I wanted to verify the accuracy of the timing mark in my '73 small block so I bought a piston stop tool to find TDC. Ran into some problems and wanted to run it by the forum to see what y'all think.

Disconnected the HEI. Removed the #1 plug. Bumped the engine with the remote starter until I felt pressure coming out the hole. Inserted the piston stop tool outer plug and tightened same as I would a spark plug. Inserted the inner bolt of the stop tool and set the head to be flush with the outer plug. Turned the engine by hand in a clockwise direction (if facing the front of the car) until I felt contact with the piston stop tool. So far so good. Marked the balancer at 0 degrees. At this point the original timing mark was in a position about 14 degrees after TDC.

Then I began turning the engine by hand in the counter clockwise direction but after several rotations and wearing myself out I never felt contact with the piston stop tool.

Pulled the tool and the inner bolt was slightly bent. Put it back in and this time instead of setting the inner bolt head to be flush with the outer plug, I set it as far as it would go which was about another 1/4". I continued with the counter clockwise direction and momentarily I felt contact with the piston stop tool. Coincidentally 0 degrees lined up perfectly with the first mark I made. However, I remembered that I had adjusted the inner bolt to extend further so I then began turning the engine clockwise to make a second mark but once again I was unable to feel contact with the piston stop tool. Pulled it again and the inner bolt was bent a little more this time. The inner bolt had obvious contact marks about 1/2" and 3/4" from the end of the bolt.

So, now what? Should I use a longer inner bolt with the stop tool? A stronger bolt?

Once I make initial contact with the piston stop tool, how many revolutions of the balancer will it take in the opposite direction for the piston to make contact the 2nd time?

Thanks for the input!

DC

 

You're not feeling the stop when you reverse the rotation for some reason. Maybe several things going on here. Try again by removing all the plugs so you are using less effort and you might be able to feel the stop on the reverse trip. Also, when you get near the top of the stroke the piston is hardly rising at all and you are still turning the crank at the same rate so you actually have great leverage up there. Get a piston stop that goes in deeper. And yes, one crank rotation = a full two strokes ( top to bottom & bottom back to top)

 

Most of those piston stop tools are junk. I ended up making my own using my lathe and an old plug which I broke out the porcelain and braze welded a 4130 stop into it. There is a lot of force able to contact the tool, so it needs to be fairly strong. I know it took me a bit of trial and error to get repeatable results. Be careful when making a tool as there can be valve clearance problems with some heads.

 

Thanks to both of you for the suggestions.

The stop tool's inner bolt is just standard 3/8" threads. I'll find a longer and stronger bolt. I'll also pull the other spark plugs to make it easier to turn the engine and feel the contact.

This is one of those projects I thought would be a 30 minute job but it whipped me in round 1.

DC