Chassis Cracks and Broken Brackets

[Ji Gantor]

Hi Huskibul,
Only if the fellow understands CrMo.
It is not complicated.
GMC does it all the time and so does any roll cage manufacturer.

Ji

[rocketfrog]

After the welding is done we can sand down the bead and make it all look great again.

Some resorters feel that a 30 year old frame is dangerous and should not be used and so they pay $10k or so for a replica frame and swingarm.
This is fine, each to their own, honestly I can not see how you can call yourself a restorer when you have started with all new parts. What did they restore? They should call themselves Bike Assemblers. If you are conserned that your frame may have unseen faults you can have it ultrasounded. This will reveal any potential problems for a fraction of the cost of a replica frame. If you feel your welding is not up to par get a boiler maker to weld up any known cracks, this to will not cost as much as you think and you will have peace of mind and a really good looking frame.

Ji

Not exactly ultrasounded, a magnetic particle test is the best Non Desructive Testing (NDT) technique to disclose surface breaking and some sub surface cracks in most cases. Radiography is the ultimate, and would take quite a few shots to examine the entire frame, however, concentrating on the high stress areas such as the major gussets and load bearing tube connections will tell you what you need to know. I have some interesting test photos from the evaluation of a YZ 250 frame which demonstrates the effectiveness of each method. I will post some photos up when I get back to work if you like. Ultrasonic testing requires a very sophisticated immersion test station or water/couplant path transducers to cover the complexity of a bike frame, contact transducers require intimate coupling with the test surface to to be effective. Because of the multiple tube diameters and variation in geometry, you would wind up spending an exorbidant amount of time calibrating and testing then recal and test for each section you are inspecting. Stress relieving the entire frame after major repair is the way to go, this is achieved by annealing the frame in a vacuum furnace then restoring the temper to original specs in the same fashion. The frame would be as good as new following this process

[Ji Gantor]

Hi Rocketfrog,
Yes please, I would love to see the test images.

Ji

[Lozza]

    Ji thats getting a little over my head but maybe i,d be better chasing the chrome moly rod/tig job now you put it that way?,i dont know about the post heating would any bloke with a tig know that ???or what would i tell him?  :-\cheers

It's really simple the slower and more time taken to heat up and cool the area of the weld (pre-post heat) the more ductile the repair will be. Pre heating can be cheap spotlights on a large frame, propane torch waved over the area, post heating can be wrapping in fire blankets and leaving the spot lights on. An example is a submarine, when welded the whole hull is heated (to 80-90 deg C maybe higher) by DC curent for a month or so.

[Ji Gantor]

Attached is an image of the TIG filler rods I carry.
From top to bottom,
Stainless Steel ER316L 1.6mm dia 1 meter long ($0.50),
Chrome moly ER80S-B2 1.6mm dia 1 meter long ($0.75),
Aluminium ER5356 1.6 and 2.4mm dia 1 meter long ($0.50),
Mild Steel S60 1.6mm dia ($0.50) 1 meter long and
Titanium Ti-Al6-V4 grade 5 1.6mm dia 460mm long ($1.75).

Ji

[Ji Gantor]

I just received some Titanium grade 5 sheet.
Grade 5 is structural grade.
The sheet is 1.6mm thick.
Titanium has its base in aluminium but with added carbon like steel.
It has the strength of steel but a little less weight.
Magnets don't stick to it.
When welding it you set the machine up as if you are welding steel.
Ti is like stainless steel when it comes to oxygen shielding. All heated surfaces need to be argon gas shielded. The failure test is visual, post welding if the bead is silver or straw brown it is okay any other colour and the bead is contaminated.
This is a very basic run down on Ti.

Ji

[Ji Gantor]

Titanium can be welded to titanium. It is difficult to weld it to aluminium but can be done, it can not be welded to steel.
The advantages are strong, light and does not rust.

Those BSA all titanium frames must have been terrible to weld in the sixties.
If you screw up a weld the Ti is ruined and must be replaced.
Once heated without proper shielding the Ti is cactused.

