I like your thinking..... para arm is not dangling down to get hit either.....
R80 special build
- Thread starter AnotherGSGSGS
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I like your thinking..... para arm is not dangling down to get hit either.....
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I had a good look today,no mono arm,I must have used it for some thing.
No yokes either,but I do have the forks.
I do have the swingarm/ bevel from an 1100s
Where is I with this....
No movement on the K arm and FD though, I do have them for now.....WIP.
Front end is all sorted bar making a spacer on the lathe. No it's not DRZ forks but something better I hope....
Swing arm is going to be twin shock based likely with mono shock on the drive side.
Mono frame.
32 bings.
I think it's going to be 2 into 1 via a y pipe.
Rear sub frame will be a custom jobbie to keep it light and minimal.
I'd post a picture but my workspace is no where near tidy enough for pubic scrutiny so you will have to wait a while.
It's an august 84' engine out of an RT with circa 5500 miles on it. Yes, you read that right.
Not much has happened since last year largely down to just life stuff and clearing other projects. Still got some clutter to clear then I can start making progress on frame reinforcement. I have however, accumulated a lot of parts.
Tank.... I think I want to go plastic. Ever one for a bit of controversy....a 100pd tank is what I have in mind. A 43 litre jobbie is a bit excessive but the 100pd gives me a lower C.O.M. but I've never seen one fitted to anything else. Not sure whether thats down to availablity or they look terrible if they are not with the associated fairing.
No movement on the K arm and FD though, I do have them for now.....WIP.
Front end is all sorted bar making a spacer on the lathe. No it's not DRZ forks but something better I hope....
Swing arm is going to be twin shock based likely with mono shock on the drive side.
Mono frame.
32 bings.
I think it's going to be 2 into 1 via a y pipe.
Rear sub frame will be a custom jobbie to keep it light and minimal.
I'd post a picture but my workspace is no where near tidy enough for pubic scrutiny so you will have to wait a while.
It's an august 84' engine out of an RT with circa 5500 miles on it. Yes, you read that right.
Not much has happened since last year largely down to just life stuff and clearing other projects. Still got some clutter to clear then I can start making progress on frame reinforcement. I have however, accumulated a lot of parts.
Tank.... I think I want to go plastic. Ever one for a bit of controversy....a 100pd tank is what I have in mind. A 43 litre jobbie is a bit excessive but the 100pd gives me a lower C.O.M. but I've never seen one fitted to anything else. Not sure whether thats down to availablity or they look terrible if they are not with the associated fairing.
I’ve seen 80PD/100PD tanks fitted without a fairing and they do look OK, fine in fact. The 43 ltr Acerbis/HPN/SWT tanks have their uses but the PD tank looks better in my opinion.
Some sneak peeks.
Over the last fews days I've been scavenging parts from the donor bike.
Forks clear the tank nicely on full lock.
Steering stops work perfectly.
Yoke mounted ignition key.
100PD tank procured.
Over the last fews days I've been scavenging parts from the donor bike.
Forks clear the tank nicely on full lock.
Steering stops work perfectly.
Yoke mounted ignition key.
100PD tank procured.
Attachments
With those parts it look almost complete. 
That "Crappe" racer thing I showed you was pretty much complete. There isn't much left of it now.
The remains will be going on ebay soon. I bought it purely as a doner. It needed a lot of work still as everything was only loose fitted and it was still missing quite a few small bits.
The remains will be going on ebay soon. I bought it purely as a doner. It needed a lot of work still as everything was only loose fitted and it was still missing quite a few small bits.
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This is the donor bike
I was going to sell most of this as a rolling chassis but recent developments have changed that.
I want to keep the matching engine and frame numbers. It's a shame to trash the powder coating but I'd rather sell the mono frame with the other engine, gearbox and unused parts as a job lot of bits.
At the moment the mono frame is being used as the mock up mule so I can strip the twin shock and begin reinforcement.
The engine was removed and 1st job underway.
Replace the sump for a GS item. That Siebenrock extension makes getting the engine in and out a pain.
The PO decided to use the horrid paper gaskets. At some point i'll remove the one between the extension and block but thats pain for another day.
Sump replaced, I can now fit the sump guard.
This gives me a nice flat platform for the bike lift.
Started to mock up a few parts to see where the tricky bits are.
The front end is off a Husky TE630 using the OEM Marzi Shiver forks (economy class version) c/w brake and master cylinder.
