FE Power Forums
FE Power Forums => FE Technical Forum => Topic started by: BigBlueIron on July 13, 2022, 12:48:21 PM
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390 crank turned .010, bearing clearance is coming in at .0015. King CR809AM010 bearings. To tight?? Hot rod/driver pickup. Not a race engine.
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I wouldn't run them that tight. I'd like to see at least a thou more clearance.
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What would you consider the minimum. Crank is being balanced and will need polished again after that, maybe that will make up a few tenths? Otherwise I will have to look for some different bearings. Machinist is fearful of trying to take one thousand off and keep everything straight and round.
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Brent is 100% correct.
You should be able to get King +.001 bearings.
Some use half a set of the +.001" to fine tune clearances.
Cheers
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Unfortunately, you won't be able to get +/- .001" bearings for a .010" under crank (.009"/.011").
I personally don't like to see under .0025" for a standard FE rod journal bearing clearance.
If he's slick with a polisher, he can take off close to a thou while keeping it straight and round.
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Speedpro / FM bearings tend to run a little big.
Also, there are CB-756P Clevites for 427s and "special" 390s, their term not mine, that are generally .001 looser. Harder to find but a nice option
Both options might be able to get you closer. FYI Ford specs are crazy tight, but I don't know anyone who goes there
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The general rule for a performance build is .001" per inch of journal diameter on rods and mains. That's not carved in stone so a minor + or - is fine, but you are a bit outside the tolerance. It would run like that and last as a mild daily driver but I wouldn't lean on it.
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If he's slick with a polisher, he can take off close to a thou while keeping it straight and round.
The crankshaft polishing process is intended solely as a surface texture addressment, not for the purpose of attempting to remove any significant sum of metal. Yes, if one is well versed with a polishing machine and technique the outcome of an effort will be better; but, this equipment and the expendables are just not engineered to permit this, and an acceptably straight and round observation will be more of a function of how critical the inspection post this effort is. ;)
And yeah, the sum of .0015" of oil clearance is a might tight for an FE engine (others vary), but if you have the critical dimensions right (round & square ??? ) and the project was for Grandma to drive to the store and church, it would probably work fine, one might even venture to say superior, and I have witnessed such. But for a hot-rod with an exuberant operator well..........; so I would probably attempt to find somebodies bearings that provide +.001" something and see if you can make for an additional value, though this may prove fruitless beyond a few tenths of dimension. Also double check the rod big-end I.D.'s for size, determine that the crankshaft journal(s) are actually ground to the hi-side of dimension, and if no other option, realize that the proper process is to cut the crank again to the next size under with an intentional finish dimension that provides more closely what your looking for. :)
Scott.
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If he's slick with a polisher, he can take off close to a thou while keeping it straight and round.
The crankshaft polishing process is intended solely as a surface texture addressment, not for the purpose of attempting to remove any significant sum of metal. Yes, if one is well versed with a polishing machine and technique the outcome of an effort will be better; but, this equipment and the expendables are just not engineered to permit this, and an acceptably straight and round observation will be more of a function of how critical the inspection post this effort is. ;)
And yeah, the sum of .0015" of oil clearance is a might tight for an FE engine (others vary), but if you have the critical dimensions right (round & square ??? ) and the project was for Grandma to drive to the store and church, it would probably work fine, one might even venture to say superior, and I have witnessed such. But for a hot-rod with an exuberant operator well..........; so I would probably attempt to find somebodies bearings that provide +.001" something and see if you can make for an additional value, though this may prove fruitless beyond a few tenths of dimension. Also double check the rod big-end I.D.'s for size, determine that the crankshaft journal(s) are actually ground to the hi-side of dimension, and if no other option, realize that the proper process is to cut the crank again to the next size under with an intentional finish dimension that provides more closely what your looking for. :)
Scott.
The advice on checking the big end is sound, if it's on the low side, you could take a smidge off easily and without going to limits. I am not a fan of the high side of crush though
Remember, old school stuff like dressing the back of the bearing, deburring, etc. All are sound within reason, and do not underestimate that bearings measure differently. Another set, different brand could be entirely different. I see it all the time. In fact, one day, I will use the two sets of BBC FM coated bearings I have. I can't prove it over 4 years of never being acceptable to me, but I am an optimist :)
Last thing is, how are you measuring? Certainly not meant to offend or accuse, but tight hand with a micrometer, less than accurate bore gauge, old bad eyes, etc, all matter.
