Flyer59 wrote:
On some types you can easily damage the casing if you change s cylinder with the engine installed
And which type is that ? ? ?
Sorry, I forgot, but Mike Busch once wrote about that. Can’t find the article at the moment (or I mixed up something, possible as well)
The most likely reason for the Cessna mentioned above to put a rod out the side of the crankcase is as a result of crankcase fretting and this should have been found as soon as the cylinders had been tourqued down because the crank would have been stiff to turn.
The fretting takes away some of the metal from the bearing web faces and as the cylinders are re-fitted with the correct torque this extra clearance in the cases compresses the bearing and reduces bearing clearance………. the rest is just a function of friction, the main bearing shell seizing to the crankshaft and being pulled out of the case as it rotates with the crankshaft, this cuts off the oil supply to the big end bearing………. exit one ( or more ) rod(s).
This has nothing directly to do with changing cylindrs in the field as long as good engineering practice is followed and you dont fall into the traps for young players !
Lovely… considering that the Swiss CAA now is of the opinion that if you want to operate an engine beyond the 12 year TBO you need to pull at least one cylinder in regular intervals to be able to check the interiors of the engine… basically, if you want to avoid that, you will need to overhaul the engine every 12 years.
As a sindeline, they also have now declared all service bulletins and service instructions and other recommendation as binding. Not only for engines but for everything.
If they keep this up, I can see people moving their airplanes from the HB register to less expensive grounds.
A_and_C wrote:
The most likely reason for the Cessna mentioned above to put a rod out the side of the crankcase is as a result of crankcase fretting and this should have been found as soon as the cylinders had been tourqued down because the crank would have been stiff to turn.The fretting takes away some of the metal from the bearing web faces and as the cylinders are re-fitted with the correct torque this extra clearance in the cases compresses the bearing and reduces bearing clearance………. the rest is just a function of friction, the main bearing shell seizing to the crankshaft and being pulled out of the case as it rotates with the crankshaft, this cuts off the oil supply to the big end bearing………. exit one ( or more ) rod(s).
This has nothing directly to do with changing cylindrs in the field as long as good engineering practice is followed and you dont fall into the traps for young players !
Are you familiar with the P210 in question or is that just a WAG ? 
I think the latter …
At any rate, I inspected the P210 mentioned above and there is not a shadow of a doubt that the main through-bolts were improperly torqued.
Whilst crank-case fretting is a real problem, far more in 4 cylinder Lycomings than 6 cylinder Contis, it would take one hellavalot of fretting to remove enough metal from the main bearing webs to change the main bearing clearance significantly as you suggest. But, if you have data to support, I’d love to see it !
Mooney Driver – what’s that about BAZL and SI/SBs? When did that come out?
Michael
I know nothing of this particular aircraft but rather than a WAG I would prefer to call it an educated guess.
Off the top of my head I can think of five or six engines that have when the cylinders were torqued down tightened up, most of these being Lycomings ( both four & six cylinder ). Following these being stripped at an overhaul agency the fretting was very clear and most of these crankcase’s ended up at Divco for rework.
My own theory as to why this fretting happens is that when cylinders are removed for rework if the through bolts are not loaded back to the normal tourque in the days it takes to get the cylinders back from rework the crankcase moves slightly and the oil in the engine does exactly what is does best and creeps into the bearing web faces. The result is a microscopic film of oil stays in the crankcase bearing webs when the cylinders are refitted and this lubrication starts the web faces fretting.
While this failure mode is much more common in Lycomings the construction of the conti will not rule it out.
