Converting an F800GS to belt drive.

Phil-H said:
Nice work. Utter madness but nice work :)
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My thoughts exactly. Thanks! :D

thefooleryoftom said:
I'd love to do this, if only I were clever enough. Great work.
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Hi again Tom! :)
It doesn't really require cleverness. Just some lateral thinking, a bit of understanding of how the bike works, and a bit of knowledge of basic engineering principles.
Alongside the conversion itself, I'm also producing a document that will explain to anyone interested how to perform this conversion, step by step. Reading it, you'll see that by making the overall motorcycle configurations as similar as they did, BMW actually did the same thing as Hansel and Gretel's dad, leaving a trail of breadcrumbs to follow.
You also like to tinker... if you've got a mind to create something great of your own, I say go for it! :thumb
By the way, I saw an F800R for the first time while I was out on a run yesterday (sadly, heading in the opposite direction). A Chris Pfeiffer edition with a German licence plate.
 
Good news!

The donor F800GT is currently down to main frame, engine and swingarm (which will be kept together as one unit for the next phase of dimensions-checking), triple clamps, forks, ABS regulator and brake lines.

Careful measurement confirms that it is possible to fit the F800GT swingarm pivots between the F800GS's vertical main frame lugs with no mods.
This means that if you want to do this conversion, you have a useful choice: you can either keep the GS frame mostly intact (and thus keep the standard rider's footpegs, gearshift lever, brake lever and rear brake master cylinder), or you can cut off the vertical main frame lugs and use the F800S/ST/GT components (which will shift back the rider's footpegs by 60mm and make the riding position a bit more aggressive).

If you want to go with the first option, all you need to do is machine the right-hand inner swingarm mounting point of the GS main frame outward by 3 or 4mm so it clears the belt-drive front pulley. :thumb
 
A bit late now but couldn't you have had a drive pulley machines to fit the GS engine? You may have been able to use a non-BMW drive belt as well which may have made it 1/3 of the price :D

I think you just want to make it as difficult as you can out of some perverse and dogged need for a good challenge! :)
 
Packer said:
A bit late now but couldn't you have had a drive pulley machines to fit the GS engine? You may have been able to use a non-BMW drive belt as well which may have made it 1/3 of the price :D

I think you just want to make it as difficult as you can out of some perverse and dogged need for a good challenge! :)
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Re. the second part: you may be right. ;) :p

Re. the first: I actually tried to do just that in mid-2012 with my '08 F800GS, and I got as far as negotiating with a US-based builder who would have shipped me two drive pulleys to specifications and a suitable Gates belt.
I aborted the experiment after the builder notified me the conversion would be US$3 200, not including shipping. At the time, with an exchange rate of R8/$, that would have worked out to R25 600 - about half the replacement value of the bike! (Assuming his price hasn't gone up since then, it would now cost me R35 200.)

To put those costs into perspective, I bought the complete base 2013 F800GS for R50 000, and the complete donor F800GT for R32 000.
Total cost R72 000. If I were buying in the lowish-mileage used sector, I could just about scrape a 2013 F800GS for R120 000.

This way, I get enough parts to do everything I want, with a belt-drive system which is proven - not experimental.
I have enough 'in demand' parts to recoup some of the cost. (I can't see a complete low-mileage F800GS engine and set of wheels hanging about for long...!)
And yes, I get the challenge, too. :D
 
Nick V said:
........................I aborted the experiment after the builder notified me the conversion would be US$3 200, not including shipping. ........................
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Hmm, precision die cast from unobtainium, hand engraved and platinum plated and machined to finish with a Rolls Royce custom built CNC mill.

Right, where's the next bit of the economy and much more interesting version of the conversion :D
 
Packer said:
Hmm, precision die cast from unobtainium, hand engraved and platinum plated and machined to finish with a Rolls Royce custom built CNC mill.
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My thoughts too, pretty much. I guess it makes a lot more sense if you're paying in Pounds or Euros.

The donor has now been stripped to the required level.
As it is now, I can remove the centre stand from the GS frame, slot it down over the GT engine, make final measurements and get ready to cut and weld in some steel plate... :D
 

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Frame modifications continued last night. :)

I can now say for certain that it's possible to either keep the lower rear vertical sections of frame intact (in order to use standard GS footpegs, shift lever, rear brake lever and master cylinder, sidestand and centre stand), or cut them off just below the original swingarm pivots (in order to use all the above items from an F800R, S, ST or GT). I chose the latter option. :thumb2

Either way, you have to machine off 4 to 5mm of the inner mating faces of both original swingarm pivot points in order to get needed clearance for the belt-drive swingarm pivots and front belt-drive pulley.

