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Engine machining & specs

GVR-4

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What's the spec on out-of-round for the block bores for the 4g63t? And to those of you who have built one of these engines before, what have you set the piston to wall clearance at? I'm using Wiseco stroker pistons.
 

iceman69510

Turn Right Racing
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Doesn't the piston mfr have a recommendation on clearance?
 

GVR-4

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Yes. The literature in the box with the pistons says .0024. People on other forums have said if you call Wiseco, they will tell you .0025. After doing a search and reading other people have said up to .004 for turbo applications. I just wanted to get some input from some of the guys on this board who know their stuff and have built a few of these engines.
 

GVR-4

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One of you guys has to have checked out-of-round of the cylinders before building it. Anyone...
 

iceman69510

Turn Right Racing
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That operation really requires a special tool to do properly. I usually have the machine shop check taper, bore, etc.
 

I have. My block has some taper and o-o-r. The taper spec is .01mm (.0003in) Which is essentially nothing. If you have bad o-o-r you should have enough taper to warrant a punch out to a bigger size. Both of these can be measured with a T-gauge and a micrometer, both acquired at your local harbor freight. If you are a rolling heavy you can get a cylinder bore gauge and a micrometer to set up said bore gauge. If you are ballin' like hell or want to open a machine shop, you can get a electronic bore gauge that can spec out a block in literally 2 minutes.
 

GVR-4

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Thank you for the reply. I knew someone had done this!

I used a dial bore indicating gage and double x master ring. My worst OOR is .0016 on #2. I'm probably going to get the .020 over ("85.5"mm) pistons and get the block bored accordingly. Now I just have to cross my fingers that the dude who sold me the pistons will exchange them for the next size bigger. It was my screw up for not taking measurements before I bought them and assuming the block was in better shape than it is.
 

Yeah, its always tempting to order parts before you measure, because measuring is soooo boring. As for a lot of wear, the 350 chevys we rebuild at school are allowed .003 taper or oor before being considered critical. Of course, a badass chevy with 400hp only has to make 50hp a cylinder with those 4" pistons. A 400hp 4g63 has to make 100hp per cylinder, so the tighter clearance makes sense. Heck, apparently the 350s have more taper and oor from the factory than our motors are allowed to have MAXIMUM.
 
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