.21 OS Max info needed

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Wasted wages

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Jan 2, 2006
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Just came into a stash of older OS Max .21 engines,, 1 of them only needs a crank to be complete..

Not sure about the different OS models,
but the two types of motors I have are
the EX and RX.
What are the differences between the two motors?

Any OS guru's out there that can shed some light about these motors?

If anyone has an old Crank stashed away they would part with, please let me know..
 

RaceMechaniX

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Apr 27, 2007
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Last edited:

ChrisHerzog

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Either way, that’s going to be to fast for you. I think you should just send it all my way and let me deal with it! lol
 

RichJones

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From what I can see the ex series was released in 1988 and the rx in 1992. Not much else I know. There’s a chart you can pull up if you Google OS Engines Timeline. I ran both the .46vr-m and the 65 vr-m in sport 40, scale, and e-hydro in the 90s. Those engines were developed in like 1980 but we’re still fairly relevant in the mid 90s. They were strong reliable engines. I have a 21 RZ-M that came out like in 95. It’s going into a sport 20 at some point just for the hell of it.
 

Wasted wages

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Either way, that’s going to be to fast for you. I think you should just send it all my way and let me deal with it! lol
Ha! OS Max and too fast shouldn't be used in the same sentence,,, but these little motors look like they could make some nice little dependable runners...

Are you hiding away any crankshafts that might work Chris ?

Anyone ??
 

ChrisHerzog

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Ha! OS Max and too fast shouldn't be used in the same sentence,,, but these little motors look like they could make some nice little dependable runners...

Are you hiding away any crankshafts that might work Chris ?

Anyone ??
All I might have is a broken one. Check with Gabe at Stumpfab.
 

Grimracer

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Dec 27, 2001
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Sorry I just saw this.. sorry I cannot help.. The OS motors in a 21 that I have run are the VZ-M and the XZ-M.


Grim
 

Joern Markset

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Oct 25, 2004
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636
The RX engine was not a bad engine at all. The outboard engine, 21 XM, is more or less based on the RX engine.
The liner used in outboard is equal to the liner that was used in the RX-B engine. You will be able to use the P/L, Crankshaft, bearings, conrod, head and carburetor from the 21 XM outboard in a RX housing. Even the outboard backplate fits directly.
Not a good answer to your question though, just some info....
I don`t know much about the EX engine (I`m way too young 😅 )
 

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