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[Fot] TR4 Race Engine Break-in Questions

Subject: [Fot] TR4 Race Engine Break-in Questions
From: tr4racing at googlemail.com (tr4racing at googlemail.com)
Date: Mon, 27 Aug 2018 14:05:03 +0200
References: <CAA640A0-A574-463E-84F9-9CAFB52ED96D@att.net> <16573018b88-1ebb-af12@webjas-vac012.srv.aolmail.net> <973963657.986204829.1535271628399.JavaMail.zimbra@telenet.be>
My piston manufacturer says about braking in:

Put the pistons in, and then drive the car to pole.

 

Means: Reckless driving from the first second.

 

Cheers

Chris

 

Von: Fot <fot-bounces at autox.team.net> Im Auftrag von van.mulders.marcel--- 
via Fot
Gesendet: Sonntag, 26. August 2018 10:20
An: fubog1 <fubog1 at aol.com>
Cc: fot <fot at autox.team.net>
Betreff: Re: [Fot] TR4 Race Engine Break-in Questions

 

 

Probably much more horsepower is lost by being too kind on a fresh engine than 
by running it at full throttle too soon;

Marcel

  _____  

Verzonden: Zaterdag 25 augustus 2018 23:33:25
Onderwerp: Re: [Fot] TR4 Race Engine Break-in Questions

 

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 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-----
Sent: Sat, Aug 25, 2018 1:30 pm
Subject: [Fot] TR4 Race Engine Break-in Questions



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