Another way to find TDC

[Syncroincity]

In torquing my crank pulley, I inadvertently turned the engine, so my pre-set TDC was gone. I was having no success going thru the injector... I pulled the intermediate shaft out, and was able to observe the #2 cyl skirt protruding out of the bottom, and by noting where #2 hit bottom center & stopped moving, I now had #1 TDC set.

[theman53]

I marked the crank nose, pulley, block, flywheel end of crank and block. I also noted some other locations on the block for 100% sure reference, but I like the IM pulling idea, always good to have another back up.

[burn_your_money]

I don't think that it would be accurate enough to set TDC. If you just need a loose guide then yes it would work but for timing purposes....

[Vincent Waldon]

I don't think that it would be accurate enough to set TDC. If you just need a loose guide then yes it would work but for timing purposes....

...the reason being that the at both TDC and BDC the crank can actually move quite a few degrees with no perceptible piston movement.

The gold standard is to index piston (or in this example, skirt) movement some amount *before* it bottoms out, from both sides of the crank's rotation.  TDC / BDC is then exactly in the middle.

[Mark(The Miser)UK]

I don't think that it would be accurate enough to set TDC. If you just need a loose guide then yes it would work but for timing purposes....

...the reason being that the at both TDC and BDC the crank can actually move quite a few degrees with no perceptible piston movement.

The gold standard is to index piston (or in this example, skirt) movement some amount *before* it bottoms out, from both sides of the crank's rotation.  TDC / BDC is then exactly in the middle.

Indeed, in fact best index is to remove timing belt from cam and set cam to#1 TDC then rotate engine either side of TDC and mark where piston reaches valve. Thus you have two marks created by same piston hitting same valve. Bisect the two points to get TDC...

[Syncroincity]

Yes, I noted a couple of degrees rotation with no piston movement, & I tried to center on half that distance. Tough to do on a freshly assembled block; I had to re-do it quite a few times before I was satisfied with it.

Even with the object-thru-the-injector-hole method you still have to deal with that play in the setting... I'm looking at an engine with no external timing marks whatsoever and the head already torqued down, I had limited options.

Lesson learned: Mark TDC on the engine somewhere IMMEDIATELY when you have it set!

[Vincent Waldon]

Even with the object-thru-the-injector-hole method you still have to deal with that play in the setting

Yup, so the same basic guideline applies... for best results one indexes the piston height thru an injector hole an inch or so below the top of their travel... from both directions.  TDC is then exactly in the middle.