Piston Machining question?!?!

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metallidart

metallidart

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First off, MERRY CHRISTMAS!!

I have a stroker shortblock that I finally decided which direction I want to go with, when I get to it. The rundown--
--1970 340 block, decks cut parallel, alignbored, main studs/girdle, priority main oiling, lifter bores bushed, bored .055/honed with plate. Sonic checked, etc. I bought it used, but got a ton of receipts for machine work.
--Scat forged 4" crank, Eagle H-beams, custom JE Pistons with a slightly higher comp ht than the off the shelf pistons (12.5 with 65cc). Recently freshened, it has been balanced, etc.
--Fluidamper, Moroso pan/pick-up, etc.

Now the question. The odd bore is because the po wanted to keep the cylinders as thick as possible, so he only bored to where he needed to go as he was ordering custom pistons anyway. Well, the compression is too high for what I want to do. I would rather see 10.5 or less with 65 cc chambers. Everything is still nice on the shortblock, I hate tearing it down, but I can't handle the compression that high. So, if I were to tear it down, can pistons that are used be cut/milled, like a slight dish? I would have to make sure they are thick enough on top, that I know. They are flattops, with two valve reliefs. I know I'd have to get new rings/bearings, have it re-balanced, and hone the cylinders. The receipt for these pistons shows almost $800 from JE, I know I won't have that kind of cash for a looong time to come!

Would it be feasible, and cheapest, to have the pistons cut?

Or would it be better to have it taken the additional .005 over and get some off-the-shelf pistons?

I keep trying to come up with what amounts to a "crutch" for the compression, but I think it would be best to just lower it and build it accordingly.

Any ideas?
 
metallidart said:
Would it be feasible, and cheapest, to have the pistons cut?

Or would it be better to have it taken the additional .005 over and get some off-the-shelf pistons?
Click to expand...

You could probably find a used set of 4.100" pistons fairly easily. But again, you would need a new hone, new rings and maybe pins/locks and a re balance. Probably be into the job for the same amount as the custom pistons were. Sounds like cutting the pistons is the most cost effective but either way you're still going to need to re balance when you cut the tops, right?

What about a thicker head gasket? What is the current deck height? Have you measured the chambers on the heads to verify? Do you have a different choice for heads?

Maybe offset grind the crank to de stroke it a hair? I don't think you'd need to rebalance if you de stroke, correct? Just different bearings which are not too expensive. Just a thought.
 
Open the chambers up to the bore size by mounting them on the bare block, mark them right and left....then scribe. After that thicker head gasket and or enlarge the chambers.
 
JE will have a part number on the pin boss at the bottom of the piston. Get that number and call JE. They will be able to tell you exactly what could be done with that piston.
 
head cc.....................................65cc
gasket cc...................................9cc
0 deck FT piston w/2 valve reliefs...6cc
top dead center volume...............80cc

80cc TDC volume in a 414ci motor = 11.5 - 11.6

should be able to mill some dish volume in, 9cc - 10cc will get the comp down to 10.5 area
 
I would go wild's rough first! no cost just some careful time.

Then if that is not enough, find out from the manufacture how much is "safe" to cut off the top of the piston.
 
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