Modifying frames?

[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.



the pics are Waddon and foale guzzi to save you loading them Greg

[smmudd83_1999]

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

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.

[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

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

[nodrog:Me]

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.

[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

[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

C@@L, when can I drop the frame off , 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:Me]

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?