Race chassis

[Grumph]

Greg, I like the looks of that bike.

The Scorpion RR frame looks like a Triumph T140 without the lower cradle tubes. Bending a big tube like that is going to be hard for a DIY person, welding a top and a vertical tube together (like the drainpipe Dunstall twin) would be easier.

Thanks - it finished up very pretty and looking very period which was the aim. It's badged as an AJS and more than one person has said to Peter "didn't know that the roadrace version of the Stormer was ever sold"....LOL Goes quite well too.

Bending big tube isn't a problem for me. There's an exhaust manufacturer in ChCh with a mandrel bender - and dies for tube up to 6 inches dia...
I know of a guy who was making Manx replica frames here who was getting them to bend up all the bits required. He'd just ring them up and order up the required number of kits. One benefit of living so far from the rest of the world Michael, is that when people buy in something like a mandrel bender they get the most versatile/largest possible as you never know what you're going to have to do....

[guyhockley]

Seem to remember a Scandinavian member of MC-Chassis Design saying he had hydroformed a 90 degree bent sauna flue of 3 inch diameter in 16 guage...

[Michael Moore]

Guy, I don't remember that (but I can't remember every comment over 20 years of the list), but hydroforming would let you have a tapered tube if you wanted it, or even various localized increases/decreases in diameter.

[guyhockley]

The AJS Stormer frames looked like the spine was fabricated from 2 pressings or tapered from a thicker tube. I was looking at a Can-Am 175 racer a few years back and the frame design looked very similar.
Prefer the "Grumph AJS", nice piece of kit.

[guyhockley]

Guy, I don't remember that (but I can't remember every comment over 20 years of the list), but hydroforming would let you have a tapered tube if you wanted it, or even various localized increases/decreases in diameter.

Found it, but I got the details wrong...

"Date: Thu, 07 Jan 1999 07:33:06 +0200
From: Tomas Tallkvist
Subject: MC-Chassis Hydroforming

Hello !

The system I am using is based on an old Highpressure cleaner, connected to
the outlet,
it feautures a pressure reducing valve so you can adjust the pressure from
5-150 bar.

It works in the same manner as an hydraulic hand pump, but you are allowed
some "minor"
leaks without trouble !

When waterforming megaphones and 2 smoke exhaust systems, no more than 30
bar is used.

The only time I used over 40 Bar was when I made an nice 90 degree bent
chimney connection
tube of 110mm dia of 1,5mm sheet to the Sauna Oven !

The only thing with this technique is that it is hard to come up with
calculations how to
cut the sheet so the final form is the one that you looked for, a better way
is to just make
10-15 megphones and get some experience...

Simple, but it works !

Tomas"

[Michael Moore]

yeah, you've got to do a fair number of practice runs to get a handle on how much the end result of a turn varies from the angle on the pattern. I watched one video in which the exhaust tightened up and then unfolded some, that's not very helpful.

If you are going to do a fuel-containing spine/monocoque hydroforming would let you know for very sure if you had any leaks.

[Grumph]

The AJS Stormer frames looked like the spine was fabricated from 2 pressings or tapered from a thicker tube. I was looking at a Can-Am 175 racer a few years back and the frame design looked very similar.
Prefer the "Grumph AJS", nice piece of kit.

Thanks. The Stormer I had here for a rebuild had been converted to a roadracer early in it's life and apparently had Irish roads history. It had been bought by an Auusie on his big OE and taken back to melbourne. I think he'd worked for a precision grinding outfit as their name was on the side. It had a yamaha YZ rod and pin, a Wiseco piston made for an RM250 Suzuki - and finger transfers cut in the bore like a TD1C. It had ben bought by a Kiwi from his estate and had sat for years in NZ. I finished off the job of fitting one of the rare 6 speed Villiers boxes to it - different engine mounts needed.
It was frankly ugly with the std tank and a Dunstall/Chuck style of seat with an apron grafted on to span the gap seat to tank.
Once running it went very well indeed. It's changed hands and I've lost track of it since.

And yes, the top short spine was two pressings welded together to form a tapered box. I simply used a top tube of 2 in OD X 2mm wall MS. Good enough.

I seem to remember that Jeff Smith was involved with the early Can-Ams and liked the AJS frame a lot - enough to do a close copy anyway.

[Michael Moore]

Tony's TZ250/350 frames used a 16g x 2" spine. He told me that if he were (and he's not) to make another one for a modern vintage TZ running on today's tires he'd bump that to 2.25" (which would be about a 30% increase in stiffness or about 8-10% over the 2" x .08" tube)).

I've wondered if the AJS spine was two U-shaped pressings or a U shape added to a full tube, now I know.

[Grumph]

Tony's TZ250/350 frames used a 16g x 2" spine. He told me that if he were (and he's not) to make another one for a modern vintage TZ running on today's tires he'd bump that to 2.25" (which would be about a 30% increase in stiffness or about 8-10% over the 2" x .08" tube)).

