Piston stop on a big block with iron heads

[Righty Tighty]

Am I doing it wrong? When I used a piston stop on my 318, it worked as expected, meaning there was definitely a positive stop when the piston contacted the....stop.

But with my 440, it was a lot harder to feel when the piston contacted the stop. Since I wasn't sure, I ended up going back to using a wooden dowel and marking twice, then dividing the two.

When I removed the heads, my suspicion was confirmed when I looked at the #1 piston. The piston stop simply slid along the top of the piston due to the sharper angle that the plug is at. I could tell because there was a line scratched in the piston made by the stop. I wish I took pictures when the heads were off so everyone could see, but the engine is back together.

Has anyone had this experience? What did I do wrong?

 

[Rat Bastid]

Because the spark plug angle going into the head is much more perpendicular to the piston stop, I’ve found that the stop needs to go much farther in to avoid what you found. It needs to go quite a ways into the cylinder to make the stop positive.

 

[Righty Tighty]

Thanks a bunch. I suspected it had to do with the angle, but wasn't sure how to correct it.

 

[Bewy]

Agree with RB. What works on engine type may not work on another. Almost has to be 'custom made'.

 

[1WildRT]

Agree with RB. What works on engine type may not work on another. Almost has to be 'custom made'.

My BB piston stop is an old spark plug with all the porcelain removed and a 4" long 1/2" diameter rod welded into the bore...

 

[RustyRatRod]

It's the angle of the dangle. You need to pull it out and put more in.

 

[Righty Tighty]

It's the angle of the dangle. You need to pull it out and put more in.

Not everyone is so blessed to have more to put in...

 

[PRH]

One mistake I’ve seen people make is not removing the rockers for that cylinder.
The stop often needs to go in far enough that opening valves would contact it.
Crane used to sell a nice large diameter solid brass stop with a hole in the center to keep air from being trapped in the cylinder while running the piston up/down.

 

[Righty Tighty]

I wouldn’t have thought to remove the rockers, thanks for the info. That piston stop looks much nicer than the cheapo I have.