BMW K bikes (Bricks)

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1Back to top Go down   Fuel Cap Leak Empty Fuel Cap Leak on Sat Apr 18, 2020 10:12 pm

zaubertuba

zaubertuba
Silver member
Silver member
Seems to be a recurring problem-A slow leak always down the left side of the tank.  Is this something just a rebuild with new gaskets could fix or is there something more ominous lurking in there?

Fuel Cap Leak Gascap11
Fuel Cap Leak Gascap10


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1985 K100RS
    

2Back to top Go down   Fuel Cap Leak Empty Re: Fuel Cap Leak on Sat Apr 18, 2020 10:16 pm

duck

duck
Life time member
Life time member
What do you mean by slow leak down the left side of the tank?

When gas comes out of the tank in the ground at a gas station it can be cooler than the ambient air temperature above ground which will cause the gas to expand. Not to mention that K bikes generate a lot of heat under the tank. If you leave it on the side stand right after a fillup and the tank is warm then . . .


__________________________________________________
Current stable:
86 Custom K100 (standard fairing, K75 Belly pan, Ceramic chromed engine covers, paralever)
K75 Frankenbrick (Paralever, K11 front end, hybrid ABS, K1100RS fairing, radial tires)
86 K75C Turbo w/ paralever
94 K1100RS
93 K1100LT (x2)
91 K1
93 K75S (K11 front end)
91 K75S (K1 front end)
14 Yamaha WR250R
98 Taxi Cab K1200RS
14 K1600GT
http://www.ClassicKBikes.com
    

3Back to top Go down   Fuel Cap Leak Empty Re: Fuel Cap Leak on Sun Apr 19, 2020 6:29 am

Dai

Dai
Life time member
Life time member
That's a Mk.1 fuel cap (pushbutton type) - there's a problem right there. A new gasket might fix it but you're better off going for the later type fuel cap.


__________________________________________________
'83 K100 upgraded to K100RS spec, '87 K100RT
Others...
'78 Moto Guzzi 850-T3, '79 Moto Guzzi 850-T3 California,'93 Moto Guzzi 1100ie California
    

4Back to top Go down   Fuel Cap Leak Empty Re: Fuel Cap Leak on Sun Apr 19, 2020 6:37 am

duck

duck
Life time member
Life time member
@Dai wrote:That's a Mk.1 fuel cap (pushbutton type) - there's a problem right there. A new gasket might fix it but you're better off going for the later type fuel cap.

It's not just the early gas cap that does this. I've had the same thing happen with 86+ gas caps on warm days.


__________________________________________________
Current stable:
86 Custom K100 (standard fairing, K75 Belly pan, Ceramic chromed engine covers, paralever)
K75 Frankenbrick (Paralever, K11 front end, hybrid ABS, K1100RS fairing, radial tires)
86 K75C Turbo w/ paralever
94 K1100RS
93 K1100LT (x2)
91 K1
93 K75S (K11 front end)
91 K75S (K1 front end)
14 Yamaha WR250R
98 Taxi Cab K1200RS
14 K1600GT
http://www.ClassicKBikes.com
    

5Back to top Go down   Fuel Cap Leak Empty Re: Fuel Cap Leak on Sun Apr 19, 2020 11:31 am

Point-Seven-five

Point-Seven-five
Life time member
Life time member
I had the fuel leak from the cap down the left side of the tank while on the side stand.  It was right after I filled the tank on a hot day.  Big stain on a white tank that had just been painted.  Bike was a 1992 K100RS with original fuel filler gaskets.

I never park on the side stand with a full tank anymore.


__________________________________________________
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
    

6Back to top Go down   Fuel Cap Leak Empty Re: Fuel Cap Leak on Sun Apr 19, 2020 11:50 am

duck

duck
Life time member
Life time member
@Point-Seven-five wrote:I never park on the side stand with a full tank anymore.

If I stop for food and gas while out riding I always eat first and then fill up with gas when leaving.


__________________________________________________
Current stable:
86 Custom K100 (standard fairing, K75 Belly pan, Ceramic chromed engine covers, paralever)
K75 Frankenbrick (Paralever, K11 front end, hybrid ABS, K1100RS fairing, radial tires)
86 K75C Turbo w/ paralever
94 K1100RS
93 K1100LT (x2)
91 K1
93 K75S (K11 front end)
91 K75S (K1 front end)
14 Yamaha WR250R
98 Taxi Cab K1200RS
14 K1600GT
http://www.ClassicKBikes.com
    

7Back to top Go down   Fuel Cap Leak Empty Re: Fuel Cap Leak on Sun Apr 19, 2020 12:32 pm

zaubertuba

zaubertuba
Silver member
Silver member
So the lesson here is, always use the center stand, period. Smile

I generally do most of the time due to the oil startup quirk, but I'm sure I've lapsed sometimes-probably right after a fillup, knowing me. Very Happy

Is there a benefit to the Mk.II cap in anyways? I'm assuming it's a bolt-on swap. It looks easier to repaint, in any case.


__________________________________________________
1985 K100RS
    

8Back to top Go down   Fuel Cap Leak Empty Re: Fuel Cap Leak on Sun Apr 19, 2020 2:24 pm

Point-Seven-five

Point-Seven-five
Life time member
Life time member
No problem with parking on the sidestand, just don't do it on a full tank. 

I'm guessing that either cap will work to keep the rain out and most of the fuel in.  Neither will hold a full tank on a hot day on the sidestand.


__________________________________________________
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
    

9Back to top Go down   Fuel Cap Leak Empty Re: Fuel Cap Leak on Sun Apr 19, 2020 2:55 pm

duck

duck
Life time member
Life time member
There's no problem with using the side stand. However, since you have an 85 with the early piston rings (built before 2/88) it may have smoky exhaust for a while after you start it when you use the side stand.  (Not a big deal.) This is because the cylinders are pointed downward when the bike leans left and the oil behind the pistons seeps past the rings into the combustion chambers. This can be mitigated if you turn the bike off and then tilt it to the right for a few seconds before putting it on the side stand. This lets the oil behind the pistons drain into the sump so there's less oil to seep past the rings. In 1988 they changed the piston rings so that much less oil seeps past them but even the later bikes will smoke on startup if you leave them on the side stand long enough.

The newer gas cap needs the key to be used each time you open it.  Yes, it's a direct fit on 85 and earlier gas tanks.


__________________________________________________
Current stable:
86 Custom K100 (standard fairing, K75 Belly pan, Ceramic chromed engine covers, paralever)
K75 Frankenbrick (Paralever, K11 front end, hybrid ABS, K1100RS fairing, radial tires)
86 K75C Turbo w/ paralever
94 K1100RS
93 K1100LT (x2)
91 K1
93 K75S (K11 front end)
91 K75S (K1 front end)
14 Yamaha WR250R
98 Taxi Cab K1200RS
14 K1600GT
http://www.ClassicKBikes.com
    

10Back to top Go down   Fuel Cap Leak Empty Re: Fuel Cap Leak on Sun Apr 19, 2020 4:31 pm

MartinW

MartinW
Life time member
Life time member
You shouldn't have a problem parking on the side stand with a full tank, if you have good cap seals and you have a hose attached to the under tank catch reservoir. The only problem will occur if someone throws a cigarette butt into the puddle of fuel that gathers under the drain hose.  Fuel Cap Leak 177381
Regards Martin.


__________________________________________________
K75s Hybrid
    

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