I've wondered if the AJS spine was two U-shaped pressings or a U shape added to a full tube, now I know.

Just to be sure, I pulled out the Starmaker manual (hey, things seem to stick to my shelves...) and yes, a full length spine, steering head to rear bulkhead, tapered and in two pieces, seam welded.
Mine was a lot shorter as the pic shows. The clever bit I copied from the Stormer was the half round piece across the frame enclosing the front of the swingarm. If, like all Villiers, the engine mounts are narrow, this gives a very stiff point to attatch to.

[husaberg]

Some fella that worked at NVT wrote this

Dr. Bauer was the head of the Wolverhampton operation, where all the design and development took place for the AMC group. A very clever and erudite gentleman, but I thought out of his depth in an industrial organisation which was supposed to make products for profit. His specialty was combustion chemistry, I think.
When I was there, we were down to just Norton and AJS on the market, along with the Villiers range of industrial engines. We did make one "oddball" Matchless, a trials version of the Starmaker motocross machine for the ISDT in 1968.
Bob Trigg headed up the design team on both the Commando and the AJS motocross/trials bikes, sold in the US as the "Stormer". I believe the design was sold to a division of Bombardier (KTM?).
There was a strong family resemblance between the two frames, the only differences on the AJS being the way the top tube joined the headstock and no Isolastics. We had real problems with fatigue failures on the top tube.

Pretty sure Renyolds made the prototype and likely the frames as well as Norton didn't have welding facilities.
Latter Commando frames were made in Spain i think. Reynolds alledgedly made more money out of straightening themfor Norton after delevery than they ever did making ones for Norton, According to something Ken wrote

[guyhockley]

Tony's TZ250/350 frames used a 16g x 2" spine. He told me that if he were (and he's not) to make another one for a modern vintage TZ running on today's tires he'd bump that to 2.25" (which would be about a 30% increase in stiffness or about 8-10% over the 2" x .08" tube)).

I've wondered if the AJS spine was two U-shaped pressings or a U shape added to a full tube, now I know.

Tony told me that when I asked if I could make a copy - still haven't got around to it...
Nigel Leaper may have agreed as there was a blog detailing restoration of Vince (Fondseca) Caundle's ex works Waddon that has a 63mm spine and he measured several others at 55mm (2.5" and 2.25"?).
Also heard of a british racer (Simon something) who wrecked his Waddon, built his own replacement frame, then went on to make a "few" more, so who knows what's out there?
https://web.archive.org/web/20110524...ddon.me/about/

[richban]

Hi Guys.

So after getting all excited about building a mono. I have switched back to a tube steel version. Its something I can do with the tools I have so I am going to get one with it. I'm not using chomo. Its mild steel for this first attempt. I have the steel now. 5 dollars a metre cheap cheap. Its 25 x 1.2. Basic design below. For this first attempt I will use the RS50 swing arm.




I started to machine a bit of steel for the head stock and cocked it up rather quickly. Turns out steel is actually not its more butter you just pulled out of the fridge. It grabbed and fung its self out of the lathe. Its bent.



Now I am left wondering about my choice of material. As the head stock is quite important I am now wondering if there is a grade of steelbutter that is better the stuff I have. Sort of spreadable butter versus Old school hard as a rock straight out of the fridge butter. Or even better frozen butter. That shit is hard.

I did a little research around welding mild steel to Chromoly. Seams its ok as long as you heat the work before welding.

[Ultralightweght]

I'd use 1040 or 1030 grade- or phone milson metals and get some hollow bar - save heaps of time machining-the next thing to check is the tool geometry - it changes if your turning something soft like alum or plastic vs high tensile or brass/bronze etc-I'm assuming also the tool is not under centre as that will hook something out of the lathe- did you have tailstock in?

[richban]

I'd use 1040 or 1030 grade- or phone milson metals and get some hollow bar - save heaps of time machining-the next thing to check is the tool geometry - it changes if your turning something soft like alum or plastic vs high tensile or brass/bronze etc-I'm assuming also the tool is not under centre as that will hook something out of the lathe- did you have tailstock in?

Much thanks. Will give them a bell next week. No tail stock rpm way high. Disaster waiting to happen really. Learning some lessons so thats a plus.

[Grumph]

Much thanks. Will give them a bell next week. No tail stock rpm way high. Disaster waiting to happen really. Learning some lessons so thats a plus.

You don't need a fully machined one piece headstock. A piece of largish OD MS tube say 2mm wall with the ends squared will do. Then you make up bearing carrier inserts in either steel or alloy and press them in once the welding's done...
I've "pressed" them in with a m'f big G clamp no probs.
Ducati and others did it like this for ages with no problems