Many thanks for the detective story.
Peter, if this is purely a function of low temperatures combined with low MP, that would mean high oil consumption at idle/taxi? What would you expect to happen if you left your (or any other) engine idling for an hour, a high oil burn? If so, there must be data on this.
Also, the steel vs aluminium differential expansion theory assumes the same temperature for piston and cylinder. In reality the piston will be hotter, and probably hotter still with a worse ring fit, as much of the heat transfer away from the piston is via the ring. You would expect a slack piston to transfer less heat to the cylinder, warming it up more, which would provide some self regulation of the piston/cylinder fit?
So I am not convinced this is the full story. It could simply be a leaking/warn ring with no direct cause in terms of mode of operation.
Interestingly enough Mike Bush did a piece on high altitude flights and he does recommend it. So I wonder I what his thoughts would be on Peter’s high altitude excursions.
Do you have the link? I’d be most interested to read it.
Peter, if this is purely a function of low temperatures combined with low MP, that would mean high oil consumption at idle/taxi? What would you expect to happen if you left your (or any other) engine idling for an hour, a high oil burn?
Yes, sounds right. But at idle the combustion gas pressure is not much, so less leaking downwards, and the oil vapour in the crankcase isn’t going to be as “vigorous” so less oil trying to leak upwards. Also people rarely idle for an hour. Well, they do sitting at the pump where I am based but that’s because they pay brakes-off to brakes-on 
Also, the steel vs aluminium differential expansion theory assumes the same temperature for piston and cylinder. In reality the piston will be hotter
Maybe… I don’t know. The average surface area exposed to the exhaust gases is much larger for the cylinder than for the piston.
You would expect a slack piston to transfer less heat to the cylinder
Not much difference because any gap will have air/gas in it and that is a very poor heat conductor.
So I am not convinced this is the full story. It could simply be a leaking/warn ring with no direct cause in terms of mode of operation.
Could be, but it’s too much of a coincidence IMHO. Why would particular ring(s) wear faster than others?
And the 0W20 seems to be improving it. I really need to get more data but we have such crap wx at present… mind you, what should one expect in November? This time last year I got down to Lucca in great wx, got rained on down there, and only just managed to get back home, right on minima.
Also my cylinder temps are the same distribution before the SB569 rebuild as after, and that was a total rebuild, new pistons, honed cylinders, etc, everything to new limits.
Peter wrote:
dummy clamps to stop the crankshaft bearing sleeves rotating,
Sorry to hear about this problem Peter, but what does this mean ‘crankshaft bearing sleeves rotatinng’ ?
What are ‘crankshaft bearing sleeves’ – does it mean the bigend bearing shells, and if so how can they rotate ?
Thought I had a fair knowledge of the mechanical layout of these engine – but I guess not.
Peter wrote:
mind you, what should one expect in November?
> 2 weeks stable dry high pressure, with sun for the whole day, like we had in central europe?
@WarleyAir – see here, especially post #10.
The customised oil filler cap:
Just waiting for the pressure gauge now 
Peter wrote:
Just waiting for the pressure gauge now
On it’s way !
I trust that you will be changing the oil filter as soon as the synthetic oil has done its work.
Of course
Done already. But due to crap wx here I have not been able to do any flying beyond recovery from Biggin hill 1 week ago.
So I have no more data beyond the flight back from Pamplona.
