R80 motor in an R65 frame?

[oz_johnno]

Blokes, I have heard somewhere (I cant remember where) that an R80 engine will fit into an R65 Frame because the R80 and the R65 frames are identical...... is this true?

OZ

[montmil]

Both bikes are SWB and share components. Don't see why the entire 800cc engine would not fit. Transmissions all same.

Keep the R65 identification on the bike and make the locals wonder how you get that performance out of a 650.

Zoom, Zoom

[Barry]

The frames are only identical if both bikes are 85 - on otherwise they are different. The R80 would still fit in an earlier R65 frame though. Which version of the R80 are you thinking of ? The 50HP R80 will have more torque (and that's why might want to do it) but the bike is actually slower than a 50HP R65.

[tvrla]

I've heard the mountings are all the same, so any engine can be swapped into an R65 frame. I've thought of putting an R100 motor in an R65 - cutting an inch off the cylinders to tuck them in closer like the 650...

[montmil]

... I've thought of putting an R100 motor in an R65 - cutting an inch off the cylinders to tuck them in closer like the 650...

'splain this to me, spokes.  

[Barry]

.. I've thought of putting an R100 motor in an R65 - cutting an inch off the cylinders to tuck them in closer like the 650...


'splain this to me, spokes.

Shorter rods or pistons ?

[montmil]

.. I've thought of putting an R100 motor in an R65 - cutting an inch off the cylinders to tuck them in closer like the 650...


'splain this to me, spokes.

Shorter rods or pistons ?

Done considered that; but all that $$-££ just to have the engine a bit narrower? I think ol' Wirespokes is yanking on somebody's chain.

Reminds me of "Don't raise the bridge, just lower the river."  

[Barry]

It'd be cheaper to chicken out before the heads touched down.  I wouldn't find that hard to do.

[Matt Chapter]

It'd be cheaper to chicken out before the heads touched down.  I wouldn't find that hard to do.

Every time the heads touch down, I find I have too.  Much better to stay (relatively) vertical.  I thought I had heard (here, anecdotally) that the best way to go fast with an R65 would be to get a faster bike?  I'd probably not bother with the motor swap myself.

[montmil]

In for a penny, in for a pound...

Do as the builder of the Daytona winning R90s of some years ago did. Move the engine forward and up. Lean to your hearts delight!

[oz_johnno]

I think spokes is on the money, You have to be good friends with someone in a machine shop.  what you do is use R65 Rods and shave down the barrels........  what I was going to do is put in an R80 engine and put a 1000cc performance kit in with it.

like this

http://flatracer.com/#/bmw-performance/4538136890

[beater]

um, a 100 motor fits, so I would think an 80 would...

j

[tvrla]

It's called a long rod motor. Essentially what's needed is custom pistons that mount closer to the crown. I've heard of them, not seen them, so can't go into any detail. But it is possible to lose an inch that way. I believe the wrist pin gets tucked in behind the rings - it's that far up.

I hadn't heard or thought of using R65 rods in an R100 engine. Are the crank journals the same diameter? It seems the problem with that solution is the piston would travel an inch farther out of the cylinder towards the crank.

At any rate, there's still the problem of getting the pushrod seals to seal when the cylinder is shortened since they won't align properly. Shorter push rods would be needed as well. Wonder if R65 pushrods woulde work?

[Barry]

Wonder if R65 pushrods woulde work?  

It could get complicated because the fact that R65 pushrods and followers work at a different angle the cam timing is affected. I understand a standard 308 cam and an R65 308 cam are different part numbers only because of this effect.  

[tvrla]

Yeah, there are all sorts of things to consider with something like this -stuff you never thought of before!