Converting an F800GS to belt drive.

Could you not bolt the 300mm discs to the new wheel and save yourself the bother of spacing the calipers?

Yep, you could. :) That's one of the options I presented, and it's probably the one I'd take if I were doing the conversion in that way.
There is one minor snag: the relevant Haynes manuals quote front disc sizes as 300mm for F800GS, and 305mm for R1200GS. I'd want to double-check that before I committed to either option.
 
I don't understand why lowering the back is such a bad idea. :confused:
Lots of folk here have lowered bikes and are tramping round quite happily.
I have a 19" front wheel and lowered the back with a HyperPro spring by an inch to match the front.
I met a chap at the BMW Club National Camp a couple of years back who had a SuperMoto 800GS with a the wheels from the 800R; 17" front & back and tubeless; and his bike was 2" lower at the back with a HyperPro spring and he was having no problems at all.
So what's the issue? :nenau
Plus getting a spring is a lot cheaper than getting special fork sections made up, and a damn sight easier to change back if needed.

SuperTed
 
over here a good chain will last about 30,000 miles and lube it about every 4 or 500 miles. Adjustments needed about every 4000 miles or more. I just made a 4300 mile trip and still no chain adjustment needed.
 
Did you consider whether a shaft drive could be used ?

I love my F800GS and it would be so much better with a shaft.
 
Did you consider whether a shaft drive could be used ?

I love my F800GS and it would be so much better with a shaft.

I remember perving over the F800GS when it first appeared on our sunny shores - then looking at the back, expecting a top-class final-drive, and seeing.... a chain.
Like that moment where a Brazilian supermodel gives you a soft smile from across the room.... walks over to you and slowly drapes her arms around your shoulders.... closes her eyes and tilts her chin up for a kiss...
And it's at that moment that you realise, every one of her teeth is rotten.

To give the F800GS shaft drive would require major re-engineering of the gearbox and rear suspension. That would need more resources than I'm likely to have in this lifetime.
So no - the only 'shaft drive' my conversion is likely to have is when BMW drive a shaft up my backside when it comes time to replace the drive belt.... :1/10
 
I wonder if it was a cost or weight issue that stopped BMW from doing it right
 
I wonder if it was a cost or weight issue that stopped BMW from doing it right

Both, I think.
The major factor would be the rear drive unit. We're talking about hypoid bevel gears made to a very high standard from expensive steel alloys, built robustly enough to transfer drive torque, carry an offset rear wheel and carry half the weight of the bike.
 
Quote Originally Posted by Flipfly:
"Could you not bolt the 300mm discs to the new wheel and save yourself the bother of spacing the calipers?"

Yep, you could. :) That's one of the options I presented, and it's probably the one I'd take if I were doing the conversion in that way.
There is one minor snag: the relevant Haynes manuals quote front disc sizes as 300mm for F800GS, and 305mm for R1200GS. I'd want to double-check that before I committed to either option.

Re-reading the original post, I realised you might have been asking if it was feasible to mount the 300mm F800GS discs to an F800R front wheel.
If this is the case, then the answer is no. :( Two very different disc designs.
On the GS, the discs bolt to the wheel hub via disc carriers. On the R, the discs are a reduced torsional-loading design with a much bigger pitch-circle diameter, that bolt to the wheel without needing carriers. Hence my suggestion that the best work-around might be to use R1200GS discs on the R wheel.
 
Well, the odyssey begins now.
My base will be a late 2012 (post-facelift) F800GS in Kalamata metallic, which I paid for at the salvage yard yesterday! :bounce1

Judging by the retail prices of used 2012 / 2013 bikes of similar mileage, I paid a bit less than half of retail for it.
A quick look around shows ABS, ASC, ESA, original handguards with spoilers, upgraded BMW bash plate, Wild@Heart crash bars and BMW LED indicators. It's also got a seat which I THINK is a standard F800GS Adventure part.

The bad news is, it was involved in an 'incident'. Fork uppers and stanchions are twisted, and the rear grab handle is bent out of shape.
Missing parts include: exhaust silencer, one indicator, screen, screen support, instrument cluster and headlight. Also some bodywork damage (which seems easy enuf for a plastic welder to knock into shape).

I'll be stripping it as soon as it gets to my garage. Watch this space...
 
First update of the new year.

As the subject line says!
Here is where we stand so far:
  • The GS is almost completely in pieces (the piccy shows what it looks like at this time).
  • Thanks to the previous owner, both fork legs, both triple clamps and the front axle are in need of straightening. :rolleyes:
  • The rest of the bike consists of two piles of parts: one pile will be kept to go back on, the other (including both wheels, swingarm, exhaust and various other bits and bobs) will be sold to generate needed funds.
  • The GS engine and frame will be separated within the next 48 hours. As soon as that happens, I have a borrowed F800ST engine I can mate to the GS frame, to start checking vital clearances.

I've also made a rather quaint discovery: the rear swingarm fitted to the F800GT is longer than the rear swingarm fitted to the F800S and ST. (General say-so puts the difference in length at 48mm. Obviously, this also means that the drive belts are also different.)
I don't know yet whether this is a straight extension in swingarm length, or whether the rear of the engine casting has been tweaked as well.

As yet, I don't have a donor F800S, ST or GT. It's a bad time of the year to look - everyone's riding and no one's selling. On the flip side, quite a few are crashing, and prospective belt-drive donors do pop up from time to time.
I'll keep looking.
 

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Phase 2.

And so Phase two begins!

The pics show the 2013 F800GS frame mated to a late 2006 F800ST engine.
This engine is a borrowed 'dummy' unit that has extremely poor compression on both cylinders, but it's still useful for testing...

