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Rough running engine (sticky exhaust valve, or blocked injector?)

SB388 is this relevant

I have the later “C” cylinders so this should not be applicable.

how many hours since last overhaul do you have on that cylinder?

A few hundred only.

Why “ No more IFR trips for a while due to need to bed newly honed cylinder in.”

One has to run the engine at high power until the oil consumption stabilises, and this is not possible at altitudes at which you can get Eurocontrol IFR routes in Europe (generally) unless you have a turbo.

After maybe 10hrs, one can run around at say FL090/100, but if you get any bad wx and have to climb above it, you run the risk of glazing the cylinder(s) and then IME it can take 100-200hrs of lots of oil burnt before the glaze comes off. We have some previous threads here on how to remove it with a nasty solvent but that also damages any engine seals so you have to give the engine a good rinse if you do that, to make sure no solvent reaches (especially) the front crankshaft seal.

One could argue the “old rope trick” should have been used (previous threads on this) but we are not allowed to work in the hangar (new rules even block cleaning the aircraft) and rain was forecast to start soon after, so pulling the cylinder and taking the bedding-in hassle on the chin was the only option. Yeah, aviation is not much fun when not flying.

Administrator
Shoreham EGKA, United Kingdom

You can still fly to La Rochelle at 3000ft

LFOU, France

Yes the plan is a few hours in the vicinity of the airport, then oil analysis and wait till that comes in, and then I can go over water. Scilly Isles is a really nice run; just right in all respects and at least one is not wasting (too much) avgas.

Administrator
Shoreham EGKA, United Kingdom

Could you fly FL100+ if turbocharged?

Yes.

I’ve just spoken to the US engine shop and their view is: always change the rings and re-hone, if the cylinder is pulled (on e.g. prop strike inspections the piston is usually left in the cylinder so no need to do that). The reason given is that there is a small risk of a ring breaking following a re-compression, plus the critical seal is not between the ring and the bore (as most people think) but between the piston groove and the ring. I can’t say I understand this, but Norvic won’t do a repair without a re-hone, anyway.

The shop also says valve overheated, looking at the colour of it (not seating properly so heat could not get out).

Administrator
Shoreham EGKA, United Kingdom



The elephant is the circulation
ENVA ENOP ENMO, Norway

Peter wrote:

The shop also says valve overheated

Well, that’s to be expected of a valve that sticks slightly open (ie no or intermittent heat transfer to valve seat)

Antonio
LESB, Spain

That would also explain why #2 cylinder was running cool on CHT. Not much heat being transferred from the exhaust valve to the cylinder head.

Administrator
Shoreham EGKA, United Kingdom

Peter wrote:

That would also explain why #2 cylinder was running cool on CHT. Not much heat being transferred from the exhaust valve to the cylinder head.

That would affect, but very little: the mass of the head is huge compared to the valve. I bet the low CHT is 99% related to a very inefficient combustion due to a poorly-filled, very low pressure- combustion chamber, both due to the exhaust valve leaking.

Antonio
LESB, Spain

I took this funny pic just before my last (aborted) flight

and there is a 4th one just around the corner; a TB21 with full TKS.

Administrator
Shoreham EGKA, United Kingdom
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