View Full Version : Motorcycle Drag Frame

09-07-2009, 04:57 PM
I wondered if silver soldering a 4130 bike frame would be a good idea? thanx Also Russ any tips would be appreciated later Mike

09-07-2009, 06:20 PM
I thought I/NHRA would only allow tig??????

09-07-2009, 07:19 PM
I have seen more cracks in 4130 with tig than other types of torch welding?? And once its painted who the heck would be able to rtell anyhow>? I have never been speced on welds on a frame yet??

09-07-2009, 09:43 PM
Early British Motorcycle frames were built up from swaged tubes pressed into cast or forged fittings. The tubes were then drilled and pinned before being sweat brazed together. Some brands that did this were Norton. AJS, Matchless, BSA, James, Triumph, Ariel, etc. They were very durable.

I don't see why you couldn't use some sort of braze or silverbraze as long as there is a mechanical fit and locking method to hold the frame together. I wouldn't make any simple joints like you might if you were TIG welding.

The only other question in my mind would be what changes might occur in the metal due to the heat needed for a brazed or silver brazed joint.

09-08-2009, 05:37 AM
I believe you can silver solder/braze 4130, but you shouldn't brass braze/bronze weld it. Chromium steel alloys suffer from intergranular penetration when high temperature brazed. The old British frames with cast lugs were using ERW mild steel which is suitable for brazing. The famed Norton 'featherbed' frames were ERW on the road bikes and thinner wall Reynolds tubing on the race bikes. The Reynolds alloys are Manganese based rather than Chromium and were developed for Bronze welding (10% Nickle bronze rods and probably a gas fluxer).

The race featherbed frames were lighter, but less stiff than the road frames (but adequately stiff when the engine was bolted in) and were 'lifed' every season by the works team. They needed the high tensile tubing because of all the curved sections.

An aircraft frame is aiming for the highest strength to weight ratio, but a bike or car frame is trying to acheive the highest stiffness to weight ratio. Generally if a frame is stiff enough, it will be more than strong enough. If any member in your frame is loaded to anywhere near the yield point of mild steel, then it is almost by definition flexing to much and you should re-design.

The USA seems to have an aversion to ERW, historically based on a tendancy to split, but that was solved for most applications years ago. Many 1960's Formula 1 cars were build from ERW and the rules required that my Van Dieman FF1600 NOT contain anything more exotic than ERW with the exception of mandatory CDS for the roll hoop.

09-08-2009, 10:08 AM
Mike... I'd be wanting to check out what the manufacturer of the tubing recommended first. Reynolds says NO to silver soldering some of their CM tubing....something to do with the tubing becoming crystaline from the silver????
However....lots of bicycle racing frames are silver soldered.
I'm thinking frame design is going to dictate somewhat the best method used to join the tubing....and NHRA/AHRA rules of course.
I know this didn't help much but I'm not a huge fan of cromoly frames. They where banned in the mudracing deal I was in. They couldn't take the constant flexing and pounding as well as DOM frames could. I know that for a fact.
A fella up here went to the US and bought a chassis that was outlawed down there but the rules up here says he can run it.
I've repaired dozens of cracks on that frame. It is a thing of beauty...built by a dragrace chassis builder in the US....ok for the pavement but lousy in the rough and tumble mud world.

09-08-2009, 02:09 PM
Here's an article on 4130 & TIG that may be useful to you, madman:



09-08-2009, 07:59 PM
I appreciate the input and time .thanx all for the replies. I just bought another bike for my second dragbike project.

09-09-2009, 07:44 PM
NHRA rules wise; it depends on how quick you're going.
Down to 10.0 sec (in a car) they don't look too close.
9.99 or quicker, you need a certified chassis (for a car, probably similar for MC)
Mild steel: Mig or Tig ok
Chromemoly: Tig only
For the cert. they will do a chemical test to verify chromemoly as well as a sonic test to verify wall thickness. visual only on the welds to verify that they go all around, even in the tight spots and no porosity. Re-cert every 3 years.
Been thru it a few times, no big deal but they do check.

09-12-2009, 09:54 AM
Well years ago i had a bike with a stock front section (750 suzuki) and a guy named Puppet made up the rear section for me out of chromemoly i think. I always wondered about welding moly to steel tube but it was a awesome frame, (we cut some 1.14 o to 60 s with that chassis) We raced in the states and ran as fast as 8.54 s and never had a inspector give our chassis a second look. BUT times change. Maybe getting hold of a rulebook might be smart.