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Thread: OS 40 MAX FP


  1. #1

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    OS 40 MAX FP

    Hello All- First time poster here. Just resurrected an old trainer 40 the past few weeks and took it for it's first flight in 2 1/2 years. Ran about 1/2 tank of 15% Nitro thru the engine prior to flight. Have a new FOX glow plug installed. Engine started fine however, slight drop in RPM when I disconnected the juice. Ran it to full power and did the 'pinch test' and did not have a drop in RPM.

    Now the issue- After a 1/2 tank of gas the engine starts to surge. Major reduction in power. Any ideas for me to check? I purchased 5% Nitro as I used pink fuel previously over the 15 years I have had the engine.

    Thanks in advance for your help.

    BTW- It sure was nice flying the old girl today.

    Geaux

  2. #2
    Moderator w8ye's Avatar
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    RE: OS 40 MAX FP

    welcome to RC Universe

    Sounds as though you had it a little on the lean side

    Attended the CutFinger Institute of DirtNap University for years but never did graduate....
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  3. #3
    DarZeelon's Avatar
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    RE: OS 40 MAX FP

    Geaux,


    I had owned an OS.40FP about 15 years ago.

    In the beginning it gave me some trouble; repeatedly stalling after 3-4 minutes of flight... It was not a pin-hole the clunk-line becoming exposed (as fuel is used up) and drawing air...

    I removed the cylinder-head only to see the nickel coating has been peeled off about ΒΌ -1/3 of the inner cylinder-sleeve surface...

    I have been running this engine on CruelPower fuel... It was only my second 'real' engine and I just didn't know better then...[:@]


    I wrote to Clarence Lee about this, but the engine was no longer under warranty...

    Eventually, it settled down ran quite decently afterward, peeled sleeve and all... about 30 more hours, until it was destroyed in a crash.


    I am convinced the sleeve was distorted, or became distorted when it heated up; probably permanently...

    Maybe they had a batch, or two, of these faulty engines.
    But it had been produced too long ago and repairing an OS engine, virtually any OS, with the cost of their parts, is just not worth it...
    Dar Zeelon - ISRAEL - ddzeelon@gmail.com
    MVVS - Jett - MS Composit - Rossi - Mejzlik

  4. #4
    Moderator w8ye's Avatar
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    RE: OS 40 MAX FP

    With an older plane like this it is best to remove the fuel tank and install all new internal parts
    Attended the CutFinger Institute of DirtNap University for years but never did graduate....
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    RE: OS 40 MAX FP

    Geaux,

    The FP .40 is a terrific and very lightweight engine and unless it was run on cruel power I doubt that the cylinder has peeled. In my experiance if the engine slows when the glow driver is removed the problem could be: a weak glow plug, to rich low speed mixture, not using a hot plug and lastly not enought nitro.

    Sags and surges half way thru the flight are related to fuel draw. Check for holes in the fuel lines, tank, tank tubes ( do what w8ye says first ) and to richen the high speed mixture. Check for tank height as best results are when the centerline of the fuel tank is level with the spray bar of the carb.

    All castor fuel may help.


    Thanks
    Francis

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    RE: OS 40 MAX FP

    Thanks all for the input. I went ahead a got me an early Christmas present. The Magnum XLS 46. Will break down the OS FP 40 and rebuild. It's been a great engine!

    Geaux

  7. #7
    Moderator w8ye's Avatar
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    RE: OS 40 MAX FP

    It'll be hard to do much of anything with the 40 FP. They have been out of production for 10 years

    I see a wrist pin, head, crankcase, carburetor, muffler, crankshaft, and connecting rod as available parts No cylinder/piston assembly in either OS 40 FP or Tower 40
    Attended the CutFinger Institute of DirtNap University for years but never did graduate....
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