The forks are 910mm centre axel to top of yoke. I think BMW made husky shim them down out of the factory. The OEM yokes work nicely apart from just needing a 20mm spacer.
The bar clamps are 28mm so shimmed to a 22mm bar for now though I'll replace with the correct size clamp down the line.
Much of the back end will be cut and carved but wanted to get a subframe and seat in place to check ergonomics.
I think I might try and adapt the seat as it feels pretty comfortable. The side hinge is useful as is the handle and seat lock!
That's it for now till more parts arrive.
I was going to sell most of this as a rolling chassis but recent developments have changed that.
I want to keep the matching engine and frame numbers. It's a shame to trash the powder coating but I'd rather sell the mono frame with the other engine, gearbox and unused parts as a job lot of bits.
At the moment the mono frame is being used as the mock up mule so I can strip the twin shock and begin reinforcement.
The engine was removed and 1st job underway.
Replace the sump for a GS item. That Siebenrock extension makes getting the engine in and out a pain.
The PO decided to use the horrid paper gaskets. At some point i'll remove the one between the extension and block but thats pain for another day.
Sump replaced, I can now fit the sump guard.
This gives me a nice flat platform for the bike lift.
Started to mock up a few parts to see where the tricky bits are.
The front end is off a Husky TE630 using the OEM Marzi Shiver forks (economy class version) c/w brake and master cylinder.
The forks are 910mm centre axel to top of yoke. I think BMW made husky shim them down out of the factory. The OEM yokes work nicely apart from just needing a 20mm spacer.
The bar clamps are 28mm so shimmed to a 22mm bar for now though I'll replace with the correct size clamp down the line.
Much of the back end will be cut and carved but wanted to get a subframe and seat in place to check ergonomics.
I think I might try and adapt the seat as it feels pretty comfortable. The side hinge is useful as is the handle and seat lock!
That's it for now till more parts arrive.
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Had another quick play after tea.
Currently at 53mm of squish on the front forks and 240mm of ground clearance.
I cant even get toes on the floor.
Seat needs to come down. I'm comfortable standing on one leg but both feet dangling is a bit excessive.
At full droop on the front forks I'm at 27.5degrees or there abouts.
Currently at 53mm of squish on the front forks and 240mm of ground clearance.
I cant even get toes on the floor.
Seat needs to come down. I'm comfortable standing on one leg but both feet dangling is a bit excessive.
At full droop on the front forks I'm at 27.5degrees or there abouts.
Attachments
Did you use the Husky fork yokes?
Cool. They’re about the only other non BMW ones that work. I rode a bike that had KTM yokes and shocks and can confirm what Mikeyboy always says about that setup - v nasty.
I would like to say it was entirely a well reasoned choice. But said bike had "engine drama" and so it was a "I wonder if" moment.
Over the last few weeks some key parts have been arriving.
Looks like the twinshock route went out the window.
Hang on a minute I hear you cry....
You're fitting an oilhead driveshaft into a mono/twinshock frame....
Yes I am and creating a 50mm(ish) offset problem to deal with for my trouble.
There is method and a good reason to my madness. All hopefully will become clear.
I have some "jigging" to do now as after a bit of butchery and hackery on a crusty twinshock swingarm I can't get enough side clearance on the OH driveshaft. I'd need to shift the engine off centre by about 1 full engine spacer to make it not clash. A few mm is one thing 1/2" is quite another.
On a more positive note.
Managed to find a 100PD tank. Not minty but these are not exactly common.
Finally...
The rear wheel route
I can measure up the spokes now. So I can build the wheel. I've built 3 custom x-lace wheels now so this will be no bother.
I toyed with lacing a g/s rim onto an oilhead hub but the angles were wildly wrong that not even some adaptors could correct.
So that idea was quickly binned.
Looks like the twinshock route went out the window.
Hang on a minute I hear you cry....
You're fitting an oilhead driveshaft into a mono/twinshock frame....
Yes I am and creating a 50mm(ish) offset problem to deal with for my trouble.
There is method and a good reason to my madness. All hopefully will become clear.
I have some "jigging" to do now as after a bit of butchery and hackery on a crusty twinshock swingarm I can't get enough side clearance on the OH driveshaft. I'd need to shift the engine off centre by about 1 full engine spacer to make it not clash. A few mm is one thing 1/2" is quite another.
On a more positive note.
Managed to find a 100PD tank. Not minty but these are not exactly common.
Finally...
