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Old 08-20-2011, 04:28 PM   #1
Other Bob OP
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School me - turning an R1100RS into a dirtbike?

I should clarify that: 80/20 streed/dirt, with the dirt being fire-roads. Think RS-into-lowered, puttering old-guy GS. Or, an R80G/S theme with an oilhead engine/driveline.

I’ve enjoyed this "airhead dirtbike" thread for quite a while: http://advrider.com/forums/showthrea...head+dirtbikes

I happened on a wrecked ‘94 R1100RS which might be a good donor for such a project. Hit in the front, snapped the fork sliders, broke the Telelever A-arm at the slider joint, otherwise cosmetic damage. The upper steering "frame" section seems untweaked, the cases are not cracked where the A-arm mounts. The alternator cover was pierced about 1/2-inch deep at the bottom by the exhaust pipe being shoved back into it.

Soooo .... mid-90's R1100GS’s aren’t hugely expensive, but this donor driveline has only 20,000 miles on it. I don’t want to end up upside down financially just to get a stock 1100GS: this project only makes sense if I end up with something special or/and cheap and there are lots of potential pitfalls.

FIRST, is there something about the ‘94 RS which would make its driveline a really bad donor for such a project. Something like unreasonably high transmission ratios, high final drive ratio, peaky cam profiles, or something else about the RS in particular that made it a VERY different engine than the GS? Can the rear drive hub take a spoke wheel?


SECOND, what about de-Telelevering this beast and going with conventional forks? If all I do is replace the front end with OEM used parts I probably should just buy a good used 1100GS and be done with it, and it’ll be cheaper. I think I’ve seen some GS’s with conventional fork conversions: can someone point me to a thread?


THIRD: What else am I missing? There are probably some obvious pitfalls: grab me before I jump! There are no salvage title issues. The owner has clear title, there’s no insurance claim.

Anyone have a CHEAP R1100GS with a toasted engine/driveline ... maybe we should talk

Thanks in advance,
Bob
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Old 08-20-2011, 07:40 PM   #2
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The prospective donor:



Inspiration (inmate here I think), nice hybrid:



Proof of concept but too over-the-top for me now (probably even 20 years ago):



This is the goal, with the RS oilhead driveline:



I have a mill, lathe, torch and little need for sleep. I can scratch build a double loop airhead-type frame if needed, though #3 above looks like got by without that mod.

Dooable, or is the RS driveline simply a wrong match for this idea?

Bob
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Old 08-20-2011, 08:00 PM   #3
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It all depends on the price of the donor.
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Old 08-20-2011, 09:18 PM   #4
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Old 08-20-2011, 09:21 PM   #5
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Even if you get the RS for free, you will still probably be better off by spending less money and getting a lot less fewer headaches by handing someone a stack of $100's for their used GS and enjoying it now instead of maybe next Spring. Remember, bike projects almost always far exceed original projected costs...procede cautiously.

And, a semi stock GS would be much easier to sell later vs a RS/GS Frankenstein...
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Old 08-21-2011, 06:08 PM   #6
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Quote:
Originally Posted by Eddy Alvarez View Post
Even if you get the RS for free *** bike projects almost always far exceed original projected costs...procede cautiously.

And, a semi stock GS would be much easier to sell later vs a RS/GS Frankenstein...
Good points Eddy, thanks for the reality check. I'll bake this idea a bit longer.

Bob
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Old 08-24-2011, 10:49 AM   #7
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In similar fashion, look at what one of my local ADV riding friends did with donor Versys...

http://advrider.com/forums/showthread.php?t=644390
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Old 08-24-2011, 03:00 PM   #8
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Quote:
Originally Posted by MotoKaw View Post
The prospective donor:


Inspiration (inmate here I think), nice hybrid:



Proof of concept but too over-the-top for me now (probably even 20 years ago):
I Bob
It may have the driveline fitted but note the purpose built back wheel not a standard oilhead rear wheel as they do not line up in the air head frame using a 1100 GS rear rim I have tried it. Another point the RS Final drive ratio may be a bit high but if you have the time and patience anything is possible. Leave it in the shed and find an early cheap GS and then you have a lot of spare parts. Good Luck
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Old 08-24-2011, 03:17 PM   #9
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Or you could talk with this gentleman he will have some spare parts left over.
http://www.advrider.com/forums/showthread.php?t=711018
WR
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Old 08-24-2011, 03:45 PM   #10
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Just get an older KLR 650 and stick a BMW logo on it to piss off BMW owners who spent too much money on a bike that is useless off-road.

BMW GS = 95% on-road, 5% off-road (a dirt road is a road...off-road means there's NO ROAD).

Yes, the GS is better offroad than a Honda VFR800. The GS can handle a dirt road easily and a VFR would be a handful (like riding on marbles).

