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old os engines

Old 04-07-2005, 10:28 PM
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Default old os engines

I just recently acquired 4 old os engines. They are: fs 91 model 1901, fs 61, 61 fsr, 50fsr. All are in excellent condition except for the 50fsr. It had been run lean and the piston and cylinder look to be damaged. I have several questions.
1. Is the piston, ring and cylinder still available for this engine and if not, will the parts for the 50sx fit?
2. The carburetor for the 50fsr is frozen and I cannot get it free. It is a 5B carb. Is this carb still available or will another carb fit?
3. I broke the piston ring on the 61 fsr trying to reinstall it back into the cylinder: is this item still available.
4. Is the connecting rod on the 61 fsr supposed to have a slight angle to it, or is it supposed to be perpendicular to the wrist pin? If it is supposed to be perpendicular, is this part still available?
5. Can I still get instructions for these engines because there were no papers with any of them?
6. I had a very hard time getting the fs61 to idle reliably in the range that I thought it should. I installed the muffler off a magnum 52 rfs that I had and installed a check valve in the pressure line. This helped the situation on the test stand, but I do not know how it will act in the air. The carb is an air bleed type. Is there a two needle valve carb that will work, or is there something else I can do to get the idle correct.
Thanks in advance for any help you can provide regarding these questions.
[email protected]

Old 04-08-2005, 09:48 AM
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Default RE: old os engines

Except for the FS-91, there are no parts available from us or O.S. for any of your other engines. They've all been out of production for too long.

A frozen carb may be able to be unfrozen if it's soaked in fuel. Take it apart as far as possible and then toss it in. You could also remove all the o-rings and use the 'crock pot' cleaning method. A search here in RCU will give you the details. The carb or carb body is no longer available, but there might be a modern one that will fit. You'll have to get us the measurement, in mm, of the outside diameter of the neck that goes into the crankcase.

While a connecting rod may have a slight offset (the rod isn't centered on the bottom boss), it should not have any angle to it. The shaft of the rod should be perpendicular to the centerline of the upper and lower rod-end holes.

Email us directly for instruction sheets.

The FS-61 sounds like it's tired and not getting a good compression seal. This could be due to a bad piston/ring/liner fit or leaky valves. There isn't a different carburetor available that will fit.
Old 04-08-2005, 06:19 PM
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Default RE: old os engines

Bax,
Will the 50sx piston, ring, and sleeve work in my 50fsr? If so, will I also need the connecting rod?
Does anyone else make the ring for the 61fsr? That is the only thing wrong with this engine. It has never been run. The bearings were just locked up from sitting for so long with no lubrication on them. I have purchased new bearings and all I need is gaskets and a piston ring to reassemble it.
Old 04-11-2005, 02:49 PM
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Default RE: old os engines

The parts for the O.S. Max .50 SX are not the same as the ones for the .50 FSR. You can't interchange them.

To get rings made contact:

Frank Bowman
1211 N. Allen
Farmington, NM. 87401
505-327-0696 (6 pm to 9pm MST weekdays)
Email: [email protected]

The Email Adderess was changed to reflect his new address by a moderator
Old 07-17-2005, 09:43 PM
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Default RE: old os engines

Anyone know where I can get a crankcase for a FS-61... This engines is in perfect condition looks like it was damaged on the maidin flight. The only thing wrong is the crankcase other than that it's clean and totaly complete...
Old 10-31-2005, 05:53 AM
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Default RE: old os engines

Hi!

I have broken my piston ring of an OS MAX 90 !QUOT!old engine!QUOT! Run beautiful when it
was ok.

I have spoken to ModelCraft here in Sweden and the do not have the spear to
the engine.

Is there a spare piston ring to this model or can i use a different ring from
a newer engine?

Sweden
Old 10-31-2005, 12:25 PM
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Default RE: old os engines

The piston ring for the O.S. FS-91 Surpass is the same part as the one for the FS-90

45403400 PISTON RNG FS91/FT160

Please contact your favorite O.S. retailer.
Old 10-31-2005, 05:57 PM
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Default RE: old os engines

Thanx! you saved my day, or not? I got OS MAX 90 2 stroke and not a FS 90.
Old 12-17-2005, 09:34 AM
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Default RE: old os engines

I found a source for piston rings in the USA. His name is Frank Bowman, 1211 N. Allen, Farmington, NM 87401-3568, USA. His email is: [email protected]. He has a long list of piston rings and I think he has the one you need.
I hope this info helps you as much as it helped me.
Old 07-25-2007, 05:08 PM
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Default RE: old os engines

Does anyone know how to set the timing marks on an OS .90 FS, looks to be 4 marks on the timing gear, viewing towards the rear of the case.. 1 at 12 o'clock
1 at 4 & 8 (these open the valves at TDC, and 1 at 10 o'clock, the drive gear has a notch so it only fits 1 way on the crankshaft.
Old 07-26-2007, 09:25 AM
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Default RE: old os engines

What you see are the ends of the screws that hold it all together. There is a small dot between two of the screws that's your timing mark.

If you send an email to the address below, we can send you a timing diagram.
Old 05-18-2008, 10:48 AM
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Default RE: old os engines

Hi,

I have a OS MAX 50 SX. Just getting started in the hobby. The engine was given to me and runned great until the bearings seemed to need replacing. I replaced the bearings, but when putting the piston sleve back in I inadvertently broke the piston ring.
My question is can I get a replacement ring for this old of an engine? If so, where?

Thanks
Old 05-19-2008, 10:14 AM
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Default RE: old os engines

The 50SX engine is a current-production heli engine. Here are the stock numbers and list prices of the parts you asked about:

OSMG7790 25303400 PISTON RING 46SF/H US$22.99

These parts can be ordered through any hobby retailer who sells O.S. Max engines and accessories.

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