The rear wheel route
I can measure up the spokes now. So I can build the wheel. I've built 3 custom x-lace wheels now so this will be no bother.
I toyed with lacing a g/s rim onto an oilhead hub but the angles were wildly wrong that not even some adaptors could correct.
So that idea was quickly binned.
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Not much progress at the moment due to life stuff, house renovation and making time to ride.
After finding there was not enough clearance it was time to remove the temporary bracing and set about the swingarm with a slitting disc and split it into two.
Lopping off the RH bearing carrier and removing most of the shaft tunnel it was time for a bit of lathe work to clean it up well enough to use.
At this point I'd already made a 40mm SHS frame as a base for the jig.
The next challenge it building the supporting structure for the K75 FD so it holds it in the correct downward angle.
My plan is to use the double u-joint to gain some downward tilt on the FD but have it fixed so it will act as a monoshock.
This has the benefit of not being reliant solely on swingarm length and gearbox UJ angle to balance the rear.
This of course requires a custom mono swingarm.
In the fab shop next door the jig is taking shape.
That's it for now. Hopefully will get a little more time on Sunday.
After finding there was not enough clearance it was time to remove the temporary bracing and set about the swingarm with a slitting disc and split it into two.
Lopping off the RH bearing carrier and removing most of the shaft tunnel it was time for a bit of lathe work to clean it up well enough to use.
At this point I'd already made a 40mm SHS frame as a base for the jig.
The next challenge it building the supporting structure for the K75 FD so it holds it in the correct downward angle.
My plan is to use the double u-joint to gain some downward tilt on the FD but have it fixed so it will act as a monoshock.
This has the benefit of not being reliant solely on swingarm length and gearbox UJ angle to balance the rear.
This of course requires a custom mono swingarm.
In the fab shop next door the jig is taking shape.
That's it for now. Hopefully will get a little more time on Sunday.
What the feck is that cutting tool you're using in the lathe, it looks like a blunt chisel
If memory serves it was a thread cutting tool. A novice goon like me has no place attempting things like that so I ground the teeth of. I think the previous owner had been at it with a grinder as well.
After some time away from home I booked a day off work and headed to the workshop.
The challenge is the compound angle. In plan the driveshaft angle needs to set over to centre the wheel. Then in elevation I want to use the UJ nearest the final drive to pitch the drive downward to help match the front without severe angle for the gearbox UJ.
Because I'm changing virtually everything the only reference point is the width of the swingarm which is set by the jig.
This is going to take a bit of trial and error.
From some 90mm SHS I can make a mating flange to suit the 37/11 K75 FD. Its a trapezium just to make life easier and the bolting centres are not on a PCD. Thanks for that BMW.
Using some paper I make a template that I can transfer to the SHS. 2x 10mm, 2x 12mm holes and one 70mm hole later (via trip to screwfix for a 70mm hole saw) I have a mating connection to the FD. It needs some fettling to fit but its close enough for now. A healthy dose of beautification is also required but I just need something that works dimensionally at the moment
Splitting the top face then grooving the bottom face I can bend the flange faces to 13 degrees outward (circa 50% of the max UJ range) then infill the gap with flat bar and weld up the grove. That takes care of one angle (the downward pitch). This puts the angle change pretty much on the centre of the FD UJ.
I can now start to mock up the shaft tunnel using the eyechrometer. The shaft tube is 76x3mm ERW tube. I don't like using ERW but there wasn't any CDS seamless in the size I wanted. Now to cut a hole in the side of the tube to accomodate the swingarm bearing carrier I trimmed up in the lathe.
Another trip to screwfix with the dog and I have a 44mm hole saw leaving in me a few mm of fettling with the file for a snug fit for the 46mm OD bearing carrier.
This is where the fun begins; the offset angle. I marked the long swing arm piece with the measurement for the face of the wheel and the centre of the frame. With a spare 1150gs hub bolted to the K75 FD I can hold the hub vertical, perpendicular to the swing arm bolt centre lines and correctly offset.
Glad I took the time to build that jig frame.
All tacked together will a couple of little braces I can try it on the bike.
I am feeling happy its coming together.
I plan on being able to run 150/17R and 110/19F 1150 wheels as well as 21/18 tubeless rims. So I use the 150/17 for test purposes.
A quick lash up of sub frame and seat I can cycle the swing arm through what will be full droop and near full compression (I'm aiming for +/- 15 degrees)
I can test the shock position too, it's a bit tight to the swing arm and the shock. I do want to use this type of shock configuration as it reduces the amount of various forces the swing arm has to deal with.
