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OS 25 Trouble

Old 08-15-2016, 01:28 PM
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Default OS 25 Trouble

Hi Everone,

I run OS 25 engines on my combat planes. All work fine except for one. I cannot start it as I don't think it is drawing fuel. Also when I manually rotate the prop it turns fine for about four or five rotations then the prop becomes difficult to turn for one revolution (when the prop is pointed to the ground). Then rotates easy again for the next for revolution then gets difficult to turn again. I am using 10% nitro fuel, 9x5 prop, mac header and mousse can. Why would the prop turn normally then be difficult to turn for a revolution? Any ideas or advice is appreciated.

Old 08-16-2016, 03:21 AM
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If it is new, then maybe it is just wearing the oil away, and is squeaky. If it has been crashed, maybe something is bent, or a G clip is off or ? If it is just squeaky tight, maybe just heat it up with a hair dryer for the first couple of starts.
Old 08-16-2016, 07:21 AM
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If the propeller will turn over smoothly for several rotations but become stuck or stiff after that for a rotation or two, you have something out of alignment. It's possible you have something bent that gets in the way once in a while, something moving out of position, and so on. The only way to check is to do a teardown and really inspect the components and their fit.
Old 08-16-2016, 02:33 PM
A. J. Clark
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Maybe the bearing is not good anymore or you have some dried up crap in the motor and bearing. Would have to take it apart to be sure.
Old 08-16-2016, 03:26 PM
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If your OS has a plated liner you may be experiencing the plating peeling off.

Certainly matches the symptoms of a peel.

Not worth fixing even if you can find new parts. IMHO
Old 08-16-2016, 05:51 PM
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This Engine has not been flown yet. I could not get it to operate correctly so I sent it back to OS. The replaced some of the cylinder and piston assembly (their description). So I doubt it is a bad bearing or that something was damaged. A tear down it is then.


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