Small Block 340 Bore size, when is going big too big?

[JimCuda]

Ok, so I pulled the 340 out and the good news was it was the factory motor. Bad news was one piston was spent and the motor had already was gone through once.

It looks like the motor was bored out from the 4.040 to 4.070. I believe this from the .030 on the piston.

Bad news is it needs to be bored out a bit more to clean up the piston bores. This was confirmed by running a bead honer through the piston bores.  I don't think I would have to take it out beyond 4.080 if 4.070 is where it is really at.

What is the max anyone has bored out a small block 340? I heard about the fabled .060 over but never knew anyone that ever ran a 340 with that big a bore.

Anyone got some machine shop stories on bore size?

[hemiken]

You will have no problems at all running a 340 out to .040 thou over bore.  Very safe, go for it.

[422STROKER]

Have it sonic checked at the machine shop.  Mine has a 4.100" bore now.

Tom

[JimCuda]

I heard that you had to do a sonic test going that big. You have confirmed that for me for sure now. Thanks

What type of crank and pistons set did yo end up going with? You run any power adder? (Turbo, SuperCharger, Nitro)

[422STROKER]

I heard that you had to do a sonice test going that high. You have confirmed that for me for sure now.

What type of crank and pistons set did yo end up going with? You run any power adder? (Turbo, SuperCharger, Nitro)

Naturally Aspirated.

Diamond Pistons and Eagle Crank 4.00 Stroke.

Tom

[Chryco Psycho]

you should be fine @ .060 , no prob @ .040 , sonic checking never hurts though

[71chally416]

I've seen a '72 360 spit the bore at .030" over with hard useage, and they're supposed to have the same bore thickness as the bigger bore 340 because the internal sand core at the foundry was the same. It's a great idea to sonic check ANY engine block you plan to invest money in, no matter what it is.