Finding true TDC

[JeepSJ]

Thanks to JDave, I now have a timing pointer. The pointer has slots to allow for adjustment when installing. I want to make sure I get this thing installed correctly. Any ideas for finding true TDC? I'd rather not pull the accessories and front cover off...again. If it was a gasser, I could use a dial indicator through the spark plug hole. Think I could get an indicator through the hole in the pre-cup if I pull an injector?

Thanks!

[Kennedy]

Without the head off it's pretty tough. A piston stop and a degrree wheel is the way that I prefer do it for gassers. Rotate till stop one direction, note degree. Rotate till stop the other way, note degree, and half way between is TDC...

[Ken Finchum]

Put a small baloon on the end of a small clear plastic hose. Insert the baloon into the cylinder thru the glow plug hole. Suspend the hose vertically. Fill the hose with water and let it drain down into the baloon. As you turn the engine over and the piston comes to the top it will force water out of the plastic hose. When the piston gets to the top, run it back and forth through TDC. The water will go up and down in the hose. TDC is at the high water point or half way betweeb the point where it is say, 1/2 inch down the tube before and after TDC. Check it both ways to convince yourself.

[tom.mcinerney]

I made a (TDC)mark with heads off. I also made a second mark at point of rotation when all piston crowns were below the deck.

I post here because my experience was that i couldn't rotate the engine with enough control using the breaker bar on a crank nut/bolt....I wanted to get a starter core , and use a wrench on the armature shaft -- so i had the reduction gear magnifying torque. But then i couldn't have simultaneously seen the results!

If you're not queasy pursuant Cowracer's nightmare you might consider , as a modification of Ken's preceding suggestion , inserting some oil into the cylinder/prechamber {both GPs and injectors access the prechambers} , and observing the level of the oil in a transparent tube (tygon/vinyl hose) attached to a [GP/Injector] compression testing adapter.

Or , still following Ken's notion , how about tape a balloon onto the comp-test adapter , surround the baloon with a clear plastic graduated tube , then observe comp peak with a dry indication [that'll blow a couple hours!].

An assistant , lying in mud beneath the bell house , barring over the flywheel is optional.

[JeepSJ]

Why didn't I think to do this when I had the heads off...?

[Kennedy]

I am assuming you just want reference to know where to time it? I'd just slap on the OE style tab and run with it. Set your timing to spec according to the tab. You can experiment by moving a couple of degrees either way until you find what you like best. In the end accuracy is not critical, it's having a solid point of reference to return to that is.

Unless I am missing something...

[JeepSJ]

The slots will let this thing move more than 5 degrees. So you are saying to just time it by sound and power? With as sensitive as these are to timing, I'd really like to be able to set it accurately.

[Kennedy]

I'm saying use a timing cover with the tab on it (mechanical pump era) and reference it when you time the engine, or try to locate your tab as close as possible to correct and go from there. It may not be highly accurate, but close enough. Once you find a setting that you like, note it somewhere safe and you can always come back to that point.