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Beemer54
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VBMWMO #8832
Joined: 09/07/2014
Posts: 64

A while back I bought an R12 which had been badly abused and the frame was twisted in every direction. I took it to a U.K. shop that specializes in Frame starightening and was delighted by how true they got it. Using the straight edge along the wheels test everything looks perfect.

Except it isn't. The drive is now badly out of alignment. With the engine fitted correctly up against the right hand bottom frame rail, the kardan shaft can only fit by being angled badly over to the left. For it to remain straight as it leaves the rear wheel drive housing the rear wheel would have to be moved over to the left by about 3/4". So by making the drive perfect I would be throwing the wheels out of alignment. I've thought of doing this and having the rear wheel respoked so that it is offset to take up some or all of this but that's not the correct thing to do. Front and rear wheels were interchangeable and a wheel with such an offset would never fit between the front forks.

So... does anyone know whether the R12 frame was designed for the wheels to run out of alignment? Or am I missing something obvious here?

Thanks in advance for any advice

Bruce Frey
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VBMWMO #6316
Texas Hill Country, USA
Joined: 10/27/2006
Posts: 574
I may not understand your

I may not understand your problem correctly, but it sounds like it might be an engine spacer issue. There are spacers on both sides of the engine that are unequal. I'll take a look at mine later today.

Did your alignment shop have the rear drive when they did the work? I think it would be necessary to do it correctly.

Cheers,

Bruce

Bruce Frey
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VBMWMO #6316
Texas Hill Country, USA
Joined: 10/27/2006
Posts: 574
I did look at my bike and I

I did look at my bike and I now think I understand your issue.

Using a long metal straightedge, the right side of my frame has roughly 35mm of offset from where the engine mounts to where the rear drive mounts. That is about as close as I can measure without taking things apart.

I don't have a long enough straightedge to span from the front of the front tire to the rear of the rear tire to check the wheel alignment, but I will try it with some string after I move things around to get better access.

Cheers,

Bruce

Beemer54
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VBMWMO #8832
Joined: 09/07/2014
Posts: 64
That's very useful, Bruce.

That's very useful, Bruce. thanks. When the frame was starightened they had the frame, engine, gearbox rear drive and wheel. they assumed that the rear wheel should be in direct line with the front ( i.e. no offset). Neither they nor I noticed at the time that the rear drive didn't line up with the gearbox output flange.

35mm is a hell of a lot of offset and I'm grateful you measured that roughly for me. If you are able to get any more info then I'd appreciate it.

Cheers,

spider rust
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VBMWMO #8708
Joined: 04/07/2014
Posts: 92
R12 Frame

Your problem I am facing too. Its quite a complex set up, with wheels and engine off set in the frame.
I have compiled a file on this, with all the dimensions to set it to orig specs.
With my frame some idiot welded in all the rivets and brackets, the same idiot who bent it so it ran like a crab.
My help came from Dietmar Nix, and Wolfgang RRRC tuning.
In my case I had no option but to remove all the brackets.
Basically you need to bolt the frame down onto a work plate, fit a pointer through the steering head, fit the engine block connected to the gearbox connected to the drive shaft to diff. Then heat the frame and carefully bend it to the correct conformation, so the alignment runs through in line. You'll need clamps which can be adjusted through the process pressing/holding the frame
to achieve the above.
Its beyond me and you need to find a welder/engineer with great empathy and knowledge to work through the process.
And who knows all the required specs.
My frame has been sitting for about 2 yrs now waiting until I finish the gearbox.
Good luck you'll need it.

Bruce Frey
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VBMWMO #6316
Texas Hill Country, USA
Joined: 10/27/2006
Posts: 574
I pulled a string line from

I pulled a string line from the rear edge of rear tire to the front edge of the front tire. The string just touches the other tire edges, so the front and rear wheels are in a straight line. It has always tracked and driven well so I am pretty confident that is right.

The offset I measured was the difference from the outside of the right side frame rail at the engine to the outside of the frame at the rear drive, not between the front and rear tires. I am attaching an annotated page from Dietmar Nix's old website that illustrates where the 35mm offset occurs. Unfortunately, there is really not enough information there to be of much use other than some of the inside dimensions.

One of these days I need to pull the engine and trans out to address a clutch issue. When I do, I will try to get some more accurate measurements.......but please don't hold your breath. We recently moved into a new house and I have a bunch of projects ahead of that.

Cheers,

Bruce

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r12z_restoration_05_2.pdf312.52 KB
Beemer54
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VBMWMO #8832
Joined: 09/07/2014
Posts: 64
Thanks Bruce and Spiderust.

Thanks Bruce and Spiderust. Dietmar's diagram explained everything -mybike has no offset and someone has fitted a longer than standard spacer on the axle to make up the difference.
I've never heard of Dietmar Nix's website and the VBMWO link to it is now broken. Is there still a live version of it about anywhere?

Once again - thanks for your help. You've saved me hours of trial and error attempting to get it right.

spider rust
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VBMWMO #8708
Joined: 04/07/2014
Posts: 92
R12 frame

Its a tricky one to understand and without help from also Vech, I would still be lost. As you now know both the front wheel and engine
are off set, so is the rear wheel. 7mm offset of the hub to rim I believe is correct for both wheels. You understand the engine block spacers. The bend in this frame is a subtle one at the rear bringing in the cardan housing and its drive shaft to run true. Its that subtle bend of the rear frame that is necessary. Wolfgang provided me with some great photos of his work shop showing how its done.
There is no one here that I trust to take this on, with exception to a German engineer I know.
I'll scan an image and post it later showing how its done.

Regarding Dietmar, I have not been in touch for a while and his web site I have not been able to enjoy.
I don't know where he is and if still contactable?

His work on this bike is truly outstanding and its such a pity its not been published in a book!
A treasure in any enthusiasts library.

VintageSalesand...
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VBMWMO #7368
Corona, CA
Joined: 03/24/2008
Posts: 295
R12 frame

Hi,

Correct R12 frames look like a banana when they are good. Straight is bad.

They have a serious curve to them.

Jeff

lui
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uk
Joined: 03/13/2016
Posts: 20
r12 frame

Hello all r12 owner.

With r12 frame is always the same problem.)))
I made same drawing regard to fix the frame.
If anyone can not find a proper frame fixer for r12 frame i can get fixed by my brother or by end of summer i ll have same replika r12 frame for sale(around 1000pounds),ourreplika frames fit perfect and ready to use))
regards

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