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).
http://www.autonewsinfo.com/wp-content/uploads/2013/10/A-A-ML-BMW-1DSC_9292.jpg

http://2.bp.blogspot.com/-8dsuqw5S0QY/USbfg-n4ZEI/AAAAAAAAYh0/SjEVhgu3arA/s640/BMW_Formel_750_Imola_racer-7.jpg
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
http://i129.photobucket.com/albums/p235/rednzep/IMAG1382_zps4cefbd1d.jpg

[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]

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


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

cheating already :laugh:

[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.

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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.
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[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....
http://i129.photobucket.com/albums/p235/rednzep/IMG_00251_zpsjpjbxnog.jpg
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
http://www.beemergarage.com/photos/robnorth.JPG
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

[Voltaire]

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.

Thanks for that info, pic showed a Tonti Guzzi frame lurking in my shed. I'm leaning towards the Dahne one as it is the stock swing arm and steering head but with top rails.

I like the guy, builds the bike races at the TT :Punk:

Might not get around to building it for a while but it sure looks cool.


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.

Yes it really is just the Featherbed frame that BMW half copied. Sampson Hi gloss...." sure thing"
beating CB 350's....unlikely as those guys go hard.


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

I'd rather go Krauser anyway

I could ask Maxheadroom for his Krauser heads and get my mate to scan them and print out a plug for a mold.....

[Kickaha]

I could ask Maxheadroom for his Krauser heads and get my mate to scan them and print out a plug for a mold.....
Give them to Nev and get him to knock em out on the CNC because it'd be that simple :msn-wink:

[husaberg]

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

I have all the writeups I can find from that time

Do you have this one.

[husaberg]

The US superbike as Kicka Mentioned was monoshocked.

[Voltaire]

I had two set of Krauser heads years ago in the UK as they fell out of favour, I however did not have the pistons as it was pre internet and info was hard to get, flogged them and went twin plug and 40mm Dells , 81 style clutch on my R100 RS...transformed it to something less sluggy.
Krauser heads make nice shelf candy.

[Kickaha]

Do you have this one.

No, but there is nothing new in that one

[husaberg]

No, but there is nothing new in that one

Ya still never had it. The bike you mentioned was the one above.
No wonder Krauser was doing ok it says he sold 1800 bikes from one shop in 6 months

[Voltaire]

The US superbike as Kicka Mentioned was monoshocked.

I think they has a choice of mono of twin shocks as there were protests.

Udo Gietl was the man behind the R90s's, pretty amazing for touring twin. Pissed Cook Neilson off....accused them of cheating... Germans would never do that :rolleyes:

[Kickaha]

I think they has a choice of mono of twin shocks as there were protests.:
The story goes the rules say the shocks can be relocated, so he relocated one to a shelf in the workshop and made it a mono

[Grumph]

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

Funny story, the RZ frame is a Rob North copy....He did a frame for Roberts for a TZ, expecting more orders...It found it's way to Yamaha and the next year's TZ had an almost identical frame. The RZ is pretty much the same frame with road fittings....North always felt ripped off by that one.

[husaberg]

Funny story, the RZ frame is a Rob North copy....He did a frame for Roberts for a TZ, expecting more orders...It found it's way to Yamaha and the next year's TZ had an almost identical frame. The RZ is pretty much the same frame with road fittings....North always felt ripped off by that one.

I think he felt a bit hard done by all around.
Likely rightfully so in some instances such as his name.
If he felt ripped off with the Yamaha he better look away from quite a few early 80's Hondas as well.
The public even used the lowboy and high boy monikers for the TZs
http://www.caferacer.net/forum/attachments/technical/13762d1429538489-would-honda-vf-250-do-honda-20vt250f-2082.jpg
http://raresportbikesforsale.com/wp-content/uploads/2012/08/MVX_250_3.jpg

[husaberg]

I think they has a choice of mono of twin shocks as there were protests.

Udo Gietl was the man behind the R90s's, pretty amazing for touring twin. Pissed Cook Neilson off....accused them of cheating... Germans would never do that :rolleyes:

Have you had a look at a k75 /k100 Frame

Rake, trail
27.5°/3.98 in (10.1 cm)
Wheelbase
59.7 in (152 cm)[9]


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316155

[trustme]

Are you going to do this yourself or get some help. I believe James Simpson Engineering in Albany might be able to help. James is a good bloke , did some frame repairs to Winston, does a bit of frame work. No doubt you will have a plan

[Grumph]

By the time you've cut all the odd bits off the K frame, then added the bits you want, it's quicker - and ultimately less work to build from scratch.
Saves the time you'd waste too removing all the factory ID from the donor frame....

