Question about heating aluminum

[2003TRD]

I have a small crack in the bottom of a fork and was wondering if I heat the aluminum, to use one of those brazing rods, will it weaken the aluminum? Its not a big crack but I want to use it to also make some threads like they show on the HTS2000 website. I just dont want to weaken the structure at all

Thanks

 

[M3 Mitch]

If you mean motorcycle fork, I would either get a new part or have the thing heli-arc welded.

The solder that can be used for repairing say aluminum irrigation pipes is OK for strength but not nearly as strong as "real" aluminum.

Aluminum is subject to metal fatigue and unlike steel does not have a "threshold" stress level below which it does not fatigue.

If this is a part that can get you hurt or killed don't try to fix it with that "rub-rod" solder.

If this is an obsolete motorcycle application, you could search the boneyards, and/or look into firms like "Forking by Frank" who do custom work.

 

[2003TRD]

Thanks, the motorcycle fork is from a CBR 954. It frequently sees 170MPH on the racetrack. The part in question is a lower fork tube, it has the axle going through it and two pinch bolts. I must have cross threaded one of the pinch bolts putting it on, so stupid me I retap the hole one size up (8mm 1.25 to a 10mm 1.5) and put a new bolt in. I took it for a short ride and notice the side I tapped has a split starting from the side the bolt is inserted on. the split is only about 1/4" in length and I dont think it is a major concern as there is another pinch bolt right next to it that is fine.

 

[Bret Chase]

you've got a crack in your fork on your motorcycle and you don't want to replace it?

are you mad? seriously, the crack is just going to get worse and eventually ( or not so eventually at 170MPH) the fork will fail and you have a very high likely hood of dying because of it. you can't scr*w with cracks in aluminum, welding it up can cause a 50% reduction in strength compared to the parent metal.

-Bret

 

[olddognewtrks]

I agree totally with the 'REPLACE IT' crowd. It's been a few years since metallurgy class, but: Steel can flex, within its limits, indefinitely, while aluminum continually degrades to the point of failure. Once aluminum cracks, that area is junk, and the surrounding metal is probably near that. Don't fork around with your fork leg

-replace it.

 

[mechtech]

That is not an area that flexes at all.
Heliarc it, then drill and tap to size.

 

[Kestas]

Don't repair it... replace it. Only with careful investigation would I even consider suggesting a repair. This is what I do for a living. In the aircraft industry, cracks are machined out and the metal is recontoured (blended) to prevent stress risers. But each part has a design limit to how much it can be thinned.

The fork aluminum is probably heat-treated (solution treat & age) for strength. Any heat you put on the part over 325°F will take away this strength.

This is a safety item. If you MUST repair it, take it to a place that professionally repairs aluminum wheels. They should have the expertise and know-how to add new metal to the damaged part and re-heat-treat it. It's a long shot... I doubt that they would even accept this type of work.

 

[Gary Allan]

Naturally anyone is going to recommend replacing it. If you want to try the repair route, just monitor it perpetually for stress cracks. Just take release forms with you to where ever you intend to get it worked on holding forever harmless any ancestors, desendants, trusts, estates, those living and yet to be born, assignents, associates, affiliates ...etc...etc..

I do this when I get "unconventional" work done on stuff. I wanted to keep my stock wheels on my jeep when I installed a hub (lockout) kit. The center hole was too small. The actual mounting surface was the "weight/stress" bearing element ..but the guy was nervous. So I gave him two copies of my "release form".

That said, I don't think I would travel 175mph on anything ..let alone patched up goods.