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  1. #1

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    OS 91FS Help!



    Hey guys, I recently purchased a Super Skybolt with an OS .91 FS and the guy who had it got it from a relative who had passed away and knew nothing about its history..the motor HAS compression but it just seems a little "gummed" up..any tips as to how to loosen it up before I attempt to fire it up? any info would be apprectiated...thanks!


  2. #2
    MinnFlyer's Avatar
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    RE: OS 91FS Help!

    Just put a little fuel in it and turn it over by hand. It'll loosen up after just a few turns
    Mike B. AMA# 42400 www.gettingairborne.com
    Ultra Sport Brotherhood #2 - Waco Brother #188 - Cub Brother #2

    \"Those are my principles. If you don’t like them, I have others.\" - Groucho Marx

  3. #3

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    RE: OS 91FS Help!


    ORIGINAL: MinnFlyer

    Just put a little fuel in it and turn it over by hand. It'll loosen up after just a few turns
    MinnFlyer has a good very good suggestion. If it seems gummed up after running fuel through it by hand, then pull the engine, pull the backplate and look at the bearings. I am replacing bearings in a Super Tigre 75, the rear bearing would hardly move at all.
    Check it out before rushing into starting it. If the bearings are bad, replace them. Why take the chance with a great 4 stroke?
    If they feel rough turning the prop by hand, they are bad and need to be replaced. Just My Opinion. Not an expert by ant means.

  4. #4

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    RE: OS 91FS Help!

    Take it apart and clean it.

    Ed s

  5. #5

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    RE: OS 91FS Help!

    Hi!
    As ED says! Take it apart first! Then if needed change bearings!
    Jan Karlsson - Supplier MVVS Products

  6. #6
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    RE: OS 91FS Help!

    I am going with Minn on this one, put fuel in it. That will loosen up the gummy stuff and will let you determine if repairs are needed. Good Luck, Dave
    If the screw ain\'t loose then things ain\'t normal.

    Dave Agar
    AMA#97144

  7. #7
    scale only 4 me's Avatar
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    RE: OS 91FS Help!

    +1,, a little gummy oil residue doesn't mean anything is wrong with the motor.. I just put one of these back into service last year that had been sitting almost 10 years,, after the first flight it was smooth as new.

    That said,,
    These OS 91 4 strokes are notorious for the rear bearings getting rusted out,, so if it feels rough back there after you run it,, yes take it apart and replace the bad parts.
    You're so smart,, you figured out how to read this!! Or maybe ya just got lucky??

  8. #8

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    RE: OS 91FS Help!


    ORIGINAL: DavidAgar

    I am going with Minn on this one, put fuel in it. That will loosen up the gummy stuff and will let you determine if repairs are needed. Good Luck, Dave
    PLUS 2
    Back Roads Outlaws Revver #165

  9. #9

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    RE: OS 91FS Help!

    Oh Sure, loosen up the gummy stuff so it can move around and get stuck in the valves, springs and bearings. With a bit of luck it might even block the crankcase breather.

    Ed s

  10. #10
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    RE: OS 91FS Help!

    " Oh Sure, loosen up the gummy stuff so it can move around and get stuck in the valves, springs and bearings. With a bit of luck it might even block the crankcase breather. "

    Not likely. The "gummy" is mostly castor and will dislove in fuel, not turn into globs.

    Les

  11. #11

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    RE: OS 91FS Help!

    Oh my goodness what is wrong with me? I can't start a arguement with anyone on this subject because I agree with everyone on this topic. [&:][:@]


    I bid on a O.S.FS.91 Surpass II (w/o pump) about a month ago on E-bay and won the bid. It looks like the engine sat for many years and it doesn't look as if it was used much. The exaust valve was stuck open, but with a little cleaning and soaking it in after-run oil and lightly tapping the top of the rocker arm with a plastic handled screw driver, it became unsiezed and in working order. The problem was old glow tar making everything stick. I pulled off the cam cover and gunk, grime and very little rust residue came out, so I filled the whole engine with after-run and let it soak in after cleaning out what I could. I feel and hear no grit when I turn the crankshaft so the bearings are sound. Also there's no play in the crank. Mostly the engine was gunked up with old glow tar from what I see.

    The carb looked and felt good, but I did have to replace the high end needle valve spring (no biggie) and right now, I'm in the middle of sanding down with different grit and polishing the muffler. I put in a new "F" glow plug in it, the previous owner had a A3 in it. Why? Don't ask. [&:]

    A couple of weeks ago I removed the rods again and polished them up removing more grime, and after soaking over night I blasted the whole engine out with heavy duty silicone spray, wiped the parts clean then re-applied the after-run oil. Mystery Oil works good as well if some were to choose it. IMHO

    The engine has massive compression and kick turning it by hand after I adjusted the valves. I think it's going to fire up! Not bad for $140.00! I lucked out this time, but even if it didn't run it still would have been worth that in parts I think. The engine was discontinued a while back, I'm glad Tower Hobbies still sells most discontinued O.S. engine parts.


    I suspect that the original owner of this motor had died or is no longer capable of enjoying the hobby, because it looks as if it sat for a long time before a family member took it to the E-bay Quickdrop. Quickdrop said that they had very little information on it other than it ran.

