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Discussion Starter · #1 ·
Just got the motor torn down completely tonight. I've got 4 pistons with the rings stuck, and all the skirts are pretty scuffed up. There are some voids in the top rings around the gaps on a few and all of the rings that were stuck were 2nds. I suppose the gap was a little tight? I gapped 'em at .019 and .023 if I remember correctly. The engine has been together for about 20k miles.


David
 

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Pay close attention to the ring gap instuctions on your next install. It is common for the ring manufacterers to specify a larger gap on the second ring than they call out for the top ring.

On a blown or nitrous race app. they generally ask for .0005 more per inch of bore on the second ring than on the top ring for instance .006 per inch of bore for the top ring and .0065 for the second ring. This works better than running that big groove between the 2nd and top rings in a blown application.
Dale
 

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David, would you mind sharing some specs on your motor? What cylinder wall to piston clearance were you running?

If you are to do it over again, what spec/clearances would you use? You mention some piston skirt scuff. Is this because you choose a piston to cylinder wall clearance too tight?

Did you do anything special with orienting the ring gaps on the pistons so that they were opposite eachother?

I'm putting together a new motor and I'm trying to learn some.

Thanks for your help,
Royce M
 

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The gap on your rings was not the cause. The second ring generally has a tighter gap than the top. We actually run our ring gaps even tighter than you had yours. Even on cars with 30lbs of boost and have never had a ring butt. The piston skirt being scuffed is an indication of the piston to wall clearance being too loose.
 

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What would you recomend for piston to cylinder wall clearance? I would have though that scuffing the piston skirt meant too close a clearance. Could you explain?

Thanks,
Royce M
 

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Generally too tight of a piston to wall clearance will cause the skirt to be gauded. Too loose and the skirt slaps the cylinder wall.
The clearance depends on the piston manufacturer.
 

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Discussion Starter · #7 ·
At this point I'm deciding whether to bore my iron block to .030 or just get an Explorer block and have it torqueplate honed .020. Gonna buy a set of The Modmax CPs I guess. I need to find someone with torqueplate to do the machine work on the next one.


David
 

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I can honestly say that a torque plate is a good idea. I had my lightning block done with a plate this time and when I got it home I ran my bore guage thru it and I found out of round spots up to .0015, I thought that was a little crazy so we put the plate back on and it straightened right back out. And this is on an '03 NVH block, not sure how bad a thinner casting would be.
Dale
 
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