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Need specifications for O.S Max FT-120 Twin Gemini ll

Old 08-25-2006, 07:42 PM
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Tailblade
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Default Need specifications for O.S Max FT-120 Twin Gemini ll

I have a O.S Max FT-120 Twin Gemini ll. I have downloaded the instruction manual for the engine but the manual does not have any specifications listed inside for this engine. I would like to know the HP rating, rpm range and sizes of props to use. Any help will be greatly appreciated.

Thank's
Tailblade
Old 08-28-2006, 10:52 AM
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Default RE: Need specifications for O.S Max FT-120 Twin Gemini ll

From the tech notes:

SPECS: Construction: Aluminum and Aluminum alloys
Displacement: 9.95 cc (X2) or .607 cu in (X2)
Bore: 24.0mm (.945") Stroke: 22.0 (.866")
Power Output: 1.7 BHP at 10,000 RPM Weight: 1090g (38.5 ozs)
Practical RPM Range: 2,000 - 10,000 RPM
Crankshaft Thread Size: 5/16-24

Length: 120mm (4.72") from backplate to front of the drive washer
Width: 196mm (7.72")
Height: 80mm (3.15")
Suggested Props: 14X9,14X10,14X11,15X8,15X9,15X10,16X6,17X6,18X6
Old 10-05-2010, 03:19 PM
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Default RE: Need specifications for O.S Max FT-120 Twin Gemini ll

Attn. Mr. Bill baxter
I have the original engine. While the specs. rpm range goes up to 11,00 with a practical range between 2,000-9,000 I am only getting 7,000 rpm using an 18-6 or 16-8 pitch prop.
Using Cool Power 15% synthetic fuel.
I had never used it since 1980, just ran it for one hour with a rich needle setting.
Can u pl. give me a hint on what am I doing wrong ???
Best
Rafeek
847-446-2899
Old 10-06-2010, 09:27 AM
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Default RE: Need specifications for O.S Max FT-120 Twin Gemini ll

You are doing nothing wrong. That's the RPM the engine will run with that propeller. Best running is 7,000-7,500 RPM. Choose a propeller to turn that RPM range and fly your model as you desire it to fly.
Old 11-12-2010, 03:49 PM
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Default RE: Need specifications for O.S Max FT-120 Twin Gemini ll

Thanks for your help Bill,
Now I have a different problem although it has nothing to do with the engines performance which was impeccable.

Due to a broken wing strut the Cub took a dive nose first.

The engine mounts in the rear sheered off and a piece of the cranck case broke off also.

So I need a new cranckase p/n 46301 000 and rear housing plate p/n 46301 800.

Any assistance u can give me in locating the rear housing backplate would be appreciated.

Best

Rafeek
Old 11-16-2010, 09:55 AM
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Default RE: Need specifications for O.S Max FT-120 Twin Gemini ll

Here are the stock numbers and list prices of the parts you asked about:

OSMG4440 46301000 CRANKCASE FT120 US$154.99 Must be special-orderedallow 6 weeks or so.
OSMG5272 46303300 CYL JACKET FT120FF US$51.99 Must be special-orderedallow 6 weeks or so.
Old 07-22-2012, 12:06 PM
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Default RE: Need specifications for O.S Max FT-120 Twin Gemini ll

I have just aquired a os 120ft gemini it does not say II on it so i asume it is a first generation it turns over well and feels pretty good the guy i got it from said it has not been flown for A FEW years and the only thing i can find wrong on it is the throttle likage arm is gone and a few little nicks on the push rod tubes i know i should get this thing checked out i bought it for a 120 tiger month biplane i have puchsed and would like to know if ther is a manual with the specs for it any where before i tear it apart i would rather have a professional do it but i dont know who would even consider this because of how long it has been dicontinued is ther tork specs and is there specific places to check and do you need to replace the head gaskets or are any of these parts available


thanks Rick Nunes
Old 07-23-2012, 06:01 AM
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Default RE: Need specifications for O.S Max FT-120 Twin Gemini ll

First off, there are no parts available that are specific to the original O.S. FT-120 twin engine. Also, there isn't a cross-reference that says what current parts may fit.

