.010 over pistons

[Mike H.]

Does any one know of .010 over pistons are available for 327 and 427 engines?
CORDially Mike

[Joe L.]

Re: .010 over pistons

Does any one know of .010 over pistons are available for 327 and 427 engines?
CORDially Mike

Mike------


I'm not aware of any pistons in 0.010" oversize for a 327, 427 or, for that matter, any other Chevrolet Gen I, Gen II small block or any big block engine. You can get 0.250 mm oversize (which is almost 0.010") for LS-series engines, though. That's because most of these engines will not sustain an overbore of much more than this.

I looked extensively for 0.010" oversize pistons quite some time ago for a 350 since I always believe in using the absolute smallest overbore possible. But, I couldn't find any "off-the-shelf". Custom pistons are always a possibility but the cost can be prohibitive versus just using "off-the-shelf" 0.020" oversize which are fairly easy to get for most engines. I always recommend going with the 0.020" oversize if it's available (even though most machine shops will try to talk you out of it because they're mostly set-up to go 0.030" oversize).

One thing to keep in mind, though: it's sometimes not possible to go 0.020" over depending upon the condition of the block's cylinders. If even 1 cylinder needs to go beyond 0.020" oversize, then you have to go to 0.030" oversize (or, maybe more). That problem would be even more exacerbated if there were 0.010" oversize available. Having an engine that didn't have a single cylinder that required over 0.010" oversize would probably mean that you were rebuilding an engine that didn't need to be rebuilt in the first place (although those are the kind that I usually do anyway). In fact, that's probably why 0.010" oversize pistons are not available. Stuff that hardly anybody wants usually isn't available.

[Mike H.]

Re: .010 over pistons

Thanks for the response Joe. I have had these two cars for 30+ years and my son will end up with them and I'd like to leave a little meat in the bores for him. The SB will clean up at .010 and the BB might, but I will have to go to .020 I guess on both. Most cars I have been working on as of late require custom made pistons so I am familiar with that route. Thanks again.
CORDially Mike

[John N.]

Re: .010 over pistons

Mike
You can get a high quality .010 over piston by buying a custom piston from JE. You send your old piston or piston of your choice to get correct dome configuration. The piston will be forged, can be made with a higher silicon content for a tighter wall clearance. The piston will be lighter than a original cast piston or and I assume a original forged piston. I have used these in several motors. One motor was the block in 57# 3963 (first known RPO684 car). The block was in the car when it ran second at 57 Bridgehamton. The previous block was lost at Watkins Glen, two weeks prior. It takes less than three weeks to have them made. Work with a good quality machinest with good equipment to determine needed overbore and a correct ring pack. Cost has been less than a $1,000 for a set.
Regards

[Duke W.]

Re: .010 over pistons

You never know how much overbore is required until you measure. Early Corvettes that had those lousy foam air cleaners can easily see .005" bore taper, and that will required at least .015" overbore.

I recommend running modern cellulose air filter elements on all vintage engines to protect the bores.

My '63 L-76 had no measureable wear on any components other than .003-.005" bore wear at 115K miles, and I attribute that to running the OE foam element for the first 50-60K miles. The butt joint separated at the third or fourth cleaning circa 1968, and the GM replacement was a cellulose element. At that point the rate of bore wear was likely significantly reduced.

Duke