odd tank fitting issue.

[jjwithers]

Unfortunately, I can's suck it up on the level of my restoration. A scraped up frame would be unacceptable. Luckily I have a tank that fits. If not, I would have to consider some modifications.
But this is another great lesson to learn. Not all frames were made equal!

In fact, i have used the frame jig on many different frames and found that many are straight but have different head angles. Some are raked out, some are pulled in.
It makes me wonder if they are flaws or done on purpose.

These inconsistencies could be part of the reason why my 77 R100/7 (with S Fairing) handled amazingly and my 77 R100S is looser. I know that many other factors are at play but I'd imagine that a few degrees of steering rake makes a difference.

[Jean]

last sentence = YEP.

[Deleted User 62]

In fact, i have used the frame jig on many different frames and found that many are straight but have different head angles. Some are raked out, some are pulled in.
It makes me wonder if they are flaws or done on purpose.

Josh, another thing you should check are the flat plates that brace the headstock. These are the plates where the frame number is stamped. These should be flat along their length when checked with a straight edge. Any bowing indicates the bike has hit something in the past...

[jjwithers]

Josh, another thing you should check are the flat plates that brace the headstock. These are the plates where the frame number is stamped. These should be flat along their length when checked with a straight edge. Any bowing indicates the bike has hit something in the past...

That is the first thing I look for on any BMW I am considering.
Eventually they make it onto the jig to be safe :
http://beemersandbits.com/2013/10/broke ... frame-jig/

[Duane Ausherman]

jjwithers, I have never seen that frame jig. Where did you get it? It could be official BMW from after 1980 and I wouldn't know it.

[jjwithers]

From what I understand, it is a BMW tool.
I have no idea when it was produced or sold.
The person who owns it picked it up about 5-10 years ago on the used market. It is definitely specific to these airhead frames in the 70's and early 80's. I think he got it from a BMW shop that was closing down.
The owner of the jig works with a guy who used to do R&D for BMW in the 80's. Both of the guys know the ins and outs of these airheads pretty well.

Here is another post I made on it a few years ago.
http://beemersandbits.com/2011/11/bmw-m ... ment-tool/

jjwithers, I have never seen that frame jig. Where did you get it? It could be official BMW from after 1980 and I wouldn't know it.

[Duane Ausherman]

It measures the same things and in a similar way, but was made a bit differently. Both would do the job well.

Notice how different two frames could be and still satisfy that jig. I have many times seen 1/4" variation between frames at the curved down tubes around the engine.

[PITAPan]

Try lifting the rear of the tank. A couple washers on top of the rubber mounts may do, or a couple under the mounts and more on top if needed. Because the tank tapers, a small amount of lift can get you clearance. I don't know if the rubber rear mounts get squashed over time but it wouldn't hurt to check the height of a set of new ones.