Modifying frames?

[Voltaire]

I have a spare BMW frame and thinking about building up a replica of Helmut Dahnes Imola 750
The frame in the pic is a modified BMW frame and it uses the stock steering head and lower frame as far as the swing arm pivot. The rest of it looks pretty easy, just the bend at the steering head would be hard ( for me).



What sort of tubing would I need?
I have a spare 900 motor, gearbox,FD, wheels ( but with discs)
for the tank I'd just put a small tank with a dummy cover.
Fairing, probably modify an existing one.
Pic of current frame

[FJRider]

For use on the road .. ??

[Voltaire]

For use on the road .. ??

no, track.

[FJRider]

An interesting project for sure.

Any engineering workshop could do that bend in minutes ... for bugger all $$ ..

[neil_cb125t]

Frames are a fun one, the company's that make them (both race developers and bike manufacturers) spend decades designing and developing them, flex, geometry strength, and performance aka weight are all things that are taken into consideration.

If you had access to the figures of your desired frame, rake, trail, swing aim height, lengths then you have a good starting point.

We considered building a new frame for my F3 race bike (ZXR400 with a ER650 twin jammed in) building a frame not hard, but making it actually perform like a frame needs to, was impossible for us at this time.

There is bound to be someone somewhere who has created a machine like what you are looking at building - become their friend and good luck. Its a great looking build!

Lastly these are the guys down here that do what your talking about - and have made small and big machines with custom frames. They built the IMD250 frame and other top performing race frames... maybe they could help?

http://www.gprnz.com/

[nodrog:Me]

.....thinking about building up a replica of Helmut Dahnes Imola 750........


I have a spare 900 motor.......

cheating already

[husaberg]

That frome looks like it had a bit of Colin Seeley in the mix.
It looks sidecar inspired.
For the Frame CDS.
looking at the race frame find yourself a period guzzi and cut out the top loop and steering head and graft it in to the BMW swingarm loop and lower rails.


I would also say that the Racing BMW likely has a spacer to move the engine forward.
I would try and use the Motoguzzi shaft set up geometry made most famous by the Dentist.

[Voltaire]

That frome looks like it had a bit of Colin Seeley in the mix.
It looks sidecar inspired.
For the Frame CDS.
looking at the race frame find yourself a period guzzi and cut out the top loop and sterring head and graft it in to the BMW swingarm loop.
I would also say that the Racing BMW likely has a spacer to move the engine forward.
I would try and use the Motoguzzi shaft set up geometry made most famous by the Dentist.

Yes it does look like another shed project....

That's a non starter due to lack of gearbox, FD and so on...

[Grumph]

No idea what that last pic is as it won't open for me.
Those frames are as flexy as fuck. I put a Kohler V twin in one for Eurodave down here. Build thread somewhere on Dotheton forum if anyone's interested.
That frame is basic as - which is Helmut Dahne to a Tee - he's the original KISS type.

The one I'd look for info on is the BMW USA bike which had a frame built by Rob North in California. Very like the triples frame, not hard to do.

FWIW, the top tubes on that one of Helmut's look like 1 1/8in OD - and i can hand bend that in 2mm wall on my bender. Mild steel is all you'd need.

[Motu]

If you had access to the figures of your desired frame, rake, trail, swing aim height, lengths then you have a good starting point.

Did you bother to read the original post?

Looks like a simple way to solve most of the Airhead flex problems - a couple of nice straight top rails like a featherbed copy should have, triangles and stuff. You'd need to have extra length on the bends and cut to length, otherwise as you say, looks simple to replicate. You could tweak the head angle while you're there, stretch it out for some longer forks and higher bars for a more relaxed stable riding position - cruise past those CB350's in style. I don't know what sort of tube is best.....me, I'd just use black tube and paint the whole thing in Sampson High Gloss.

[Kickaha]

The one I'd look for info on is the BMW USA bike which had a frame built by Rob North in California. Very like the triples frame, not hard to do.

There were three of those built, (I think) there was one for sale on ebay about 2-3 years ago which was the Luftmeister turbo bike

Knock one up for me will ya

https://munsty.smugmug.com/Motorcycles/Rob-North-BMW/

[husaberg]

There were three of those built, (I think) there was one for sale on ebay about 2-3 years ago which was the Luftmeister turbo bike

Knock one up for me will ya

https://munsty.smugmug.com/Motorcycles/Rob-North-BMW/

http://www.beemergarage.com/photos29.html

Kicka get a RZ350 frame. North frame or not that bike is Ugly i see why the OP wanted to do the imola rep.

[Kickaha]

Kicka get a RZ350 frame. North frame or not that bike is Ugly i see why the OP wanted to do the imola rep.

It's only the bodywork and that's easy to change

I'd rather go Krauser anyway

[husaberg]

It's only the bodywork and that's easy to change

I'd rather go Krauser anyway

Maybe just the Krauser heads
I have a write up here with the late 70's BMW US superbike stdish braced frame

[Kickaha]

Maybe just the Krauser heads
I have a write up here with the late 70's BMW US superbike stdish braced frame

The heads have problems and you need the correct pistons for them as well, there was a new set on Ebay last year

They monoshocked one of the frames

I have all the writeups I can find from that time