BMW K bikes (Bricks)

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1Back to top Go down    Fitting a flat seat frame on Mon Sep 11, 2017 1:18 pm

MMWW

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Gentleman, I'm calling in your wisdom once more.

A bit of background... I bought a K100 at the beginning of summer with the brilliant and very original idea of turning it into a flat tracker style bike. I'd been looking for about a year for a suitable project bike... something that needed some work doing to get it mechanically in shape before tackling the aesthetics. My budget has been very tight and I've been doing hours of reading on here to make sure I'm ordering the right parts etc.

So far I've changed the main rear seal, cleaned and lubed the splines, serviced the water/oil pump (going through 4 of those fiddly seals in the process!!), general oil change and have just ordered some new tyres (thanks for the help on the other thread chaps).

I ordered a flat seat and hoop frame and am looking to fit it onto the bike. It looks like a lot of people going for this look simply cut a few inches off the rear of the frame and weld on top the new hoop system to create a flatter sitting position for the 'streamline' seat.

Has anyone got any experience doing this while not compromising access to the battery, coolant reservoir etc? The seat frame I've received is a tad narrower than the current frame and so if welded straight on will make it impossible to remove the current battery.

Given budget I didn't especially want to order a smaller battery in case it has the same problem. If anyone has fitted a generic hoop frame to their bike I'd be interested in hearing your top tips.

To any purists out there this bike was in a pretty sad state when I got it and would've been broken for spares, so I'm trying to keep it alive!

Cheers
Mike

    

2Back to top Go down    Re: Fitting a flat seat frame on Mon Sep 11, 2017 2:12 pm

Two Wheels Better

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I'd highly recommend having a chat with a person who makes motorbikes frames and/or talking to a Very Good Welder who can interpret your needs. The K frame is of very stout construction and as such could be a good base for modification by someone who has the requisite skill. It's just that the current 'subframe' is quite an intergral part of the mainframe. As for access to batteries and coolant bottles, that's all gunna have to change as lopping off and re-welding of a rear 'loop' of unknown metallurgy and varying dimensions which differ from stock will be a project in itself.


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1987 K100RS, Big Block '93 K11/K12 hybrid, '09 K1300GT, '07 K1200R, '04 R1150RT, '95 R100 Mystic, '77 R75/7.
Have we accomplished half of what we dreamt we would? There may still be time.
    

3Back to top Go down    Re: Fitting a flat seat frame on Mon Sep 11, 2017 2:21 pm

MMWW

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Good tip. Luckily for me a welder has moved in next door to where the bike is being worked on, I just haven't been able to catch him yet. Will have a word with him but in the meantime any personal experiences on this sort of thing are appreciated!

Cheers

    

4Back to top Go down    Re: Fitting a flat seat frame on Mon Sep 11, 2017 7:13 pm

Dai

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From someone who used to build bikes... that loop at the rear of the frame helps transfer the suspension forces across the frame. I've never cut a K-frame at that point but I'm betting that if you cut the weld carefully you'll find 25mm-50mm of push-fit tube going into the main frame. Anything that replaces it has to be at least as strong and has to go in at least as far to take the suspension forces. In theory you could cross-brace where the rear-mudguard front mounting point is, but your welder needs to really know what he's doing if you go that route. The gearbox helps with force distribution but I wouldn't want to rely on it alone.


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'83 K100 upgraded to K100RS spec
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'78 Moto Guzzi 850-T3, '79 Moto Guzzi 850-T3 California,'93 Moto Guzzi 1100ie California,
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