Rotax Engines - Are we being (crank) shafted?

[M61A1]

In a regularly used 582, I have found that bearing clearance is quite a good indicator. When new, they have a certain clearance, during run in, that clearance often grows just slightly. For many hours, the clearance just remains the same, but you can get a good indication of impending failure from the moment you measure it and the clearance has increased. We're not talking large measurements here, but the difference of maybe 0.02mm over a period of monitoring.

 

As mentioned previously....ANY engine can stop suddenly, and for many reasons.

 

I can only assume that Rotax just charge whatever they believe the market will bear. They are by no means a "special" engine, a basic two stroke with a rotary valve that was superseded in the early 70's, with a simple reduction and two CDIs, and the 912 isn't much better. Very overpriced for the technology, they just have a captive market.

 

 

[facthunter]

One track, where do you think those flakes of glass hard metal go?. Easily jamb a roller or cage and it's over. Even a small area of metal surface flaking is enough to ruin the bearing. It's softer underneath.You would have to check your motor each hour and by the time the clearance has reached the figure you quote it it's failed in a practical sense and you can't count on it keeping going at all.

 

M61A1, yes it is a fairly ordinary motor but the hours quoted are in the ball park for other Two Stroke motors like them used in other applications like road bikes where they aren't delivering constant power, so should last twice as long. If certain less demanding applications run 2X the time I would see 50% as a reasonable safety factor. Pushing two strokes to their absolute limit of life expectancy is not good policy. Their basic reliability is not as good as a 4 stroke in general. They are a more critical engine to operate. Sensitive operation gets better reliability. If they run lean it's not safe either. Nev

 

 

[Yenn]

It was an ancient engine and several years ago, but the surprising thing was that it sounded so sweet.

 

I dasagree about looking in the ports for condition assesment. The 502 I had in Thruster was checked out by Tony Hayes, who you may remember was the self appointed Thruster expert. He told me that my engine had been overspeeded and had damaged bores. It ran so well and looked OK to me so I completely disregarded what he said.

 

One day I had a faltering in the engine and rather than cross some tiger country i put down in the next door paddock. I looked in the ports and could see tram tracks, so pulled down the engine and guess what! Those tram tracks didn't exist, the bores were perfect, it was just a trick of the light. Carbie icing was the cause of the misfiring in my opinion. That engine ran for another 100 plus hours before I sold it after putting in new rings.

 

 

[Hargraves]

A very interesting disscusion but one in which the most important safety feature of the 582 and its one outstanding differance with the other types is not mentioned. The very history of its development was entirely reliant and emphatic on thermal energy control (to keep it warm) as the case was at the time. This operational necessity is the very reason their able to easily handle the high load stress and speeds of aviation operation. Does anyone seriously believe a pressure lubricated slipper bearing is superiour to a properly manufactured cageless pressure lubricated roller bearing the reasons for not employing them is enginerring housing size requirments more than anything. N B when was the last time you saw a turbine with slipper mains. Cheers Hargraves

 

 

[facthunter]

Turbine bearings are spray lubricated. Excess pressure is not good for them. Roller bearings don't need much oil and cooling is one of the most important functions of the oil. I would say the High RPM's are a big factor in choice of anti friction bearings. I can't see why a plain bearing wouldn't be OK. Most turbo chargers are plain bearing and it's easy to make a jet engine out of one of those.. Big ends have cyclic loads that generally make cages necessary. Nev