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1995 R100R engine into 1975 R90/6 chassis?

zenduddhist

New member
Hey all,

I have a very nice 1995 R100R Mystic and a 1975 R90/6. The R90 runs just fine, but the R100R engine is really sweet. Lots of power, runs very, very smooth, great response, etc. I prefer the ergonomics of the R90/6 versus the Mystic.

I had this crazy idea of taking the R100R motor out of the Mystic and putting it in the R90/6. I know it's a nutty idea because I would be trashing a beautiful example of a Mystic. But just out of curiousity, is there an "easy" way to do it?

Thanks!
 
Hey all,

I have a very nice 1995 R100R Mystic and a 1975 R90/6. The R90 runs just fine, but the R100R engine is really sweet. Lots of power, runs very, very smooth, great response, etc. I prefer the ergonomics of the R90/6 versus the Mystic.

I had this crazy idea of taking the R100R motor out of the Mystic and putting it in the R90/6. I know it's a nutty idea because I would be trashing a beautiful example of a Mystic. But just out of curiousity, is there an "easy" way to do it?

Thanks!

See bold type.

Seriously, they're your bikes, you can do what you want, but if you've got 2 airheads in good running condition, why mess with it? Sounds like you just want a little more "oomph" out of the R90 so you can be comfortable and have a little more power.

Have you looked at what you could do to tweak the ergos on the Mystic to make it more likeable? That may be a direction you could go.
 
It would be easy to medium difficulty. Off the top of my mind, at the very least you'd have to:
- find a '76-on flywheel (you could use the rest of your '75 clutch if in good condition)
- change the ignition trigger setup to the '79-80 "points in can" system and rewire the bike to match it
- modify or reconfigure the engine breather
 
Hey all,

I have a very nice 1995 R100R Mystic and a 1975 R90/6. The R90 runs just fine, but the R100R engine is really sweet. Lots of power, runs very, very smooth, great response, etc. I prefer the ergonomics of the R90/6 versus the Mystic.

I had this crazy idea of taking the R100R motor out of the Mystic and putting it in the R90/6. I know it's a nutty idea because I would be trashing a beautiful example of a Mystic. But just out of curiousity, is there an "easy" way to do it?

Thanks!

The comment that I would have, is that anything is possible providing you have really deep and I mean deep pockets. I see from time to time where guys and gales have this vision of what if? Dive into it and all of a sudden the piggy bank went dry. Thus the project gets abandoned....

The 1995 R100R Mystic and 1975 R90/6 are beautiful pieces of machinery just the way they are. If you prefer the ergonomics of the R90/6, that's where you want to invest your money wisely.

Just my two (2) cents worth! Gotta quite saying that as here in Canada, the Government has now started to phase out the penny....
 
Why don't you try putting the R90 tank and seat on the mystic instead? Probably would need a little modification, but,ess work than an engine and drivetrain swap
 
My guess, and the operative word here is guess, is that what makes the R100 engine sweeter than the R90 are a lighter flywheel and lower compression pistons. (My guess comes from owning a '76 R75/6, an '84 R100 and my current R90S, in that order.) IIRC, the R100 also has smaller diameter carbs. As such, it probably makes less power but runs more smoothly and revs more freely. It would be easier, and cheaper, to replicate that in the R90. I'd start with a lightened flywheel and see how that feels. Then, if that's not enough, you could either lower the compression or dual plug the cylinders (either would let it run better on the lower octane gas currently available). I'd bet that the flywheel mod would get you 80% of what you're looking for.
 
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