If I decide to get a bit more feel from the footpegs at a later stage, I'll swap out the rubber-topped GT footpegs for K1200S all-aluminium footpegs.

I considered re-using the GS front chain sprocket guard, but it won't fit over the front pulley. I will be able to re-use the front belt-drive pulley guard if I cut the rear portion off it.

Rear coil-over shock absorber:
It would be possible to use the GT shock by fitting it to the upper or lower swingarm pivot and making up the difference in spacing using some kind of spacing block in machined aluminium or welded steel.
It's also possible to use the GS shock by fitting it to the upper swingarm pivot, but its lower pivot AND the swingarm lower pivot are both male linkages. I'll have to design and fabricate some kind of male-to-male connecting mechanism.
That is what I'm going to do, and the mechanism will also be designed such that I can vary a) the leverage exerted by the swingarm on the shock, and b) the distance between the shock's lower pivot and the swingarm pivot, to tweak the rear ride height.
 
Nick V said:
Hi again Tom! :)
It doesn't really require cleverness. Just some lateral thinking, a bit of understanding of how the bike works, and a bit of knowledge of basic engineering principles.
Alongside the conversion itself, I'm also producing a document that will explain to anyone interested how to perform this conversion, step by step. Reading it, you'll see that by making the overall motorcycle configurations as similar as they did, BMW actually did the same thing as Hansel and Gretel's dad, leaving a trail of breadcrumbs to follow.
You also like to tinker... if you've got a mind to create something great of your own, I say go for it! :thumb
By the way, I saw an F800R for the first time while I was out on a run yesterday (sadly, heading in the opposite direction). A Chris Pfeiffer edition with a German licence plate.
Click to expand...

I'd be very interested in reading that, sounds fascinating. I'll wait for trailblazers like you to finish up before looking ;)

Yeah I don't mind the Pfeiffer one, but I wouldn't own one. Bit tarty for what it is. I'd like the pipe off one, though...
 
Rear engine mountings and rear shock absorber linkage tweaking to continue this week. Couldn't get to the build this weekend due to time commitments.

I found a composite that I threw together about 3 months back to determine if the idea would work aesthetically. These are '13 GT components on an '08 GS, but it's representative enough. Especially considering that the only tool I had available was MS Paint. ;)
 

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sethmopp said:
Looks like the one BMW should have made
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Well, if you want something done right... ;)

The 650 and 700 are more road-biased than the 800 (at least their front tyre dimensions are a bit closer to optimum).
But during the times I've ridden them, I always found them lacking on the road. Power output isn't what it should be and the standard wind protection is woeful. And coming from an 800, the 650's braking was perfectly OK if I was commuting or pottering. But high-speed group rides were a little bit dodgy.

An S1000XR or Multistrada this ain't. But for my purposes, it'll be pretty darn close. :)
 
Must admit to liking the idea of an F800GSA but with the wheels off a 700 (tubeless tyres), and the belt drive would be a bonus.
 
Prep for steel-cutting and welding.

Most of the templates for the new additional rear engine mountings are far along. All that's needed now is tweaking of the templates for a combination of maximum strength and lowest mass. (There is going to be quite a bit of additional high-tensile steel lumped onto the rear of the frame).
The job will be done in three stages:
  1. A round tube with the same inside diameter as the main rear frame crossmember will be cut in half lengthwise, and welded to the bottom side of the crossmember (so it can add strength without interfering with standard placement of the GS fuel tank).
  2. With engine and frame connected via the four upper engine-mounting screws, a main locating plate will be bolted to the GT engine's rear mountings/swingarm clamps. All triangulation members making up the connections from this plate to the crossmember will be welded in.
  3. Four additional triangulation braces will be welded in, connecting the main rear frame crossmember to the four main frame tubes extending upward and forward from the cast-steel side lugs.

After that, powder-coating in some exotic colour as yet undetermined. :p

One thing I forgot to do before pulling the bike apart was to determine its static ride height and static pitch attitude. I can't currently simulate these conditions using what I have available, so tomorrow I'm going to use a steel rule, set square and spirit level to take relevant measurements.
The reason I need these measurements is to determine a) whether the rear suspension will be based around the GS or GT coil-over shock absorber, and b) to determine the exact static length between the frame and swingarm shock-absorber mounting points. Once I have that all-important measurement, I can finalize the design of the rear shock-absorber linkage.