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My question is. Did you use a bore gauge to measure the ID of the rod bearing and the rod bore? Also, is the .0015 clearance, the same, on all rod bearings or, is that the smallest clearance?
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I should have specified the clearances "I" wanted when I dropped the parts off. That is completely on me, idk why but it just didn't cross my mind. The shop ground the crank per their book resource which called for .001-.0025. And they landed it pretty much in the middle of that. They did a fine job, this was lack of communication on my end.
I asked him to do what he could on the polish, we will see what it is then and I will probably order some different bearings and see how they do before re cutting a fresh cut crank.
When I asked if .0015 was to tight I already knew the answer...
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Last thing is, how are you measuring? Certainly not meant to offend or accuse, but tight hand with a micrometer, less than accurate bore gauge, old bad eyes, etc, all matter.
This^^
A light vs heavy touch on a micrometer easily makes for a .005 difference. And if all the gauges/micrometers aren't calibrated to each other with a verified checker, then all numbers are pretty much meaningless anyway. A 1" calibration checker, or whatever they're called, is really necessary. Then mark any differences between all gauges and micrometers so that number can be added/subtracted from any final numbers you come up with. They can easily vary by +-.005, if not more, depending on age and quality. Just a couple of things to keep in mind when trying to determine exact clearances.
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Last thing is, how are you measuring? Certainly not meant to offend or accuse, but tight hand with a micrometer, less than accurate bore gauge, old bad eyes, etc, all matter.
This^^
A light vs heavy touch on a micrometer easily makes for a .005 difference. And if all the gauges/micrometers aren't calibrated to each other with a verified checker, then all numbers are pretty much meaningless anyway. A 1" calibration checker, or whatever they're called, is really necessary. Then mark any differences between all gauges and micrometers so that number can be added/subtracted from any final numbers you come up with. They can easily vary by +-.005, if not more, depending on age and quality. Just a couple of things to keep in mind when trying to determine exact clearances.
That's a great point, checking your mics against a standard should be a daily occurrence for the guys that use them every day and a good habit upon usage for the DIY'ers. However, if they're off, no need to add/subtract numbers, you just use the micrometer wrench and readjust the barrel. Your micrometer for checking bearing clearances on an FE will be a 2-3" micrometer, so it should be a 2" standard.
Bore gauges will never be "off" because you set them to the micrometer or setting fixture that you're using each time.
Another good point that you made, is that a micrometer is a "touch" tool. If I gave 20 guys the same mic and told them to measure a crank journal, there would probably be a tenth or two (.0001-.0002") spread between all the measurements. Even using the barrel against the clutch can sometimes show a .0001" difference.
I also agree with Scott, there are probably specific situations where a .0015" oil clearance might live, but it will be a very specific situation: all .0015" measurements across the board, no taper or out-of-round situations, very light viscosity oil, and a life of idling around. I would also have to lump in new, rigid connecting rods in with that. Back "in the day" guys were having to do all kinds of stupid stuff to make FE's live at high-rpm/high-hp, including honing the rod journals out of round. Now we slap in a good set of Molnar rods and turn 'em way up.
In the OP's situation, it's quite possible that the tolerances just stacked up against him and that's the clearances that he got. If you hand a machinist a bunch of parts and tell them to go to work, they don't generally put everything together, measure clearances, and then adjust everything to fit. Unless given specific instructions, they just grind/machine everything to spec: main housing bore to middle of spec, crank journals to middle of spec, rod big ends to middle of spec, etc.
When I send a crank to my local grinder, I give him specific instructions based on what's worked for me in the past. I've got 2 cranks at the grinder right now getting "adjusted". I only use coated bearings and bearing selections have been straight up stupid for the past 2 years, so I have to use what's available on the shelf and "adjust".
If this were a SBC, then you could just go buy a set of .009" or .011" bearings and mix and match. However, the amount of bearings out there for FE's are few and far between. That's why your new aftermarket blocks are all cut for Cleveland bearings. You can't even get a true "X" main bearing for an FE, you have to grind the tangs off Cleveland bearings and use those.
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What Brent said, but no kidding, if you are confident in your measurement, I'd consider trying a second brand of bearing.
Might be a get out of jail free card...truth in lending though, probably not returnable if you drag a bore gauge over them.
