welding a frame....

[VMX Andrew]

does anyone know about the pros and cons of welding a frame.ive just bought a cr500 and found a big crack underneath the motor where the frame rails run....looks like they have bottomed her out or something,anyway whats the best way of goin about fixing it.can i leave the motor in and weld it that way so the frame wont go out of postion or should i pull the whole motor out,sandblast it...there is some minor rust around the crack too..... weld it with some  kind of special welder...  then paint it and so on....any help or info from anyone would be a bonus thanks....      

[vandy010]

you gotta weigh up just how thorough you want to be with it.
do the job right and do it once and you'll be rewarded by knowing it's the goods.
best job, motor out, clean it up as best you can, get it TIG welded.
2nd choice is solid wire MIG, then oxy or stick welded.
if it's only a small size job the frame shouldn't pull too much but to play it safe, just spend a few extra minutes thinking it through.
TIG, then MIG is my choice.

[oldfart]

Best to get it sand blasted to remove all old paint work at the same time it will reveal any cracks .If its a main rail you may need to gusset or dowl the joint .....pre heat with the oxy then tig weld ( check to see if the frame is moly tube or mild steel )

[holeshot buddy]

sounds like you have an 84 cr500 frames are pox they all go there after you weld it i would brace it and run a good skid plate 








it ran last time i started it 

[Lozza]

IMO MIG welders should have similar restrictions to what there is to the sale of firearms, to prevent these type situations.
First option would be to take the frame to someone who knows what they are doing.
Second is Bronze welding with an oxy last is tig.NO sticko's, no MIG's.EVER
The success of the welding will depend on the way in which the weld is pre and post heated. It will need gentle pre heating to slowly bring a large area of the frame up to temp then welding then slowly bring the frames temp down.This ensures a ductile weld just the thing for a frame

[GMC]

Take the motor out, the frame won't move much unless you are taking tubes out alltogether, and you will need the access to get around the problem area.
Sand blasting the frame would be good, but at least clean the area that needs the repair.
Run a angle grinder or die grinder through the crack to "Vee" the area which allows more penetration (not just a weld sitting on top).
TIG is the best for this sort of repair, but MIG is okay too, so long as you know what your doing re: light tubes. Don't take it to your local MIG welder if he has only ever welded heavy plate. Stick is too awkward in tight spots & bronze is one of the worst things to use, it offers no strength in a butt weld situation & it's a bastard to get rid of in order to weld it properly.
Take a good look at all your frames, you will see that they were MIG welded at the factory in the first place.
Cro-Mo will become brittle in the heat affected zone ( the area next to the weld) but other steels won't be bothered too much. Technically a Cro-Mo frame should be heat treated in an oven after welding, but you may get away with a small repair depending on how hard it is ridden & stressed. If it's a known weak spot in a frame then it may need extra gusseting also.

[VMX Andrew]

thanks everyone for the replys...i think ill go with gmc.... the tig welder sounds like its the right move.  

[maicomc490t]

Andrew,

You have three choices to ensure the safest and most effective weld.

1) TIG

2) TIG

3) TIG

And even more importantly take it to someone who KNOWS bikes. Guys like Laurie Alderton in Sydney are the way to go (actually not sure if Laurie does TIG but with him if he says he is going to fix it using a box of matches I'd trust THE MAN)

Once you have identified potential areas for cracking (or a possible re-occurence) monitor those areas religiously and avoid the temptation to powdercoat a frame with known bogies as the heavier powdercoating can and will often mask an immenent frame or bracket breakage - go with normal paints.

Every time you wash the bike have a look - let it become your obsessive compulsive disorder!!!

See you at the back of the pack in '08 

[Tim754]

Strange as it seems, I take my Wasp Reynolds Tubing  frame bits and pieces to three trusted engineers. They all push the the Tungsten and  other Inert gas welders away and Oxy heat then nickel/bronze all ? Tim754

[brent j]

Lots of pros and cons on this one.

Mig is easy and gives a good clean weld, pretty well matches low hydrogen and that's good enough for structural work.
Bad part of Mig is the cold start, You need to make sure the start of the weld is getting penetration. Puts a lot of heat into a small area. I seem to remember that's why you can't use it on aircraft stuff.

Gas, slow but controlable, does tend to spread the heat but that's not really a bad thing.

Tig, like gas but faster and more concentrated heat. Can give a bigger temperature difference in a smaller area, as opposed to gas.

Stick, can be a bit too harsh on light material and again puts a lot of heat in a small area.

Moly tube is generaly supplied in "normalised" condition. This means it has (or should have been) heated red hot and alowed to cool in air. I figure gas welding moly is ok as long as you use a good filler rod (triple deoxidised). The spread of heat from gas welding will allow the entire joint to stabalise and cool evenly. I've often wondered about Tig with the high, localised heat input and how much this could stress the joint.
GMC, how do you deal with this in your frames? I've looked a pics of yur work (impressive!) and wondered if you've heated the joints afterwards with the gas to relieve the joints. When you think of it you would be putting the material back to "as supplied" condition ie normalised.

Then there's nickel bronze. All the specialist frame makers use this . As GMC says not much strength for a butt weld in tube but seems to work on everything else. How often does a Cheney or CCM frame break?

Funnily enough when you check Crome-moly tube manufacturers reccomendations a lot of them reccomend bronze welding.

Brent

[GMC]

Yes, Cro-Mo is usually supplied in the "normalised" condition. This basically means it is at it's strongest & most flexible state. Drill bits for instance are strong & tough but snap easily. You don't want steel like this in your frame.
Cro-Mo also work hardens, just like stainless, you can usually only bend a tube once.
Their are probably some home remedies to normalise Cro-Mo again, but I leave it up to the experts & take all my frames & swingarms (Cro-Mo or 6061 alloy) to guys that heat treat stuff for a living. They take my alloy swingarms back up to T6 (temper No 6) and normalise my Cro-Mo frames. I think the process is something like cook in an oven for 4 hours and then let cool.
Look up heat treaters in your local yellow pages if your keen.
MIG' a quick & clean way to weld things but is best suited to production type welding as it has its limitations. When I say that you could get away with using a MIG I don't mean those gasless systems. Allthough I have never tried one I don't know anyone in the industry that use one. The flux cored wire that replaces the gas I believe defeats one of the main benefits of MIG.
Cold start as Brent said & other hicups with MIG is why it's rarely used for pressure vessals. Gas tanks are usually welded by submerged arc (wire feed with a powder fed around the weld for the flux.
Tig welding is a clean neat way to weld things & is best suited to thin & exotic materails. It is very good for repair work but it is much slower than MIG.

Mig is wire feed & Tig uses a tungsten electrode & arc to create the heat source and you then feed the filler rod in by hand, not unlike fusion oxy welding but with a concentrated heat source.

The Cheneys etc. are all a work of art. The frame tubes though are never put end to end & bronzed though, which is basically what a cracked frame tube is.
All their joints are either overlapped with gussets or tubes notched around another tube so that the join is strengthened by the 3D profile. If you were repairing a Nickel Bronzed frame then I would repair it with Nickel Bronze.
By using Nickel-Bronze & Reynolds tube also gets around the heat treating & brittle weld area problem.

[500Fool]

You didn't mention Oxy Geoff. Good as any of the others, was the only way Aircraft crome moly was welded for 50 years. Also has the advantage of heat treating as you go.