Block boring

[Ken/Alabama]

Can anyone tell typically how far a 39-40 81A block can be bored ? I have a good 81A block that’s had the sleeves removed when I got it so I wanted to just go to 3 3/16” std but I have a nice already balanced rotating assembly I want to use but the pistons are 3 3/16” +.040.

 

[Pete]

Can anyone tell typically how far a 39-40 81A block can be bored ? I have a good 81A block that’s had the sleeves removed when I got it so I wanted to just go to 3 3/16” std but I have a nice already balanced rotating assembly I want to use but the pistons are 3 3/16” +.040.

Back in the "good ol' days", this would have been no problem.
Today, the reality is, MAYBE.
Rust and scale is the enemy.
The only safe way is to have the block acid stripped and then sonic checked.
Acid stripping is the only thing that will take the scale out.

 

[Ken/Alabama]

Thanks Pete, The problem is that there is absolutely no one around here that can do either one. I might just go for it anyway. I’ve had worse things to happen.

 

[Ken/Alabama]

Got to looking around. I’m thinking I’ll go with std 3 3/16” pistons and I have a nice set of 29A rods and a Mercury crank to go with it. It’ll cost me a set of pistons and a balance job.

 

[alanp561]

Thanks Pete, The problem is that there is absolutely no one around here that can do either one. I might just go for it anyway. I’ve had worse things to happen.

I don't know where you are in AL but if you're anywhere Chattanooga, Roberts and Sons, 4285 Bonny Oaks Dr., Chattanooga, TN, 423 698 4097, is the place to go. I've been very pleased with their work. Bobby, the owner, races vintage flathead dirt cars.

 

[Ol' Ron]

Like Pete said, this was quite normal back in the day.Also Balancing is another thing we never did, because there were no one that did it. Bells in NJ did it and after 3 months of waiting, we finaly got it back. Also for street piston weight isn't that important, it;s the big rid end you have to worry about. always keep your rod and cranks together.. Now our engines never ran more than 5k, and the hydro engines were always balanced, but by then more people were dolig it. So turn around wasn't bad. I have a ste of "small 2" "H' beam rods coming for a late crank turned down. This will be a balancing problem I'm told?????