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os 40 sr tuning

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Old 07-31-2009, 09:47 AM
  #1
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Default os 40 sr tuning

I have an OS 40 SR. The carb is located behind the crankcase with a pressure fitting that puts out lots of pressure. 12 lbs of pressure to be exact while spinning the engine with an electric starter. The instructions say that the pressure tap has to be used for fuel tank pressure because the carb is a non suction carb. By pressureizing the tank with pressure from the pressure tap I can't get the engine to run properly. The engine runs pretty good with muffler pressure only.
Has anyone every owned this engine and figured out a way to get it tuned properly.
I was thinking maybe a perry pump for glow engines might be worth a try since the pressure is adjustable on the perry pump.


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Old 07-31-2009, 10:22 AM
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Default RE: os 40 sr tuning

There are many variables that you didn't cover. % nitro fuel, size prop, tuned pipe or open exh., which glow plug, in plane or on test stand, location of tank. It could be something simple or maybe not. I never had one of those motors but wanted to work with one. Is it rear or side exh.?
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Old 07-31-2009, 10:59 AM
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Default RE: os 40 sr tuning


Quote:
ORIGINAL: BarryReade

There are many variables that you didn't cover. % nitro fuel, size prop, tuned pipe or open exh., which glow plug, in plane or on test stand, location of tank. It could be something simple or maybe not. I never had one of those motors but wanted to work with one. Is it rear or side exh.?
Barry,
It is side exhaust.
OS 8 glow plug, side generic muffler, FAI Fuel with low Nitro content, 9/8 Topflight wood prop, tank in plane with tank center line about the height of the needle valve.
According to perrypump.com the pump would not work on my engine. The engine must have a high and low speed valve. Mine has only 1 needle valve. Also it is not recommended for non pump Perry carburetors.
I can't change my carb because it is built into the crankcase backplate. Looks like they want to sell a combination of a Perry pump carb and and a pump. I may try that combination on my Supertigre G21 .46.
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Old 07-31-2009, 11:21 AM
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Default RE: os 40 sr tuning

I believe that engine was designed to spin a MUCH smaller prop at high RPM .
Is this the engine??

http://www.cartage.org.lb/en/themes/...SMAX/OSMAX.htm
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Old 07-31-2009, 01:17 PM
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Default RE: os 40 sr tuning

Quote:
Please only reply if you have had sucess tuning this particular engine.
I could offer all sorts of knowledge on this type of engine. Unfortunately for you I do not meet the specific
criteria!

Ed S
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Old 07-31-2009, 01:53 PM
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Default RE: os 40 sr tuning

Wow Ed, I guess I should have read that small little line closer, Had I seen the criteria, I would have stayed out also [&o]

Peter J.
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Old 07-31-2009, 03:02 PM
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Default RE: os 40 sr tuning

Capt. I would modify that last sentence in your initial post by deleting it and maybe you will get some help from some other very knowledgeable folks. That is not a carburetor engine. It is a venturi engine and only runs wide open or off. The venturi is so large there is no pressure drop to create a vacuum and help the fuel to flow. The engine is designed to run 21 -22k rpm's so you need a smaller prop. 8x6, 8x8. On the test stand. if you put it in a plane all of your landings will be dead stick and the way you shut off the engine in the air is to pinch the fuel supply line. Look in the Q 40 forums to see how that is done. Wow, you have a Tiger so to speak by the tail.

Good Luck.
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Old 07-31-2009, 03:50 PM
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Default RE: os 40 sr tuning


Quote:
ORIGINAL: BarryReade

Capt. I would modify that last sentence in your initial post by deleting it and maybe you will get some help from some other very knowledgeable folks. That is not a carburetor engine. It is a venturi engine and only runs wide open or off. The venturi is so large there is no pressure drop to create a vacuum and help the fuel to flow. The engine is designed to run 21 -22k rpm's so you need a smaller prop. 8x6, 8x8. On the test stand. if you put it in a plane all of your landings will be dead stick and the way you shut off the engine in the air is to pinch the fuel supply line. Look in the Q 40 forums to see how that is done. Wow, you have a Tiger so to speak by the tail.

Good Luck.
Barry,
I deleted the last sentence in my original post. Maybe that will now open up the flood gates. P Johnson's first reply has the picture of the engine if anyone is interested.
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Old 07-31-2009, 04:32 PM
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Default RE: os 40 sr tuning

Yep, that is a pylon or rat race motor. Has a very limited use in RC.
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Old 07-31-2009, 05:55 PM
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Default RE: os 40 sr tuning

Yes, that is an old pylon motor. I'm pretty sure that it has a drum rotor in the back end, since the carb is set into the middle. Almost all the other pylon engines used a steel disk rotor, which need careful adjustment to run right, but the drum is more forgiving. At the '73 Nats in Lake Charles, a couple of Japanese pylon fliers came over to compete and this was the motor they were using.

One of the things you must understand about pylon engines is the props. Top Flite and Rev-Up made the props that were used back in the day, and not one of them were ever used in stock configuration. The first modification is to cut down the diameter to 8 1/4 to 8 3/8". Then you need a pitch of about 7 1/2" with the peak pitch at the tips. The hub can be washed out about 1/2" of pitch. As someone stated, typical rpm is in the 21.5 to 22.5K range for this type of engine.

