep tension on the chain so the tensioner doesn't unload, and hand crank the engine (for ever it seemed) 'till the chain came back around. This procedure still makes me nervous. Autoholic is quite right, a hydraulic tensioner would be a welcome upgrade. The stock manual tensioner is kind'a silly, but in '65 it was really "trick".
The one thing that Ford did get absolutely right was the non-adjustable rockers with the different thickness lash caps to adjust the valves. Many European high performance engines to this day use this style of overhead cam lash adjustment. Rock soild...especially compared to the later "elephant foot" adjustable rocker. All of the pictures of Pete Robinson's cammers with the valve cover off show non-adjustables in use. The clips between rockers to make lash caps changes possible was quite ingenious.
Very cool motor, indeed!
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Hot Rod's article on the engine is very enlightening, all of it done in 90 days. The SAE papers for the engine are incredibly interesting, to a car junkie engineer. I also have the GT-40 papers but haven't read them yet.
Ford in the 60's was nuts about racing, they had a hand in everything. Some of the most iconic engines ever made are Fords, from the 60's. 289 HiPo, 427 FE, 427 SOHC, DFV, 255 DOHC "Indy", Boss 429... there even was a 302 SOHC experimental.
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Here is a belt driven Cammer.
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Belts stretch more than chains. The difference is that you can take up most of the stretch in static, and dynamic stretch is easier to control with an idle pulley that is spring loaded. Belts are meant to stretch, where chains aren't. I can't find the video, but a few years ago I saw a mod motor on a dyno and watching the tensioner pulley at work was interesting. It was very active.
Awesome engine in that shot though. Is that the recreation of Sneaky Pete's Tinker Toy?
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Jay, have you ever given serious thought to a spring loaded, oil pressure driven tensioner? There are some simple designs out there that could be adapted for use on the SOHC.
I have, and in fact Bill Conley and I have had a few discussions about it. I think it would require a custom or modified chain tensioner arm, so that it would pivot on bearings, and an oil-pressure driven piston or stop that would push against the arm. As you say, probably wouldn't be too tough. One of those projects I haven't gotten to yet...
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There is plenty of design freedom in the area to come up with something. The downside will be cost, an elaborate part made pretty much as a one-off isn't a cheap part. I have a CAD model of the SOHC I can use over the holidays to come up with an idea floating around my brain. It involves a bearing at the pivot point of an arm, with a spring loaded tensioner. Thinking about it, I don't think a ratcheting tensioner would be a good idea. As you noticed, it fluctuates too much with RPM. Allowing the piston that tensions the idler gear to freely go in and out will allow the chain to relax when it is not being stretched. Eventually keeping the chain at a maximum amount of stretch could result in wearing out the chain and gears faster and does not adjust based on stretch at that moment in time. I could be wrong here, but if you look at a dynamic tensioner for a belt, it doesn't keep the belt at 100% stretch. It keeps the belt at a specific amount of load.
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Jay,
You seem to like the variable cam timing due to the chain. If the chain stretch is eliminated, either by a dynamic tensioner or a gear drive. would you ever consider creating a set of cam gears to function like a vari-cam?
http://www.jalopyjournal.com/forum/threads/varicam-anyone-anyone.629885/
Man would that create a very trick SOHC, mechanical advance cam timing to go along with mechanical advance spark timing and less chain stretch variation in the timing. It would be a real old school version of a modern day mod motor with VVT. Put a mechanical fuel injection system with a Spica pump and you're looking at one highly sophisticated, all mechanical engine.
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Belts stretch more than chains. The difference is that you can take up most of the stretch in static, and dynamic stretch is easier to control with an idle pulley that is spring loaded. Belts are meant to stretch, where chains aren't. I can't find the video, but a few years ago I saw a mod motor on a dyno and watching the tensioner pulley at work was interesting. It was very active.
Awesome engine in that shot though. Is that the recreation of Sneaky Pete's Tinker Toy?
No it's Jim Green's Assassin top fuel dragster. Jim builds all of his cammers with belt drives now. Belts do not increase in length over time like chains do (hence my earlier statement) and they are extremely efficient (95+%) and they dampen vibration and shock loads. https://www.youtube.com/watch?v=MjCJTtIUKI4
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Pretty much every NASCAR and Pro Stock engine runs a belt. Probably not a bad option...
