Cam degreeing help

shiftycapone

shiftycapone

wandering the desert
Joined
Oct 26, 2007
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I am in the middle of degreeing in my cam and could use a few pointers. Yes, I used the search feature and found a good thread or two but I have questions yet...

How are most finding true TDC? Making a piston stop or what? The head is on the truck. I rigged up the dial indicator on a rod in the injector bore riding the piston, took the max piston height in both clockwise and counterclockwise rotations. I got the same readings (duh), but not on the degree wheel, so I need to adjust the wheel. Is this a satisfactory way of finding true TDC or not?

Secondly my readings are not matching the numbers on the cam card. This could be attributed to my needing to adjust the degree wheel, which I am now realizing as I am putting it into words. I am taking the numbers at .050" as stated by the builder, and am coming up with the same numbers every time, so maybe it is the wheel and not the installed readings that are off.

This is the degree wheel I am using:JEGS Performance Products 81622 JEGS Precision Degree Wheel

I can provide whatever information is needed to get this resolved. For what its worth I was recommended .070" for clearance between valves to pistons. To give a crude check I used the adjusting nut to lower the intake valve .070" and rotated the motor, the cam swung through without contact, even with the added lift. So in theory the cam would work fine and without contact, but I would like to see exactly where it is. Thanks in advance!
 
Search the drop valve method, it'll be just as accurate as the rod on top of the piston. Take your reading below TDC, so you don't have to bother with the dwell of the piston. There isn't that much dwell, but there is some. Mark your balancer (or make note of the degrees on the wheel) at something like 0.100" below TDC, then split the difference. Do it two or three times so you're confident in the number. If you do it right, should be consistent every time.

When you were doing it the first time and getting different numbers between CW and CCW rotation, were you taking in account of the backlash in the gears?
 
Yes I would back up with sufficient rotation to account for gear lash. I will try the drop valve method.
 
Anyone else with their own methods?

Also, after I take the two readings with the drop valve method and have marked the degree wheel the TDC mark on the wheel should now be my true TDC, assuming I am starting out with the pointer on the TDC mark correct?
 
When you do the valve drop or any other method that positively stops the piston below TDC (consistency is key here), you have 2 marks or recorded degree numbers. Turn the crank to the exact center of those two marks(this is TDC). Then, without moving the crank "zero" the wheel.

You can use 2 pointers if you like, use 1 to find TDC and then add one at 0*.
 
The reason you are seeing two different readings for the tdc mark is not due to gear lash. The piston is connected to the connecting rod and that to the crank. Gear lash is associated with the difference in the crank to cam measurements when measuring valve motion. The reason you see two different measurements is due to piston Dwell at tdc. Go until you get .005 from tdc CW and CCW. Exactly half way between these two is true TDC.

As far as your numbers not meeting what your grinder specd, those specs are supposed to be read off of a pushrod. When you start subtracting .050" numbers factoring for lash and adding to it due to rocker ratio multiplication of lift everything gets out of whack. Reading it off of the pushrod will give you a true .050" number that will match what the grinder told you it would be unless the numbers were factored for rocker ratio and lash. Also, unless your cam was ground on a CNC like a Landis, the .050" numbers can be off by as much as 3 degrees but will usually be around .5-2.5 off.

Goodluck.

Zach
 
teddybear said:
Don't be offended but are you sure you're taking it off the intake lobe and not exhaust?
Click to expand...
Positive, it is the intake lobe. Thank you for your concern thoughLOL
Hamilton Cams said:
The reason you are seeing two different readings for the tdc mark is not due to gear lash. The piston is connected to the connecting rod and that to the crank. Gear lash is associated with the difference in the crank to cam measurements when measuring valve motion. The reason you see two different measurements is due to piston Dwell at tdc. Go until you get .005 from tdc CW and CCW. Exactly half way between these two is true TDC.

As far as your numbers not meeting what your grinder specd, those specs are supposed to be read off of a pushrod. When you start subtracting .050" numbers factoring for lash and adding to it due to rocker ratio multiplication of lift everything gets out of whack. Reading it off of the pushrod will give you a true .050" number that will match what the grinder told you it would be unless the numbers were factored for rocker ratio and lash. Also, unless your cam was ground on a CNC like a Landis, the .050" numbers can be off by as much as 3 degrees but will usually be around .5-2.5 off.

Goodluck.

Zach
Click to expand...

Drop valve method worked, took the readings and split the difference on the wheel. Did it a couple times and worked every time.
Also I was taking the numbers from the pushrod, no crazy mathematics were used. Just keepin it simple. The cam was ground on a CNC machine as well. I am going to check the installed centerline tomorrow. Captainchrysler and I had a pretty good conversation on the subject which cleared up a bit of confusion. I tried calling you Zach but I only got the shops voicemail.
 
shiftycapone said:
Positive, it is the intake lobe. Thank you for your concern thoughLOL


Drop valve method worked, took the readings and split the difference on the wheel. Did it a couple times and worked every time.
Also I was taking the numbers from the pushrod, no crazy mathematics were used. Just keepin it simple. The cam was ground on a CNC machine as well. I am going to check the installed centerline tomorrow. Captainchrysler and I had a pretty good conversation on the subject which cleared up a bit of confusion. I tried calling you Zach but I only got the shops voicemail.
Click to expand...

I apologize, we had a lot of calls yesterday.

Zach
 
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