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Old 11-09-2010, 02:46 PM   #1
word1 OP
I'm working on it...
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Joined: Jul 2004
Location: Rome, GA
Oddometer: 510
Airhead (well, /7 at least) Gas Cap examination

If you haven't taken a look at your Gas Cap recently, maybe it's time.

The cap contains two easily replaceable parts which might need replacement.

The cap on my '78 RS was slightly sticky to remove the other day, and I took a closer look only to find that the bottom gasket had turned into some type of rapidly deteriorating, and brittle, waxy substance.

As you probably know, the plastic ring you see on the outside of the cap doesn't seal gas. The bottom (inner) gasket is the actual gasoline seal.

These part numbers and descriptions were shamelessly borrowed from MAX BMW Motorcycles' on-line parts fiche:

51 25 1 453 148
The old gas caps used to come with a red bottom gasket, which sealed gasoline. It was never available as a replacement part until about 1985 when BMW made a black sealing ring available. This is the gasket for the actual cap. It replaces the old red gasket that breaks down. This ring goes right over the threads to where the red ring was on the bottom of the cap.

16 11 2 307 360 'Ring'
This is the gasket that goes in between your fuel tank and the gas cap assembly. It does not seal gasoline; it prevents rain/snow/ dirt from getting to the overflow trough built into the tank.

BTW, I would suggest evaluating the bottom gasket in a non-destructive (read: very careful) fashion. If it's red (ish) in color, you want the replacement parts 'in hand' before subjecting it to any probing.

I also suggest replacing the outer ring, even if it looks OK. The new ring has a pronounced downward shape (long gone on my old one) and helps the cap fit properly on the tank.

Both parts are under $15 US, and replacement took just a few minutes.

Ride it.
If it breaks, Repair it.
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Old 11-09-2010, 03:53 PM   #2
Beastly Adventurer
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Joined: Jul 2010
Location: Central Florida
Oddometer: 2,529
Thanks! my /6 has a /7 tank and cap. Didnt know there was a seal on there. Mine is completely missing!
1974 BMW R90/6 Bettie #1, 04 Triumph Bonneville
Originally Posted by Martin Blank
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Old 11-17-2010, 09:12 AM   #3
mach schnell
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Joined: Apr 2008
Location: Fl & Vt
Oddometer: 1,844
Timely info for me, thanks.

I seem to have a different issue though. The threaded part is disintegrating and I can't quite bring myself to spend about $150.00 for a new complete gas cap from my dealer. Any suggestions?

You can always count on the Americans to do the right thing, after they have tried everything else.
-Winston Churchill
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Old 11-17-2010, 07:02 PM   #4
Stay Horizontal
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Joined: Jul 2009
Location: Melbourne, Oz
Oddometer: 2,665
Yeowch ..

they come up on ebay..keep a watch.

boxerboy81 screwed with this post 11-17-2010 at 07:07 PM
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Old 11-17-2010, 07:30 PM   #5
Formerly SaddleSoar
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Joined: Feb 2008
Location: east of Dallas
Oddometer: 1,010
OK, so this is kinda weird. I was just thinking about these caps tonight. I need like 4 of them...

Think about it, almost all tanks that come up for sale on ebay or ibmwr have no caps. Someone or everyone is hoarding caps. There has to be a modern fit for these. I know it has to be vented and fit a weird area with a flared top. Someone somewhere has to have figured this mystery out. Someone needs to come clean and help the rest of us poor slobs out here.

I mean if I can go to a local auto retailer and get a stinking air filter that fits my /2, surely there is options. Its a source of frustration if you cant tell...

What would it take to machine them like these are. They are only $15.00-$25.00. Would it be that hard to make them so they vent properly?
Giving the horses and the wife a break from riding...

CurlyMike screwed with this post 12-13-2010 at 06:18 AM
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