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As a gear and gearbox designer by profession (and degreed mechanical engineer, licensed and recognized by IL, P.E. #062.068693), this topic of a gear drive for a SOHC motor is of particular interest to me. If I could help in any way with a potential design I would be more than willing to. If that were to only check someone else's design over or to assist in coming up with a design I would relish at the opportunity. I have been limited in my ability so far to accurately conceptualize the layout in my cad program, however, as I do not have an accurate model of a SOHC engine, and do not have a SOHC engine to create a model from!
As for my qualifications to help, I am a contributor to the AGMA (American Gear Manufacturer's Association) and know some of the highest quality gear manufacturing facilities in the business (Chicago is a large hub for the Gear Industry). I can help optimize gear geometry, can run gear design calculations per AGMA standards, and can create actual blueprints with appropriate GD&T (geometric dimensioning and tolerancing) per the latest ASME Y14.5M-2009 standard (as opposed to simple drawings with plus/minus tolerancing, which routinely induce unacceptable tolerance stack ups, or simply do not convey the true intent of the part as it would need to function in application).
I freely admit that I am a completely biased party to the discussion of whether a gear drive makes sense for use in this application, and if the standard method of a stretching chain is already good enough (or perhaps even desirable), predictably repeatable in how much it stretches, able to be accurately compensated for, cheaper, easier to maintain, etc. then there's no question that as an engineer I would absolutely advise my management to stick with the simple solution that already works. I question however how predictably repeatable the amount of stretch is, and whether there would be more precise alternatives to vary the advance if done so intentionally, as opposed to reacting and correcting for whatever the given advance or retard is provided by the system, without really having control over it.
Additionally I question the power consumption of running the chain as opposed to a gear drive. I'm not a chain and sprocket designer so I can't really comment with confidence on the losses, but I would imagine a chain that long and heavy would require more power to throw around than the gear sets would be.
Also one thing that I do know for sure is that in power transmission a chain is about the worst case you can get with respect to overhung load on the shaft. The chain tension itself (without any load along the chain at all) will already cause a (potentially significant, depending on the amount of tension) radial force on the shaft at the sprocket, and then the shaft will have to then also transmit torque when the system is rotating. This is a classic case of combined loading in torsion and bending. Don't get me wrong, the separating forces of a gear set will cause overhung load as well, but only as the torque increases on the system, and the gear set will have significantly lower radial forces than a chain, and can even be designed to limit the separating forces as well. Now this could all be minutia, and have no real world effect if fatigue failure of the sprocket shafts never occurs in the current design, but then again who's to say it wont happen at the most inopportune moment, like right when its reached its fatigue life and is at its highest stress during a pass at Drag Week and decides to relieve itself from the engine to catch some sun ('cause if it were to happen at all, that's the most likely candidate of when). As an engineer I would call that a failure, David Freiburger would call that Un-Good.
Some quick comments on the proposed gear design:
Be careful with double helical. There are a few design considerations that should be investigated before choosing that geometry that I can get into longer detail on that not everyone will probably care about, as I've already gotten way too in depth and long winded as it is.
Some questions about the design:
How much face width can you get away with? This will be key in determining whether a double helical is really the best option.
Last thing:
Don't believe in the limitations of any given rule of thumb for any type of engineering problem. There's always exceptions to the rule, and if you know the design criteria, the optimal engineering solution (for the given criteria, which may only apply to this one thing) rarely falls in line with rules of thumb. Most of the time however the truly optimal engineering solution is not chosen due to compromises that make life easier for other considerations, like cost, manufacturing, and assembly which of course are valid and usually more important criteria in industry. For this case the double helical system could very well be the optimal design, but I also know that if you show me that system I could probably design the "worse" spur system to be quieter, stronger, and cheaper. There's a lot of questions to be answered before being able to make those kinds of determinations though.
Sorry for the long reply, I'm just a gearhead.
Calvin
P.S.
I think the links to the scans of the Car Craft article may be broken. I only see X's.
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I can still see every picture Calvin.
Thanks for your thoughts. As of right now, this is all just theoretical. I have a CAD model of a SOHC, and from a few different measurements compared with those from an actual engine, I've found out that it's pretty accurate. Of greater interest right now (at least to the SOHC community) would be a dynamic chain tensioner. It would be cheaper and easier to implement. I plan on doing some designs for one in the coming weeks.
