Combat head repair

Hi

I am going to attempt a repair on this damaged fin , and I was wondering if anyone had effected a repair with a satisfactory outcome
Without any song and dance to a similarly damaged fin, and would like to share!



Cheers J

Re: Combat head fin repair

I have done very similar on one of my Guzzi heads, and quite a bit worse on a few brit bikes. On the Guzzi, I realigned it with a packer between the next fin. Gouged out a groove with a burr to prep the edge and then just mig'ed it as that was all we had at work at the time.
Depending on the length of weld, do several tacks then weld between each tack and allow to cool - don't want the valve seats dropping out.
Filed it flat rather than using a grinder as that can embed muck leading to inclusions in the aluminium and make any subsequent welding a bit more difficult, should you need to fill any low spots.
Seasy.

If its a mid fin, it can be easier to cut the others off for access so you can get a decent bead on and then repair them back. Works fine if you have the broken bit, or an otherwise knackered head to donate the fin.
I have done it, again with a mig, just building up a bead along the broken edge and letting it completely cool. And repeat until done. Dress to shape. Can be fiddly.
This can be a good plan when you are doing foreigners, just keep it under the bench.

I'm sure tig would be neater, but we only really did heavy stuff so there were dozens of mig sets around. Anyway you would dress it either way.

Re: Combat head fin repair

Not had that problem, but if it were mine i would suck up to the best TIG welder you know (alloy) and go from there... Unless of course you know where there is a MIG set up for this "fine" work. Doesnt need much weld on it to hold it secure forever...

Re: Combat head fin repair

Hi
Sorry guys the fin isn't broken off ,it's been forced up on the head side and broke the barrel side . I want to fix it without busting it off. olChris suck up to a welder..........it looks worse in the flesh , I only have map gas heat. Cos if I do bust it off I'll need those tips aforementioned.


olChris if reading this saw your carb question post, priceless !!!

Re: Combat head fin repair

Of course if it all goes to pot....I do have a decent and clean bare Combat head I would sell you for a fraction of the price of a Full Auto

Re: Combat head fin repair

Hi
Was doing my cracked fin tonight. Heated it wedged it grooved it , filled it. Obviously did not get it right it seemed to go back to its original position. I have been told you can't shrink ally but you can stretch it maybe this is the problem.

It's either going to need a couple of ally weld tacks or plastic metal to get the shape.

That is like putting a sticking plater on when you've just cut off a leg!

J

Re: Combat head fin repair

my fin repair

Re: Combat head fin repair

Absolutely spot on buddy , you made a fine job, I take my hat of to you.

J

Re: Combat head fin repair

the 2 fins are actually welded together, so it went one as one piece.

Re: Combat head fin repair

Thanks for that ,I was scratching my head thinking how did he do that. It's a great looking job. I'm going to get that fin to sit down , it just looks untidy as hell.

Cheers J

Re: Combat head fin repair

Madass140 wrote:

the 2 fins are actually welded together, so it went one as one piece.

Click to expand...

So, are you saying that the lower fin in the repair is just hanging under the upper one that is welded in place? That would mean that it is not welded in and would also not be contributing to the cooling of the head. I would think that it might vibrate against the head as well and make quite a buzzing sound.

Re: Combat head fin repair

That's the old girl ready for valves . Looks ok to me.





I do like that!

Re: Combat head fin repair

Back a few years I raced a much modified air cooled XR600R engine in Baja races. We welded larger fins on all the heads we ran to increase cooling. It was standard practice, everyone did it.
After welding we normalized the casting at 400F for 24 hours, then skinned the gasket surfaces and did the valve job. They ran a long time that way, the extra cooling and tighter squish band helped suppress detonation.

Re: Combat head and barrels

Cheers dave ,I'll get you to weld my next fin. Ta



Sticking these on the bat , I'm no liking the 828 shape of them but they are spot on otherwise.


The followers have been ground also.

J