It may be possible to locate a throttle arm that will work, but we'd have to do a lot of checking in the old manual, if it's still around. It's not in electronic format.
Old 07-23-2012, 07:46 AM
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Default RE: Need specifications for O.S Max FT-120 Twin Gemini ll

so the engine i have is actually in pretty good shape it turns over easy and seems to have decent compression if its been setting is there any oiling holes or specific locations that i should look to clean ?or soak it in a cleaner? would this hurt the gaskets?also is there a manual that would be available for me to use to check this enginge out before running it? I like this engine and it sure would fit this 120 tiger moth and i dont want to damage it because i dint take the time to ask would os consider cleaning it up?

sorry for so many questions thanks for your time will wait for your reply
Rick Nunes
Old 07-23-2012, 07:09 PM
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Default RE: Need specifications for O.S Max FT-120 Twin Gemini ll

I have the engine and manual. Will scan them and send them email in few days.
Pl. remind me if you dont get it by Wednesday.
Rafeek
Old 07-24-2012, 06:07 AM
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Default RE: Need specifications for O.S Max FT-120 Twin Gemini ll

We do not clean dirty engines. We do only that amount of cleaning needed during a repair to prevent introducing dirt to the internals. If it has burned-on fuel residue, it's up to the owner to clean that off.
Old 09-06-2012, 03:04 AM
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Default RE: Need specifications for O.S Max FT-120 Twin Gemini ll

 bill was wondering can i mount a new 120 ax inverted or upside down i have a sulivan on board glow driver i bought but never have used and i have a pulse 125 ready for the engine now but was wondering if it would be ok to do this with the glow driver even if the tank is higher than the fuel inlet                                               

                                                                                                                      thanks rick nunes
Old 09-06-2012, 07:37 AM
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Default RE: Need specifications for O.S Max FT-120 Twin Gemini ll

Try it and see how it works out. If the engine runs well without ignition help, then you're OK.
Old 10-30-2012, 06:57 PM
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Default RE: Need specifications for O.S Max FT-120 Twin Gemini ll

just wondering if anyone knows where I can get a cyl. or jacket for my old o.s. 120 twin 4 stroke engine I have the sleeve just need the jug? or is the gemini 2 120 twin jacket or jug interchange, any info would be greatly appreciated thanks..........Steve
Old 10-31-2012, 12:16 AM
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Default RE: Need specifications for O.S Max FT-120 Twin Gemini ll

i did put the 120 ax on the pulse upside down and it had the sulivan glow starter it ran great for about 6-7 min and then just die couldnt figure it out until while it was idling on the bench a allen srew fell down on the table i shut the plane off and guess what it was off the head of the brand new 120 it had ran three times i have 7 os engines two 55 ax 46 ax 120 ax 95v four strke and havent ever checked the heads to see if they are torked or tight never had two is this something to worry about i tighten it up and it ran three full tanks with no problems do you think i should worry about damage to the engine from alll the bolts being loose and leaning THE ENGINE OUT ? i did not remove the head to check it i just tighten it up as best i could

thanks rick nunes
Old 12-16-2012, 02:36 PM
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Default RE: Need specifications for O.S Max FT-120 Twin Gemini ll

Bax,
Are the crackcases for the FT-120 & Ft-160 compatable?

Thanks

Rafeek
Old 12-17-2012, 07:33 AM
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Default RE: Need specifications for O.S Max FT-120 Twin Gemini ll


ORIGINAL: slskn

just wondering if anyone knows where I can get a cyl. or jacket for my old o.s. 120 twin 4 stroke engine I have the sleeve just need the jug? or is the gemini 2 120 twin jacket or jug interchange, any info would be greatly appreciated thanks..........Steve
No idea. You'll have to check the web and magazines for dealers who might be selling old engines or parts.

Old 12-17-2012, 07:34 AM
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Default RE: Need specifications for O.S Max FT-120 Twin Gemini ll


ORIGINAL: napacp

i did put the 120 ax on the pulse upside down and it had the sulivan glow starter it ran great for about 6-7 min and then just die couldnt figure it out until while it was idling on the bench a allen srew fell down on the table i shut the plane off and guess what it was off the head of the brand new 120 it had ran three times i have 7 os engines two 55 ax 46 ax 120 ax 95v four strke and havent ever checked the heads to see if they are torked or tight never had two is this something to worry about i tighten it up and it ran three full tanks with no problems do you think i should worry about damage to the engine from alll the bolts being loose and leaning THE ENGINE OUT ? i did not remove the head to check it i just tighten it up as best i could

thanks rick nunes
Usually, it's not a problem. If the engine runs well, the compression and fit is still good, and no damage happened...at least not enough to cause problems.
Old 12-17-2012, 07:35 AM
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Default RE: Need specifications for O.S Max FT-120 Twin Gemini ll

ORIGINAL: rafeeki

Are the crackcases for the FT-120 & Ft-160 compatable?

Thanks
They are not the same. Differences in carburetors and cylinder mountings.
Old 12-17-2012, 07:59 AM
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Default RE: Need specifications for O.S Max FT-120 Twin Gemini ll

Thanks

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