BMW K bikes (Bricks)

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Motorbike Mike

Motorbike Mike
Life time member
Life time member
OK guys, I'm after some help for quite a rare bike I think.
It's a 1984 K100 Basic that I rescued from a chap that owned the K for some years but didn't know what he had or how best to look after it. It never even made it back to the dealer to have the rear disc replaced under warranty for the later solid version! The bike was a non runner (last on the road in '92) when I bought it but was soon running again with fresh fuel and a good battery. I built it back up and rode it for a while last year-it's a real flier! I believe that the mileage is genuine when you look at the factory paint on the bolt heads and the underside of the motor.
It's a bike to be kept original, NOT to be chopped up into a Cafe Racer so here's where my issues begin. As 99% of us know the K's have an Achilles heel, the petrol tank. It's corroded through under the fuel pump which isn't a problem for me as I can weld aluminium but, if I repair the tank I'll have to paint it and if I do that I'll have to paint the rest of the bodywork to make it all match and as I said, I don't want to restore the bike.
I need an early K tank in Polaris silver (576) with the fuel level sensor at the front left, in nice condition, a pair of side panel too if possible. Does anyone have a tank that they'd part with? I'll pay the asking price and shipping costs.

Thanks in advance.
Help save this endangered species-'84 petrol tank wanted. Cimg2713

Help save this endangered species-'84 petrol tank wanted. Cimg2712


Help save this endangered species-'84 petrol tank wanted. Cimg2710


Help save this endangered species-'84 petrol tank wanted. Cimg2711


Help save this endangered species-'84 petrol tank wanted. Cimg2810

    

Point-Seven-five

Point-Seven-five
Life time member
Life time member
I would make the repair, get some Polaris silver and ride it that way while I look for an original tank.

I say this because I suspect a good tank in that color is like rocking horse poo, and I think you will find that a proper repair will match the rest of the bike quite nicely.  At least you will have a decent looking rideable machine while you pursue your quest for the grail.


__________________________________________________
Present:
1994 K75RT
1991 K100RS
1988 K100RS SE

Past:
1994 BMW K75S
1992 BMW K100RS
1982 Honda FT500
1979 Honda XR185
1977 Honda XL125
1974 Honda XL125
1972 OSSA Pioneer 250
1968 Kawasaki 175
    

Laitch

Laitch
Life time member
Life time member
@Motorbike Mike wrote:I can weld aluminium but, if I repair the tank I'll have to paint it and if I do that I'll have to paint the rest of the bodywork to make it all match and as I said, I don't want to restore the bike.
If you can weld aluminum effectively you're way ahead of a lot of us. I would think using Cold Front putty should confine the heat enough to leave the exterior tank paint intact, unless you're welding along the bottom seam.

If you don't want to restore the bike, paint the tank a color that will blend with the dark seat and headlight cowl. You'll be the envy of the neighborhood.Wink  Nobody will accuse you of trying to restore the bike.Smile

I hope a Polaris silver tank in good condition shows up for you while you're still in a good condition to ride the bike.
cheers


__________________________________________________
1995 K75 73,000 miles
Help save this endangered species-'84 petrol tank wanted. Usa-lo10
    

Point-Seven-five

Point-Seven-five
Life time member
Life time member
Waiting for that Polaris Silver tank certainly is one very effective way to keep the mileage low for future generations.  Maybe even forever...


__________________________________________________
Present:
1994 K75RT
1991 K100RS
1988 K100RS SE

Past:
1994 BMW K75S
1992 BMW K100RS
1982 Honda FT500
1979 Honda XR185
1977 Honda XL125
1974 Honda XL125
1972 OSSA Pioneer 250
1968 Kawasaki 175
    

Stan

Stan
Life time member
Life time member
Even though you can weld aluminium, it may be worth the time to consult professional alum welders who may have ideas on how to save paint work. I had welding done on my tank and thought I was up for another paint job, but the welder showed me how they wrap the tank in cold wet cloths and keep the temperature of the weld at a very specific setting. The repair was under the tank and the upper part of the tank was safe.


__________________________________________________
1983 K100 basic vin 0003960 colour red  GONE
1987 K100RT vin 0094685 colour, orange peel, sorry, pearl..GONE
F800R black
    

Motorbike Mike

Motorbike Mike
Life time member
Life time member
ainsjac wrote:Even though you can weld aluminium, it may be worth the time to consult professional alum welders who may have ideas on how to save paint work. I had welding done on my tank and thought I was up for another paint job, but the welder showed me how they wrap the tank in cold wet cloths and keep the temperature of the weld at a very specific setting. The repair was under the tank and the upper part of the tank was safe.
The point of internal corrosion isn't the tanks only issue. It has two more external corrosion spots at the front on each side where it looks like it's been put down hard on the floor, breaking the paint. The stock tank can't be saved without getting repaired and painted.

    

Motorbike Mike

Motorbike Mike
Life time member
Life time member
@Point-Seven-five wrote:Waiting for that Polaris Silver tank certainly is one very effective way to keep the mileage low for future generations.  Maybe even forever...
A guy's gotta have a dream, right?

    

Motorbike Mike

Motorbike Mike
Life time member
Life time member
ainsjac wrote:Even though you can weld aluminium, it may be worth the time to consult professional alum welders who may have ideas on how to save paint work. I had welding done on my tank and thought I was up for another paint job, but the welder showed me how they wrap the tank in cold wet cloths and keep the temperature of the weld at a very specific setting. The repair was under the tank and the upper part of the tank was safe.
Ally welding isn't that difficult, my view is if you can gas weld, you're nearly there. the difficulty I had an issue with was that I viewed aluminium as a soft metal and would therefore not need much heat-WRONG! 
Aluminium dissipates heat very well (hence it's use in engines blocks etc) and this is a major consideration when attempting a welding job. It took me quite a while to understand how many amps I would need to make a good weld. There are other welding set variations to be considered but I won't go in to that here.

I can't save the tank with welding-see reasons above.  Very Happy

    

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