The short version, rings flex.
Piston pushes ring up, it's flat and against the lower face of the
groove. Gas pressure charge travels through the side gap on top past the upper
face of the ring and gets behind it right before TDC @ ignition point.
At that point the ring flexes and seals the top and lower faces of the ring
against the groove faces, and the charge is trapped behind the ring; this is
for pressure retention & max ring expansion. When the piston starts to go
down, the ring flexes back flat against the upper groove face and loses the
charge behind it and relaxes a bit.
Repeat this every combustion stroke.
The above is with power on.
On closed throttle (decell), there's a vacuum on top of the piston
so there is not a pressure charge to fully expand the ring, so it doesn't
flex the same.
This flexing of the ring will give it a very very slightly ) face as
a result, it's not perfectly flat.
So ring seating isn't just to to get the initial "burnishing" of
ring/cylinder wall, it also establishes the profile of the ring face for the
best seal under both full open and full closed throttle.
It's all in the ring FLEX!
This is also why ring side clearance is so critical, I scrap more pistons
for this being out of spec than for any other reason, especially if the
engine was running rich.
My break-in routine is-
Initial start, run to temp, 1 maybe 2 heat cycles, retorque & check all.
(If new cam, 15-20 minute @ 2k rpm)
No excessive running beyond cam break-in and basic tuning with no load!
On track, 2-3 warm-up laps @ part throttle, vary RPM 4-5k, use some
engine braking.
2-3 more laps with more throttle and engine braking, same rpm.
2-3 more laps using full throttle, maybe 85-90% revs, and intentionalrepeated
HEAVY engine braking from WOT in top gear.
After that I usually do a retorque andfollow-up; next time out should be good
to go.
This open/closed throttle runningsubjects the rings to the loads that it will
have under normaloperation.
HTH
Glen
-----Original Message-----
From: Paul Ricco via Fot <fot at autox.team.net>
To: Friends of Triumph <fot at autox.team.net>
Sent: Sat, Aug 25, 2018 1:30 pm
Subject: [Fot] TR4 Race Engine Break-in Questions
FOT,Good afternoon and we hope everyone is having a great weekend.We have a
couple questions for those who have had experience and success building TR4
race engines. The information might be helpful others on the forum as well.1.
We have seen a few different recommendations for initial run-in. They seem to
range from 5 minutes to 20 minutes at approximately 2000 RPM?s. How long and
how many RPM?s are people running them for?2. How long are people leaving the
break-in oil in the motor? a. Are people taking out the break in oil right
after the run-in and replacing it with regular oil before leaving for the
track? b. Are people running a few sessions under load at the track with
it in and then switching? c. Something else? If so, what are you having
success with?Again, we are really gearing the questions towards race engines
due to complication of breaking in the race motors at the track with limited
time and the track session schedules.We are trying to avoid re-starting the
entire referendum up on oil brands again, so we apologize if we do. We are
really trying to get to how people are breaking-in the TR4 motors
successfully.Thank you for considering my questions,Paul
Ricco_______________________________________________fot at
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