    E-bay photos for those who care:







    Engine after it was cleaned and polished up a bit with a new high end spring and making ready to run:







    All my engines are spotless and gone through when I buy them used. Be forwarned however, that everyone should be careful buying a used glow engine from E-bay. Buying things used without seeing it hands on is like eating a box of chocolates, never know what you might get. This time I lucked out.


    Pete




  12. #12
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    RE: OS 91FS Help!


    ORIGINAL: Oberst

    I put in a new ''F'' glow plug in it, the previous owner had a A3 in it. Why? Don't ask.
    Best plug I found I found for my os91s is the Thunderbot RC long,, Yes an Idle bar plug,, I don't know how many guys have told me that won't work and you must buy the $8 OS plug,, but my motors purr like a kitten on 15% with that plug.. I had one Hobby shop Know-it-all almost refuse to sell me one when I told him what engine it was going into. Must be magic.

    You're so smart,, you figured out how to read this!! Or maybe ya just got lucky??

  13. #13

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    RE: OS 91FS Help!


    ORIGINAL: scale only 4 me


    ORIGINAL: Oberst

    I put in a new ''F'' glow plug in it, the previous owner had a A3 in it. Why? Don't ask.
    Best plug I found I found for my os91s is the Thunderbot RC long,, Yes an Idle bar plug,, I don't know how many guys have told me that won't work and you must buy the $8 OS plug,, but my motors purr like a kitten on 15% with that plug.. I had one Hobby shop Know-it-all almost refuse to sell me one when I told him what engine it was going into. Must be magic.


    Yea, yea, the only reason why you have that plug is because it says "Thunderbolt!" [:'(]


    Pete

  14. #14

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    RE: OS 91FS Help!

    I'm rebuilding 3 of these right now. One was seized. Loosening it up with WD-40 didnt work, so tried glow fuel, that worked but only to a point. Turns out the tappets were also seized and had no compression. At that point I went with the hot dip in a crockpot with antifreeze. Loosened it all up, disassembled and did a thorough cleaning. Found a stuck ring on the piston and replaced the bearings down too. Nice and clean, just waiting on the ring from tower. That one was a low time engine that was stored long term improperly. Absolutely no carbon around the valves. Mine are OS.91 Surpass. I have 4 that will eventually go in DS B-17 I'm slowly stocking up for. Not far away from retirement and that will be the first project. The others will get new bearings. And one had to send the head to Clarence Lee for an exhaust port insert. I just need to find one more engine as a spare.

    Edwin

  15. #15
    scale only 4 me's Avatar
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    RE: OS 91FS Help!

    There's a guy on Fly-ing Giants that is selling 3 NIB,, page 4 of the engine section

    http://www.***********s.com/swapshop...ct=29891&cat=5
    You're so smart,, you figured out how to read this!! Or maybe ya just got lucky??

  16. #16
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    RE: OS 91FS Help!

    "Must be magic. "

    Not magic, just plain luck. I worked at Hobby Shack/Hobby People after I retired, and I wouldn't count on one of those things on a bet.

    Les

  17. #17
    scale only 4 me's Avatar
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    RE: OS 91FS Help!

    You're probably the guy who didn't want to sell me the plug that day,,, did you work at the Balboa store in the 90's?

    I've used those plugs for almost 20 years in many different motors,, they work just fine for me.. I'd rather be lucky than good any day.
    You're so smart,, you figured out how to read this!! Or maybe ya just got lucky??

  18. #18

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    RE: OS 91FS Help!

    WOOHOO! The ring and the head from Clarence Lee came today. Back in bidness. Sorry for the hijack.
    Edwin

  19. #19

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    RE: OS 91FS Help!

    Edwin, if you ever need a ring again contact Frank Bowman. He makes rings for just about any engine you can imagine
    the email is. ringmaster46@msn.com
    Chris Murphy

  20. #20

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    RE: OS 91FS Help!

    Well aware of him, just forgot until you mentioned it. Thats what the brain does sometimes.
    Edwin

  21. #21
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    RE: OS 91FS Help!

    "You're probably the guy who didn't want to sell me the plug that day,,, did you work at the Balboa store in the 90's? "

    Don't remember a store on Balboa, but I opened the first one on Convoy, then moved to the second (current) one.

    Les

  22. #22
    scale only 4 me's Avatar
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    RE: OS 91FS Help!

    Not Balboa Island,,,. Balboa Blvd in Encino. Must not be you
    You're so smart,, you figured out how to read this!! Or maybe ya just got lucky??

  23. #23

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    RE: OS 91FS Help!

    Hi!
    Methanol will not remove any old congealed castor oil inside an engine!!
    The only way...If you really care about your engine, is to take it apart and change bearings! That's the way we pyonracers do it! Cannot understand why people hesitate about doing it when it's soo damn easy to do!!!!
    Jan Karlsson - Supplier MVVS Products

  24. #24

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    RE: OS 91FS Help!

    ++5 for your post. Guess people are afraid of replacing anything themselves. Changing bearings is not a big deal as I found out. Easy to do, and if your tearing down an engine anyway, why not replace the baaringsat the same time??

  25. #25
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    RE: OS 91FS Help!

    " Not Balboa Island"

    No, no. Not Balboa Island, Balboa Avenue, San Diego:-)))))))))))))))))

    Les


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