dave williams
09-30-93
- -> In discussing a engine problem with several people, the concept of
  -> "normal movement of the oil control ring" has come up. I apparenlty
  -> mistakenly believed that the oil control ring was fixed to the piston
  -> rather than floating freely in the gap.
  -> If someone could educate me on the movement of this ring I would
  -> greatly appreciate it.
- The rings normally move in the cylinders.  This is probably caused by the 
  cylinder bores being slightly out of line with the crank axis.  I don't know 
  if any studies have been done to determine exactly how much the rings move, 
  but William Jenkins (former Chevrolet engineer, later head of Chevy's drag 
  team) says that on the big block NASCAR engines they ran back in the 1960s, 
  the rings spun enough to cause measurable wear in their grooves after a few 
  races. 
- There's definite evidence that the rings must be able to move to provide a 
  good seal. 
- Two strokes normally use pinned rings to prevent movement.  They presumably 
  don't seal as well as free rings, but catching the edge of a ring gap in a 
  cylinder port is a no-no. 


[email protected] (Dave Williams)
Ford  19 Jan 1998
- -> "Direct measurements of the friction force associated with the
  -> piston assembly have been made...  Friction forces are highest just
  -> before and after top-center at the end of the compression stroke.
  -> The high values at the start of the expansion stroke under firing
  -> conditions are caused by the piston slap..."
- That's because when the plug fires off the charge, the pressure increase 
  blows the top ring out against the cylinder wall.  It's designed to do that 
  to increase the seal during the high pressure region of the cycle without 
  having to drag a high-tension ring around the rest of the time. 
- A common detonation-type failure is for the top ring land to get ripped off.  
  This is attributed to various things, but it's usually the result of a 
  pressure spike simply wedging the top ring immovably in the bore. With 80 
  pounds or so of crank and reciprocating mass, plus flywheel, clutch, 
  driveshaft, axles, and tires, you have the next best thing to an immovable 
  force - something's gotta give, and it's the top of the piston. 

[email protected] (Dave Williams)
mc-engine  08 Sep 1999
- -> any good. They were round, but bumpy. When you put them in the bore
  -> they showed light at small parts all the way around the bore, real crap.
- Strange.  Most modern rings are made from cast iron.  The as-cast shape is 
  machined eccentric and then a section is cut out.  When bent to fit the bore 
  the finished ring is round.  Some rings are machined round and then cut; the 
  finished ring is flexible enough to conform to the bore. 
- An older process (dating back to Bollee in the late 1800s) used hammerformed 
  steel wire of rectangular cross section.  I've never seen any that I know 
  of, unless they were part of a multipiece oil ring. 
- It would be interesting to know if those rings were poorly formed steel 
  rings or unmachined, as-cast iron rings. 

[email protected] (Dave Williams)
fordnatics  06 Jan 2001
- -> 99% of all stock rings in pushrod Ford and Chevy V8's measure
  -> 5/64" on the top and second, and 3/16" for the oil ring.
- ...and in 99% of high performance or racing applications, there's no reason 
  to change, either.  Nitrous, boost, or detonation can really hammer the top 
  ring; a 1/16 or .043 ring will break or lose tension while a 5/64 ring will 
  often survive.  Not to mention the 5/64s are usually dramatically less 
  expensive.