OS 48 rehab
01-11-2002, 10:24 PM
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OS 48 rehab
I'd appreciate some help.
My OS 48 won't hold a high speed needle setting, though it will idle just fine.
This engine has been flow for 8 seasons. Generally compression seems very low, though occasionally, especially if one turns it backwards through compression, it seems fine.
Valve clearances are where they belong. Flooding the intake and exhaust chambers with thin fluid reveals no leaking through the valves.
Does this mean it's time for a new ring? If so, must I also replace the sleeve? Any other things I should try ? Thanks.
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My OS 48 won't hold a high speed needle setting, though it will idle just fine.
This engine has been flow for 8 seasons. Generally compression seems very low, though occasionally, especially if one turns it backwards through compression, it seems fine.
Valve clearances are where they belong. Flooding the intake and exhaust chambers with thin fluid reveals no leaking through the valves.
Does this mean it's time for a new ring? If so, must I also replace the sleeve? Any other things I should try ? Thanks.
If you use email please use [email protected].
01-12-2002, 03:32 PM
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OS 48
GoNavy:
Assuming you have done all the usual things like changing glo plugs , trying a different
batch of fuel and checking for air leaks in your
fuel system, there may be a couple other things
you can check. I had an OS 40 4st that had a
worn main needle and seat on the carb that
produced the symptoms you describe. Once replaced
it ran fine. Also the 'O' rings in the carb could
be starting to leak after eight seasons of wear.
Eight seasons does not necessarily mean the
engine should be worn out however. Alot depends
on the enviornment the engine has been run in
and how it has been adjusted and maintained.
Does the engine show any tendency to quit
in the air or overheat?
We need a little more info to help....
Sam AMA 458180
Assuming you have done all the usual things like changing glo plugs , trying a different
batch of fuel and checking for air leaks in your
fuel system, there may be a couple other things
you can check. I had an OS 40 4st that had a
worn main needle and seat on the carb that
produced the symptoms you describe. Once replaced
it ran fine. Also the 'O' rings in the carb could
be starting to leak after eight seasons of wear.
Eight seasons does not necessarily mean the
engine should be worn out however. Alot depends
on the enviornment the engine has been run in
and how it has been adjusted and maintained.
Does the engine show any tendency to quit
in the air or overheat?
We need a little more info to help....
Sam AMA 458180
01-12-2002, 11:29 PM
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os 48 rehab
SDM: Tks for the comments.
High speed needle was replaced five seasons ago after bending in a mishap. No big crashes. Entire life was in the same Midwest Mustang. I have not checked o rings but will try that.
Engine was run on 10 or 15% nitro, 16 to 18% oil, usually 50/50 syn. castor, ie Byron or Sig. After run oil used. After two seasons I settled on 11/6 zingers. There were enough occasions that resulted in prop and spinner thrown: probably twice a season. Flown about 150 total flights, all warm weather, well, for northern Wisconsin, i.e., above 55.
I did recently change fuel tanks because of the uneven running, attempting to better align center of tank to carb. That did not help. Problem started early this last season and got progressively worse.
Why would I generally have low compression, but not always? If the valves are closing, I think of perhaps a sticking ring. Someone suggested never to run castor in an OS. It's the only OS I've had. It's also the only engine ever to survive this long. Tks.
High speed needle was replaced five seasons ago after bending in a mishap. No big crashes. Entire life was in the same Midwest Mustang. I have not checked o rings but will try that.
Engine was run on 10 or 15% nitro, 16 to 18% oil, usually 50/50 syn. castor, ie Byron or Sig. After run oil used. After two seasons I settled on 11/6 zingers. There were enough occasions that resulted in prop and spinner thrown: probably twice a season. Flown about 150 total flights, all warm weather, well, for northern Wisconsin, i.e., above 55.
I did recently change fuel tanks because of the uneven running, attempting to better align center of tank to carb. That did not help. Problem started early this last season and got progressively worse.
Why would I generally have low compression, but not always? If the valves are closing, I think of perhaps a sticking ring. Someone suggested never to run castor in an OS. It's the only OS I've had. It's also the only engine ever to survive this long. Tks.
