Cooling Fin Repair

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Cooling Fin Repair

Postby jOe » Sat Jan 22, 2022 9:06 pm

I have an OEM cylinder with a fin broken off. What’s a good repair method?
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Re: Cooling Fin Repair

Postby EKHKHK56 » Sat Jan 22, 2022 11:11 pm

Hello Joe. I’ve had good luck with a wire feed, prep everything than put the cylinder in the barbecue or stove and heat to 200. Weld tacks to position than stitch in with short welds about half inch. Weld on left then switch to right and so forth. Let cool slowly do not quench. Erik ps if no fin available mild steel plate with roughed up finish will work, or knock a fin off your neighbor’s Sportster for donor. :D
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Re: Cooling Fin Repair

Postby jOe » Sat Jan 22, 2022 11:45 pm

Thanks Erik; Grilling the cylinder at 200 I’m surmising is to get the impurities burned off. How long ?
I’m trying to locate a junk cylinder locally as a donor. compressor, lawn mower? Hmmm…
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Re: Cooling Fin Repair

Postby chuckthebeatertruck » Sun Jan 23, 2022 9:48 am

I never learned how to wire weld iron and don’t trust myself on thin sectionals. So, I usually use silver solder. Harris safety silv40 and safety silv flux. A turbo torch is borderline, but a small oxy/acyt set works for fin repairs.

Depending on number of fins, sectional thickness, size of break, and where on cylinder, I may or may not preheat much beyond the join. Small repairs I generally don’t but more extensive ones I heat the cylinder to “uncomfortable” and start from thinnest and smallest to thickest and largest fin. I do use a very hot high o2 flame cone to burn out impurities before dialing it back and fluxing for the join.

Cool it slowly. Stash it in a warm oven, bury in some sand, flip a pail and welding blanket over it, etc. Flux wipes off with hot water.

Check your bores after and hone as needed.

Fin repair is fun, really.

I also have used industrial grade epoxies. Works surprisingly well for sticking fins on and filling. I like lab metal for filling in any lines at the join. Some guys will flow more silver or even a small amount of pb-free soft solder to totally hide the join.
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Re: Cooling Fin Repair

Postby EKHKHK56 » Sun Jan 23, 2022 2:00 pm

Bring up to that temp and wait a couple minutes. It works very well, first time was experimental and with excellent results every time. Heating definitely helps remove solvents etc and mimics operating temperatures and mass the cylinders normally run at, and allows weld to take to the casting better. I’ve fixed a few dozen no problem. You want nice hot short welds, with beads that fill more than stack. Preheat repair fin also. I had a set of cylinders all restored, bore and valve job and went to install them and a fin fell off. It was goo bobbed with epoxy, I don’t recommend that! I have seen some silver soldered but solder doesn’t seem to hold the paint very long, nothing is like good old steel.
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