Finally, you need a pretty clean airplane to use it on. A quickie has way too much drag to go well with it, and might not hold up too well to the vibration (plastic films melt where the wing contacts the fuselage). An old F1 or a modified Q40 will go good.

Since parts are hard to find, I would suggest you avoid fuels above 30%, though back in the day 65% was the norm.

It should run well on pressure. Mufflers were not used.
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Old 08-01-2009, 08:25 AM
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Default RE: os 40 sr tuning


Quote:
ORIGINAL: HighPlains

Yes, that is an old pylon motor. I'm pretty sure that it has a drum rotor in the back end, since the carb is set into the middle. Almost all the other pylon engines used a steel disk rotor, which need careful adjustment to run right, but the drum is more forgiving. At the '73 Nats in Lake Charles, a couple of Japanese pylon fliers came over to compete and this was the motor they were using.

One of the things you must understand about pylon engines is the props. Top Flite and Rev-Up made the props that were used back in the day, and not one of them were ever used in stock configuration. The first modification is to cut down the diameter to 8 1/4 to 8 3/8''. Then you need a pitch of about 7 1/2'' with the peak pitch at the tips. The hub can be washed out about 1/2'' of pitch. As someone stated, typical rpm is in the 21.5 to 22.5K range for this type of engine.

Finally, you need a pretty clean airplane to use it on. A quickie has way too much drag to go well with it, and might not hold up too well to the vibration (plastic films melt where the wing contacts the fuselage). An old F1 or a modified Q40 will go good.

Since parts are hard to find, I would suggest you avoid fuels above 30%, though back in the day 65% was the norm.

It should run well on pressure. Mufflers were not used.
Thanks HighPlains drifter.

I will try a different prop and see if I can get it to Run with the pressure nipple hooked up to the fuel tank. I will have to keep the muffler on it as the neighbors at the flying field call the park rangers if planes don't have adequate silencers.
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Old 08-20-2009, 10:16 AM
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Default RE: os 40 sr tuning

Hi, have done some flying with piped OS 2S over the years and one thing I would try in your situation is a cooler plug than the OS#8...! Have an old OS.40 SR nib but have not run it yet...Good luck..!!...Cheers/Harald
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Old 08-21-2009, 11:15 AM
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Quote:
ORIGINAL: canardlover

Hi, have done some flying with piped OS 2S over the years and one thing I would try in your situation is a cooler plug than the OS#8...! Have an old OS.40 SR nib but have not run it yet...Good luck..!!...Cheers/Harald
This morning I cranked the engine after changing to a 9/7 wooden prop and raising the height of the fuel tank a tiny bit. It starts up nicely and screams just like it did with the 9/8 prop I had on it previously.
Contrary to a previous post the engine idles down pretty good at about 1/2 throttle. I am using only muffler pressure to pressureize the fuel tank. I also shorten the fuel tank clunk fuel line inside the fuel tank. I plan on flying the plane tomorrow to see how it does. It was running pretty good on my 7 previous flights but it was wanting to stall on inside loops.
Back in the late 70's to early 80's I had the engine on a Sig 4 star 40 and was not using muffler pressure. That plane is history so I don't know if the fuel tank in the 4 star 40 was mounted higher or lower than the tank in my Great Planes Escapade.
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Old 08-21-2009, 12:40 PM
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Default RE: os 40 sr tuning

Quote:
Contrary to a previous post the engine idles down pretty good at about 1/2 throttle.
The following depends upon the performance you desire.

A tuned pipe engine set up for absolute maximum performance will run in a very narrow RPM range. Once it drops out of that range it is virtually impossible to get it back without major needle adjustment. Therefore, if the combination you have has a good idle the maximum performance range has not been reached.

As a guide, the current F3D tuned pipe engines are using props around 6.75dia x 8.0pitch. All figures approximate and closely guarded secrets.

Ed S
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Old 08-22-2009, 08:46 AM
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Default RE: os 40 sr tuning


Quote:
ORIGINAL: Ed Smith

Quote:
Contrary to a previous post the engine idles down pretty good at about 1/2 throttle.
The following depends upon the performance you desire.

A tuned pipe engine set up for absolute maximum performance will run in a very narrow RPM range. Once it drops out of that range it is virtually impossible to get it back without major needle adjustment. Therefore, if the combination you have has a good idle the maximum performance range has not been reached.

As a guide, the current F3D tuned pipe engines are using props around 6.75dia x 8.0pitch. All figures approximate and closely guarded secrets.

Ed S
Ed, you are correct on Max performance. I installed a Perry Pump on the engine several days ago and it would scream at W.O.T. but wouldn't idle back at all. I have since removed the Perry Pump as I am going to be flying the plane as a sport plane rather than a raceing plane. I have never had a tuned pipe for this engine. Captain Buford
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Old 08-24-2009, 09:14 PM
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Default RE: os 40 sr tuning

capt, used to use them in boats in the 80's.

