greybull

I know that is a silly question, but there is actually a reason I asked this way. I have a 1972 matching numbers base coupe. 350/auto. Nothing special but it is 99% original. I am doing a frame off resto, sticking with original and NCRS as far as I can, and can afford. (I know, it's a base model for crying out loud, what am I nuts ;-)

Just got some info back from the engine shop and a couple cylinders are scratched, too deep to hone out. It will lose some compression about 3/4 of the way down the stroke. So... considering this, I can bore it out +.30, or I can overbore and sleeve it back to the original 4.00. At least I think that is an option, I'm not really a qualified motor head, I'm more body and paint adept. I know a bit about the pros and cons of sleeving versus boring, but if anyone has some real pros or cons on this, including which is considered the bigger no-no as far as those folks who would be looking at the car because of the matching numbers, I'd sure appreciate any thoughts. I understand both options are a big hit as far as keeping the "original" tag on it, just trying to make sure I don't devalue it any more than I have to.

Thx

ezobens

The car (engine) will still be numbers matching if you bore it out-
Sleeving the block just to get back to a 4" bore will not make it any more original and just adds a bunch of extra machine work, money and complexity to the rebuild for ZERO value.
No point in sleeving the block unless the bore is scored so badly it can't accept a standard overbore piston (Usually .060 over is the limit).

TheSkunkWorks

Agree with ezobens.

If .030" over will clean it up, that's all you need to worry about doing this time around.

That said, I'd have the machine shop put in writing on your work order NOT to mill your stamp if/when they true up your deck, with the understanding that you take its contribution to your car's value very seriously.

Swiftrider08

Bore it and be done with it. Just think about the "what if" during a significant overbore to install a sleeve some built up stress in the block is relieved and the block cracks. Now your numbers matching is gone for good. Most likely that would never happen with a good machine shop, but what if?

mr303

Bore it and just don't tell anybody, easy fix.

terrys6t8roadster

They have to bore it in order to put sleeves in it, why pay the price for the sleeves. T

bashcraft

Not sure where this is coming from. I've installed sleeves in many blocks and never had one crack.

OP, where did you get the idea that sleeves might be better than just boring it?

Anyway, the block will need to be decked after the sleeves are installed so your matching #'s would be gone.

Kerrmudgeon

+.30 over is the answer. New pistons, proper "new" clearances. Better than some used, some new(sleeved).

tom00799

Bore it. The cost of sleeving will out weight the cost of new superior pistons and rings.

greybull

Thanks for all the replies here. Pretty much follows what I was thinking, very good point on making sure the machine shop takes extra care on the numbers. I know I've stressed it to them, but not sure how good they heard me though.

Will go with the +.30 bore and see what that gets me.

Thanks again for the input, I know enough to know I don't know everything and I appreciate those willing to share what they know.

hugie82

The numbers will only be affected if the block is decked. A bore of .030 over is more than acceptable and leave room for another rebuild for next time. If I was you, I would take this opportunity to bump the compression up with new pistons. It's a win win!

63mako

If the wear is minimal and your going back stock you can buy 4.005 4.010 or 4.020 pistons.
http://www.summitracing.com/parts/na...make/chevrolet
Good time to bump compression with a Hypereutectic flat top and a cam upgrade since your rebuilding.
http://www.summitracing.com/parts/sl...make/chevrolet
http://www.summitracing.com/parts/cc...make/chevrolet
http://www.summitracing.com/parts/fel-1094

Indiancreek

Bore it. None of the cylinders are round anymore anyway. You'll have a better engine bored and honed with new stuff.

greybull

Was thinking right along these lines since I am making this a driver, so figured to go ahead and push the compression up a little, re-cam it with a little more performance, and since my radiator is gone and core support is rotted on the bottom going to a Dewitt direct-fit.

Thanks again for the added info.

jb78L-82

Listen to 63mako-he knows his stuff!!!

I rebuilt my OEM L-82-.030 over-355 now-New JE forged Racing 9:1 Pistons/Rings, AFR 180 64 CC aluminum Heads, Felpro .015 Head Gasket, and 63makos roller cam recommendation and the engine is a beast. I made sure that the numbers were preserved as well. Preserve the numbers! The numbers matching block may actually matter to someone later-may not be today but 10-20 years down the road it could....

greybull

Yes, I am for the most part preserving everything, even to the point of boxing up any stock parts I take off and use something non-standard, that I will pass onto the buyer when I sell it in case someone further down the road want's to take it closer to NCRS standards.

jb78L-82

Exactly!!

I reused my OEM aluminum intake. L-82 valve covers, and stock air cleaner assembly and stored the 882 heads and even the L-82 cam (not that anyone would use it again). You never know what people would want...great move.

greybull

Sorry, did not know what OP meant, finally got it. D-oh!

Anyhow, this was just some old knowledge that sometimes boring out too far can leave the walls a bit thin, making heat and cracking an issue so one would bore and sleeve in order to make sure there was enough cylinder wall there. As I said, I'm not exactly the motor guy and am not sure of what all thresholds may be on a 350 block like this. Sounds like from all the others that this block can take a +.030 boring plus a few more maybe.

63mako

It will generally take a .030 overbore if core shift is not an issue. Sonic testing will determine this. That said if you overbore .020 you have another .030 rebuild available down the road and thicker cylinder walls.

Indiancreek

A Rodeck or any other aluminum block is ALL sleeves as are many like the Caddy 4.1. Really there isn't required as thick of a cylinder wall as many say online. The sleeve manufacturer at least the one who makes those I use will tell ya 0.064 will work in a resleeved engine. That is the same number that Rodeck stated as the minimum wall thickness for their blocks. Most things you read online want well over 0.100.
Often if the boring bar will offset bore most can be saved at 0.030, as long as the rod journals were true to the centerline of the crank the wear will be to the thrust sides. Often moving the hole 0.007 to 0.010 may stay in the 0.030 over range.
If your engine has many miles on it at all, the cylinders are not round any longer. If you rering it, you'll have ring seal issues. If you're going through all the trouble and expense, do the rebuild.
Your numbers can be saved if the shop is careful or you could have them restamped. Many will say that the restamping will devalue the entire thing, and that's true I think, but it's an option.