As for the gear drive, I haven't tried to design the gears in CAD however I think there would be enough room for a double helical gear drive. The primary reason why I'd go for a helical gear, it wouldn't have any play by nature of having at least 2 teeth always engaged on each gear. Double helical, due to having zero axial thrust loads. A spur drive might cut it, but if you're doing a gear drive on a SOHC you're already going for overkill. The major problem would be tolerances, everything would have to be just right so that the gears don't interfere with each other. I don't have the financial resources to pursue this right now, but if one day I can, I will.
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Hi, Devil 69 The problem I see is the Gear mesh with difference in the heads and gaskets, It would be great to see how it would work, Jay has researched and done more than anyone I know of I will never turn mine eight grand {I hope} and that is were the stretch comes in from what I have read, no rev limiters back then. thanks Leny Mason
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I'm just an observer on this topic, not having had much to do directly with a Ford Cammer engine for some years. But, unless you have the sort of facility that Formula One teams use, and a budget to go with it, I believe a gear drive would not be the best approach. My own daily driver engine, also used to set the ECTA E/F CC record, is a dual overhead cam V8. It has +/- 160K miles on it and the chain drive is still just fine. I'd think a side-by-side comparison might be in order to see what might be easily adapted from one to the other without going so far astray as to go to gears with all their inherent clearance difficulties. JMO
KS
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The difference between your modern DOHC V8 and the 427 SOHC, is that the timing chains aren't as long and the mod motor has a dynamic tensioner for each chain. The chain will still stretch at lower RPM's. In my opinion, what matters more is the rate you load and unload the timing chains. Every time you shift, you change RPM's in a rather shot period of time. The easiest thing to do, would be to create a dynamic tensioner.
I've been thinking about this, what the design should look like. There are two trains of thought right now.
1. Go for a hydraulic based tensioner, using oil from the passenger side head. Hydraulic based tensioners are used in most engines today. The problem with this, is that if the oil pressure was to ever drop, the tensioner would be relying on spring pressure that might not be enough.
2. Go for a spring based tensioner, similar to how drive belt tensioners are designed. The benefit of this design, is that it could easily be made to work on the SOHC and oil pressure wouldn't matter. Thinking in terms of a vintage look, this is also more likely to have been a possibility back in the 60's. The idea I have in my mind, would still use the tension bolt as part of the assembly to set initial spring pressure.
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I'm working on a design for a spring loaded piston / ram, that fits on the tension bolt. The backside of the spring would be held in place with a nut and washer. At the tip of bolt, would be the piston / ram that encloses the spring. The idea would be that the spring would exert enough force against the piston / ram, to take up any slack in the tensioner. If this idea could work, it wouldn't require any new parts to be made, other than a simple metal ram with a hole in the middle to fit the spring and the bolt. Looking at McMaster-Carr, there are springs of a suitable size and spring pressure. This idea would mean that the tensioner would have to be free enough to move on its own.
Thoughts? It wouldn't be a hydraulic solution, but it would take up slack in the system. McMaster-Carr has some springs that could put well over 100 lbs of force per inch on the tensioner, a few even over 1,000 lbs/in. It's a cheap solution, keeping everything stock. We're talking less than $50.
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Joe -
Using just a spring will cause significant resonance problems with that chain drive. You need an oil damper in the system.
Even with hundreds of pounds of tension on that SOHC chain, it has still been shown to jump around quite a bit. Big-time damping is a must if you are not cinching it up fairly tight.
Look at all of the production OHC chain tensioners out there. You'll see oil-fed pistons (often backed with springs) for a good reason.
- Bill
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Thanks for the feedback Bill. I'll have to make some changes. Besides needing to incorporate oil pressure, is there any particular reason why the stock tension mechanism can't be used? Bore the mechanism out a little bit and put needle bearings around the bolt? Or redesign the whole thing to ride on an off the shelf bearing?
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Another belt drive Cammer.
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Joe -
A few years ago I was thinking of a simple solution that would provide spring tension and oil damping. It involves redesigning the stock tensioning screw to allow for a spring-backed piston on the end. You'd probably only need 0.5 inch of travel or less for the piston.
Inside the piston would be a strong die spring (oval profile coils) and it would be fed from a flexible line plumbed to the main oil gallery. Getting the diameters and forces right would take a bit of doing, but I think it would work well to dampen the chain harmonics. You'd use the existing screw to tighten the tensioner to a given force, and let the spring / oil-damped piston take up small movements.
