shaheed

with the front cam timing mark lined up, i find the rear alignment tab on the OT itself rather than on the scribe mark above the OT. with my other car it always lined up on the scribe mark. does this suggest timing may be off by a tooth or is this a normal variance?

hosrom_951

Shaheed,
I never use the flywheel OT mark to make sure piston 1 is at TDC, even if the camshaft mark is aligned with the rear cover.

The best thing to do is to remove the #1 spark plug, insert a long screw driver in and while aligning the cam, you will see the screw driving getting higher (the piston pushes the screw driver upwards). Once the screw driver reaches the highest point, is where TDC is on the crank. When i did this, the OT on the flywheel AND the lower flywheel groove were not indicating TDC (PO's mechanic didn't align the flywheel correctly during a clutch job). Using the screw driver method, i always get TDC on the crank more accurate this way.

This way, one always eliminates being off by a tooth or more on the crankshaft.....

Hope this helps (even a little bit)

m42racer

"The best thing to do is to remove the #1 spark plug, insert a long screw driver in and while aligning the cam, you will see the screw driving getting higher (the piston pushes the screw driver upwards). Once the screw driver reaches the highest point, is where TDC is on the crank. When i did this, the OT on the flywheel AND the lower flywheel groove were not indicating TDC (PO's mechanic didn't align the flywheel correctly during a clutch job). Using the screw driver method, i always get TDC on the crank more accurate this way"

More accurate? What about the amount of degrees the Cranks turns while the Piston is at dwelling at the top of the stroke. On these engines that could be quite alot could it not? It probably would be a least a tooth. There is a correct way to do this and I do not think your way is.

theedge

Its a pain using the piston method. I tried. Its great to get you in the general area of TDC if you cant find the mark though.

I got it pretty close, but it was difficult trying to gauge what was the "middle" of the dwell.

Porsche-O-Phile

The piston method works great. . . with the head off.

I prefer to use the bellhousing mark myself - far easier and you've gotta' be down there to remove the starter bolts anyway!

m42racer

Actually there is a tool made for this job. It screws down the Plug hole and has a dial indicator at the other end. You would bring the piston to TDC and zero out the gauge. Then you would turn the engine backwards maybe a full stroke then back clockwise up to say 0.020" before the zero mark on the gauge. At thos point you would mark the front pulley. Then turn the engine further clockwise past the zero point until the gaugae read 0.020" again. You would then mark the pulley. You would then split the 2 marks and find the center. That would be true TDC removing any of the Piston dwell. The proper way would be to use a degree wheel, but this way will allow the same result without having to fit a degree wheel.

Now you say, where do I get this tool. Most engine builders I have bbe around either make them or I think there arev suppliers to the engine building world who sell them. If you understand how this works, heres a good tip when using the screw driver method. I have seen this done at the race track, when this tool was not available. Instead of reading the gauge at 0.020" each side of zero, he measured the distance from the end of the screwdriver to the Cylinder Head. This was done when the Piston was veryclose to the top. Then he turned the engine clockwise further until the same distance was measured down to the head. At each position the pulley was marked and the distance between the 2 marks split and this was TDC with the dwell removed. These engines with a Long stroke and long Rod do dwell at TDC for many Crank degrees.