Sprocket alignment-how many shims are too many?

ddinham · ddinham's Garage

Was aligning the camshaft sprockets tonight and started with the base count of 4 shims on #4-6 and 3 shims on #1-3. I had to add one shim on the right side #4-6 to get it within spec. When I switched over to the left side # 1-3, I had to add 2 more shims to get within spec. Is there a limit to the amount of shims one should use? Is there a point where stacking shims to get within spec points to other problems?

TIA
Dana

Flat6pac · 08-09-2012, 05:23 PM

I would redo the measurments. Once you take it off the table its hard to check and it will eat the chain wheels.
Make sure you tighten the nut or bolt close to spec to pull the cam forward into the chain wheel.
Bruce

ddinham · ddinham's Garage

Bruce,
Reading your response, I think you are saying that I have too many shims and should start from scratch?

Eagledriver · 08-09-2012, 08:23 PM

I've only built 4 engines, but I've never seen anything other than 3 or 4 shims.

-Andy

Flat6pac · 08-10-2012, 04:18 AM

I dont usually count shims but install or remove them as needed to come in on the measurments.
I dont consider starting over but it only takes a few minutes to do the math with a bar and the depth guage to make you assured of your work.
Bruce

Walt Fricke · 08-17-2012, 09:57 PM

Dana - what motor? Makes a difference in how you measure, doesn't it? Older motors you measure down to the 1st (right side) IS gear, and use that as your base. At some point , didn't Porsche close off the hole used for this purpose, and said just start with X, then for the left side add the usual Y as before. 3.2s??

Flat6pac · 08-18-2012, 03:02 AM

On a Carrera the numbers are from the nose of the intermediate shaft but you still have to measure from the front of the case so you need to know the depth to the IS and factor it in with the other math.
Bruce

ddinham · ddinham's Garage

Walt,
It is a 7R case. In the end, I took Bruce's advice and just relied on the micrometer/depth gauge to get the correct settings and sort of ignored where I was on shim count. My biggest problem was getting consistent measurements. I was using the Stomski alignment tool so that helped but it was difficult getting the same measurement twice.

Bruce,
As always, thanks for your help.

Dana

4sd911 · 08-18-2012, 07:46 AM

Quote:

Originally Posted by ddinham

I was using the Stomski alignment tool so that helped but it was difficult getting the same measurement twice.

I had a problem with the Stomski's strait edge, it wasn't quite strait. I could flip the bar over and get a little different reading. With the + or - 10 thou. measurement room and the shims being 20 thou. on one side it didn't make any difference, the other side was right at the 10 thou. max. By checking the measurement twice by flipping the strait edge I could get a average measurement. I also checked with a hand held strait edge, that is tough by your self.

Walt Fricke · 08-18-2012, 08:59 PM

The first time I tried this I used a borrowed depth micrometer and a stgraight edge made by sawing off the small arm of a carpenter's square. Holding things on by myself. I must have measured each side a dozen times. I made a graph and picked a kind of average. It seemed to work.

Years later, when I got the Stomski tool, I was able to use just a digital caliper. I didn't even have to attach the "foot" I had purchased to make its non-moving end steadier when attached to the caliper. The depth mike set I had purchased lies dormant. And the sprockets were spot on from a previous measurement with the carpentry piece. I was almost disappointed.

With one of my engines I am having a different issue. This motor, which I purchased, was made from two separate case halves. The machinist did a great job, it ran well, I kind of regret tearing it down because even the rod bearings, even after 100+ race hours shifting at 8,200 rpm, looked like they could go another hundred, etc.

But there are four "lips" involved with the straight edge. Two where the IS end cover bolts on, and two which are outside those and are where the motor hanger mount fits. In a normal engine the IS part is a bit farther out, and the edge rests on that, and just clears the others. But somehow things aren't quite that way here. I think I will have to make nicely flat steel shims to make the IS part stick out some, and add those into the calculations.

But my Stomski straight edge seems to be dead straight on both sides.

kwikt 911 · kwikt 911's Garage

On another note.... when all is tightened down. Is there any in and out movement with the camshafts?