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Old 04-06-2013, 09:45 AM   #1
aguyinthesky
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Default turning/ miling/ cutting piston

Im building a hybrid ej22t shortblock with n/a heads. Because the the pistons stick out past the deck a scosh, it limits the type of headgasket i can use which will drop my compression to around 7.5:1. Which is way lower than i want for boost.
Does anybody know where/how i go about milling/turning/cutting the piston 1mm to flush with the deck? i.e. what kind of machine shop would do this?
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Old 04-06-2013, 10:42 AM   #2
azn2nr
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But......milling the piston down changes cr too
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Old 04-06-2013, 01:59 PM   #3
aguyinthesky
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right, thats my point. If i mill the pistons down to flush with the deck, i can run a thinner headgasket without fear of the pistons kissin the valves.
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Old 04-09-2013, 02:00 PM   #4
aguyinthesky
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Nuthin? Noobboody knows anything that could help me out?
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Old 04-10-2013, 07:29 PM   #5
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If you take 1mm off the piston and 1mm off the head gasket you will still have the same piston to head clearance. Why not just use the thicker head gaskets.
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Old 04-10-2013, 07:32 PM   #6
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I don't think it is a good idea. But if you want to send them to me I will take 1mm off the total height for $100.00. Pm if you want.
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Old 04-10-2013, 07:52 PM   #7
aguyinthesky
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Quote:
Originally Posted by dgm_wrx
If you take 1mm off the piston and 1mm off the head gasket you will still have the same piston to head clearance. Why not just use the thicker head gaskets.
The thin head gaskets i want to use are dangerous because of the protruding piston at TDC. Thicker gaskets would just lower my compression.
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Old 04-10-2013, 10:39 PM   #8
Subikid90
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Milling the top of the piston will also lower your compression
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Old 04-10-2013, 11:04 PM   #9
aguyinthesky
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Ej22t heads w block has cr of 8.04:1. with the better flowing heads, it drops the cr to 7.57:1. If the pistons are milled from a 28cc to 26cc dish coupled with an sti compressed .6mm (.0236") HG as opposed to stock 1.30mm the outcome is 8.18:1 which is what i am aiming for and will achieve for my boost.
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Old 04-11-2013, 09:28 AM   #10
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not sure what your options are for thicker gaskets, but why dont you just send the block out to have the decks milled down however much and run a thicker gasket?
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Old 04-22-2013, 02:03 PM   #11
vica153
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For that sti headgasket you'll want to shave off ~.030" from the piston height. That will reduce the piston dome volume by ~4-5cc. Depending on exact piston/head volumes that will land you in low-mid 8s CR.

They aren't exactly round, so technically turning it on a lathe isn't the best idea. It would probably work fine though. I'd set it on a mill clamped on the wrist pin area. Any decent machine shop could do it easily. If you can't find a place, then send them my way.

Last edited by vica153; 04-22-2013 at 02:57 PM.
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Old 04-25-2013, 06:27 PM   #12
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Are you saying that you would set the piston skirt on the mill and clamp on near or around the wrist pin? Would you think that is better then putting the piston into soft jaws on a lathe bored to the same size as the piston?
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Old 05-03-2013, 01:41 AM   #13
Mister Tanker
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There are milling fixtures specifically designed for clamping pistons that use the wrist pin bore. There are also special jaws you can purchase for lathes that grab the piston by the oil ring groove.
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