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RE: [TR] TR3A Piston Ring Gap

To: <>
Subject: RE: [TR] TR3A Piston Ring Gap
From: "Randall" <>
Date: Fri, 7 Apr 2006 17:05:51 -0700
> I have bought County Brand pistons and liners (86mm) with Deves
> rings. The
> info supplied with the ("Set") rings said that the "normal" gap
> should be .008"
> - .014". The Haynes manual says .003" - .010" for the TR3,
> .010"-.015" for the
> TR4.
> I have measurements between .003"-007", each/every ring,
> each/every cylinder.

Ed, IMO .003" is way too tight (even though that was the factory figure).  I
would file them to .010".

The rings get quite a bit hotter in operation than the cylinder walls do,
which means the rings expand more than the cylinder wall.  This reduces end
gap.  When the gap reaches zero, it starts to dramatically increase the
force between the ring and cylinder wall.  If you're lucky, it will just
wear the ring and wall, but in extreme cases it can actually cause the
engine to seize and/or the rings to gall and ruin both rings and cylinder

The differential expansion also depends considerably on the ring material
... I'd guess the original TR2 rings were simple cast iron while the Deves
replacements are probably chrome-moly steel.  So Deves very likely knows
more about what gap to use than the factory did.

The rings are too hard to literally use a file on, you'll need an abrasive
of some sort.  Abrasive cloth (aka crocus cloth) is one way.  Fold it
double, then slide it through the gap with the ring laying on a flat surface
and holding the gap closed on the cloth with your fingers.

Or a Dremel abrasive cutoff blade works too, if your hands are steady
enough.  Be careful though, and wear eye protection.


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