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Too much piston height?

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My1GLaser

15+ Year Contributor
1,565
31
Dec 4, 2006
Bartow, Florida
I have searched and searched, but could not find much at all about this issue. I am building a 6 bolt w/.020 over Wisecos & Manley H-beam rods. Up until now, all my clearances have checked out well and I am happy so far with the build. But..

My pistons are sticking out of the block .007 on 2 cyls and .009 & .010 on the other 2. I was planning on using a Mitsu MLS HG which I mic'd @ .054. I am running +1mm valves & HKS 272s, so I am not sure if that HG will be thick enough for valve clearance due to this piston height. The block was decked and the head has been milled, but I do not know how much material I am missing total. (I'm an idiot for that :nono:)

1. Is there a Vfaq for claying the pistons, and is it necessary?
2. Is using a thicker custom Cometic HG an acceptable fix for this piston height? I was thinking about going with .062, which is .020 over stock. Does that sound right, or do I have to clay the pistons to know for sure? I don't mind going thru all that, I just don't know how until I read up on it a little.

Damn I think I am a little sick over all this. :barf: I have put a lot of time and money into this build after my first 1g was totaled 6 months ago. But, I have not rebuilt a bottom end before and this is a little nerve racking. I know there are people rebuilding motors out there who might have had similar issues, so thanks for your insight.
 
Am I supposed to replace the hyd lifter with a solid one for this test? Has anyone done this test that can chime in? I believe that is what these articles are telling me, but I have no idea where to get solid lifters to fit this head. And of course I will be checking the cyl with the piston that sticks out .010, but I will probably check all 4. This is more than I bargained for, but what else am I gonna do...destroy my new motor? Oh well!
 
I talked to the guy that did the machine work on the head I am using. He said that with the Mitsu MLS gasket I am using and the .007-.010 piston height, I will have about .041 to .044 quench area which is actually almost perfect. I still better check my valve clearances.

This is supposed to be good for suppressing knock due to increased velocity of the air at TDC. It drives the air around the CC faster and helps to keep the mix cool and moving to fight off hot spots. I am hoping that will help fight off some of the knock I will surely encounter with my 9:1 Wisecos. (Boy I hope I made a good choice there...nothing like second-guessing AFTER the bottom end is together. :coy:) Maybe its like cold feet or something...

I have read very little about this quench area on dsm forums, but it is supposedly an important factor to set up properly when building your motor. Having lower than .035 is too close for contact reasons, and more than .060 is undesirable. I have read that .040 is what engine builders shoot for. I wonder how this translates to DSMs since most of the info is from V8 guys that are more old school. I am not knocking it. I just obviosly have a lot to learn about building a motor. More than I thought it would be at the beginning.
 
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