I'm also undecided as to the front forks. I've seen some pretty nifty correspondence on ADVrider about intrepid souls who transplant fully-adjustable Marzocchi Shiver internals to '08-'12 GS forks, and others who have made successful use of White Power 4860 forks.
Has anyone on UKGSer ever done something like that?
 
Nick V said:
Rear engine mountings and rear shock absorber linkage tweaking to continue this week. Couldn't get to the build this weekend due to time commitments.

I found a composite that I threw together about 3 months back to determine if the idea would work aesthetically. These are '13 GT components on an '08 GS, but it's representative enough. Especially considering that the only tool I had available was MS Paint. ;)
Click to expand...

That does look very nice :thumb2
 
Engine mountings, continued (Part 2).

The new rear engine mountings are now on their third major design evolution.

The first design was made up of a complicated series of steel pieces that would have demanded laser-cutting (and thus made them more expensive). There were also 16 pieces in total, and every one was different from every other one.
The second design retained some components of the first, including the main base plate (which bolts to the engine's rear mountings), and was made up mainly of square steel tubing. But it would have involved some complicated cutting which had to be extremely precise.
The third design is composed of a half-round section of tube, an extended version of the main base plate, and twelve additional steel pieces (four of which are extended triangular braces to transfer and dissipate stresses around the rest of the frame). Six of those pieces are simple sections of rectangular steel plate. With a bit of a stretch, everything can be cut and milled by hand. :D

I'm still working on ideas for the rear shock absorber linkage. I want to use the GS rear shock, I want the upper shock mount to the frame to remain 'As-is', and I want the bottom shock mounting point to interface with the swingarm's shock mounting point via a male-to-male linkage that will be adjustable for both length and leverage.
 
The design of the templates for the new rear engine mountings has been finalized, and the templates have been completed. Cutting of steel to begin soon (I hope!)

The rear shock absorber has been trickier than I anticipated. I've managed to simulate the static ride height of a factory F800GS by spacing the centre stand legs and engine sump upwards. What that's revealed is that if I try to incorporate my adjustable-leverage/adjustable ride-height add-on linkage, the F800GS rear shock absorber will simply end up too long, meaning that I'd have to cut about the rear swingarm anyway.

My current thinking is to graft the lower female linkage from the GT shock (red arrow, attached picture) to the GS shock, retaining the GS rebound-damping valving and rebound-damping step motor (the motor inside the shock, actuated by the ESA system).
The GS shock unit will otherwise remain exactly the same. This will allow a simple bolt-on solution.

Luckily, I know this is possible. An Italian suspension company manufactures an 8mm-longer replacement lower linkage for the R1200RT rear shock, which requires the same procedure to install it.
Unfortunately, I don't have the required tools to disassemble and re-assemble gas-pressurized shock absorbers - so both shocks are going to my local suspension guru for him to do the job.
 

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A quick update. (Yes, there has been progress - in fits and starts.) :D

The original forks, triple clamps and front axle have been straightened. What you see here is a test fitment to determine whether the front axle needs modification. It does, and so does the left-front wheel spacer.

From the same suspension specialist came the hybrid rear shock. It consists of the shock casing, splash guard, spring and preload adjuster from the F800GS shock, and the lower (female) mounting from the F800GT shock. This kills two birds with one stone - I can use unmodified upper (main frame) and lower (swingarm) mountings, and ESA functionality remains unaffected.

The next major tasks will be welding-in of the laser-cut engine mounting plates to the rear of the main frame, and machining of adaptors to fit the F800GT four-piston front calipers to the GS forks.
 

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zippygser said:
Hi there Nick, do you have any updates on your project, great job so far btw
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Hi Z! :)

Nothing major has happened since the last update - most of my spare time is currently being taken up by a project to convert a caravan into a mobile business for my girlfriend.
The project is still on my mind at all times, though. This will definitely not be one of those that's shunted to the back of the garage and left to gather dust!

In the meantime, though, the hand-drawn plans for the rear main-frame modifications have been given to an architect friend, who is using AutoCAD to convert them to *.DXF format. The DXF drawings will then go to a metals-cutting firm for the components to be laser-cut from 3mm and 6mm high-tensile steel.
From there, I can weld the frame!
 
Progress...?

Hi Nick,
Just wondering what, if any, progress might have been made on the project since the post in April.
Its been a few months now, or are you so busy riding it that you don't have time to write about it?
SuperTed
 
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