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advice on Surpass 120 back bearing

Old 08-02-2003, 01:36 PM
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Default advice on Surpass 120 back bearing

I put a new back bearing in an old Suprass 120 I.

It was generic bearing from a local bearing supplier - not the official OS part. (A Koyo bearing to be specific.)

I popped the bearing seal off both sides of the new bearing before installing it. i.e. the ball are exposed to the back of engine... ie. you can see the balls when you take the back plate off.

The original bearing had the back bearing seal in place.

I removed it on the assumption that oil will flow more easily to the front bearing and cam gears by doing so.

In retrospect, perhaps that was not wise.

Can you offer any guidance regarding the bearing seals on the back bearing?

P.S. The engine had alot of carbon build up, the back bearing was literally disintegrating, and there were metal particles (from the gear) in the oil residue in engine. Despite these signs of a well worn engine, the parts appear to be in remarkably good shape. My dissasembly experience left me rather impressed with the quality of this OS engine.
Old 08-04-2003, 03:12 PM
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Default advice on Surpass 120 back bearing

In the past, the FS-120 had no shields on either side of the bearing. New ones have bearings that come packed with a type of grease, hoping to be more proactive in preventing corrosion.

We've not found any real difference, but the unshielded bearings will stay cleaner if a lot of after-run product is used.

Sorry we don't have a 'perfect' answer for you. Just add a LOT of after-run oil and your bearing will last as long as possible.
Old 08-04-2003, 09:34 PM
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Default advice on Surpass 120 back bearing

Thanks! No perfect answer required!
Old 08-05-2003, 11:12 AM
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Default advice on Surpass 120 back bearing

Another answer, Jim;

Run a bit of castor in your fuel (I add 1 ounce per gallon to all-synthetic fuel), and run your engine dry at the end of every flying session.

Remember that methanol is extremely hygroscopic (attracts moisture); any fuel left in an engine will draw moisture, then when the methanol evaporates, guess what is left?

After run oil is a good idea, but I have found that it can cause aggravation on the first start of the next flying session; especially if you use an electric starter. If the oil is present in sufficient quantity, it can hydro-lock the engine- and if you've got a powerful starter trying to turn the engine over, conrods, valve lifters, etc., can be damaged. This is not common, but can (and has) occurred.

Having said that, let me add that many, many people use after-run oil with no drama. I used to, but got out of the habit when I began flying helicopters. There usually is no practical way to use it on a helo, and I did damage a 48 Surpass that was hydro-locked due to excessive after-run oil in the crankcase.

The castor leaves a thin film of protective oil that synthetic oils cannot match. For an engine in normal use, I have yet to see any bearing rust since I started adding the castor.

For long-term storage, of course, you want to load that puppy up with oil.

Just another perspective...

Steve

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