Repairing Spark Arrestor

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mcman56
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Repairing Spark Arrestor

Post by mcman56 »

I'm in the process of reviving not restoring a vintage motorcycle. The outer core of the spark arrestor has multiple rust through spots but from mount to inlet looks/ feels structurally sound. The end will have to support an internal tube but little strength is actually needed. I would like to make a decent repair that retains the official marking on the outside. I do not want to simply cut the marking off and attached it to a new piece because it may look like the spark arrestor portion was removed not repaired and the marking is an attempt to cheat. (California is very serious about spark arrestors.)

Are there any ideas on this? The ID is about 1.95 so I ordered a short piece of 2" exhaust pipe thinking I could trim it down on a lathe and get a force fit inside the arrestor. I could even drill holes and use screws or spot welding to attach it so the hanger bracket. (I have a mig welder but am not good with thin sheet metal.) It seems like some kind of solder or brazing could be used to fill gaps between the housing and old piece but I don't know what. My only heat tool is a MAPP torch and sort of doubt it would be hot enough for brazing this. Searching for low temp braze brings up that "weld to everything" aluminium rod that I have no experience with. Would something like that actually flow up and fill the rust holes for cosmetics? I could also just cut off most of the rusted areas. This was a 4 stroke so not oily inside. I was able to bead blast but it may not be 100% clean. Would epoxy be a better choice? Or, is my train of thought simply wishful thinking.

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liveaboard
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Re: Repairing Spark Arrestor

Post by liveaboard »

If you want it to look ok, you need to make a new tube.
You could patch the holes, maybe; but not to a cosmetically pleasing outcome.
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Bill Shields
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Re: Repairing Spark Arrestor

Post by Bill Shields »

Cut out the section with the marking...suggest a cut off wheel.

Make a new arrestor and cut out a similar section

Have a GOOD welder splice it in (let him make the cutout).

Grind it down and it will look like it never happened

This assuming that there is something to weld in the area of the 'marking'..until you get into it you really will not know.
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Jon W
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Re: Repairing Spark Arrestor

Post by Jon W »

Looking at the pictures… could you make an outer sleeve/overlay that covers only from the side of the bracket around to the underside of the lettering? Fillet weld (or pop rivet?) the perimeter of the patch with low temp alum rods and your MAPP torch?
Jon W
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Harold_V
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Re: Repairing Spark Arrestor

Post by Harold_V »

I'm having a little trouble with the idea that aluminum rod will adhere to steel. Am I wrong?

The exhaust system operates at elevated temperature. I suspect that the heat involved would not be in one's best interest if low temperature solder is used.

I can see how a sleeve might be applied as suggested, but it most likely would require TIG for assembly. Just thinking out loud, mind you.

H
Wise people talk because they have something to say. Fools talk because they have to say something.
Jon W
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Re: Repairing Spark Arrestor

Post by Jon W »

My mistake, I thought outer sleeve was aluminum.
Jon W
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mcman56
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Re: Repairing Spark Arrestor

Post by mcman56 »

The outside sleeve idea may work and may be more compatible with the size of material on its way. It may also provide a more desired repaired vs modified look.

The inner material is maybe 0.030 thick and the patch maybe 0.060. When using heat to get the exhaust apart, I could get a couple of inches red at one time with a MAPP torch. Is a red color hot enough for standard brazing rods? (I do some mig welding but have only brazed something once.) It would be nice to have something that flows relatively easy to fill and smooth.

This is the end of the exhaust. At full temperature, I'm guessing you could momentary touch but would not want to hold your hand on it so somewhere less than 200F.

They claim this aluminium stuff sticks to anything. Is there another type of lower temp process? What exactly is silver solder?
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mcman56
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Re: Repairing Spark Arrestor

Post by mcman56 »

Jon W wrote: Wed Feb 23, 2022 3:30 pm Looking at the pictures… could you make an outer sleeve/overlay that covers only from the side of the bracket around to the underside of the lettering? Fillet weld (or pop rivet?) the perimeter of the patch with low temp alum rods and your MAPP torch?
The outside sleeve worked out to be an acceptable option. Thanks for the idea. I can just hose clamp temporarily until I verify it runs OK. If I did want to weld such a thing, what would be the desirable process? Would bronze welding work out the same as TIG for this purpose? I have thought about buying more equipment but am not sure which. It looks like gas welding equipment has gone up in price while Chinese TIGs have gone down. My few attempts at TIG have not been that great so would you say gas welding is much easier to learn?
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Harold_V
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Re: Repairing Spark Arrestor

Post by Harold_V »

My thoughts:
TIG requires a little practice and is least likely to result in failure. You have superior control over the resulting joint.
It's very possible that you'd have trouble with gas, be it brazing or gas welding. When you apply heat to the two pieces, they're likely to expand at different rates, moving away from one another. With TIG you should be able to slowly apply multiple tacks that would avoid that problem.
You might also benefit by using the hose clamp while tacking to assure little to no movement by the split piece, which is most likely made from flat stock and will have a potential to expand open when heat is applied. The clamp would restrain it while the tacks are applied.

H
Wise people talk because they have something to say. Fools talk because they have to say something.
frankMCG
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Re: Repairing Spark Arrestor

Post by frankMCG »

Bill Shields wrote: Tue Feb 22, 2022 9:18 pm Cut out the section with the marking...suggest a cut off wheel.

Make a new arrestor and cut out a similar section

Have a GOOD welder splice it in (let him make the cutout).

Grind it down and it will look like it never happened

This assuming that there is something to weld in the area of the 'marking'..until you get into it you really will not know.
Hi and sorry for bothering you! Are there any suitable MIG welders for thin sheets similar to this situation? Which one would you recommend?
Thanks in advance
Frank
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Re: Repairing Spark Arrestor

Post by 318J »

Any mig welder that can run .023 wire or smaller will work in this kind of situation.
-Sam
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"Preserving the Past and Ensuring Our Future"
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