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Cam Orientation For Valve Clearance

S

smallfry99

New member
Joined
Aug 9, 2012
Okay, I Have a 1992 940 Turbo. 530 head. Bought the performance camshaft from IDP. Now after a week time to recheck the valve lash.

Question: I was ready to check clearances with the cam lobe peak facing 180 degrees away from the shim. (that is how I had seen it done before and it is the part of the cam that would allow a finite number when checking). Then I saw a video and a listing here that say to set the 2 cam lobes facing upward for each cylinder and check the gap on the flat side of the lobe. But, I checked. The IPD cam has no "flat" side. Yes, there there are 2 sections on each lobe that are almost flat but are slightly curved. Even a degree or 2 in rotating the crank/cam changes the gap when trying to align the "flat" side of the lobe horizontal to the shim. Forgive me, I am learning...

Any help on the correct method is greatly appreciated. Thanks
 
Any place on the base circle away from the lift ramp is ok. Some OEM lash procedures have you do 4 valves at TDC #1, then the other 4 at TDC #4.
 
When the pair of lobes on the cam for a cylinder are upward in a V shape, the piston in that cylinder is at the top of it's stroke, the beginning of the power stroke. This is called TDC, or top dead center, on that specific cylinder. On every solid lifter cam car I've owned the procedure is to check and adjust lash at each cylinder when it's at TDC. Because the cam rotates half as fast as the crank, set the cam so that cylinder 1 at TDC, the crank gear mark will line up with the belt cover TDC mark. Then rotate the crank another 180 degrees for each cylinder. The firing order is 1-3-4-2.

TLDR the lobe doesn't need to be straight up, just set each cylinder to TDC.
 
That is also a valid way, and how I usually do it.
The point I was making is that the claim about the flat vs the curve of the base circle is not true.
 
Static TDC is different than Dynamic, not to confuse things.
So best to do some measuring, and open a book or new webpage?
 
mikep said:
Any place on the base circle away from the lift ramp is ok. Some OEM lash procedures have you do 4 valves at TDC #1, then the other 4 at TDC #4.
Click to expand...
I’ll add a bit to this as well.

With longer duration cams, the ramps can interfere when checking lash as you would with a stock cam ( both lobes pointing up in a “V”). So what I do now is put one lobe straight up to check, and there will be another lobe just about straight up on another cylinder so you can check that one as well. Then rotate engine over until the next set of lobes points up and then check those ones.
 
h20ham said:
Static TDC is different than Dynamic, not to confuse things.
So best to do some measuring, and open a book or new webpage?
Click to expand...
Huh?
I mean there’s slight, and I mean slight, differences due to deflection in an engine but I don’t think that applies to anything here.
 
culberro said:
I’ll add a bit to this as well.

With longer duration cams, the ramps can interfere when checking lash as you would with a stock cam ( both lobes pointing up in a “V”). So what I do now is put one lobe straight up to check, and there will be another lobe just about straight up on another cylinder so you can check that one as well. Then rotate engine over until the next set of lobes points up and then check those ones.
Click to expand...
I thought about mentioning that, but it was early. When I had students good enough to teach valves, I made them put a paint mark on each one when adjusted. Then I went back to check them myself. We also ground valves and cut seats. Not anymore. I tried this year, never even got started.
 
mikep said:
I thought about mentioning that, but it was early. When I had students good enough to teach valves, I made them put a paint mark on each one when adjusted. Then I went back to check them myself. We also ground valves and cut seats. Not anymore. I tried this year, never even got started.
Click to expand...
I do the bounce around method and I just write it down as I go so I know where I’ve been. I keep records of every check so I’ve got a rolling history
 
culberro said:
Huh?
I mean there’s slight, and I mean slight, differences due to deflection in an engine but I don’t think that applies to anything here.
Click to expand...
The distance from centre of wrist pin in piston, crank timing from what is close to BTDC and ATDC and the length of the con rod all play a part.
merely saying it is worth thinking about
 
h20ham said:
The distance from centre of wrist pin in piston, crank timing from what is close to BTDC and ATDC and the length of the con rod all play a part.
merely saying it is worth thinking about
Click to expand...
I'm legit confused.
This is a thread about checking valve clearance to the camshaft.
How does what you're saying have anything to do with this?
 
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