Vintage BMW Motorcycle Owners

Most oven cleaners are also lye (Sodium Hydroxide) as are some types of engine cleaner. Lye emulsifies hydrocarbons turning them essentially into soap. That works very well for degreasing, or in this case de-sludging.

Not for nothing but before using such a strong chemical that frankly I have never heard of being used for the purpose, I would suggest looking into some kind of mineral cleaner, carb cleaner, or vehicle related cleaner. The reason I say this is perhaps you are correct and the stuff you are seeing is ONLY sludge and varnish. I shudder to think what a powerful caustic material might do to the liner of the tank. I mean the factory liner may be intact and could be damaged. Also, IF there is rust, what will the caustic stuff do to it? Could it possibly burn or hole the tank if the liner is not intact.

You can get a gallon of carburetor cleaner at most auto parts shops. LOL, to be honest, I won't promise it won't dissolve the liner either as I have never had the problem of sludge in my tanks. But, I would feel better using it than lye.

I will check with my friend at his shop and see if he suggests anything, he has seen the problem before and a lot. St.

Hi St. I haven't done anything yet. One reason is that I'm waiting for a new gas cap to arrive. Right now I have no way to close off the top when I am sloshing things around. I agree that the Draino method would remove the factory coating. That same thing will probably happen with sloshing nuts and bolts around. I don't think that's the biggest problem. I've heard of coating from Germany that comes out like the original reddish one. One factor for me is something that could clean without ruining the outer paint. Currently I just have about a half a gallon of lamp alcohol which seems to soften things. I may first try more alcohol and the nuts and bolts. To keep the gunk from getting into the vents of the new gas cap I thought I'd put a soft sheet of plastic over the cap threads when it's screwed in.
Dave

Search McMaster Carr for rubber plugs. Might be something there to act as a stopper. Maybe you can find something similar at a local hardware store. Especially something that has expansion capability...fits in the hole, then tighten the nut and it balloons the plug to a larger diameter...would help stay in the hole.

These come in many different sizes.

Perhaps if you let the tank sit with carb cleaner or some kind of varnish remover without using the nuts and bolts, you might be able to save the original liner IF it OK. The nuts and bolts from what I have heard is to break up rust or score the tank of rust.

Since I can't see into your tank from here, LOL, I am sort of assuming things may not be so bad. If you can see rust in the bottom of the tank, then by all means I would say go with the most aggressive way to remove it.

Sadly, sometimes a tank can look great on the outside and when cleaned of rust on the inside, it is pin holes. I got a parts bike like that, Nice vinyl tank cover, perfect paint on the outside. When I cleaned it up, it was Swiss cheese.

Patience, and remember, the gunk didn't form over night it might take a bit to get rid of it. I know, it is frustrating, good luck. St.

Thanks for the plug suggestions Kurt and Ray. McMaster-Carr is one of my favorite businesses. My new cap did arrive yesterday. I'm going to try to stretch a thin plastic over the threads and see if I can screw it in and seal the tank without gooping up the new cap. And St. thanks for the reminder to be patient.

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The R65 is a bit of an odd duck. The /7 tank won't fit the twin shock R65...the part number matches over to the '85 on bike though.

So how have things turned out? St.