Broken Fin

[bishboy]

Took me a while to find where I had filed this 

This is not me but something I found a while ago, it's someone repairing a YZ465 barrel.  Thought it might be handy.



This first photo shows one of several broken fins to be repaired.



You can see I have already removed most of the paint and have cleaned and sanded back the affected areas. The plan was to weld up the fin by making multiple passes with the tig welder rather than weld on a fin from a donor cylinder.

Next the cylinder was pre-heated in an oven. Aluminium is a very good conductor and will quickly draw heat away from the weld and into the surrounding mass.  This can affect penetration and the time and energy required to puddle the aluminium at the weld site.

A concern was the rod compatibility. But good results were obtained with a general purpose aluminium rod I already on hand.                                                                                                                       
This next photo shows the first run of aluminium bead made with the tig welder.



After 3 passes it looked like this,



After several more passes, there is more than enough material to shape the repaired fin.



Next is the repaired fin after a little shaping with a grinder and hand file. There is still some work to do but I was pleased with the weldability of the cylinder and the overall result (after a little more work).

[kdx Geoff]

That's looks like a good repair. I'll look at welding when l need to take the barrel off.

[kdx Geoff]

Thanks to the swingarm bolt it took me a while to get back to this.

I'd just use devcon, & use plastic or something to shape until it hardens then dress it up with a file, coat of gravy all good.

Cleaned the break with brake clean and blew it off. Attached the formwork with ultra blue and let it set for a couple of hours.




The Devcon is quite viscous but still flows so the fin had to be level and then l had to resist the temptation to touch it for 24 hours 




Removed the formwork and gently filed the patch to the fin profile.
 


Apply paint.
l gave the repaired fin a quick rub with steel wool and painted it just to see how obvious the repair is.




If l had the barrel off l might go down the welding path but we'll see how durable this repair is. 

Thanks for your input oldstuff    I've blocked out some of the other comments 

Cheers

Geoff