[swarfie]

Saves the time you'd waste too removing all the factory ID from the donor frame....

And renumbering it:shifty::shutup:

[husaberg]

By the time you've cut all the odd bits off the K frame, then added the bits you want, it's quicker - and ultimately less work to build from scratch.
Saves the time you'd waste too removing all the factory ID from the donor frame....
Highly logical, but not everyone enjoys your skill level. That said logic likely applies to any BMW owner.
ps Its a race bike.
One thing i will say is looking at the BMW the wheelbase needs to be kept ultra short.
As it will not need to be leaned over as much in any given corner.
If ever there was a engine lump begged to be put in a large dia spine frame the BMW twin would be it.
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the pics are Waddon and foale guzzi to save you loading them Greg

[smmudd83_1999]

http://www.autonewsinfo.com/wp-content/uploads/2013/10/A-A-ML-BMW-1DSC_9292.jpg

http://2.bp.blogspot.com/-8dsuqw5S0QY/USbfg-n4ZEI/AAAAAAAAYh0/SjEVhgu3arA/s640/BMW_Formel_750_Imola_racer-7.jpg
What sort of tubing would I need?


Looking at the result you want, modifying that existing BMW frame is actually a lot of work. You have to fabricate a frame jig first as any warp in the pivot to head in any of the three planes, however incremental, can really eff things up for you.

Taking a good look at these pics, this looks a lot like an older Guzzi frame (pre-Lino Tonti). Or Seeley. Which were awesome handlers for their day. It would be easier to start with that and then modify the steering head then trying to modify the existing BMW frame upper loop, rear loop etc.
Your starting point for this project is to pick a frame that requires minimum input to begin with. Think long in terms of the $s, you can easy spend a couple of grand for a quality fabricator to do the job, so don't shy away from paying a couple of grand for the right frame!

I'm guessing if you are asking about what material to use for the job you won't be doing the job yourself?
For my 2c worth, start with a cold drawn steel. Traditionally, people used to go for reynold 531 but mills will only run limited runs at extortionate prices. The metallurgy of steel is a degree in itself, modern equivalent is ???dunno maybe around 4130 grade? I would stay away from the harder or heat treated grades. Frames were brazed/manganese bronze welded, which makes a lot of sense. The tube is normally 1 1/8" or 1 1/4". No thinner. 17 gauge commonly, 18 gauge for a lighter race frame. As this houses a BMW engine (plus tuning) I'm thinking you want to stick to at least 17 gauge.

You'd have to research which steel to use. I haven't broached the subject of steel-chromo or moly as it's a bit beyond me. And maybe, at the end of the day, it won't be all that critical anyway?

Good luck with your project. Don't be disheartened by the technicalities. Reading the science, and trying, experimenting and in the end having a go is always to be applauded.

[Grumph]

And renumbering it:shifty::shutup:

See husa ? There's a man who knows how closely it would be scrutinised for "correct period" detail...

In Nz there's not a lot of choice for frame tube. Mostly ERW mild steel seamed tube. A version available which is DOM and looks seamless but is much less bendable...
Some CrMoly available from car frame builders - mostly in sizes too big for our use.

I use mild steel in generous gauges, never less than 16G or 1.6mm wall. Manganese bronze weld with biggish fillets as it's relatively soft tube.
Haven't broken one yet...

[Voltaire]

here is a stock frame I had a go on a few years back after experimenting with some Chrome Moly tube, trying out gas, brazing, and mig then whacking them with a hammer to see which was strongest.
Started on the frame then went for stock which I have been using on the track for about 3 years.
Note engine position was going to be moved forward and up.
When you see that the stock BMW sub frame is held on with 4 8mm bolts you have to wonder if doing welded joints could be any worse.

http://i129.photobucket.com/albums/p235/rednzep/IMG_02471_zpsm6brxziz.jpg

[husaberg]

Only BMW I covert. Other than the Kobas flying Brick.
both have their cams placed in the correct order on top of their valves

[Voltaire]

Only BMW I covert. Other than the Kobas flying Brick.
both have their cams placed in the correct order on top of their valves

Can't say I'm a big fan of them myself :innocent:

I rode a Brick once, 400 KMs around the hills of Chang Mai, I remember the day out, boring brick not at all.

[nodrog]

here is a stock frame I had a go on a few years back after experimenting with some Chrome Moly tube, trying out gas, brazing, and mig then whacking them with a hammer to see which was strongest.
Started on the frame then went for stock which I have been using on the track for about 3 years.
Note engine position was going to be moved forward and up.
When you see that the stock BMW sub frame is held on with 4 8mm bolts you have to wonder if doing welded joints could be any worse.

http://buzzword.org.uk/2009/gremlin.jpeg

https://horticulturetalk.files.wordpress.com/2010/07/scotts-roundup-gc.jpg

[swarfie]

See husa ? There's a man who knows how closely it would be scrutinised for "correct period" detail...

