Out of Round Cylinder Bores

[LAR]

After honing the cylinders out on my stock 340 block to .005 oversized, it is out of round a little. I am putting a stroker kit together and I can get Pistons and Rings that are for a .005" oversized 340. So my stock bore 340 cleaned up really well. at .003" all shadows and marks were gone in the bores.

So now I'm at .005" on the trust sides, and the other sides are tighter by about .001" or so. I know this is due to the pressure put on the thrust side of the pistons and cylinders (sides that are toward the camshaft and outside of the block). So between the cylinders is tighter by about .001" or so.

What do I do? I really don't want to spend $160 to get the block bored out to .010 oversized or the next step, .020 oversized. I want to leave the cylider walls as thick as possible, especially with the extra stress of a 4" stroker crank.

So should I just go with what I have, or get it bored out?

Thanks,

Lar

[tsteiner61]

Here is a quote from the Mopar Engines book, 9th Ed. p.35.

Having a STRAIGHT bore that is ROUND with NO TAPER is THE single most important step in building a race engine that produces good horsepower, high rpm and/or high specific output.

And yes, the capitalized words are in the book that way.

Spend the money. .010 over shouldn't be any problem for a 340 block even with the stroker kit.

[DartByU]

Good straight round bores are very important if your looking for the max. horsepower, but you may not be able to go just .010-.020 oversize, I had a 71 360 block that only had a few thousands wear on the stock bore and I went to a very good machine shop and ask them to blueprint the block and bore it .010 or .020 oversize with a torque plate , but due to the crappy machine work done to it at the factory they had to go .060 oversize to get all the clyinders straight and square to the crank!!! Good thing that year block has thick clyinder walls, they sonic checked it and said I had plenty of metal left.

[LAR]

Thanks for the input. I guess I'll get them round. I wasn't sure if a thousandth or two was "good enough". I guess it isn't. Now I just need to find a good machine shop with a torque plate.

[meepmeep]

You might think about going to forged pistons that run a .009 clearance and hone it straight may save you from boring it.Buy 1 piston and start measuring,some will clean up.Just a thought.