TDC confusion need help...

[lindy 911]

See previous post.

[911pcars]

Originally Posted by ertech

Thus is what I did
Removed the # 4 plug
Put my compression tester in
As I approached z1 the #4 cylinder was building pressure so I assumed I was on #4 compression, my rotor was pointing at 1
Past the z1 and rotated a full 360 to z1 no pressure buildup on 4
Took dist off and lined up the rotor to the mark pointing at 1
Thanks all for your help

Does this look right?

That works as well. You also could have saved a step after identifying TDC, end of compression for Cyl. no. 4 by confirming, then, if needed, adjusting the rotor with no. 4 spark plug wire on the cap.

Confusing to some is that in a 911, cylinders 1 and 4 are paired cylinders. If one piston is at TDC, compression stroke, the other piston will also be at TDC, but on the exhaust stroke. On all 4-stroke cycle engines, the following method determines physically paired cylinders:
Firing order: 153624 (a firing order used on some 6 cyl. engines)
1-5-3
6-2-4
The paired cylinders on the above engine are 1-6, 5-2 and 3-4. Try the above formatting with the 911's firing order of 162435

As for which method is faster to identify TDC-compression:
a) Confirm compression on cylinder no. 1 (or no. 4 as above).... or
b) Remove valve cover and confirm slack in the valve train (intake and exhaust) for no. 1 cyl.

.... it depends on what's easier/faster/more convenient to perform. YMMV.

Hope this helps,
Sherwood

[ertech]

I for sure did the easiest way by confirming compression on 4 and lining up spark plug wire 4 with rotor

Thanks for confirming my method was ok