I've pulled apart a zillion motorcycle engines in my long history as a bike
wrench and found broken rings in probably a third of them. It doesn't take
much to have an episode of detonation--a tank of bad gas, a botched tuneup.
Most folks just shrug it off and drive, unless it's really bad. But even a
rattle pulling a long hill is enough to erode the piston top and crack the
rings.
The other thing that cracks rings is overheating. If you lose your coolant
or otherwise overheat, the temperature of the rings skyrockets. I used to
gap the rings more than spec in four stroke racing bikes. Two strokes are a
bigger problem because the ring is pinned to keep it from popping out into
the exhaust port. Too much end gap and the ring will hammer the pin loose.
Too little and it will seize. It was real common to pull a seized bike down
and find a deep score where the ring gap was.
Bottom line--never let your engine detonate--even a little. And toss an
extra couple thou into the ring gap (or even better, use total seals).
-----Original Message-----
From: jmwagner [mailto:jmwagner@greenheart.com]
Sent: Monday, June 26, 2000 10:01 AM
To: WEmery7451@aol.com
Cc: fot@autox.team.net
Subject: Re: TR-3/4 Engines
Don't know 'bout the origins of those pistons... but I broke down a motor a
couple years ago...that had obviously experiences a relatively recent minor
rebuild... replacing a piston and putting in new rings... (no bottom end
work)...
Like you... many of the rings were broken... and in pieces.
My assumption was... whoever did the rebuild... was probably an amateur...
and
he didn't check his ring tolerances... hence when they expanded... they
had
nowhere to go! (you know what I mean)
Just throwing that into mix... in addition to the possibility of a lot of
mileage and/or a poor piston design.
--Justin
WEmery7451@aol.com wrote:
> Dear Fot:
>
> After counting engine heads in the garage and trying to remember how many
> heads were sold and scrapped, my estimate is that I have torn apart
> approximately fifteen different engines over a period of 36 years. Some
of
> you have disassembled many more.
>
> This last engine had weird looking pistons, and I wondered if they were
one
> of British Leyland's designs or options, or someone else's pipe dream.
The
> pistons were flat domed with the normal two compression rings and one oil
> ring above the connecting rod to piston pins. Below these pins was an
> additional oil ring.
>
> The engine either had seen a lot of mileage, or the piston design is poor.
> The top compression ring was broken on all four pistons, and small pieces
> were broken out of three of four pistons at the top compression ring.
Just
> curious, Bill Emery
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