[email protected]
dragnet  29 Sep 1995
- -> Also, I overheard a conversation along time ago about, "file fitting"
  -> rings and ring installation. I have not seen this term used in any of
  -> the documentation that I have
- The reason you have a ring gap at all (other than installing the thing in 
  the first place) is because the ring gets hot and expands.  A typical ring 
  gap is around .016" on a 4" bore motor.  When running, the ring grows enough 
  to close that down to .005 or .006.  The tighter the ring gap, the more 
  power you make, instead of blowing combustion pressure out the breather 
  tube. 
- You could ride the curve of increasing benefits all the way up until the 
  ring ends just barely touched, then back off .0005 or so.  That would work 
  fine until the engine leaned out, detonated, or overheated. Then the ring 
  ends would butt up solid and you enter a rapid positive feedback cycle where 
  the tight ring drags on the cylinder wall, which makes the ring hotter, 
  which makes it drag more... in a very short time you would have your 
  cylinders punched out to the next oversize without even having to pull the 
  heads. 
- So you need enough gap to compensate for extreme conditions.  Now, most 
  builders don't check gap at all - at Joe-Bob's Excellent Auto Repair, you're 
  probably lucky if the mechanic installs them right side up, much less checks 
  the gap.  So ring makers typically make the gaps at the wide end of the 
  engine manufacturer's suggested range as a safety factor. 
- Some ring makers give even more clearance.  When I was putting together a 
  455 Pontiac last year, I went through several sets of rings - from different 
  manufacturers, mind you - that had gaps from .024 to .031!  We wound up 
  reusing the stock rings, which were barely out of spec.   
- "File fit" rings come deliberately oversize, with zero or negative gaps.  
  You file them to whatever gap you want.  It's not a big deal as long as 
  you're careful.  Takes maybe an hour for me. 

[email protected] (Dave Williams)
mc-engine  06 Sep 1999
- -> who likes big gaps, I'm going to continue setting them to miniscule
  -> and running in the motor carefully.
- David Vizard says you can tell when the ring ends begin to butt because 
  they'll be shiny where they touch.  I think it might be hard to tell with a 
  file-fit ring.  He also says the ring end gap will grow .003 or so on a 4 
  inch bore motor shortly after it fires up, from rubbing off the black stuff 
  most rings are coated with.  I have verified this.