New hyperutectics in an old bore

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TheCraigMachine

TheCraigMachine

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Hey guys. Im in the process of trying to build up another 318, and I have a few options, each varying in cost. One shortblock I have has been rebuilt sometime in the past with a .030 overbore and fitted with rebuilder pistons that sit a whopping .105 in the hole! The bores show very, very little wear. Using the ring gap method of checking bore taper, i only get a difference of .002 from the top to the bottom. Most of the crosshatch is still visible in the bores.

Id like to be able to fit this block with some new .030 over KB399 pistons and run the stock 318 heads with bigger valves and porting. My question is, can I run hypers in a used bore? Ive always heard that hypers had to be "fitted" to the bore to keep from breaking the skirts, but Im not so sure about that. If thats the case, then why do ALL of the GM LSx motors clatter from piston slap? Those engines run hyper pistons and loose PTB clearance, and run for hundreds of thousands of miles without issue! The KB website states that their hyperutectic pistons can be ran with as much as .005 of piston to wall clearance without fear of breakage, so I think i may be able to pull it off.

Does anyone here have any experience in slapping some hypers in a used bore?
 
If the piston to wall clearance is in spec then you're good. Might want to run a ball hone through it.
 
I never installed rings without a fresh hone at least. Sounds like asking for ring seal problems. I,d use a cheap cast ring if I did so if I had to redo it I wouldnt be out much.
 
use what ya got, and take advantage of that low compression! throw a little bower on it! :)
 
mopardude318 said:
use what ya got, and take advantage of that low compression! throw a little bower on it! :)
Click to expand...
Haha this thought crossed my mind! With a calculated 8:1 compression it would be perfect for a huffer sittin atop the machine, but unfortunatley that isnt an option for this project. As far as honing goes, id let the machine shop handle that. Think im going to drop the block off and let the machinist be the deciding factor here.
 
It will work fine if your bores are in tolerance.
Hone them and put it together, remember hypers like alot of ring gap, on the top ring.
Like around .030" KB has a chart on their web site to caculate the gap.
Use cast iron rings and a fresh hone.
 
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