In Nz there's not a lot of choice for frame tube. Mostly ERW mild steel seamed tube. A version available which is DOM and looks seamless but is much less bendable...
Some CrMoly available from car frame builders - mostly in sizes too big for our use.

I use mild steel in generous gauges, never less than 16G or 1.6mm wall. Manganese bronze weld with biggish fillets as it's relatively soft tube.
Haven't broken one yet...

+1 on that. We built the Matchy frame in 1987 out of a combination of mainly ERW and some seamless 1.6mm tube, braced where necessary and all bronze welded. Broken it a couple of times (but touchwood not for a while now), and readdressed the gusseting in a couple of places. It's light and as strong as it needs to be...the secret to any frame. Sidecars are under a huge amount more stress than a solo chassis though :yes:

[Voltaire]

+1 on that. We built the Matchy frame in 1987 out of a combination of mainly ERW and some seamless 1.6mm tube, braced where necessary and all bronze welded. Broken it a couple of times (but touchwood not for a while now), and readdressed the gusseting in a couple of places. It's light and as strong as it needs to be...the secret to any frame. Sidecars are under a huge amount more stress than a solo chassis though :yes:

C@@L, when can I drop the frame off :lol:, box of Waikato and a flat white ( gotta be more than $5 and a bag of chips)

[AllanB]

Maybe call someone like F1 Engineering in Hamilton - they straighten frames so presumably have suitable gear.

[nodrog]

Maybe call someone like F1 Engineering in Hamilton - they straighten frames so presumably have suitable gear.

aucklanders don't like going there.

[Voltaire]

Totally nailed this multi quote thing...



Maybe call someone like F1 Engineering in Hamilton - they straighten frames so presumably have suitable gear.

Damn man, where is your # 8 wire sprit?


aucklanders don't like going there.

That's those Wonga par oh a blokes, that's like a 4 hour trip from there.

( can you explain the Gremlin and the Weedkiller.... )

[AllanB]

Totally nailed this multi quote thing...




Damn man, where is your # 8 wire sprit?



That's those Wonga par oh a blokes, that's like a 4 hour trip from there.

( can you explain the Gremlin and the Weedkiller.... )

Well I was going to say - man-up and just crack out the welder, how hard can it be, Burt Munro did it using a army knife, hacksaw and a soldering iron, but frames are kind of important things ....

I have a DVD somewhere here with Indian Larry welding up chain links then cutting out the down tubes and welding the chain links in. Looked cool. Got to have faith in your work.

Shit if those Orange County hobos could tack up those creations without them breaking your project must be a breeze :-)

[Grumph]

Shit if those Orange County hobos could tack up those creations without them breaking your project must be a breeze :-)

While i tend to agree - from what little I saw of the series, they had a man who could TIG pretty good doing the frames. And using the sort of tube you could make a NASCAR frame from....
Most never make a frame because they overthink it IMO. An eye for stress and a willingness to copy proven work is really all you need.

[AllanB]

While i tend to agree - from what little I saw of the series, they had a man who could TIG pretty good doing the frames. And using the sort of tube you could make a NASCAR frame from....
Most never make a frame because they overthink it IMO. An eye for stress and a willingness to copy proven work is really all you need.

Agree re Orange - there were people in the background doing the grunt work. And F- me those bikes must have weighed shitload!


Suppose the question in NZ is if you are using it on the road will you need a engineer to sign off the design and cert welder the sticky stuff?

[Grumph]

Agree re Orange - there were people in the background doing the grunt work. And F- me those bikes must have weighed shitload!


Suppose the question in NZ is if you are using it on the road will you need a engineer to sign off the design and cert welder the sticky stuff?

Back before the regs got tough I did a bit of modification on road frames. Won't even look at it now. Ironic that race stuff which is more highly stressed requires no certification whatsoever....
I seriously doubt if there's anyone formally qualified in NZ to do motorcycle frame structural analysis, and with enough experience to make it meaningful. On the other hand i know of about 5 people who can look at a frame and say yes or no....and none of them are formally qualified. Best welder I know has let his cert lapse...most of the car race teams in ChCh still use him though.

[nodrog]

( can you explain the Gremlin and the Weedkiller.... )

the weedkiller is for your driveway, the gremlin is so I don't get infracted up the arse again for quoting an image.