1975 R90 gas-tank help!

Hey folks,

First of all, this is my first time posting on here - I just joined the BMW MOA and I'm very happy to be here! I bought my 1975 R90/6 back in November, and now that it's slowly starting to warm up in Canada I'm starting to get some work done to get her ready for spring.

The first thing I think I need to tackle is the gas-tank. The bike has been sitting for some while, and the previous owner didn't do too much to prevent interior tank damage and now the red lining seems to be lifting, or 'bubbling'.

Since the bike was kept on the side-stand, only 1 side of the tank seems to be affected, the rest of the tank is in really good shape actually.

What would be the first step? Should I think about an acetone soak and try to remove and reline the whole tank?

Thanks in advance, I'm having trouble uploading pictures at the moment but I'll do my best to get some posted tonight.

Welcome to the forum! You're in the "honeymoon phase" of your new ride! Enjoy!

Probably going to need to clean and reline the gas tank. Snowbum has a section on gas tank cleaning here and also discusses relining the tank:

https://bmwmotorcycletech.info/fuelmiscl.htm

He also has some additional mention of gas tank sealants at the bottom of this page:

https://bmwmotorcycletech.info/chemicalsetc.htm

The issue is going to be using something that will strip the interior lining but not hurt the existing paint on the tank. It's going to take some prep work and if the instructions are followed, should result in a good job.

As for pictures, ensure that the size of your images are around 1Mb...no need for larger and eventually if too big, they won't upload.

Sorry for the massive images hehe, I gotta figure that out still.


As for the links, thank you very much! Snowbums info will be very helpful!

Ooooooooh! does that look pretty!

Yes, that's a pretty bike and worth doing whatever you need to do to make it even better......Anyway, if you look you will find lots of stuff on here about the POR-15 treatment. There is a fairly lengthy procedure to do it right and again, do research in my name and others about this......Here is a video.....IT IS GOOD STUFF.....Good luck...……

https://www.youtube.com/watch?v=fZoz_PDxksc

Your R90/6 is very nice! Your paintwork is great, and if you’re not inclined to risk it with DIY tank-cleaning or coating procedures or materials, I’ve been very happy so far with GTL Advantage’s http://gastanklining.com/ work on my two airheads. It’s about $500 plus for them to do each tank, plus the cost of shipping to and from CA (another $100 each way for UPS or Fedex to move the fairly enormous box they use to pad up the tank, from MI to CA). Kind of a big gulp when compared with the cost of any of the DIY products, but, nonetheless, I couldn’t buy a new tank, or have the original pearl white paint and pinstriping replicated, for anywhere close to similar figures, so it seemed sensible to me. My tanks have come back with fresh red linings, and the original paint just as I sent them.

Don't touch that tank!

Unless your an expert I would stay away from acetone or any of that stuff that could mess up that really nice original paint. Normally I would strongly suggest Red Kote tank lining but the prep and final coating work is a huge risk and takes a ton of prep and very strong protection measures for the exterior finish. I did get stuck with a /2 sport tank, Holt BMW paint & pinstripe and a peeling falling apart bad Kreme job on the inside, never again I said. I went with the Por-15 treatment with that gas tank and managed to not screw up the brand new paint job.

The Por-15 stuff that I used recommended a real good flush (multiple flushes) to knock away as much flaking liner as possible followed by a good soaking of a diluted mix of white vinegar and water to etch the bare metal surface. After that you may end up wearing out a couple hair blow dryers making darn sure the interior is very dry before you do the liner step. I went way overboard with the masking and insulating the nice, new and very expensive Kent Holt paint and pinstripe work. It paid off and no damage to the exterior.

Red Kote tank liner is more of an epoxy type substance and uses M.E.K. to thin it as well as a final prep before adding the liner. Both the liner material and the M.E.K. will peel the paint right off your tank if you have seepage or don't mask it properly, so unless you have really good (magical) masking skills I wouldn't use that on that gas tank. Its way to nice!

Por-15 and its prep work is a good alternative but you still have to do a really good job of protecting the exterior paint and pinstripe. You also have to remember to never leave fuel with ethanol in that tank for any length of time because it will not hold up.

You can send it out and trust the shipper to deliver and the service provider to be careful.

If your going to ride the bike on a regular basis and not obsess about the interior of the gas tank you can always give it a real good flush and rinse, install a couple in line fuel strainers and use only non ethanol fuel. Even with that you have to keep the fuel fresh, use Stabil or S 1000 fuel aditive and keep the gas tank full to avoid moisture build up and rust.

Sent a gas tank to Bob's BMW for interior refinishing several years ago. You could explore to learn if they still offer this service.

