rebore 302

jason lycett · 03-29-04, 05:37 AM

Hi all
i have a 302 that needs a rebore. The block is currently +30 thou overbored. Is it possible to bore it out to +60 thou without any problems? I intend to fit alloy pistons with a rev limit of 6,000 rpm (10:1 compresion). And another question, are standard rods from a 1976 motor with uprated ARP bolts ok for 6,000 rpm (approx. 350 bhp)?

Kevin M · 03-29-04, 08:46 AM

Find someone with a sonic tester and have the block sonic checed. It's the only way to know if the block is good for another overbore.

Kevin

jason lycett · 03-29-04, 11:11 AM

The block has been crack tested and is ok for another rebore. I see that various company sell +60 pistons, but i just wondered if that causes any issues?

Kevin M · 03-29-04, 12:06 PM

If sonic testing shows that there is enough metal for the re-bore, then it should be OK. The rods should also be OK if they have ARP rod bolts. It wouldn't hurt to have the flash ground smooth and have have them shot peened also.

Kevin

Steve Toner · 04-01-04, 02:20 PM

There's a discussion about max overbore on the Ford Windsor Small Block Engine Forum. They seem to think .040 is marginal, and .060 is a bad idea. At least that's how I read it...

40 Bud · 04-01-04, 09:01 PM

Steve , thats the same thing I have been told for several years by different engine builders. These cars run hot enough in traffic without aggravating the problem with thin cylinder walls.

Bill Musarra · 04-02-04, 06:01 AM

There is another answer. If you like the way the engine is setup now, then bore it and resleave the cylinders to the original size. Any reputable shop should be able to do that for you.
Bill

Howard Jones · 04-02-04, 12:09 PM

Sorry .30 thats it most of the time, SBF are just too thin in the cylinder wall area. If you can get it sonic checked for real cheep(free) then that might be a good idea but if you build up a marginal wall thickness motor with a bunch of new parts and it breakes, well you get the picture. Any money you spend on your old block from here on out would be better spent on a used block that can be simply rehoned or rebored .30. This is what I would do with my money.

Steve Toner · 04-02-04, 01:25 PM

Howard,

Jason's in the UK, and apparently the availability of 302s is not so good there. Check the link I posted - the guy who asked basically the same question on that forum was from the UK as well...

Howard Jones · 04-02-04, 03:32 PM

Ya, I guess it is a problem getting something heavy like a motor across the Alantic and still keep the buget inline. This is pretty much our problem with the chassis's. They are expensive to ship to the USA and so I guess this is part of the reason why GT40's are rare item over here.

But I still think that even if it costs a little more, I would take the time and try and find a block that is on its orginal bore to rebuild before I started down the road of trying to go to 40 thou on a 302.
Now, I know it can and has been done, sometimes after a sonic check has reveiled a nice thick cylinder wall, but most of the time the cylinder wall just ends up very thin, or the boring process uncovers a block that is beyond repair after spending good money on what was a used up block.

I can only say what I would do, and that would be to try and find another block before I spent any real money on the 30 over one. At 350Hp this motor is in the margin when it comes to thin cylinder walls @ 40 thou over.
Can it be honed at 30 over and try to find some "big" 30 over pistons that will fit the honed bore corectly. I used to go thru all the pistons at the Yamaha shop with a mic to find the smallest ones when I bored my race bikes so that I could get one more bore out of them in the end.

Anyway, good luck.

Steve Toner · 04-02-04, 04:12 PM

Depending on the cost of another block in the UK, Bill's suggestion to sleeve it may end up the preferred option...

jason lycett · 04-03-04, 05:42 AM

Thanks for the input guys. I must admit i am a little confused as some say it is ok and some not. As stated a new block will cost big money, and i would ideally like to keep it and go to +40 thou pistons. I was hoping to raise my compression from 9:1 to 10:1 by decking my heads, but maybe the increase in temperature would be too marginal.
I may speak to some builders in there opinion,or save up for a new block!