Oversize Pistons?

1989 4.0, Will I run into any problems boring my block out .60 over for oversize pistons? I have a pretty good gouge where a piston ring broke. Also is it recommended to replace cam bearings while its apart? they look pretty good. Thanks

A machine shop should be able to tell whether or not the gouge will be gone with a .060 overbore.

I would do cam bearings, along with crank and rod bearings, but thats just me. How many mile are on the engine? Are yo doing a complete rebuild, or just fixing the cylinder wall?

I am supplying the machine shop with pistons and crank bearings (I'm having the crank ground as well, This is going to be a complete rebuild with a reman head. I'm supplying the parts because my cost is more than 40% less than retail,little perk of being in the parts/repair industry. The shop is more than three hours away and its the closest one, I do not want to waste my money in freight back and forth. When I did my sb chev I went .60 over and was told not to go any more or run the risk of getting to close to the cooling jacket. This is the info I'm after, My stupid mitchel on demand just says n/a for piston sizing.

I would be somewhat concerned about a machine shop that can't provide that information.

The piston manufacture should also have it.

I babble too much, I guess what I'm trying to ask is : Can I bore 60 over without compromising longevity/creating problems down the road? I know I can because pistons/rings are readily available.Thanks!

bcmaxx said:

I babble too much, I guess what I'm trying to ask is : Can I bore 60 over without compromising longevity/creating problems down the road? I know I can because pistons/rings are readily available.Thanks!

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Depends on the specific block you're dealing with

the renix blocks have the thickist sylinder walls of all th 4.0 and should handle .060 over bore just find but it would be a good idea to have it sonic tested to make sure that the casting didn't shift when it was build........I have heard of people going .100 on a renix but that would req. a for sure sonic test before the boring started!!!!!!!!


If your going to have the crank turned. Why not find a stroker crank and rod and put it in(258 crank and rod)

a stroker can be expensive but.....sense your already buying piston, and having the crank turned and probable having the rod reconditioned the only added cost would be buying a 258 crank!.....just a thought!


Flash.

bcmaxx said:

I babble too much, I guess what I'm trying to ask is : Can I bore 60 over without compromising longevity/creating problems down the road? I know I can because pistons/rings are readily available.Thanks!

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+.060" is accepted as the standard for "overboring" a block - although there are some that can go rather larger (RENIX 242's, most AMC engines, and some early Hemi V8's come to mind.)

Mike Parrish (formerly: Accurate Power) has been able to take a RENIX 242 out to 4.000" (+.125"!) with ultrasonic checking for core shift. I've checked a couple of RENIX blocks at school, and going to +.100" wouldn't have presented a problem blind - 10 out of 12 cylinders would have survived +.125" bores without any trouble, and the two short were good for +.110" to +.115", as I recall.

Any automotive machine shop should have an ultrasonic checker, but I'd honestly not worry about doing it to any of my own RENIX blocks if I was only going to +.060". However, a machine shop should check anyhow - and have the resources to do so.

FYI, .100" is considered the bare minimum for cylinder wall thickness in an iron block. I don't know what it is for an aluminum block with sleeves, and I don't know what would be different for "wet sleeves" vice "dry sleeves." I usually just replace wet sleeves, don't bother much with dry sleeves, and aluminum blocks belong in the scrap aluminum skip anyhow...