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.
Mooney Driver – what’s that about BAZL and SI/SBs? When did that come out?
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 !
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.
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 !
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)
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 ? ? ?
The biggest risk is removing more than one cylinder at a time and worst case scenario is all the cylinders at same time.
The greatest problem is moving the crankshaft with no pre-load on the main bearings (provided by the through bolts) thus allowing a bearing to shift in it’s saddle and cutting off it’s oil supply. This results in a catastrophic failure – guaranteed. .
Could be some idiot moving the airplane whilst all the cylinders are getting overhauled or poor technique when installing the cylinders.
R & R ing cylinders is not rocket science, but nonetheless, most mechanics seem to take a very nonchalant attitude to this high risk maneuver .
Most recent catastrophe I’ve seen: P210 on a flight from Midlands UK to Bordeaux, engine threw a rod, un-eventful dead-stick landing on-airport, luckily.
The engine had a “full top overhaul” just 15 hours before the failure.
Probable cause: Improperly {read NOT] torqued through-bolts.
It depends. On some types you can easily damage the casing if you change s cylinder with the engine installed. Of course for cost reasons everybody does it.
The feeling I get is that there is a bigger risk if you remove the piston.
There is a specific procedure involved in installing the gudgeon pin (wrist pin) and if you bodge it, the plugs will rub against the cylinder wall, hard, and while this rarely just stops the engine, you get lots of aluminium everywhere and eventually that will lead to having to open the engine. A lot of engine shops seem to do this incorrectly.
Safety wiring on an oil filter is pretty easy to visually check, so I would put that in a different category (sheer stupidity).
