Cracked 2T Pipes

I can tell you this on all of my bikes I have had issues with fmf pipes cracking...when I switched to cpc I never had another issue with a crack... Likewise with procircuit on other bikes... I don't know the issue but it has been a reoccurring issue for me...my extensive study ktm 300 cracked, cr500 2 cracked, yz85 leaked where the fmf was attached... Procircuits... Nothing cpc nothing...

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I’ve tig welded many many pipes and I can say that if it’s cracked, it will crack again, in most cases it’s the metal actually failing from too many heat cycles, or stress risers and vibrations. Stainless will shine much longer here than chromed or coated steel. Also, even a crappy mig weld is a lot better than a good fusion weld. Gusset may or may not help, hard to say.
I welded one guys rotax aircraft pipe so many times it looked like a spiderweb of welds going all directions.

I haven’t owned a fmf pipe for a long time but back in the day the ones I had were not very well made.

That Has Not been my experience in 30 plus years of welding professionally

Norma Stitz said:

...... a crappy mig weld is a lot better than a good fusion weld.

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???????

If this is indeed what you think then you are not a competent / experienced TIG welder. Like anything else the difference is in the preparation and execution. Neither one will stop a crack from reforming if you just run a quick cover pass. You must remove all evidence of the crack entirely, not merely hide it under a weld. IME due to the purer metallurgical capabilities, and the ability to control every aspect of the weld, the TIG weld is a far better choice than any MIG weld. But ultimately it boils down to the skill, knowledge, and experience of the welder.

The Quote; "Garbage in, Garbage out" comes to mind. FWIW

If by "Fusion" you mean TIG without adding filler then that's your problem. Stainless is about the only metal that allows this due to how it flows in the liquid state. Steel and other metals do not allow this and with the topic at hand the resulting shrinkage will put too much localized stress on the repaired spot (without the appropriate filler being added) and will re-crack due to the increased localized stresses and the thinner resultant cross section.

When welding a crack it helps if you drill a small hole at the ends of the crack.

So I have 3 500's, one is a snow bike, one is a sand bike all ported out crazy with every mod I could make for power, one is a trail bike AF for singletracking, then I have enough extras to probably put together a couple more bikes. Anyway my sand bike runs a FMF fatty, my snowbike is currently on a Gnarly and my trail bike runs stock. I literally have a stack of over a dozen pipes that I go through every year or so, blow out all the dents, fix cracks, install gussets etc. It's my experience all pipes will eventually crack but there are things that make it happen much quicker.

Bad crank bearings will turn the thing into a shaker and crack the pipe quick. Loose motor mounts will have the same effect. Any serious tension when installed from bends or tweaks in the pipe will cause cracks quick as well.

The early stock pipes and FMF pipes were a single layer near the ignition cover, the later ones had 2 layers of sheet and seem to last a little better. My crack repairs are made with oxy/acetylene but I would tig em if I had accesss to a tig welder. I drill the end of the cracks, I plug the ends of the pipe, lightly pressurize and heat out the dents. I like RTV on the flange seal letting it sit for 24 hours before use and it seems to cut some of the vibes down. The rubber mount on the right side will sometimes add tension and needs modification mostly on the Gnarly's, I have a few PC pipes but don't run them as they don't create the power how or where I like it on the 500.

s.back said:

When welding a crack it helps if you drill a small hole at the ends of the crack.

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Yup, drill. Out of the stuff I have access to, I'd braze the thing with gas.

LoudHandle said:

???????

If this is indeed what you think then you are not a competent / experienced TIG welder. Like anything else the difference is in the preparation and execution. Neither one will stop a crack from reforming if you just run a quick cover pass. You must remove all evidence of the crack entirely, not merely hide it under a weld. IME due to the purer metallurgical capabilities, and the ability to control every aspect of the weld, the TIG weld is a far better choice than any MIG weld. But ultimately it boils down to the skill, knowledge, and experience of the welder.

The Quote; "Garbage in, Garbage out" comes to mind. FWIW

If by "Fusion" you mean TIG without adding filler then that's your problem. Stainless is about the only metal that allows this due to how it flows in the liquid state. Steel and other metals do not allow this and with the topic at hand the resulting shrinkage will put too much localized stress on the repaired spot (without the appropriate filler being added) and will re-crack due to the increased localized stresses and the thinner resultant cross section.

Click to expand...

mkay, well we can have a weld-off sometime but this wasn't my problem, just relaying my experience with tig and mig, which id be extremely surprised if was less than anyone here. To me a fusion weld means no filler.

Also, im not sure I buy that drilling a hole will help in a thin sheet metal weld like we are discussing. In those cases a proper weld will always be stronger than surrounding area and the cracks will happen other places.

I agree...of all the pipes I have welded up, I have never had them recrack at the new weld. maybe I will take a picture, I have at least a dozen stock pipes and probably a half dozen FMF, maybe one PC. They sit on a shelf in my garage and turn into a habitrail for mice....little suckers love those pipes almost every one has dog food in it when I pick them up.

It's hard to ever get as strong of a weld on a used exhaust pipe as when it was new. Not only from the metal being weak from use around the weld site, but also because you can't ever get the backside of the metal clean. As you weld it will keep pulling impurities up from the bottom side. If it cracks once you will probably have to plate it to keep it from happening again.