SOHC Cam Timing (Long)

[fastback63]

Question for Jay and or other Cammer experts. I'm mocking up my Cammer engine and checking piston to valve clearance and need to know where to take measurements, in order to achieve accurate readings for cam timing. I have a copy of the Ford publication but as anyone who has read it knows it only gives a method for checking stock Ford cams. The cams are Comp Cams #138-000-9 R& L respectively. Here's the deal, I have verified TDC and when I go to check the timing events @ .050 as per Comps cam card with a dial indicator the readings I get don't match the specs given. I have my indicators set on the valve retainer, as I have been told that is where it is checked on this engine. I have tried it both with the specified lash, .020 and with 0 lash and no matter what it doesn't  come out correctly. Based on what I know about the subject and other experience with overhead cam engines, I know it will run as I have them set, I just want to be accurate. Also, in order to get the cams set at what I believe is 'straight -up' both cams end up advanced as far as I can get them on the sprockets with the dowel holes. The timing chain supplied didn't have any markings on the links to match the timing dots on the gears. I'm wondering if I am one tooth off between the main drive sprocket and the left side cam. Anyway thanks in advance for your help.  BTW tech guy at Comp was worthless, I don't think he even knew what a Cammer is. Thanks again Randy

[jayb]

Good to hear that you are getting the motor together.  Here's a couple of hints:

- First, the 138-000-9 number is not the grind number.  There should be a 4 digit number for each lobe, for example 8594 or 8596.  Knowing that would help with the degreeing procedure.

- The timing events at .050" lift given on Comps cam card are at the lobe, not at the valve.  So if you are measuring off the retainer, you won't get the correct results.  I'd forget about trying to measure at .050" lift, and just use the intake centerline method  to get the intake lobe centerline.  In case you don't know about this, you have to measure the degrees of crank rotation at .050" before peak lift, and .050" after peak lift, and then split the difference between the two to get the intake centerline in degrees.

- Comp's cam cards are not always very accurate for the SOHC.  I have seen them off on lift and duration, especially a few years ago.  The most recent ones I've seen have been accurate, but in any case I would advise you to pick an intake centerline angle and just degree the cams as described above, without relying on information from the cam card.

- If the cams are at the end of their adjustment on the sprockets when they are degreed straight up, you are definitely off a tooth on the sprockets.  I would reset the chain one link over in the sprockets and try again.

- Make sure you have the cover bolted in place and the chain is tight before you degree the cams.  If you tighten the chain without the cover in place, there is no support for the nose of the stub cam, and you will bend it out of place.  This will throw off your degreeing operation and potentially damage the stub cam, especially if it is a factory cast stub cam.  Also if you try to degree the cams with the chain not tight, you will be off  on the degreeing.

Hope that helps - Jay

[fastback63]

Jay, thanks for the speedy reply. The cam grind #is 8564 R112. SN W3634-11 and W3635-11 respectively. I did have the cover in place when I tightened the tensioner. I will definitely do the centerline method on final assembly. Couple more questions. What do you use for a retaining clip on the stub shaft. The groove is about .100 wide and all the clips I have found about .040 wide. So even if I put two there is till about .020 slop in and out. A spacer maybe? and also who make a stainless steel header flange for the pond heads? Gonna have to build headers, going in a '63 1/2 Gal. The other one goes in a '57 Bird. Thanks again, Randy

[BH107]

I have the link count for the timing chain in my reference materials at home. It tells you how many links to where the original chains were marked, and we mark the chains like the originals to make setup easier.

[jayb]

The retaining clips I use are thick, although probably not .100" thick, maybe more like .080".  I got mine from Doug Garifo at Precision Oil pumps.  And I'm afraid I don't know of anyone making stainless steel flanges; all the ones I've seen are normal mild steel.

[FErocious]

The timing events at .050" lift given on Comps cam card are at the lobe, not at the valve.  So if you are measuring off the retainer, you won't get the correct results.  I'd forget about trying to measure at .050" lift, and just use the intake centerline method  to get the intake lobe centerline.  In case you don't know about this, you have to measure the degrees of crank rotation at .050" before peak lift, and .050" after peak lift, and then split the difference between the two to get the intake centerline in degrees.


  I would definitely check the lobe at the .050" lift on opening/ closing side, where the lift curve starts and ends.  The intake centerline method will make you believe the camshaft lobe was ground in error;  at least in most cases. Most modern camshaft lobes are asymmetrical and will not show maximum lift at the centerline.  If the manufacturer, camshaft designer/ grinder states that the checking method is the centerline method, then the lobe is probably symmetric. To the OP ...What method does Comp Cams indicate on the cam card ? .050" lift? .050" either side of max lift?

[jayb]

All the SOHC cams I've checked on my camshaft checker have had the peak lift centered on the lobe centerlines, so I'm pretty confident you can use that method to degree an SOHC cam.  I've seen lobes before with peak lifts off center, but only really old ones, not new ones.  Can you give an example of a cam or lobe that does have the peak lift shifted from the centerline?  I'd be interested in learning more about that, particularly if its a modern lobe.

[fastback63]

Pretty sure I have it figured out. First of all Jay was right, when checked with the centerline method the cams are back in the 'normal' range on the sprockets. Secondly I realized that the mistake I was making was that I forgot to factor in rocker arm ratio into my calculations. If you take .050 (cam lift) and multiply it by 1.3 (rocker ratio) you get .070. When checked at .070 at the valve retainer the specs come in a lot closer, and also correlate to the centerline as measured. This makes sense because the readings I was getting were 'short' on both opening and closing making me think that my cam was not what it was supposed to be according to the cam card. Because of the design of the cams and rockers it is really not practical with the equipment at my disposal (dial indicators) to accurately measure cam lift at the cam. Lift at the valve retainer is much easier to measure as the motion is in a straight line, as opposed to the cam end where it is swinging through an arc. On a pushrod motor it can and should be checked at the lifter because it has the correct angle to the cam lobe. The tech guy at Comp just kept saying 'it's checked at the cam' over and over. Again I don't think he understood this cam layout. Hope all this makes sense. Thanks again to Jay and all who responded. Randy