This has allowed a very important measurement to be taken..... free float on the FD UJ
I have 12mm of free movement at horizontal. So this allows me to trim the driveshaft tunnel down to length. I need to do some research on how much free float to leave.
12.76 degrees of upward swing before I hit the subframe.
Now then......weight!
As much as I would love to build this swing arm out of Ali that is well beyond my metal gluing skills so having chosen steel you are no doubt thinking it'll be a boat anchor hanging off the back with horrendous unsprung mass.
Well an LWB twinshock swingarm with driveshaft, final drive and brake shoes (no fluid) weighs approx 12kg
My swing arm in its current form, with K75 FD, oil head drive shaft, no fluid and no brake caliper....11kg.
There is obviously a lot of metal and weld still to go on but that big hunk of 90x5 SHS also needs a lot of trimming down. I was fearing I'd be closer to 15kg at this point. This may actually work.
The challenge is the compound angle. In plan the driveshaft angle needs to set over to centre the wheel. Then in elevation I want to use the UJ nearest the final drive to pitch the drive downward to help match the front without severe angle for the gearbox UJ.
Because I'm changing virtually everything the only reference point is the width of the swingarm which is set by the jig.
This is going to take a bit of trial and error.
From some 90mm SHS I can make a mating flange to suit the 37/11 K75 FD. Its a trapezium just to make life easier and the bolting centres are not on a PCD. Thanks for that BMW.
Using some paper I make a template that I can transfer to the SHS. 2x 10mm, 2x 12mm holes and one 70mm hole later (via trip to screwfix for a 70mm hole saw) I have a mating connection to the FD. It needs some fettling to fit but its close enough for now. A healthy dose of beautification is also required but I just need something that works dimensionally at the moment
Splitting the top face then grooving the bottom face I can bend the flange faces to 13 degrees outward (circa 50% of the max UJ range) then infill the gap with flat bar and weld up the grove. That takes care of one angle (the downward pitch). This puts the angle change pretty much on the centre of the FD UJ.
I can now start to mock up the shaft tunnel using the eyechrometer. The shaft tube is 76x3mm ERW tube. I don't like using ERW but there wasn't any CDS seamless in the size I wanted. Now to cut a hole in the side of the tube to accomodate the swingarm bearing carrier I trimmed up in the lathe.
Another trip to screwfix with the dog and I have a 44mm hole saw leaving in me a few mm of fettling with the file for a snug fit for the 46mm OD bearing carrier.
This is where the fun begins; the offset angle. I marked the long swing arm piece with the measurement for the face of the wheel and the centre of the frame. With a spare 1150gs hub bolted to the K75 FD I can hold the hub vertical, perpendicular to the swing arm bolt centre lines and correctly offset.
Glad I took the time to build that jig frame.
All tacked together will a couple of little braces I can try it on the bike.
I am feeling happy its coming together.
I plan on being able to run 150/17R and 110/19F 1150 wheels as well as 21/18 tubeless rims. So I use the 150/17 for test purposes.
A quick lash up of sub frame and seat I can cycle the swing arm through what will be full droop and near full compression (I'm aiming for +/- 15 degrees)
I can test the shock position too, it's a bit tight to the swing arm and the shock. I do want to use this type of shock configuration as it reduces the amount of various forces the swing arm has to deal with.
This has allowed a very important measurement to be taken..... free float on the FD UJ
I have 12mm of free movement at horizontal. So this allows me to trim the driveshaft tunnel down to length. I need to do some research on how much free float to leave.
12.76 degrees of upward swing before I hit the subframe.
Now then......weight!
As much as I would love to build this swing arm out of Ali that is well beyond my metal gluing skills so having chosen steel you are no doubt thinking it'll be a boat anchor hanging off the back with horrendous unsprung mass.
Well an LWB twinshock swingarm with driveshaft, final drive and brake shoes (no fluid) weighs approx 12kg
My swing arm in its current form, with K75 FD, oil head drive shaft, no fluid and no brake caliper....11kg.
There is obviously a lot of metal and weld still to go on but that big hunk of 90x5 SHS also needs a lot of trimming down. I was fearing I'd be closer to 15kg at this point. This may actually work.
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Wow, rather you than me. I get frightened just standing near a lathe.
Looking forward to seeing further progress.
Looking forward to seeing further progress.
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