I won't get to it until the end of day, but I can see what I have on the shelf too. Not too much .010 stuff, but the last 390 I did we cut the crank and I think I chased clearances a bit, I'll look
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The most accurate way to measure clearance is to use a bore gauge/ball anvil micrometer combo. Measure your bearing shell thickness with the ball anvil mic. Add that to journal diameter. Set a flat anvil mic to that dimension, then the bore gauge to the mic as normal. Measure the bore without the bearing shells in them. The bore indicator will leave indentation marks in the soft bearing material and that does affect accuracy. Using the bore gauge on the hard iron bores does not indent.
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The most accurate way to measure clearance is to use a bore gauge/ball anvil micrometer combo. Measure your bearing shell thickness with the ball anvil mic. Add that to journal diameter. Set a flat anvil mic to that dimension, then the bore gauge to the mic as normal. Measure the bore without the bearing shells in them. The bore indicator will leave indentation marks in the soft bearing material and that does affect accuracy. Using the bore gauge on the hard iron bores does not indent.
That's another way of doing it as well.
However, if you have a good, quality bore gage, the anvil will not hurt the bearings. There will be no precision difference between those two methods, but a quality mic won't leave tracks that dig.
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Just heard from the machine shop. They where able to bring clearance up to .002.
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The reason I asked about using a bore gauge, is that if your using factory rods, the big end bore, can fall between, 2.5907 - 2.5915 a .0008 tolerance and they won't all be exactly the same in any set I've measured.
They can be honed to the same upper limit on all the rods and pick up maybe .0005 there but, in any case, you will have the same size on all rods and if the journals are all the same, you should have the same clearance on all of them.
Regarding measure the rod journals, with a mic, as Brent says, you need to use a "standard" to set the mic (gauge blocks are best) but, you also need the test the end of the travel, in this case a 3" standard, to make sure nothing in the mic is warn. But, the actual best way, is to use a gauge block set and check the mic at 2.438.
For the inexperienced mic users, they make a "indicating" mic. They are expensive new but, can be found at a affordable price on Ebay. All users of that kind of mic, will get the same reading:
https://www.ebay.com/itm/134142947458?hash=item1f3b8af082:g:KTUAAOSwtSViolIu
If you do indeed have .002 clearance, for your application, I think you'll be fine with good lighter wt oil.
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Take your micrometer to the machine shop and check yours against theirs. You will be surprised. We had the problem with telling the machine shop what we wanted on rod and main journal sizes, and they always came back a "little off". Took the micrometer and checked their standard against our micrometer, and they didn't calibrate theirs to the standard. It was their machinist mistake, and the boss had him start calibrating their micrometers for each crankshaft grind job. My local machine shop has quit grinding crankshafts because of the cost to repair the machine and the cost of replacement machines. It is getting nearly impossible to find a reputable shop in the greater San Antonio area that can even do a multi-angle valve job or turn a performance crankshaft. We are the 9th largest city in the USA, but haven't got a really good professional machine shop. EPA has killed most small shops. Joe-JDC
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Using a mic and adding up the numbers is not as accurate as a dial bore gauge. The mic method does not take housing bore distortion and bearing crush distortion into account. A good quality dial bore will have a very light spring and will not drag a meaningful line into the bearing - just cosmetic. My local crankshaft guy can consistently remove a half thou or less from a crankshaft journal with a grinder. As mentioned, a heavy hand on a polisher ain't the tool for that task - it will just indent around the oil holes and around the radii
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Clearance confirmed at .002. Decided to live with it, good or bad. Rings gapped and pistons are in. Now to order a reduced center timing chain. Way to much slop, block was aligned honed and it was mentioned it was pretty bad.
Just an update for anyone that was wondering.
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Piling on if that’s ok…
Any issue with .003”? Have one with a couple at that size, just a cheap hotrod combo, figuring on maybe running 40wt and calling it good?
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I always aim for rod bearing clearances between .0025-.003 and like it when they hug .003”.
You won’t need to run 40W oil. JJ ran with .003”/.003” and 5W-20.
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>Unfortunately, you won't be able to get +/- .001" bearings for a .010" under crank (.009"/.011").
Why I have a crank and a set of 351C rods+pistons in a box. The shop that did the crank did it a bit "short" and bearing clearance mics out at .0011~.0008. No .010 bearings with -.001 available unless I pay for custom. Not worth it for stock parts. If I decide to use them, I'd take it to a different (better) shop and turn that crank .020 as needed to get the .002~.003. Last time I looked at the set, I'm pretty sure the guy put the pistons on the rods in the wrong orientation. Needless to say, that shop isn't around anymore.