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Pro 04 Exhaust Fire


jordan80
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The middle exhaust box of my 04 250Pro seems to have caught fire! At first I thought the crank seals had gone by the amount of smoke being produced, but during disassembly I found the middle box to be blocked and small bits of aluminium came rattling out. I tried blowing through it but it's completely blocked with the sound deadening fibre. (Yes I did have a big black circle on my face. TE HE)

Gasgas UK want

Edited by jordan80
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They are normally a perforated can inside an sheet alloy can. Often the perforated can gets oil-soaked or sodden. It sounds as if the oil has court fire and the two cans have become separated (or one has melted). Nothing is lost if you open it up so file all the welds off and see if it can be repaired.

Don't forget to check to see if it has melted the air box!

Ralphy

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They are normally a perforated can inside an sheet alloy can. Often the perforated can gets oil-soaked or sodden. It sounds as if the oil has court fire and the two cans have become separated (or one has melted). Nothing is lost if you open it up so file all the welds off and see if it can be repaired.

Don't forget to check to see if it has melted the air box!

Ralphy

I've seen modified mid-mufflers that have a large retangle cut out of the back and then re-welded after messing with the internals on factory bikes. That way, you don't have to worry about misalignment of the end collars where the headpipe and final muffler attach (before you try to take the rectangle off, take care to carefully grind off the rosette weld on the rectangle in order to release the internal brace from the flap). I would imagine that a perforated core (that would fit the internal diameter of the collars inside) could be cut in half, inserted in the mid-muffler and then tacked together, the muffler re-packed and the flap welded back on, taking care to rosette weld the internal braces. The "rosette" welds (small, round weld marks) on the outside of the mid-muffler (like the one that you would align the kickstart lever angle to) are at the ends of internal braces that connect the left and right shells in order to dampen the pulses that would quickly cause cracks in the muffler due to exhaust pressure/pulses.

You might try that first as those buggers are expensive.

Jon

Edited by JSE
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I melted down my orginal 04 mid muffler in a long run from work to home one day and it had been repaired many many times since so I decided to replace it. I went with the 2003 mid muffler which is steel and was cheaper. Highly recommended. Direct bolt on. Yeah it was a pound heavier but i figure i would just skip mc donalds that week and it would be a wash. I would rather the mounts not falling apart on me and have the luxury of steel. ;)

--Biff

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  • 3 weeks later...

Many thanks for the advice chaps. I cut a square out of the side and found just packing material blocking the thing. The perforated tube? had completely melted into small aluminium blobs rattling around in the bottom.

A steel version is only slightly cheaper but still the wrong side of

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Many thanks for the advice chaps. I cut a square out of the side and found just packing material blocking the thing. The perforated tube? had completely melted into small aluminium blobs rattling around in the bottom.

A steel version is only slightly cheaper but still the wrong side of

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The middle exhaust box of my 04 250Pro seems to have caught fire! At first I thought the crank seals had gone by the amount of smoke being produced, but during disassembly I found the middle box to be blocked and small bits of aluminium came rattling out. I tried blowing through it but it's completely blocked with the sound deadening fibre. (Yes I did have a big black circle on my face. TE HE)

Bignose

Just curious, what oil mixture are you using to get enough oil in there to start a fire ?

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The fuel ratio is 70:1 . Thrashing it around a field chasing an 8yr old on a mx bike caused considerable heat to build up.

I may have located a secondhand item. If it doesn't materialise I will try to repair it using the great adice given here.

Many thanks

Bignose

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I've got a montesa so not sure if the gas gas is the same but i just repacked my expansion chamber!

I got a friend who is a welder which helped a lot. I cut the thing in half along the existing welds leaving half the weld on either side (aparently this makes it a lot easier to weld back together, rather than a straight but joint) I didn't cut though the connecting ends so as not to have alinement issues, but cut just behind then so they both stayed solid and on one side. Check with who ever is going to weld it back up so they can tell you the best way to cut it. You wouldn't even know that mine had been opened once it was welded back together.

Then spent a good hour cleaning it up (Petrol) worked best. Then repacked it. The same stuff that goes in your muffler. The packing is cheap and my bike sounds like a new bike now, i did but a new muffler on as well though. A lot better than 250 quid if you've got some one who can weld it for you. :huh:

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Just curious, what oil mixture are you using to get enough oil in there to start a fire ?

I use 80:1 but after a lot of trials riding then a 50 mph run to work this happens. Not just with gasgas but i have seen it on a 315 r as well. I would rather that the oil in my mix not burn but to keep the piston well lubed. That unburnt oil collects. I choose golden spectro

--Biff

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