P-47 Man

I'm having problems with achieving a good top end throttle from my old O.S. FS-40. I'm only able to get about 9000 rpm's swinging a 10X6 prop at full throttle. This is an old vintage FS-40 purchased back in 82. I have taken it through a complete engine restoration clean up, valve adjustment, and tried many different adjustments on both the needle valve and the air bleed screw. The engine does run smoothly, but I just can't get a good top end speed. Any help or suggestions would be appreciated.

Bax

My Feedback: (11)

The old O.S. Max FS-40 usually woudn't turn over 9,000 RPM. They weren't timed for high RPM. If you're getting 9K with a 10 x 6 prop, then the engine's running about where it should be...especially considering its age.

P-47 Man

You have confirmed what a few others have said to me about this engine. The engine is currently powering a World Models Attack Sport Plane. Our club field is grass so take-offs are a little slow, but once airborne, the plane flies great. Thanks for getting back to me.


Dewey

Mike Ledbetter

I don't doubt Bax's expertise, but I have an O.S. FS-R (ringed) that runs much faster than that with an 11X5 prop. Around 11,000 rpm on the ground, in fact (at about 2,000 above sea level). I bought it off EBay and have no idea how old or how much use, except it seems in excellent condition.

Tower sells rebuild kits for those engines. Is yours the ringed or the non-ringed model?

Regards.

Warren

My Feedback: (72)

9000 isn't too far off; what brand prop are you using?

RPM alone doesn't tell the story.

LSP972

My Feedback: (13)

Mike, he's talking about a four stroke engine. OS only makes them ringed.

Camperman, try a 10x5; should get you a bit more rpm and some additional "take-off thrust"... You might also try an 11x5 wood prop, which will be lighter (and easier to spin) than a composite prop.

I've got an old & tired 48 Surpass; not quite as old as yours, but it has a LOT of fuel through it. It began getting weak, so I imagine it needs a new ring at the very least. The optimum prop for it has always been an 11x7; I put a 12x5 APC on there, and it revived a bit and pulled the LT-40 with authority.

Playing with props won't take the place of a needed overhaul (if yours does need that), but it can't hurt.

P-47 Man

Mike, my engine is a ringed model. At this time, I'm probably going to continue to fly with this engine with it's current condition, but if it's performance deteriorates, I will look into the rebuild kits that you mentioned. I appreciate the help.


Dewey

P-47 Man

Warren, I'm using a Zinger 10X6 prop. I realize that by going to an APC prop I would achieve a little better performance.


Dewey

P-47 Man

Steve, I'm going to try a 10X5 prop like you suggested. I have tried an 11X5 with some improved performance. As you pointed out, I'm looking for additional thrust and rpm's on take off. I plan on going back to the field tomorrow. I will let you know how I come out.


I appreciate everyone's help and advice.


Dewey

jaka

Hello!
20 years ago I run several of these OS FS .40s, I still have one new in box.The best standard sport prop for them was a 11x6. All all my OS FS .40s turned these props at around 9000rpm on just 5% nitro.
This was at sea level.
At this altitude a 10x6 and a 11x5 prop i too small prop for this engine regardless of prop manufacturer and modeltype!
If your engine only turns 9000rpm with a 10x6 prop something is wrong! My OS.26 turns 10000 rpm using 10x5 prop on 5% nitro and a modern SAITO or Magnum .30 turns a 10x6 prop at around 10000 rpm.
I would guess wrong cam timing and /or bad ball bearings or a worn out engine(ring).
If you want good performance from any engine you have to change ballbearings from time to time and replace the old bad ones with C3 or C4 racing ball bearings. I prefer to use Swiss WIB C4 bearings in all my engines...open noot sheilded, they make very good ballbearings. Nelson uses them and so does MVVS in some of there engines.

P-47 Man

I appreciate the info.


Dewey