I have a 396 that was rebuilt .40 over. Is this the maximum it can be bored? If the motor dies, is the block then junk???
thanks. Sorry, yes .040! It is a '67 block #3902406....thanks again

I'm sure you meant .040, not .40 ;) I think .060 is the recommended max, but opinions may vary

If your 396 is a '65 or '66 block, then it can be bored out to 427 specs. The 396 and 427 for these two years shared the same cast iron block.

You'll have to verify your block #'s first, however.

Charles

Are you sure about a 396 boring to 427 specs?
My understanding is if you bore a 396, .060 over,
you will get a bore of 4.154. A std bore 427 has a bore of 4.250. Close.

Your best bet is to have the block 'sonic checked'. I've seen 65-66 427's bored .100" - .150" over. If the 396 and 427 were cored the same, you'll have real thick walls. Sonic check will tell for sure. A quick check would be to compare two blocks looking down into the water jackets with the heads off.

I've got the same block as you, a '67 #2406. I'm not sure about yours, but mine was cast in '66 and does have the "thick cylinder walls" that "should be safe upto .125" over" according to the machine shop, but like others have said make sure you get it sonic checked if going that far over!

Here's a nifty trick I picked up on here, if you have a freeze plug out take a normal #2 pencil and try to fit it between 2 cylinders through the freeze plug whole... if it fits in, the block doesn't have "extra thick walls", if it doesn't fit your probably safe smile.gif

Good luck!

All this talk about the 65-67 blocks makes me wonder about the 68-72 396's and 402's blocks and their cylinder wall thicknesses and how far I could go with boring my 71 402. So what do you guys think?

You could always get it sonic checked, but I'm willing to bet only .060" to be on the safe side, maybe a tad more but nothing like .125".

Chev65,

Just went through this on my '71 402 block. Did the #2 pencil thing and thought everything was ok, sonic checked - .060 over is the limit, maybe .090 if you could get the pistons. A stock 427 bore of 4.25 is pushing it. Not worth the risk of weakeing the cylinders that much. If you really need the 4.25 & larger bore - get a 454 block to start with, its much easier and more productive in the end.

SSChevelle:

If you are currently at 0.040 over stock bore, then you can always take it to 0.060 to clean it up on future rebuilds.

Unless you put alot of mileage, I don't think you will have the cylinders wear enought that 0.060 wouldn't clean it up...

In the event that you break something, then likely you would only damage one cylinder (unless its a catastrophic failure).

If one cylinder is damaged, then you can have that cylinder "sleeved" and then bored/honed to the same size as the other cylinders...

There's nothing wrong with a sleeved cylinder, but they can be expensive to install.

I currently have a #406 block in my Chevelle that has 2 sleeves...

about 10 years ago, I got my engine from a guy that threw a rod, but luckily only took out the one cylinder (we mag'd the block, and it was okay). My machinist installed a sleeve, and all has been fine... 5 years ago, I cracked another cylinder, and had that sleeved... No problems...

Thanks for telling me how far I can go with boring my 402 block too, that'll help me out in the future.I heard that re-sleeving isn't good for high rpm engines, but BB's aren't really high reving motors. I think my engine rebuilding teacher was telling me how one time a sleeve came loose and starting going with the piston, but they did use sleeves on the 427 ZL1.

I heard that re-sleeving isn't good for high rpm engines, but BB's aren't really high reving motors. I think my engine rebuilding teacher was telling me how one time a sleeve came loose and starting going with the piston, but they did use sleeves on the 427 ZL1. Now I am not a machinist, but the sleeves are pressed into the block with some intereferance (like 0.005" or something), plus the cylinder head/head gasket would keep teh cylinder from moving with the piston anyway...

I have had my 396 (with one sleeve at the time) up to well over 6500 RPM, and 7000 a few times (maybe more on a missed shift :eek: )
Never a problem...

They also use sleeves on a lot of engines... Likely the problems with sleeve can most likely be attributed to poor machinists practices.

I'd prefer not to have a sleeve, but then I'd also prefer to have 750 HP... It all comes down to budget...

That's another thing about sleeving is you have to be real careful on what your doing when sleeving a block, I also heard there not that expensive to do either.