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O.s.91 4stroke

Old 11-19-2002, 01:04 AM
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Default O.s.91 4stroke

I'VE GOT A O.S. 91 4S WITH 6 HRS ON IT NEVER HAD A PROBLEM UNTIL LAST WEEK WHILE I WAS IN FLIGHT THE MUFFLER ELBOW
BROKE, THOUGHT MAYBE THIS WAS A FLUKE BORROWED ONE FROM A FRIEND OF MINE ,SECOND FLIGHT OF THE DAY 2 MIN INTO IT THE SECOND ONE BROKE. THE MOTOR WAS ON A ULTRA STK .60, NEVER HAD A CRASH OR A HARD LANDING WITH THIS PLANE, TURNING A 14X6 APC PROP . THE MOTOR HAS BEEN SENT BACK TO O.S. DOES ANYONE HAVE ANY IDEAS?

THANKS

STEVEN11
Old 11-19-2002, 03:57 PM
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Default O.s.91 4stroke

Steven,

If the exhaust manifold breaks, it means that you're getting either a lot of vibration, or you're doing a lot of violent aerobatics.

The muffler would need to be supported in the latter case, and you'll need to see what the vibration cause would be.

Even a light airframe will help cause the engine to move around more.
Old 12-04-2002, 06:32 AM
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Default O.s.91 4stroke

Bax : I too was puzzled about Steven's muffler breaking off while in flight. I was present for both failures and I know for a fact that he was not doing violent aerobatics. I also held this plane up while Steven ran the engine at various speeds (from idle to max r.p.m.'s) and I could not detect any vibration. I also have been present each time that he has flown that airplane, and I never saw him land hard.
I believe that there is a defect in the threads, (maybe a burr or too deep and sharp).
I hope O.S. will find the problem soon , but I know it's not Steven's or his Hangar 9's fault.
Old 09-03-2003, 04:40 AM
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Default Broken elbows

My flying buddy has one that has broken three elbows. It only has about 20 runs on it. Of course the muffler always gets lost too.

I do notice a little vibration but the prop and tru-turn spinner are well balanced. Could it be the crankshaft?

Prop or engine has never hit the ground and the first elbow broke on one of the very first flights.

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