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dirtsurfer 02-17-2011 11:56 PM

R80 to R100 conversion
I'm looking for a two up tourer and quite fancy an R100 but a nice 1985 R80 Rt has caught my eye. I am thinking R100 conversion might be in order for two up touring. What's the consensus?
Also is it just a matter of changing the barrels or is some carburetor adjustments in order? Please point me to the threads where this topic has been done to death, reincarnated , then done to death again. Thanks

jellycow 02-18-2011 12:06 AM

Get the R80, ride along for a few months and then decide if you still 'need' those extra HP. The torque and smoothness of the R80 engine will suit most so just give it a try.
(Then spent the money saved on the 1000cc conversion on suspension or brakes or anything.) :D

But to not-quite-answer your question:
The swap is simple, someone will point you to some thread. Swap barrels, re-jet the carbs and you're done. The heads are not a must to swap for they might work if you want torque. Most depends on your demands.

Rob Farmer 02-18-2011 12:34 AM

To do a full conversion you need heads, barrels, pistons, Final drive with a matching speedo. It's simpler to just buy a 1000 in the first place. As jellycow says though If you like the 80 buy it and try it you may be quite happy with it.

davorallyfan 02-18-2011 01:43 AM

I've a Seibenrock kit 1000cc heading my way at the moment to upgrade my R80GS - just wanna get the back sliding a bit more on the windy gravel roads.

Kit has lightweight pistons, pins, new nicasil barrells, pushrods, ss tubes. Uses the R80 head.

10 hp extra is what they say - we will see.

The Au$$ie dollar is magic at the moment.

PaulRS 02-18-2011 01:46 AM

You could fit Siebenrock 1000cc conversion kit.

Only barrels and pistons.
These are a straight fit, no use to alter heads, exhaust and carb's, they are designed to work with the std R80 config.

I've fitted them on a mate's R80 hack and was amazed by the way it worked out.


bikerfish 02-18-2011 03:38 AM

I put 300,000 miles on an r80gs, lots of it 2 up. with that bike needing some TLC, I've been using an r100/7 and an r100r. usually 2 up also. I honestly can't tell much difference. the 1000cc motors have a little bit more grunt, but the 800 is smoother.
if it were me and the r80 is in good shape, I'd leave it alone and ride the wheels off it!

jellycow 02-18-2011 03:45 AM

bikerfish, I'm being curious here. Was there a difference in MPG between the 80 and the 100's?

DaveBall 02-18-2011 08:05 AM

Jellycow, if you are going to tour like the average European couple, then the R80RT will do you fine. If you plan to tour like the average American couple and want to take everythign inculding the kitchen sink, then an R100RT is still not enough for you.

If it was me, I would go for the R80 and see how it goes. They are the smoothest running boxer built and have just about as much power as the R100. All they really need for 2 up touring is some upgraded suspension, i.e. good quality heavy duty shocks and springs on the back and possibly upgraded springs inthe forks and slightly heavier oil. They get good gas mileage when ridden properly and can get down right poor mileage if you are trying to ride it like a crotch rocket. Normal gas mileage forthe R80 should be in the range of 45-50MPG and some have been known to get as high as 55MPG (or so I have been told), while the R100 will usually top out at around 45MPG. Thr R80 does have lower horsepower, but with the gearing it has, you really don't notice it much, maybe on a high speed pass up hill.

For touring you will want reliablity. The stock R80RT will do what you need to do and get you back with no issues.

supershaft 02-18-2011 09:49 AM

I thought I would put in my $.02 dirtsurfer since it is different from most everybody's.

I think it is funny how so many on the net are all for after market big bore kits in order to get another 70 or 90cc's over a "1000's" 980cc's and the resulting cylinder walls and gasket sealing surfaces that are too thin but then advise against BMW's own "big bore" kit which is what a 1000cc BMW really is if you think about it. The main differences is that the BMW setup gets you 200cc's instead of 70 or 90 and it leaves the cylinder walls and gasket sealing surfaces with just enough to work correctly. There are lots of good reasons why BMW stopped hogging her out at 1000cc's!

800's are a bit smoother but I don't notice it that much. I guess it is because, judging by inmates mileage reports, I ride at higher speeds and RPM's. I don't get NEAR the reported mileage on the net and neither do a bunch of my friends and customers from what I have heard growing up and working in a BMW dealership and then working at three more of them so far plus having my own shop. Vibration wise, 1000cc's never bothered me.

Power wise? I think there is a substantial difference in the additional 200cc's. I have converted many a R80GS and the back to back difference is HUGE. It's hard to keep the front wheel on the ground in first! Yes, if I converted I would re-gear and get a different speedo as well but all the extra power is what gives you that option! Personally, I can't see running smaller than 1000cc's when the external dimensions of the engine remain the same. The weight barely changes as well. I wonder if a 1000cc weighs less than a 800? Either way, it's a win/win as far as I am concerned. You get a bigger bore that still isn't TOO big.

Hawk Medicine 02-18-2011 02:37 PM

Buy the R80 and skip the conversion.

Touring on an Airhead is all about what you leave behind, not what you take with you, so a few personal items and a couple changes of clothes, a few spares and your Significant Other is all you need. For that, an R80 should be perfectly adequate.

Of course, if you're both (Ahem...) overweight and you like to carry a lot of crap with you, skip the Airheads entirely and buy a used K-Bike. A decent K100 won't even notice the extra weight and they have a rep for bulletproof reliability.

I've owned/ridden most iterations of the airheads and the R75's and R80's are some of the sweetest/smoothest and longest lasting engines that BMW built, despite the fact that I prefer the added torque of the R100 engines.

It's all a matter of taste!

McHaven 02-18-2011 02:47 PM

I did 600 miles on my R80 today. The R80 has got to be the smoothest airhead engine around. A couple of times I entirely forgot I was on the bike. You don't even notice a R80 beneath you. And it as all the power you'll need.

bikerfish 02-18-2011 05:17 PM

to answer the mileage question, I get around 50 on either engine. I'm past being ricky roadracer, I ride at a respectable pace, but I still smell the roses.
you want power? get an oilhead or a k-bike.
if you want a good touring bike that will take you and yours all over the place and aren't a speed demon, that r80 will work just fine. as mentioned above, do some suspension upgrades and put 100k on that thing!

labradog 02-20-2011 05:38 PM

Ride the R80
All my old bikes were R75s and R80s, mostly run 12 months a year, rain or shine. I didn't have a bike for 19 years, and I just got an old R100S, for which I always had a hard-on back in the day.

I enjoy my bike, it's in decent running condition. While there are differences in the performance, they exist in a part of the riding experience that I virtually don't use. Don't get me wrong, I enjoy a quick ride sometimes. And I do dig the twin front disc brakes. But honestly, for 99% of my riding there is no meaningful difference from the engine size.

davorallyfan 02-21-2011 01:37 AM


Originally Posted by PaulRS (Post 15218569)
You could fit Siebenrock 1000cc conversion kit.

Only barrels and pistons.
These are a straight fit, no use to alter heads, exhaust and carb's, they are designed to work with the std R80 config.

I've fitted them on a mate's R80 hack and was amazed by the way it worked out.


Waiting to be amazed:wink:

davorallyfan 03-03-2011 01:15 AM

Smoother than the 80 and more boof through the middle. :nod

And it aint run in yet.

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