Hey Guys,

Some minor digging in various threads and websites have 50/50 answers telling me different things for TDC with my heads off and I want to get this as accurate as I can.

Right now, I have the cylinders bare as the heads are finishing up at the machine shop so now would be a perfect time to check TDC as I'm the second owner of this car and it's sat for a while so who knows what was done to it. I don't have a dial indicator or a degree wheel and the balancer doesn't have any marks on it with the exception of a single slash on it. The factory timing tab is still visible on the block so I'm looking to mark the balancer with a grease pencil, timing tape, etc so I can have a permanent reference point.

What's the best method? Crank it until #1 piston comes completely to the top to mark TDC? Is that compression or exhaust? Is this an accurate method and if not, what else do you recommend without having degree wheel, dial indicator, etc.?

 

The number 1 piston will be at the upper most top of the cylinder and the line on the balancer should be pointing to the "0" mark on the timing tab.

 

You need one of these. It's called a piston stop. You rotate the crank one way until it hits the stop and mark the balancer there. Rotate the other way, again mark the balancer and split the difference. That is TDC. Whether it's compression or exhaust stroke depends on the cam, not the crank.

 

The piston stop or a dial indicator are the most accurate methods because they do not rely upon using the mark on the balancer which may have slipped. If the balancer has slipped your reference for TDC could be off significantly. Since you have the heads off make it as accurate as possible because this is the base from which valve timing and ignition timing are measured.

You could make a piston stop by bending a piece of metal and clamp or bolt it to the block, it does not have to be fancy.

If you use a piston stop or a dial indicator mark the TDC location on both the inner and outer rings on the balancer. This will let you know if the balancer has slipped or slips in the future and the mark on the inner ring will provide a reference to where TDC is located without relying on the outer ring.

 

In agreement with all of the above:

The only two ways to confirm TDC with adequate precision are the piston stop (either bolted to the head or threaded through the spark plug hole) or the dial indicator.
The piston "pauses" for several degrees at TDC and BDC, moving too slightly for you to see or feel without extra equipment, and potentially leading to marking the balancer a few degrees off.

As for compression or exhaust: Without the cam installed, they're the same thing.
Think about it.

- Eric