Cam degreeing sanity check

H

HopRod

Member
I purchased a cam for my 8BA from a well respected company that rhymes with spider, and have started to degree it. I am trying to find the intake CL and compare it against the cam card. It is supposed to be installed at 110 intake CL. From what I measured I keep getting 123* CL. My method is as follows: Located TDC of #1 piston and set degree wheel to 0*. Timing marks are in alignment on the crank and cam gears. With a dial indicator on the intake valve I rotate the crank to put the cam on the highest lift point and Zero out the dial indicator. I then reverse rotation to 0.100 below max lift and then move it forward again to get to 0.050" below highest lift. I note degree mark on my wheel at 80*. Keep rotating to high point and go 0.050" beyond, mark degree wheel, 167*. 80+167=247 then /2 = 123.5*

What am I doing wrong?
 
With your degree wheel centered and the dial indicator on the intake valve. Rotate the engine until it reaches .050 lift. Read degree wheel. Continue around until you come to .050 before closing. Read the degree wheel and do your calculations.
 
One detail I don't see is if you set the clearance to zero prior to reading the lift on the valve. All readings must be at Zero lash to be accurate for the C/L . I have found on many cams the C/L is always way off its not unusual to see upwards of 10 degrees of error. To correct this its difficult it usually takes me many days to get the C/L per the timing card. I always move the cam gear bolt pattern to get the cam timing correct.
Ronnieroadster
 
Make sure you verify that you have accurately determined TDC on the cylinder where you're installing the valves - use the "positive stop method" to ensure you have correctly found TDC. Also, if you don't have a timing cover on the engine, make dang sure the cam is not WALKING OUT of the block - as the cam thrust direction on an 8BA is toward the timing cover - opposite of 32 - 48 engines. As you turn the crank, the cam will want to move forward . . . completely screwing up all your cam timing readings. As Ronnie noted, make dang sure you have the valve lash set to ZERO.

I frequently need to change/move the cam timing - as it may not match the card. I do this on my milling machine with a rotary table. I replicate the pattern and "move it" the number of cam degrees that I need - and then add a new cam gear timing mark. This sounds a bit difficult, but if you have the necessary equipment, doesn't really take that long.
 
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How much of the valve train is installed? Is it possible the valve is not dropping down following the cam profile? If so, push it down manually and you can go past and back it up to your second measurement point. I recently got a cam from them and it was only a couple of degrees advanced relative to specs. It was the third one though! The first two they sent were the wrong cam, short on lift by 0.025”, but I eventually got the correct cam. So, worth checking (though I doubt I would notice the difference )
 
Ronnieroadster said:
One detail I don't see is if you set the clearance to zero prior to reading the lift on the valve. All readings must be at Zero lash to be accurate for the C/L . I have found on many cams the C/L is always way off its not unusual to see upwards of 10 degrees of error. To correct this its difficult it usually takes me many days to get the C/L per the timing card. I always move the cam gear bolt pattern to get the cam timing correct.
Ronnieroadster
Click to expand...

I did set the clearance to Zero. In fact, I lifted the valve off the seat 0.001" and then zero'd my indicator.
 
Bored&Stroked said:
Make sure you verify that you have accurately determined TDC on the cylinder where you're installing the valves - use the "positive stop method" to ensure you have correctly found TDC. Also, if you don't have a timing cover on the engine, make dang sure the cam is not WALKING OUT of the block - as the cam thrust direction on an 8BA is toward the timing cover - opposite of 32 - 48 engines. As you turn the crank, the cam will want to move forward . . . completely screwing up all your cam timing readings. As Ronnie noted, make dang sure you have the valve lash set to ZERO.

I frequently need to change/move the cam timing - as it may not match the card. I do this on my milling machine with a rotary table. I replicate the pattern and "move it" the number of cam degrees that I need - and then add a new cam gear timing mark. This sounds a bit difficult, but if you have the necessary equipment, doesn't really take that long.
Click to expand...
I did both methods to find TDC and verify against each other. Did the positive stop method and also used dial indicator on top of the piston and very carefully watched the dial. I did notice the cam trying walking out, but made sure to keep my thumb on the cam pushing back into the engine.
 
I went to check again last night and found the following issues contributing to my readings. 1) I only had 3 bolts in the cam gear and by luck, the one I didn't put a bolt in was the smaller hole that indexes the gear to the cam. So there was some small room for error in the mounting holes. 2) For Sh!ts and giggles, I advanced the cam gear one tooth and re-checked. Things are looking better and measured CL of 106.75*. Obviously too much now. So I need to set it back to normal and advance the cam 7* with the bolt holes to get my 110* ICL.
 
The fun part of checking the cam timing per the timing card something very few will attempt. Your doing a good job and discovering why your readings were off. Now comes the fun part of getting the bolt pattern to the point where your happy with the readings. I will say at 110 you will be very happy. Not many realize the cam gear holes are oversize except for one or maybe two depending on who made the gear.
Ronnieroadster
 
Also, you need to check both the intake and the exhaust on the same cylinder - as the amount that the cam "is off" may not be the same (though it should be). I've seen plenty of cams where the advertised lobe-centers or the grind itself was off - some to a very high degree. Some of the biggest names in the market, produce some of the most inconsistent stuff today.

So check both lobes and determine if the cam timing can be fixed with just a re-drilling of the cam gear.

Good luck! Hopefully just a new bolt pattern can correct the issue . . . if not, send it back.


BTW: You have a couple highly recommended cam grinders here on the Barn - 'Pete' and 'Kiwinus' (Tony). You might check with them on their products and recommendations.
 
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