Ji

[Ji Gantor]

Attached are some titanium foot pegs that are on the market for sale.
These pegs have been welded not CNC machined.
The blue colour is clearly seen.
So is the light brown colour.
I would be very interested in finding out how they welded these units.
I did not take this image.
It is from Geoff Ballard's catalogue.
If anyone is offended by its use here I will remove it on request.

Ji

[Ji Gantor]

Attached is an image of a flexible enclosure filled with argon gas ready to weld titanium.
There are other methods but this is the best way to ensure no contamination.

Ji

[tony27]

From memory the BSA frames were done in vacuum chamber, problem was the frame was not able to be fixed at a gp because of this. Didn't suzuki also built a featherweight bike with a titanium frame etc at one stage leading to the minimum weight rule coming about. From what I understand titanium isn't ideally suited to mx frames as it is prone to work hardening which leads to fatigue when asked to flex during landing etc

[mx250]

From what I understand titanium isn't ideally suited to mx frames as it is prone to work hardening which leads to fatigue when asked to flex during landing etc

IIRC you are right - but then if you're a race team just get a new frame - which was part of the expense  (I think you find even the steel frames are replaced regularly).

[Ji Gantor]

I am unsure about Suzuki but Husqvarna followed BSA and got it right.
Then FIA banned the use of titanium in major components to try and keep the cost of bike racing down.
NASCAR followed FIA and they can not use Ti in major parts to this day.

Ti is certainly cheaper today than back then and we have better methods to join it.

Why am I going on about Ti, simple just about all new header pipes or mufflers are Ti, footpegs, valves and so on.
As we trash these components we will have to replace them or fix them, so now is a good time to start learning. I intend making some trick parts for my VMX bikes out of Ti.

Ji

[Ji Gantor]

I also know of fellow races that use titanium screws, nuts, and bolts on their VMX bikes.

But before we jump feet first into Ti we need to now some of its problems.

First it is not cheap to purchase in comparison to CrMo 4130.
It has to be TIG welded with lots of argon use.
It sparks or flames when bead blasted.
The shavings from drilling, milling or grinding can catch on fire if left in the corner.
It is brittle from the word go. Of course there are a few different grades of Ti some of which are very ductile but we would not be using them for our purpose.

Ji

[Ji Gantor]

Lets also start a list of where Ti parts could be used on a VMX bike for weight savings.
Every nut and bolt,
Spokes,
Spoke nipples,
Rim locks,
Rims,
chain sprockets,
gear shift lever,
Brake lever,
Handle bars,
Hand levers,
Throttle body,
Fork springs,
Shock spring,
Fork dampener rod,
Bash plate,
Air box,
Seat base,
Fuel tank,
Footpegs,
Exhaust pipe including header and muffler,
Exhaust springs,
Engine valves,
Intake manifold,
Axles,
Front number plate,
Cable guides,
Flywheel,
Drive chain,
Chain guard,
Front and rear brake backing plates,
Front and rear brake stays,
Triple clamps,
Front and rear hubs,
Piston,
Clutch basket,
..........
Thank goodness FIA stopped us from making frames out of the stuff.

Ji

[firko]

It is difficult to weld it to aluminium but can be done

It can indeed be done but I wouldn't be relying on any aluminium/ti welded joint under even the slightest stress.

The BSA works frames were welded in an inert chamber at the Raleigh bicycle company, one of the few companies in the UK set up to weld Ti successfully in 1965/6. The problems with the Ti frame weren't any deficiencies in the welding itself but with the actual design of the frame. Titanium and Reynolds alloy steel posess totally different stress properties causing the loads to be distributed differently. Because it was new technology the BSA engineers built the Ti frame to the exact same design as the steel version which invariably failed under race conditions. After observing Beezers dramas with the Ti frame Husqvarna realised that it was mainly design deficiencies rather than the actual materials that caused the failures so they designed a frame specifically for titanium and consequently had few problems. Suzuki and Yamaha both experimented with Ti but opted out for various reasons. Suzuki achieved such low weights on their RH/RN works bikes with liberal use of titanium nuts/bolts and fixtures and lightweight magnesium castings. The frames were made from wafer thin chro-mo and were regularly replaced. Pipes often lasted only one moto.