Finding TDC on a bolted up motor???

Is there an ACCURATE way to find TDC on an SBC that's been bolted up? If there's some way to do it without pulling it apart and using a dial indicator, please tell me.


Thanks,
Ed

 

A dial indicator actually won't do the job to within more than 2 or three degrees--you can do better, head on or off. A Chevy, like a flathead, has some dwell at TDC with almost no vertical motion over several degrees.

 

On a Chevy, you block the piston a bit before TDC with a special obstruction tool. Turn the engine by hand until it hits the obstruction, mark your degree wheel or balancer, then turn the engine the other way until it hits and mark again. Turn by hand with wrench, of course.. Half way between marks is TDC, more accurately determined than by indicator.

 

The tool is simpler for a Chevy than for a flathead--just a sparkplug shell with a bolt through it. Beat the *&%^$%# out of a plug until only the threaded shell remains. Wait for wife to go to mall, heat the shell on the stove to soften it a bit. Thread the inside, I think 3/8 coarse works on small plug engines, I don't know for pre-1969 type. Thread through a longish bolt with tip rounded to a safe contour, and first put a lock nut up top. Extend and lock it a short distance into the chamber.
If heads were off, usual tool would be a simple strap across cylinder held by two head bolts and a bolt through the middle as adjustable stop.

 

cant you just pull a plug, put a screwdriver in its holes and rotate the crank until you see the screwdriver reach its full height? I've seen it work before.

 

Thank you Bruce. That's the exact response I was looking for -- an easy, foolproof, accurate method that doesn't involve pulling the heads. You just saved me $20 that I would have spent on a new head gasket!


Ed

 

It can be done several ways,each one a little more or less accurate than the other.
I would ask why you are doing it ,to set ignition timing ,cam timing ,check accuracy of harmonic balancer?
To set timing, the object into the plug hole works.A piece of brazing rod will do fine.

 

Here's a home-made tool very similar to what Bruce is talking about.

In my case I used one of the gizmo's that raise the spark plug to help in a cylinder that oil fouls.
After it was cut down, it was drilled and tapped for the bolt you see.
The bolt had additional threads spun on with a die and aside from rounding the nose on the bolt - which I feel is important - that was it.

Depending on the engine it's used on you can get the bolt at a pretty good angle so you don't want to bash it with the piston coming up. Treat it like a girl . . . light kisses work the best....

 

[ QUOTE ]
The tool is simpler for a Chevy than for a flathead--just a sparkplug shell with a bolt through it. Beat the *&%^$%# out of a plug until only the threaded shell remains. Wait for wife to go to mall, heat the shell on the stove to soften it a bit. Thread the inside, I think 3/8 coarse works on small plug engines, I don't know for pre-1969 type. Thread through a longish bolt with tip rounded to a safe contour, and first put a lock nut up top. Extend and lock it a short distance into the chamber.
If heads were off, usual tool would be a simple strap across cylinder held by two head bolts and a bolt through the middle as adjustable stop.

[/ QUOTE ]

looks like this;