For the arm pivot, I would recommend an oilite bronze bushing. There's enough oil splash in there and the movements are minimal.
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Bill, that's pretty much what I'm trying to design. I want to retain the stock tension bolt, which would be used to tension the chain normally. The problem I'm seeing with this however, is making it oil pressure driven By coming up with a new bolt of sorts, the inside could be hallow which would be feed with oil.
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Very cool guys! You too may have the best or perhaps optimal fix in mind. Once again, Jay's foresight to create this website, allowing a lot of FE thoughts to come together, may pay some nice dividends!
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So many issues with the chain drive. And no issues at all with the belt drive.
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This is the way Mercedes solved it on their SOHC V8s
Works flawless year after year
http://www.ecklersmbzparts.com/diagram/view/index/id/110
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So many issues with the chain drive. And no issues at all with the belt drive.
No issues with the belt drive? How about cutting up the SOHC valve covers so the belt drive will fit? Same with the modifications to the front cover? Sealing the shafts that come through the valve covers? Fitting all the other components on the front of the engine? The chain drive isn't perfect, but it works, and is a better solution than that big ugly belt drive, in my opinion...
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This is the way Mercedes solved it on their SOHC V8s
Works flawless year after year
http://www.ecklersmbzparts.com/diagram/view/index/id/110
That design is typical of OHC timing chain tensioners. They use a chain guide that pivots about one end, with some sort of spring loaded tensioner on the other end. It pushes the guide into the chain, taking the slack out of the chain. Many modern systems that do this, use oil pressure in the tensioner mechanism that pushes against one end of a chain guide. Eventually, the chain guides have to be replaced as they are sacrificial pieces.
So many issues with the chain drive. And no issues at all with the belt drive.
As Jay pointed out, there are a lot of known problems with a gilmer belt drive that have to be accounted for. Also, most people who want a 427 SOHC under the hood of their ride, don't wan't to take a "blue tip wrench" to it. A properly designed timing belt system, has some sort of spring loaded tension mechanism. While you can take most of the slack out of a timing belt in static, you don't want any slippage here. Chances are the cogs on the gears would all stay in the right place, but the belt would stretch just enough to put some harmonics in the valve timing, as we see with the stock chain drive. If your goal is to eliminate the harmonics within the 427 SOHC's timing, you either need to go with a gear drive or have a dynamic chain tension mechanism created.
Jay likes this within his engine, however I believe that this is an uncontrolled variable that is unpredictable, engine to engine. If I had a crap ton of money right now. I'd build one of these engines and study it. But the fact that you have to study it within your engine shows that there is a problem. Not everyone who owns one of these engines wants to have to come up with some sort of testing apparatus in order to understand how it is impacting their engine. Also, not everyone wants the timing to have any variation in it. From a failure mode standpoint, allowing the timing chain to experience a harmonic wave that effects the amount of tension on the chain, is putting the chain through a cyclical loading instead of a constant load. A dynamic tensioner helps diminish fluctuations in loading on a chain, which helps a little to extend the life of the chain. This might not be a serious problem on the 427 SOHC, because an owner likely wouldn't put enough miles on the engine to ever need to worry about a timing chain's service life.
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Well i had mercedeses as dailydrivers since the early 80s. And i
don't had to replace any chainguide yet.So i don't want to call them
sacrificial any more than any other parts of the engine.I have rebuilt
many engines that was totally worn out (300000-500000 km)
but the chainguides was OK to reuse. The tensioner is hydraulic
operated, on some very high milage engines you can hear a slight
knock from the tensioner when cold starting till the oilpressure
builds up. Some times i had rolled in a new chain just for "better
safe than sorry" on some high milage ones i had
So i would say a good enginered chaindrive is more or less trouble free
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They are designed to last, but it depends on what the chain guides are made of. Today, I'm pretty sure they use PTFE but I could be mistaken. They are sacrificial because when they push into the chain, you have essentially an extremely dull chain saw. Normally these chain guides have a pretty generous curve to them, so that the chain isn't grinding against a corner. A well used chain guide should have a noticeable groove, like below... For preventative maintenance, it would most likely be in the engine's best interest to replace these when you replace a timing chain. Unless we're talking Ferrari, these aren't that expensive.
(http://imagecdn2.panjo.com/images/c48efdf4-00cc-4f7c-aef8-2a8c22ba59c2.JPG)