KeithB

My Feedback: (1)

I have an OS FS 70 Surpass II that has between 100 and 150 flights. Recently I've noticed a clattering noise at startup that goes away when the engine is throttled up.

Shortly after the clattering began I also started to notice it bogging down in flight, specifically in vertical and inverted flight such as pulling through loops.

Last night I reset the valve clearances according to the manual, and today I ran the engine again and the clattering was still present, and possibly louder than ever.

One other observation, when I rotate the prop with my hand I notice that sometimes I feel resistance in points that I wouldn't expect it to (sort of feels like it's catching on something momentarily). If I reverse directions and then go forward again the "catch" is sometimes gone.

My guess is that this might be a bearing problem, but I'm not sure.

Any help you can provide would be appreciated.

Thanks,
Keith

Bax

My Feedback: (11)

Keith,

Without seeing the engine, it's really not possible for us to determine what the problem may be. It could be carbon buildup inside the cylinder, it could be excess wear on the cam lobes, it could be carbon on the valve stems, causing sticking. I thing you get the picture....

Sometimes, the resistance you feel on a four-stroke engine is the valve springs resisting the lifting of the cam lobes. With older engines, it can become more prominent because compression is lowered.

The bogging-down may be caused by the fact that the piston/ring/liner fit is starting to go, and the engine's losing compression, which will be more noticed when you're demanding power from the engine.

The clatter when the engine's cold could be piston slap against the liner due to a worn piston. It goes away when the engine warms up.

These are all just speculation. The engine really should be torn down and carefully examined.

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KeithB

My Feedback: (1)

I took the engine apart planning to replace the bearings when I noticed that the base of the piston connecting rod has scratched the bottom and sides of the inside of the crank case. It has also left scratch marks on the cover plate.

The bearings seem fine, but maybe there's something wrong with them, otherwise why would the connecting rode be scratching the crankcase. I know that if the crankshaft gets hit firmly it can push back and cause scratching, but I don't think this occurred and it was still very firmly in place.

At this point I've completely disassembled everything, I've smoothed out the scratches with 1000 grit wet sand paper (the portion that was scratched doesn't have any parts that touch it so I think the sanding will be fine), and I'm cleaning everything thoroughly. After I'm done I'll reassemble the engine with new bearings. Hopefully everything will then be fine. If not I'll probably have to send it in for service.

BTW, this motor is only 6 months old.

Do you have any idea why the connecting rod would be scratching the crank case? There is almost not clearance there. Could it be from the engine getting hot?

Thanks,
Keith