The first spacing conflict I found was that the GS frame's bottom-most engine mountings were touching the ST engine's swingarm mountings. Those engine mountings - along with their locating bar - were removed by hacksawing very close to the frame's cast-steel side lugs.

After that, the frame turned out to be a surprisingly good fit. As expected, the four upper engine mountings are in identical locations on all versions of this engine.
The second spacing conflict is that the engine's belt-drive pulley just touches the right-hand frame lug. If the inner part of the frame's right-hand swingarm mounting point were machined outward by 2mm or so, that would cease to be an issue.
At this point, I need to borrow an S/ST/GT swingarm for space testing. There should be no problem with locating the swingarm between the frame lugs, but I want to make 100% sure before proceeding. If there are serious problems, I'll cut the frame lugs accordingly, and use S/ST/GT rider footpegs, footpeg mountings, gearshift lever and rear brake cylinder (on these bikes, these components bolt to the engine, not the frame).

The heavy round frame tube joining the cast frame lugs is going to serve as the main 'locator' for fabricated engine mountings that will extend downward and join to the belt-drive engine's swingarm mountings. The rear part of the frame will also be braced accordingly.

Other odds and sods:
  • The upper front frame mounting points on the ST engine are tapped for M10x1.5 screws. The same mounts on my GS engine take M12x1.75 screws. So I may have to drill out and re-tap the frame mounts of the engine I eventually buy.
  • The ST engine has an externally-mounted oil-pressure switch next to its engine-temperature sensor. The GS engine has a blanking plug where the oil-pressure switch 'should' be. I don't know at this time where the GS engine takes its oil-pressure input from.
  • Belt-drive engines and chain-drive engines seem to have different oil/water heat-exchanger arrangements. I have a feeling this shouldn't result in radiator / radiator fan clearance issues.
  • Belt-drive engines and chain-drive engines also have different water pumps. There is likely to be a clearance issue arising from the direction in which the water pump orifices point.
  • The sump casting is also different between belt-drive engines and chain-drive engines. If I want to use a 'standard' BMW GS bash plate, I'll have to change sump plates.
  • Obviously, I'll also have to change the left-hand engine cover to get the oil dipstick level in the right place.
 

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Careful examination of both engines last night revealed some drawbacks in terms of upper crankcase, lower crankcase and sump castings:
  • The belt-drive engine has four lugs on the rear of the crankcase and two lugs on the sump (i.e. three lugs on each side), for mounting standard footpegs, shift lever and rear brake hardware. So far, if you want to shift the footpegs back by 60mm, you can cut the lower cast lugs from the GS frame and use the abovementioned belt-drive hardware. If you don't, you can retain the lower cast frame lugs, use GS components, and leave the engine lugs unoccupied. So far, so good.
  • The GS engine has four lugs on the front end of the lower crankcase half (i.e. two lugs on each side). These are the lower mounting points for crash bars. And it's a snag, because the belt-drive engine doesn't have them. I want to use the Wild@Heart crash bars that came with the bike, so I'm going to have to add other mounting points.
  • The GS engine has four drilled cavities on the underside of the sump, and one long horizontal mounting cavity at the lower front of the engine. These are used to attach bash plates. Again, the belt-drive sump doesn't have them. And again, it's a snag, because the bike came with the factory BMW aluminium bash plate, which I want to use. Luckily, the belt-drive sump DOES have three drilled cavities, also on the underside, but in different locations to the GS engine. So what I'm thinking of is to modify the bash plate with new mounting holes in the correct locations.
    You can't swap sumps between engines, because they have different sump-bolt patterns.
 
Phase 2.5

By sheer, sheer luck, and by just happening to look in the right place at the right time, I found, look-seed and paid for an accident-damaged F800GT yesterday.
Rear-end and right-hand side damage, missing panels and indicators, and a small, repairable hole in the RHS engine casing. (I suspect but can't verify that someone shunted this bike from behind and caused the rider to drop it).
I paid roughly 25% of the retail price for an intact bike of the same vintage.

So my parts donor has finally arrived! :D A quick look around reveals that it has every single major part I need.
This seems to be a 2013 bike (the 'seller' I spoke to was an intermediary, specializes in repairing Jap sportsbikes and didn't know the year model). It has ABS and ESA. I couldn't verify it because I couldn't turn the ignition on, but I think it might have RDC as well.
By my reckoning, it's also low-mileage. Low enough that it still has its original front tyre, and the handlebar grips were virtually unmarked.

Collection and strip-down to commence this Saturday. :thumb

Meanwhile, progress on the new rear engine mountings has been coming along slowly, but steadily. The more I think about it, the more heavily I'm leaning toward a 'monocoque', box-frame type of construction for the mounting. It makes the most sense for balancing maximum strength against the space limitations around the swingarm pivot (the two major obstacles are the forward portion of the fuel tank and the upper drive belt run).
 
Engine mountings, continued.

I realised last night that there was no way I was going to get accurate positioning for the rear engine mountings if I didn't address the top front ones first.

I removed the GS frame from the ST engine, drilled out the top front engine-mount bolt cavities to 9mm, then 9.5mm, then 10mm, then tapped the holes to M12x1.75.
After that was done, I re-installed the GS frame.
Perfect fit around the top four engine mountings, with no up/down play around the top fronts. :thumb
Now I can proceed with the new rear mountings in earnest.
 
Good interesting work. Thanks for posting.

My pleasure! :)

A random thought: I'd be willing to bet that at some stage, the design engineers responsible for the 798 cm3 F-series engine specified that it should have a knock sensor.
The attached piccie supports my point. That mounting point is exactly the size and shape that would support the kind of knock sensor found on late K1200s and K1300s, and previous-generation R-series. It's in the optimum place, too: just right to pick up high-frequency impulses (detonations) from the combustion chambers.
 

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