Sprocket parallelism

logician · 10-10-2002, 11:18 PM

Hi,

Has anyone out there checked chain sprocket parallelism? I'd like to check the parallelism in my 930 engine, because I suspect a previous mechanic may have mixed up the shims. I've read the procedure and it looks pretty sensitive to errors. If you've got any words of wisdom on the procedure, I'd appreciate hearing from you.

Thanks!
-Juan

ChrisBennet · ChrisBennet's Garage

I've done it and you're right, it is sensitive to errors. I found it necessary to have an extra set of hands to hold the straight edge. Stomski Racing makes a tool so you can do it a little easier.
-Chris

RoninLB · 10-11-2002, 04:35 AM

I believe Pelican has a good inexpensive one..............Ron

ChrisBennet · ChrisBennet's Garage

Ron,
I couldn't find it on Pelican. Here is the Stomski Racing one.

-Chris

RoninLB · 10-11-2002, 05:25 AM

thanks Chris..I gotta buy one before I open her up..................Ron

TimT · 10-11-2002, 01:50 PM

Ron, your rebuilding it?

RoninLB · 10-11-2002, 02:54 PM

No Tim..not rebuilding...Rudtner just did the final smog on the '77..and I got brand new E-cams in the closet..spoke to PMO on the Ride..anyway, as soon as I get my act together I gotta do the prep work..SSI/fume detector/Monty/Aircraft Spruce EGT system/MSD...the previous rebuild, 40k ago, saw 8.5 RS pistons/Raceware studs & rod bolts/Competition Engineering/etc..so I figure with 2 Big Rides and 10k of easy street driving/1 DE and it being tighter than a crabs a$$, and it being a carb eat carb world, I just gotta do it...I use 2 pocket warmers all winter...........Ron

Wayne 962 · Wayne 962's Garage

The sprocket parallelism is tough to do, even with the engine out of the car. I recommend the Stomski tool in my new book...

-Wayne

GIBSON · GIBSON's Garage

It is tricky to measure, a true straight-edge is critical. I have a depth gauge that slips up against the straight edge and stays in place pretty well so I can get accurate readings.
I think it's important and worth taking some time to do it.
Here's my 73 set up to check the backspacing:

speeder · speeder's Garage

Bruce, What did you use to get your cases clean? I have my motor out now, got it pretty clean w/ a steam cleaner, but want it to look like yours. Very nice.

304065 · 10-11-2002, 09:41 PM

A former colleauge of mine decided to tear apart his 68 911S motor to put on some solid tensioners, and lo and behold, he found that the PO had installed the port cam sprocket backwards, e.g. with the cup facing forward. The port chain was cutting into the aluminum case and there were chips in the sump. So I would definitely make sure that the chain alignment is straight as a string: the Stomski tool is worth it, even one time.