What about when you want to cross a river with muddy banks and a rocky bottom? On the KLR, you just ride through it. On the GS, the gigantic pig gets stuck the second you get near the muddy edge of the river and you have to call in a helicopter to pull it out.

Hey, I love my GS, but I don't pretend it is of any use off-road....

I don't want to talk you out of a crazy project. I'm all for crazy projects, but if you have visions of travelling to the middle of nowhere, forget about it....
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Old 08-24-2011, 06:29 PM   #11
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Quote:
Originally Posted by Eddy Alvarez View Post
In similar fashion, look at what one of my local ADV riding friends did with donor Versys...

http://advrider.com/forums/showthread.php?t=644390
Enjoyable thread, thanks for the link Eddy.


Quote:
Originally Posted by Whale Rider
*** note the purpose built back wheel not a standard oilhead rear wheel as they do not line up in the air head frame using a 1100 GS rear rim I have tried it.
My BMW experience is zero, but if I'm following you correctly the blue-frame machine above is the hybrid offspring of an oilhead Paralever mated to an OEM airhead frame, made possible by a custom hub to center the wheel and crank in the same plane. If true I had two thoughts on this:



A) My original idea (which turned out not to be so original, as usual) was something like the Bakker/Dursma frame to replace the stock BMW casting. That should eliminate the wheel/crank/headstock centering problem. I think that it is within my fabrication abilities, but I like the peace of mind that a full duplex-loop frame brings. Frame weight isn't an issue: it'll be easier for me to skip a few cheeseburgers than try to engineer a trellis cantilever upper frame with an appropriate safety factor.

B) Your comment reinforces the idea of an airhead/featherbed type full duplex loop frame, like the blue one above in concept but built from scratch to fit the 1100 oilhead engine & Paralever. Thoughts? See below ...


Quote:
Originally Posted by mdmaroon
Just get an older KLR 650 and stick a BMW logo on it *** BMW GS = 95% on-road, 5% off-road (a dirt road is a road...off-road means there's NO ROAD). *** I'm all for crazy projects, but if you have visions of travelling to the middle of nowhere, forget about it....
I agree, 100%. I had a '05 KLR650 and loved it. Very versatile. But I'm not fortunate enough to live in beautiful British Columbia, where OFF ROAD is within striking distance. My circumstances for the semi-immediate future (next decade) have me stuck in SE Michigan, a concrete shithole. Dirt isn't TOO far away, but I found I was using the KLR like you describe the BMW above. I've lived in Michigan my whole life so there isn't anywhere I haven't ridden in the immediate area. Anywhere worth seeing is a few day's away, and that sucks on a KLR for a chap of my girth so the KLR is gone. I need the "95% road" to get me to the "5% dirt" with enough energy left to explore some mild trails and still get home without being crippled. Time sucks, just like gravity.

I have no dillusions of an epic trip RTW trip, any Way Round. Most of the time an old Harley works just fine for me. But too many times I've seen a dirt road or trail I want to turn down, and if you think a GS handles like shit in the mud you should try a Shovelhead FLH some time.

This project, if it happens at all, will be the result of the confluence of a few timely circumstances. First, the fact that the donor bike appeared at all. Second, I have a mill, lathe, torch, and Diacro tubing bender that I've been itching to use. They are idle, that sucks. A home-made duplex/featherbed type frame doesn't present any insurmountable tasks: I've never made one but I'm game to try and I have the tools and time so ...

I'm still thinking it over, but I'll probably pull the trigger soon.

Bob

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Old 08-24-2011, 08:05 PM   #12
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Here is my concept that is under construction at the moment. Many hours spent in the shed already. Had a crash on my 1100 and smashed the side out of the gearbox housing. I bought the bike back and repaired it from a donor 1150 so ended up with a whole lot of spare parts. so I had to build something that would hold the swingarm. This is what I came up with after many hours on the computer studying bike frames 900RR, HP2, KTM990 Enduro etc etc

WR
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Old 08-24-2011, 08:14 PM   #13
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Swingarm pivots look like this
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Old 08-24-2011, 09:39 PM   #14
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Looks good Whale Rider! The frame reminds me of the tube trellis used by Ducati to bridge the gap over the rear cylinder of their 90-degree twin and connect the swingarm pivot to the steering head.



Yours would bridge the crankcase and accomplish the same goal, yes?



Looks like a very strong design!

Bob
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Old 08-25-2011, 12:00 AM   #15
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Thanks Bob, I am going with a single backbone everything is triangulated. I hope it all works OK. Its going to be a little while yet before I have to become a crash test dumby. Once I get it standing on its own wheels I may start a build thread of my own just starting to to put the tubes between all the mounting points. Good luck with yours.
WR
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