Probably much more horsepower is lost by being too kind on a fresh engine than
by running it at full throttle too soon;
Marcel
Van: "fot" <fot at autox.team.net>
Aan: paulricco at att.net, "fot" <fot at autox.team.net>
Verzonden: Zaterdag 25 augustus 2018 23:33:25
Onderwerp: Re: [Fot] TR4 Race Engine Break-in Questions
Th e s hort 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 intentional repeated
HEAVY engine braking from WOT in top gear.
After that I usually do a retorque and follow-up; next time out should be good
to go.
This open/closed throttle running subjects the rings to the loads that it will
have under normal operation.
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
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