The Hallman Project - life wasn't meant to be easy.

[mx250]

While Loz is working on the VB's chamber I thought I would fiddle with Project Hallman. Got a 'farm' DT frame from Jim G and a RT frame with extranious sidecar bits welded to it from Jimson (thanks guys ). A bit of cutting and clean, and playing mix and match I got the following.

It is a DT250/360 top frame with an RT lower loop offered up.
 






I'll have to go to my welding expert George and ask his opinion but I think the DT frame will have to be trashed - the frame rails have been bent and cracked with some amatuer engineering/welding to get a long travel rear, and there is a lot of extra 'farm' welding all over the frame which has been pretty dickie - there are holes blown through the tubing. All too much trouble and agro to patch I reckon. Time to start again. I'll use this frame to practice .

[Nathan S]

Is it just the way it looks in the photos, or does the later frame have slightly larger diameter tubing?

I think I've got a spare DT250A/B frame if you need another.
The old sidecar frame is working its way around the forum: Tim > Me > Jimson > You > ? 

[mx250]

Is it just the way it looks in the photos, or does the later frame have slightly larger diameter tubing?

They are different dia.

I think I've got a spare DT250A/B frame if you need another.

Thanks, I'll keep it in mind. I'll need to talk to George but Project Hallman will probably go into hibernation shortly when the VB returns.

The old sidecar frame is working its way around the forum: Tim > Me > Jimson > You > ? 

The butt stops here .

[bigk]

I have a DT1 frame if you want another one, can send VIN if you need it.
Cheers,
K

[JC]

G,

As you've probably found already, DT frame's engine bay is longer than for DT1/2/3 cos later engines are about 1" longer. DT swingarm is also shorter by about same amount to compensate.

[Nathan S]

Looking at the photo of the Hallman YZ, and now I'm wondering:
Wouldn't it be easier to simply shorten a DT-A frame to take the DT1 type motor?
And maybe lengthen the rear section to keep the shocks vertical(ish) with the longer DT1 swing arm?

[mx250]

Looking at the photo of the Hallman YZ, and now I'm wondering:
Wouldn't it be easier to simply shorten a DT-A frame to take the DT1 type motor?

Thats pretty much what I'm doing. With the DT/RT and the DT2MX and the Hallman the down tubes and the craddle under the engine are slightly, 25mm, more narrow than the DT/MX. Thats what the pixies show; the DT1 loop is slightly narrower and slightly shorter. I'll re-angle the DT's down tubes to line up with the DT1's bottom loop.

[Nathan S]

I was thinking that it might be possible to simply cut the ~25mm of length out of the DT frame (top tube and bottom rails), and then re-make the mounts to take the DT1 engine?

But you're talking about 25mm of extra width, while JC's talking about an extra 25mm of length.

This thread is doing me no good at all.... The 71 YZ250 is (IMHO) one of the sexiest bikes ever built, and the idea of building one myself makes me all gooey inside.

[JC]

Nathan,

I think you'll find they're shorter and narrower. I'd probably go the way yr suggesting too, but then its not my project.

Hope it turns out nicely for you Graeme. It is a bike worth replicating.

[Freakshow]

Well its in the same colours 

[firko]

Just a shot out of left field but would a '74ish DT175 frame, suitably modified and disguised be closer than the hacked around DT1 OR DT250 version? I too like this project and would be attempting it myself if I wasn't burdened down with a shed full of other projects.