305 small block help???

[hunterlucas]

I bought a project square body and I’m redoing the motor. Well I wasn’t aware of the timing mark on the harmonic balancer when I took it off and I’m at the point of finding tdc. I already have my heads on with new bolts. If I were to take the piston 1 side head off would I have to replace the bolts again or will it be fine since the motor hasn’t ran? My plan is to take off the head, get piston 1 flush with the block then put the head back on.. thanks in advance

 

[legopnuematic]

Use a piston stop in the #1 plug hole, roll engine clockwise to stop, mark, roll counter clockwise to stop, mark, split the difference, there is TDC.

No need to take the head off to find tdc.

 

[hunterlucas]

Once you roll it and it stops, why would I need to go counter clockwise?

 

[1lejohn]

You have to roll it back to find the distance between the two marks. The piston is not really at TDC when you roll it over and hit the stop. It's somewhere in its travel. Then you go back and mark the balancer again.

When you find the two marks you measure the distance between them and divide it in half. That will be TDC. Make sure you mark the balancer for reference at this point. I recently had to do it to my engine.

 

[hunterlucas]

Thank you

 

[xm20k]

It's called dwell there are a few degrees at the top were the piston does not move but the crank and rod does stopping the piston short on either side alows you to find the center of the dwell to be right on TDC.


This dwell occurs at the bottom as well it's just not important out side of maybe an R&D use case.

 

[75gmck25]

A piston stop is cheap, and there are lots of online articles that explain exactly how to use one. You can even make one by drilling out an old spark plug and inserting a bolt.

Also remember that GM used a different place to mount the TDC pointer over the years. Sometimes it’s exactly at the top of the timing cover (12 o’clock) and sometimes it’s more like 2:00 o’clock. Buy a bolt-on timing tab (it bolts on to the timing cover bolts) and adjust it as necessary so it matches the TDC line on the harmonic balancer.

 

[Ricko1966]

Thank you

BTW you don't have to replace head bolts on SBC.