OS 61 Engine Help - RC Groups
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Nov 10, 2017, 06:44 PM
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Discussion

OS 61 Engine Help


Hi everyone

I bought a used OS 61 at a swap meet and it looks to have OS61 FSR ring, piston and liner......the piston has two notches not 1 and when i turn it over at one point you can see the piston notch under the pin through the exhaust port,

The other strange thing is that the crank case has its numbers machined of like a Enya 50 CX but hasn't been re-stamped.

Will the engine run ok with the FSR Piston?

Thanks

Johnkpap
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Nov 10, 2017, 07:45 PM
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I am assuming you are talking a OS 61 VF rear exhaust engine?
Nov 11, 2017, 12:18 AM
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Quote:
Originally Posted by tiporare
I am assuming you are talking a OS 61 VF rear exhaust engine?
Yes sorry I had a brain fade
Nov 11, 2017, 12:34 AM
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doxilia's Avatar
John,

The skirt of the VF and FSR should be different given the location of the exhaust port on each engine. If you can see the inside of the engine from underneath the piston through the port, you have a problem. That engine shouldn’t be started.

David
Nov 11, 2017, 02:06 AM
AMA 46133
Quote:
Originally Posted by doxilia
John,

The skirt of the VF and FSR should be different given the location of the exhaust port on each engine. If you can see the inside of the engine from underneath the piston through the port, you have a problem. That engine shouldn’t be started.

David
LOL if the op can see beyond the skirt of the bottom of the piston I don't think the engine will start. Something very fishy with this engine, don't you think?
Nov 11, 2017, 02:57 AM
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Thanks everyone.... as I suspect I bought a dud

But at $40.00 I can't complain too much I is worth more in spare parts

Johnkpap
Nov 11, 2017, 08:38 AM
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doxilia's Avatar
You just need to find a VF piston and sleeve...

David
Nov 11, 2017, 09:07 AM
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Quote:
Originally Posted by doxilia
You just need to find a VF piston and sleeve...

David
Trying to find a OS61 FSR crank case would be a lot easier ............for the moment it can live in the dead engine parts box
Nov 11, 2017, 11:55 AM
AMA 46133
Quote:
Originally Posted by doxilia
You just need to find a VF piston and sleeve...

David
Is Dave Shadel still in business? He used to sell all kinds of pistons and liners for the O.S. .61's.
Nov 11, 2017, 01:55 PM
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doxilia's Avatar
I think if you put a wanted ad, one may pop up.

David
Nov 11, 2017, 07:24 PM
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Quote:
Originally Posted by doxilia
John,

The skirt of the VF and FSR should be different given the location of the exhaust port on each engine. If you can see the inside of the engine from underneath the piston through the port, you have a problem. That engine shouldn’t be started.

David
Actually, I dont think the engine would be harmed at all because of the piston skirt clearing the exhaust port. In the pre muffler era, a few engine manufacturers made piston skirts shorter than the corresponding stroke measurement in order for the skirt to clear the exhaust port and momentarily expose the crankcase to the atmosphere. Since the pressure within the crankcase at the top of the stroke is less than atmospheric pressure, a dose of fresh/clean air was introduced. This improved volumetric efficiecy and gave more power (at least that was the theory).

This is not done with modern engines in modern times, because of the use of mufflers. This is because instead of clean air entering the crankcase, the muffler assures that contaminated air will enter instead.

If no other parts interphere with each other and if it shows good compresion, I would attempt to start the engine and see what kind of power it delivers sans muffler, just for curiosity.
Last edited by RC YEAGER; Nov 11, 2017 at 08:17 PM.
Nov 11, 2017, 08:22 PM
AMA 46133
>>This is not done with modern engines in modern times, because of the use of mufflers. This is because instead of clean air entering the crankcase, the muffler assures that contaminated air will enter instead.<<

Since an RC engine relies a lot of accurate fuel air mixture from the carburetor won't the piston skirt clearing the exhaust port make the mixture more lean?
Nov 12, 2017, 02:55 AM
Registered User
John, I had a OS61VF that needed piston/liner, I live in the UK and the best place that I could find for parts was down your way, the parts were a reasonable price, I just got stung with import tax .
I used World hobbies in Australia for the parts and they had an extensive stock of discontinued OS parts, this was about 12 months ago although I can no longer see any OS parts listed on their website, I would still give them a call.
Bear in mind that quite a few OS engines have interchangeable parts, there are a few good threads on this if you search.
hope this helps.
Nov 12, 2017, 12:58 PM
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Quote:
Originally Posted by SeismicCWave

Since an RC engine relies a lot of accurate fuel air mixture from the carburetor won't the piston skirt clearing the exhaust port make the mixture more lean?
I presume that since the uncovering of the crankcase was also a precise/rythmic event, occuring on every revolution and for a given degree of crank rotation, the extra air became part of the final "controlled" mixture and probably resulted in the needle valves been opened way more than in engines without sub-piston induction, for extra fuel at any given RPM's.

Also, perhaps the manufacturer took the extra crankcase air into consideration when selecting the correct carb jetting.

Whatever the correct explanation might be, It seemed to work. The Super Tigre G.20/23 was an engine that used sub-piston induction.
Nov 12, 2017, 01:02 PM
AMA 46133
Quote:
Originally Posted by RC YEAGER
I presume that since the uncovering of the crankcase was also a precise/rythmic event, occuring on every revolution and for a given degree of crank rotation, the extra air became part of the final "controlled" mixture and probably resulted in the needle valves been opened way more than in engines without sub-piston induction, for extra fuel at any given RPM's.

Also, perhaps the manufacturer took the extra crankcase air into consideration when selecting the correct carb jetting.

Whatever the correct explanation might be, It seemed to work. The Super Tigre G.20/23 was an engine that used sub-piston induction.
It will be interesting to find out more about it.


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