Scudrunners

Avcan moderators are now encouraging pilots
to lean the mixture during engine break-in.

Too bad they never read what Lycoming wrote:

[quote]engine temperatures should be monitored closely to insure that [b]overheating does not occur[/b][/quote]

Perhaps AvCan moderators are unaware that
excess fuel is used to cool the engine, which
runs hot during break-in, for at least two
reasons of which they are totally unaware.

I don't mind their political nonsense, but this
is really malicious.

I have my ideas, but what all makes an engine run hotter on break in?

1) rings are not seated, so extremely hot combustion
gases blow by into the crankcase and heat up the oil.
In fact, that's how you know that break-in is complete -
the oil temp falls.  If you want, you can instrument the
crankcase with a manometer and see the step drops in
pressure as each individual cylinder seats.

2) high combustion pressures behind the rings are
used to force (and grind) the ring surfaces against the
cylinder walls with metal-to-metal contact.  This
is why you run a [s]sh1t[/s] special (mineral) oil during
break-in, which is supposed to break down under high
pressure.  Actually, break-in oil is a myth but that's
another story.

3) crappy baffles and seals.  Often missing, broken
or incorrectly assembled after engine R&R in the field. 
Critical to get a good seal here and frequently isn't.

I'm not a [i]King Of Aviation[/i] though, so what would I know?

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[quote]successful break-in not only means the use of a straight oil of the correct grade but also the use of high power settings. High power settings mean high combustion pressures which, due to the piston ring design, forces the piston ring out to rupture the oil film. This is the key to the break-in process.

As for engine operation, it is all about generating high cylinder pressure and [b]maximising the engine cooling[/b]

[b]Be careful with engine cooling as the increased friction from the wear process will increase the cylinder wall and piston temperatures and so particular attention should be given to providing adequate engine cooling[/b]

When climbing, keep the airspeed up, decreasing the angle of climb so that increased ram air is available for cooling. [b]Be generous with the fuel mixture. Keeping a rich mixture will provide charge cooling of the combustion chamber[/b]

[b][i]The mixture should only be leaned sufficiently to restore power loss from an overly rich mixture[/i][/b][/quote]

I have broken in many aircraft engines over the decades,
and you want to do everything you can to keep the CHT's
down while the rings are seating - including full rich mixture.

Some aircraft (on floats) the mixture was just an on/off switch  >:D - damn is all the thinking being modified by medical "wild weed"

Can we get a link to the avcan thread you're referencing?

This one I think. It's growing.

http://www.avcanada.ca/forums2/viewtopi ... 4&t=109456

Down near sealevel here in the lake basin we got told never worry about leaning at all during training ... at least under 5Kmsl. Now if you're living in the mountain village at 10K i'd imagine you'd have an adjusted mixture control lever marked to the optimum rich position for that altitude when firewalled for take-off ... so it's possible we have some confusion here between one who climbs from sealevel and the one at 10K. Wouldn't your mountain full rich mixture be a different setting than mine ?

Just means it can run rough if excess rich takeoff/cruise in high ops so "in accordance with airframe manufacturers operating instructions" (Continetal link: under TEST FLIGHT B. 1.) "lean for field elevation where applicable and lean to maintain smoothness during climb" ... "cruise at 75% with best power or richer mixture".

what is best for engine break in

Right - when the rings are seating.

A broken-in engine is totally different than a
brand-new one, and must be treated differently
regardless of what grim young men think.