timing gear alignment question!!! please help!!!

hillelson1 · 07-20-2006, 05:18 PM

i have been rebuilding a 1988 930 motor. i have been fallowing the "how to rebuild and modify your porsche 911 engine" i am at the point where i am checking the tolerence of the cam gear alignment to see if i need to add shims. the book doesn't make any sense. could some please give me a desciption of the process and the #'s that i should come up with in a SAE format since i only have a SAE caliper. the book is confusing because it says to add the same amount to both sides but the left is farther back than the right so the #'s in the book must be wrong it says to add something like 43.MM to each side.
you input would be highly appreciated
thanks
-Larry

Eagledriver · 07-20-2006, 07:09 PM

It's not that hard if you think about what you are trying to accomplish. You want the sprokets to be aligned within .010 inches (.25mm). The right bank is easy. You measure the depth to the face of the intermediate shaft sproket. You then measure the depth of the right cam sproket. These are measured from the face of a straight edge that bridges the gap between the sprokets. The straight edge rests against the front of the crank case so that it is perpendicular to the crankshaft axis. You put shims behind the cam sproket to get the depth the same.

The left sproket is uses the same method except you have to do some math to add the distance between the front sproket on the intermediate shaft and the rear sproket on the intermediate shaft. The distance to add is 54.8mm (do your own math to get inches).

Keep in mind the sprokets are "dished" so that the right sproket has the dish "in" and the left sproket has the dish "out". They will not be in alignment with each other if you don't get that right.

This is not that hard a concept but the actual measureing is hard because you have to keep the staight edge stable and measure carefully because the tolerance is small.

-Andy

hillelson1 · 07-21-2006, 07:29 AM

thank you andy that cleared it up for me

Wayne 962 · Wayne 962's Garage

Be sure to check the updates and corrections page for the book. On the early additions, there was an error there:

Quote:

Page 159 - The value 54.8mm should be subtracted, not added to the value. Also, the shim thickness is 0.50mm, not 0.25mm

The corrections page for the book is here:

http://www.101projects.com/911-Rebuild/corrections.htm

-Wayne