Bent fin on head fix?

[MrBultaco]

I have a bent fin on the head of my 650. If I break it trying to bend it back, can JB Weld or other be used to glue it back on? Picture shows a crack almost he whole length from underneath. I should leave it, but you know....
Thanks for any input.
Tom

 

[Jim]

You'd have to do some research to double check me, but I don't believe JB Weld is a very good heat conductor. Most epoxy's aren't. I'd say there's about a 100% chance it'll break if you try to straighten it.

 

[Mailman]

I can only tell you what I think I’d be inclined to do. It’s already cracked most of the way through. If you don’t address it, it’ll likely just fall off on the road somewhere. The depth of the fins there and the limited space, look to rule out a heli arc repair.
In my mind the best band aid fix would be to finish breaking it loose , grind off any edges that might’ve turned up , then grind a slight bevel, top and bottom, leaving the center contact spot intact. Then JB Weld the fin back on and then grind the JB Weld after it cures with a Dremel, back to NEARLY flush.
Just my idea.

 

[Jim]

I should leave it, but you know....

Like a scab that itches ain't it?

 

[MrBultaco]

Jim, I think it will break even if I heated it. I'll check for other epoxies that are better heat conductors.
Mailman, I thought doing what you said, but thought I'd check here 1st. Thanks

 

[Jim]

Jim, I think it will break even if I heated it.

The difference in temps. between the "plastic" and liquid (melting) state with aluminum is dangerously small. You'd need about 1000-1100F. And since the head is designed to dissipate heat, It'd take gobs of it. Think oxy/acetylene torch with a rosebud tip.
I'd definitely recommend against it.

 

[Paul Sutton]

Check out Aluminium solders or low temperature brazing. You will see them on Ebay and they do not require flux. Easier to do if the head is off. It will be important to choose the correct melting point i.e. not to high to avoid head warping and not to low so it drops off on a hot day. Peanut may have some advice here as he has used these products on his Lambretta and will know if it is feasible. Also search Youtube for demos of low temperature aluminium brazing:

 

[mrtwowheel]

I think I'd take a chance on bending it. Stuff a piece of wood, the right thickness, between that fin and the one below it for some support. Beat the thing, it will bend or break off. If it breaks off you could straighten, smooth, round the broken edge until it looks like it might belong there?

Scott

 

[MrBultaco]

I found a Loctite epoxy with a max. operation temp @ 350 degrees. How hot do these 650s get?
I don't want to take the head off for this.

 

[Jim]

For what it's worth Tom, Lycoming's overhaul manual allows for the complete removal of a head fin. And those engines run a lot hotter than our XS's. Up to 475F.
If it broke off, you could smooth it out like Scott said and just leave it. It won't hurt a thing

 

[Jim]

I found a Loctite epoxy with a max. operation temp @ 350 degrees. How hot do these 650s get?
I don't want to take the head off for this.

Looks like your fin is on the exhaust side. You'll be pretty close to that.

 

[MaxPete]

 

[MrBultaco]

It's actually under the right intake.
I think I'll just complete the other jobs this resto/mod needs and ride it. If it falls off, I'll deal with it then.
Thanks to all for your feedback.

 

[Jim]

Good choice.

 

[MrBultaco]

It's really funny. I've had this p.o.s. for about a year, cleaned the engine and bike 3-4 times with various gunks/brushes and never noticed it. A friend was over on Sunday and the 1st thing he saw was the bent fin!

 

[Jim]

and never noticed it.

Got a kid with a "red" bicycle?

 

[59Tebo]

If it runs, I'd just leave it alone, and run it. IMHO, if it falls off, it falls off. If it bugs you that much, during your next tear-down, find another head on the flea-bay and swap it out. Functionally, (or cosmetically) I don't think it's a big deal.

 

[xjwmx]

I would leave it alone as a study in self-discipline and vanity. Besides this is the kind of thing that isn't really going to look better when it's fixed, and nothing looks worse than a bad cosmetic fix.

 

[MrBultaco]

Got a kid with a "red" bicycle?

View attachment 121439

I wouldn't be surprised if the PO ran into his kid's bike in his shed. This bike has been neglected for 30+ years. It had a broken steering stop and lots of damage on the right side. Banged the left also.

This fix was purely cosmetic and I'll 'just' let it go for now.
Thanks again for all your input my forum friends...
Tom

 

[TwoManyXS1Bs]

This is the only thread I recall covering fin restoration.

http://www.xs650.com/threads/street-tracker-number-plates-and-fab-work-all-metals.47547/