w.pasman

Hi Bax,

There seems to be some serious problem with my OS50SXH engine. Just over a month ago I replaced the rear bearing, we talked about it in this thread

[link=http://www.rcuniverse.com/forum/m_3091960/tm.htm]http://www.rcuniverse.com/forum/m_3091960/tm.htm[/link]

We could not locate the problem then, the problem seemed solved after complete remounting the thing. Now, exactly 42 flights later, the bearing is toast again...

Besides the rattle, I also heard a whining sound that I did not notice at previous bearing failures. And I have heard quite a few...

What bothers me also is that the gasket of the back plate seemed damaged, at the highest place, so just near the liner. The gasket has been damaged, the surface is not completely flat anymore but a bit sandy, although it is still one piece. The gasket seemed stuck/melted to the housing when I opened it up. There is also a black trace at that place, on the inside of the back plate where it slides into the housing; and the aluminium of the housing (on the inside, where it touches the back plate) looks grey instead of clean metal at exactly the same place. Looks like hot gases were going through there, as if there's a leak in the gasket. I'm always careful to clean the stuff before reassembly so I really wonder what's going on here. All four bolts of the back plate were still in place and not loose. I never noticed oil leaks at this place, and I'm always keen on oil leaks because that's the first hint to engine troubles.

Of course I need to know what's going on here; and also whether I should replace the gasket if I reassemble this engine?

I also noticed that the piston has become a little brown on the top too, where it had only brown on the sides last time.

Since the last bearing replacal I was doing (1) extra running empty after the flying day (2) pumping through the system after the last flight (a minute or so turning the engine with the starter, to sqeeze all remains out of the engine (3) putting twice as much afterrun oil.

I'm not running hot I think, I have been running on a single glow plug all these 42 flights and apart from the noise I had great power. Doing tictocs without problems, down to the last flight I did to now. Also I could hold my finger on the back plate for several seconds. There seemed enough smoke coming out...

Can you please help me further finding the problems with this engine: what's going on with the gasket and with the bearings?

Please let me know if you want to see photos.

w.pasman

BTW The gasket is not damaged all through, only at the inside. Just as if hot gases were blowing against it at the inside, but not yet long enough to get all through. The black scoring also goes halfway underneath the gasket, not fully to the outside.

Here are two photos: