I have a 1995 850R and have an engine from a 1100RS, the most powerful 1100. I want to change the barrels and heads over to make a quick cafe racer, something along the lines of Oliver who has the lovely 1100 on here.
Now I know the cranks are the same and the crankcases, even down to the head studs, soooooooooooooo
Has anybody done this or similar. I know the injectors are the same although the inlet tracts are different, may not be a problem, and I will need an 1100 "brain" to hold the injectors open longer, anything else that anyone can think of. I will keep the gearing short at first so it should accelerate well.
All help welcome, I can photo the process and make a thread if anyone is interested. Ta
People do this sort of thing all the time with 883 Harley Sportsters. I was able to change the jugs and pistons on my '88 Sportster and instantly convert to 1200cc.
I don't know the thickness of the cylinder wall on the BMW 850 but a conversion might be as simple as overboring your cylinders, changing the pistons, and enrichening the fuel mixture somehow.
With the 883/1200 Sportster conversion you must either used dished pistons or machine the head space to get compression down to acceptable levels.
Doing a conversion has some advantages over a stock 1100. You will pay insurance on less CCs and maybe the valves are smaller on the 850 heads? Smaller valves might sound bad, but on a Sportster smaller valves make more torque on the bottom end (sacrificing some top end). Since most of our riding is in the low end it works out better than stock (in my opinion).
You really have me interested in your project. Start looking at realoem.com and comparing part differences between the 850 and the 1100. What you are saying sounds like a little work, and might even cost more than simply trading bikes, but you will learn a lot and get some nice benefits. You will learn things about motorcycles, and wrenching that you'll never forget.
Hi Combat, you seem to have missread my post a little, I have a complete 1100 engine with 67,000 miles on it but to change it would involve rebuilding the whole bike. My idea is to swap the cylinders and heads, change the ECU for one from an 1100 and see what I have got.
A few other subtle mods. front exhaust box and trim from my 1150r, R90s type screen, single or humped seat and hey ho, a cafe racer, an 1100rs motor ( 90+ bhp ) in an 850r with an 850 rear drive, should be very quick up to 110mph.
I have been on the realoem site and from there it looks like a goer, just wanted to know if anybody had done anything similar! Ta
richierex wrote:I have a 1995 850R and have an engine from a 1100RS, the most powerful 1100. I want to change the barrels and heads over to make a quick cafe racer, something along the lines of Oliver who has the lovely 1100 on here.
Now I know the cranks are the same and the crankcases, even down to the head studs, soooooooooooooo
Has anybody done this or similar. I know the injectors are the same although the inlet tracts are different, may not be a problem, and I will need an 1100 "brain" to hold the injectors open longer, anything else that anyone can think of. I will keep the gearing short at first so it should accelerate well.
All help welcome, I can photo the process and make a thread if anyone is interested. Ta
Hi there,
thanks for referring to my bike! Actually you could do this mod without any problem. I have asked the oilhead experts in the leading german oilhead forum. You can easily transplant the pistons, cylinders and the heads of an r1100rs onto an r850r. You could also swap the motronic but you can also keep the r850r motronic - same just needs to be re-coded which your friendly dealer can do ...
But what do you gain? A couple of horses versus rough engine behavior ... The engine of the r110rs runs much rougher than the r850r engine. On the other hand would it not be the same work to transplant the whole engine?
Anyway it is no problem and it would be nice if you shared your efforts with the oilhead community.
Hi Oliver, I really want the torque of the 1100 and would like to try it with the 850 rear drive ratio. The roads round here can be hilly with plenty of corners. Also the 1100rs is more powerful than the 1100r and I have a cat and tip that was on my 1150, that has now got a y pipe and Akrapovic titanium can on it.
would you advise a chip change on the 850 - 1100 conversion, I think I need to open the injectors for about a 1/4 longer to allow for the bigger engine, or is there a coloured plug that would do it?
I will take plenty of photos and write up the job when I start it. Cheers. Ta
Well the fuel injection is controlled by the motronic. The injectors are the same on both models. Either you swap the motronic as well or you get the motronic of the r850 recoded. A change of the chip is always advisable. Likewise a change of the pistons and the camshafts. These 3 items will deliver about 15-20 HP and plenty of torque ...
Off course you will also have to swap the color-coded plug (under the seat in the fuse box).