1 - Are you using the orignal pressure fitting, If I remember they were a reducer fitting, had a 5 thou hole. One of the carb bolt on screws.

2 - It will need a tuned pipe to work correctly.

3 - The carb has limited control over the throtal.

4 - I used to run 60% nitro.

They were a good motor though were a pain to set up.

Cheers
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Old 08-25-2009, 03:51 PM
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Quote:
ORIGINAL: The Ghost

capt, used to use them in boats in the 80's.

1 - Are you using the orignal pressure fitting, If I remember they were a reducer fitting, had a 5 thou hole. One of the carb bolt on screws.

2 - It will need a tuned pipe to work correctly.

3 - The carb has limited control over the throtal.

4 - I used to run 60% nitro.

They were a good motor though were a pain to set up.

Cheers
The Ghost,
The pressure fitting is not at one of the 4 carb bolt on screws but it is above the carb slightly to the right side.
I am not using the pressure fitting. It is making way too much pressure. The pressure fitting is more than 35 thou and less than 40 thou inside diameter.
I am wondering how to reduce crankcase pressure to the fuel tank vent to increase fuel tank pressure just a tad bit more than the pressure generated from the muffler pressure fitting.
I wonder if anyone makes an adjustable pressure regulator so I can bleed off most of the pressure?
The pressure fitting is making more than 12 lbs. pressure just spinning the engine with an electric starter?
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Old 08-25-2009, 08:01 PM
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Default RE: os 40 sr tuning

You might look into one of the adjustable clamps used on smoke systems. If you compress the pressure line, less goes thru. Same principle as an adjustable bleed, but no moving parts, light, and readily available.
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Old 08-26-2009, 07:17 AM
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Default RE: os 40 sr tuning


Quote:
ORIGINAL: wrstew

You might look into one of the adjustable clamps used on smoke systems. If you compress the pressure line, less goes thru. Same principle as an adjustable bleed, but no moving parts, light, and readily available.
WRstew,
That is a great Idea. That will keep things simple and that way I will have something adjustable.
When the Ghost mention a 5 thou pressure fitting that is about 1/7th the diameter of the pressure fitting on my engine.

Thanks,
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Old 01-01-2010, 12:53 PM
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Default RE: os 40 sr tuning


Quote:
ORIGINAL: canardlover

Hi, have done some flying with piped OS 2S over the years and one thing I would try in your situation is a cooler plug than the OS#8...! Have an old OS.40 SR nib but have not run it yet...Good luck..!!...Cheers/Harald
Harald,
After flying my G.P. Escapade for the last few months with the 40 SR I can tell you that the engine is very thirsty for it's size. It has lots of power and will run without using the pressure tap on the crankcase to pressureize the fuel tank. I have blocked off the pressure tap with a fuel dot even though the owners manual says that it has to have tank pressure to run, the carb still has suction enough to drain the fuel tank.
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Old 02-11-2010, 09:14 PM
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Hi All,

Ive just found this thread talking about the 40SR, Ive found 3 engines around all my stuff, and I'm just re-building an A/C I was thinking of using one .40, so I took all the 3 engines out and started cleaning them all, Idisassemble them to clean them well, the last time those engines where used didn't got cleaned nor oiled, and that was a lot of years ago, 2 of them are already cleaned, and assembled back have a lot of compression, and I was looking for the engine manual, does anyone have it?, the other thing Ive found out is that my engines are different, doesn't have the hole on the back-plate, the carb is mounted on the usual position, its a 4B carb, and have an original O.S pipe, and has a pressure outlet. I want to get the 3 engines started and wanted to see the manual basically a parts listing and a explosioned view because I couldn't disassemble the whole front crankshaft part with the bearing and everything.

thanks

Daniel

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Old 02-12-2010, 06:52 AM
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Default RE: os 40 sr tuning

Hi Daniel, I think you refer to what is usually called the OS.40FSR engine rather than the .40SR.
Anyway, congratulations to having 3 of these jewels and I sincerely hope you will have them running soon. Attach a photo of the leaflet I have and a pic of my little collection of these engines.....hope this helps....Cheers/Harald
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Old 02-12-2010, 09:19 AM
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Wow, Great collection you have out there !!! I was looking for that leaflet, now I can have a little more information about the engine, I think i need an extractor, or the tool showed there to remove the drive washer, i think its the only minor dis-assemble that I'm missing, do you have ideas for me to remove it, so the whole crankshaft and bearing can come out, soon I'll post some pics of the engines.

thanks

Daniel


Quote:
ORIGINAL: canardlover

Hi Daniel, I think you refer to what is usually called the OS.40FSR engine rather than the .40SR.
Anyway, congratulations to having 3 of these jewels and I sincerely hope you will have them running soon. Attach a photo of the leaflet I have and a pic of my little collection of these engines.....hope this helps....Cheers/Harald
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Old 04-05-2011, 10:35 AM
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Default RE: os 40 sr tuning

Nice collection of FSR engines.
There is/was in fact an SR engine with side exhaust and rear intake, just like the OP describes.


Edit/addition: The 40SR engine is also shown on the OS history site; http://www.osengines.com/history/ostimeline05.html

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