Debra
01-24-2007, 06:32 PM
i have several questions
i have two books; "all about 2 strokes" from model airplane news, and harry
higley's "model airplane engines"
i run os engines almost exclusively, i love the power, reliability and ease
of use. i have ringed and non ringed versions.
in the subject of replacing a piston ring they both only give the situation
of a removeable front bearing housing. my os 46 ax and 46 sf ringed, i
removed the piston by first removing the sleeve, then slide the connecting
rod off the crankshaft. installed the new ax piston first then slide the
sleeve over it. on the ringed engine, how do i get the sleeve to fit over
the piston once the piston is on the crank? do i somehow compress it thru
the muffler opening? what do i do with it?
the os four strokes are shown as having a hole in the rear of the crankcase
to push out the pin, but my os 91 fs II w/pump has none, how do i replace
the piston ring in that one?
Both my os 91 fs II w/pump & os 120 fs III w/pump i hadn't run for a few
months (i put synthetic oil in the crankcase). at strart up, the 120 would
not richen, i continued to open the needle valve from the initial 3 turns. i
sent to hobby services, they installed a new pump, ring and sleeve (i
overheated it being lean, the exhaust manifold was loose). i received it
back, still won't richen, no change, i sent it back asking them to trouble
shoot and test run.
my 91 fs also wouldn't richen. using a syringe, i gently pushed fuel thru
the pump, i choked it and fuel came out of the carb, at start it still
wouldn't richen. i plan to now install a new pump on that one. in this
situation (same as the 120), the pump should be the problem.
i read in harry higleys engine book; at the end it discusses pumps, it says
to use a syringe gently push alcohol (denatured?) thru the "in" port of the
pump to flush the fuel out. i use only wildcat w/synthetic oil. os type f or
hangar 9 4 stroke plugs.
thanks for any info
jon b.
Dear Mr.B,
Your ringed O.S. engines assemble the same as your 46AX with the lapped piston, i.e. you just line up the piston with the bottom of the sleeve and push the sleeve in- It may take a little rocking back and forth of the piston to get it started. A taper in the bottom of the sleeve allows it to slip over the ring.
I am pretty sure your 46SF uses a "pinned" ring to keep the ring from rotating. Be sure the notch in the ring aligns with the pin in the piston before pushing the sleeve into place and the ports in the sleeve align with those in the case, otherwise the ring can catch in one of the sleeve ports resulting in breakage.
If neither your O.S. 91 or 120 will not richen it could well be that you have the idle mixture needlevalves turned in too far so that they do not withdraw from the high speed jet as the throttle is advanced. Try backing out the idle mixture needlevalve a turn or two. If the engine now advances to full throttle set the mixture a little on the rich side, reduce to idle speed and reset the idle mixture. I would appreciate hearing if this solves the problem.
Good flying,
Clarence Lee
i have two books; "all about 2 strokes" from model airplane news, and harry
higley's "model airplane engines"
i run os engines almost exclusively, i love the power, reliability and ease
of use. i have ringed and non ringed versions.
in the subject of replacing a piston ring they both only give the situation
of a removeable front bearing housing. my os 46 ax and 46 sf ringed, i
removed the piston by first removing the sleeve, then slide the connecting
rod off the crankshaft. installed the new ax piston first then slide the
sleeve over it. on the ringed engine, how do i get the sleeve to fit over
the piston once the piston is on the crank? do i somehow compress it thru
the muffler opening? what do i do with it?
the os four strokes are shown as having a hole in the rear of the crankcase
to push out the pin, but my os 91 fs II w/pump has none, how do i replace
the piston ring in that one?
Both my os 91 fs II w/pump & os 120 fs III w/pump i hadn't run for a few
months (i put synthetic oil in the crankcase). at strart up, the 120 would
not richen, i continued to open the needle valve from the initial 3 turns. i
sent to hobby services, they installed a new pump, ring and sleeve (i
overheated it being lean, the exhaust manifold was loose). i received it
back, still won't richen, no change, i sent it back asking them to trouble
shoot and test run.
my 91 fs also wouldn't richen. using a syringe, i gently pushed fuel thru
the pump, i choked it and fuel came out of the carb, at start it still
wouldn't richen. i plan to now install a new pump on that one. in this
situation (same as the 120), the pump should be the problem.
i read in harry higleys engine book; at the end it discusses pumps, it says
to use a syringe gently push alcohol (denatured?) thru the "in" port of the
pump to flush the fuel out. i use only wildcat w/synthetic oil. os type f or
hangar 9 4 stroke plugs.
thanks for any info
jon b.
Dear Mr.B,
Your ringed O.S. engines assemble the same as your 46AX with the lapped piston, i.e. you just line up the piston with the bottom of the sleeve and push the sleeve in- It may take a little rocking back and forth of the piston to get it started. A taper in the bottom of the sleeve allows it to slip over the ring.
I am pretty sure your 46SF uses a "pinned" ring to keep the ring from rotating. Be sure the notch in the ring aligns with the pin in the piston before pushing the sleeve into place and the ports in the sleeve align with those in the case, otherwise the ring can catch in one of the sleeve ports resulting in breakage.
If neither your O.S. 91 or 120 will not richen it could well be that you have the idle mixture needlevalves turned in too far so that they do not withdraw from the high speed jet as the throttle is advanced. Try backing out the idle mixture needlevalve a turn or two. If the engine now advances to full throttle set the mixture a little on the rich side, reduce to idle speed and reset the idle mixture. I would appreciate hearing if this solves the problem.
Good flying,
Clarence Lee