Thanks for all the input, I really appreciate it. I did some searching in the forum and I found lots of mixed reviews about POR-15.. the Red Kote seems promising too, but I really would hate to mess up the finish.

Anyone know the official name for BMW brown btw? My grandad used to have an R100(?) in the same colour, with international orange rims. What a beauty that was!

I’m going to look around for professional help - I plan on using this bike as my daily commuter - year round, believe it or not. I’ll be in the one place in Canada where that’s possible.

I’m also planning on taking a trip across the country, and potentially to Europe so I want this baby to be in tip top shape. I’m currently in Calgary, if by chance anyone knows a local shop to have it done.

Thanks!

Your bike’s metallic brown was called “Havana Gold”, paint code 511, per Snowbum’s encyclopedic listings. The name is a tobacco (or maybe weed, too) reference from the ‘70s when Cuban cigars were a semi-exotic/illegal thing for U.S. smokers. Really.

thomhplatt said:

I’m currently in Calgary, if by chance anyone knows a local shop to have it done.

Thanks!

Click to expand...

Try Anderwerks Motorrad Specialist located right there in Calgary.

Just generally, if located in Calgary with a BMW you should get to know the folks at this shop.

The Alberta Air Marshal is in Lethbridge and he may have other options if Paul's suggestion does not pan out. His contact info is in the the Airhead magazine. If you do not have access to the mag, then PM me.

Members from another BMW forum I belong too have used common white vinegar to strip the interior of the tank.

In your pictures I really don't see any rust, just some crud. If it was me I wouldn't reline the tank. Some flaking of the old lining is going to happen normally.

I would clean the tank the best I can using a pressure washer on the inside, then have a good look to see that there are no rust spots or leaks in the tank seams. If that was still good then I'd air dry the tank, install new screens on the petcocks and if you are really worried, some small filters on the fuel lines to the carbs. Seeing as your bike is an older one that will require premium ( no ethanol in most cases ) I'd fill the tank and go ride. I would try this procedure first and see how it goes. In other restorations I've taken gas tanks to rad shops to have them clean the inside and the chemicals do a really good job, they can even line it for you, but the chemicals will destroy the paint. So in my view less is more in your case.

If you use anything abrasive, like nuts, screws or anything else to help clean the inside you will cause more problems. Same goes with harsh chemicals. For something to rust it needs oxygen, so don't keep the tank empty or leave ethanol gas in it during storage, as it attracts moisture.

48012 said:

Why do people insist on replacing the lining on these tanks?
All relining will do is screw up your perfectly good tank.
The steel tank on your automobile is unlined.

- Plug the petcock holes with a couple of rubber stoppers
- Fill tank half full with hot soapy water
- Use a liquid laundry detergent soap for best results
- Close fuel cap and slosh soapy water vigorously
- Drain, Rinse with clean water and Repeat
- Air dry fuel tank
- Re-install petcocks, remount the tank and away you go. ��

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I think most automotive fuel tanks have been plastic for awhile. Pinhole leaks from corrosion that makes a home in the tank lower seams is not an uncommon issue for BMW motorcycle tanks that have had water accumulate (from condensation and/or hygrophilic alcohol fuels) below the top of the reserve fuel straw. I think I see some indications of corrosion in the photographed tank seam that I would want to stop before it metastasizes, but others with greater experience and judgement could take a more relaxed approach to interventions. If your petcock filter screens and carbs are not getting blocked by bits of tank liner, dealing with the lining may optional.

PGlaves said:

Try Anderwerks Motorrad Specialist located right there in Calgary.

Just generally, if located in Calgary with a BMW you should get to know the folks at this shop.

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I actually do know Dave from Anderwerks quite well - my grandfather used to go to him, then my uncle, now me. 3rd Gen. Airhead. He will be a huge help for a lot of the maintenance.

48012 said:

cycleman2’s advice is on the money

- Plug the petcock holes with a couple of rubber stoppers
- Fill tank half full with hot soapy water
- Use a liquid laundry detergent soap for best results
- Close fuel cap and slosh soapy water vigorously
- Drain, Rinse with clean water and Repeat
- Air dry fuel tank
- Re-install petcocks, remount the tank and away you go.

Click to expand...

Thanks again for the input. I would rather do less now if I can get away with it, and prioritize this next winter if I think it needs it. I was under the impression this was quite a bit worse than some seem to think. I'll give the soapy water a try and hopefully get good results, if not then I'll reach out to some pros. For now, I'm keeping it full of premium petrol. Thanks again - I'll update on how to soap goes, and I'll be posting more as I slowly restore this bike for a long trip next year!