opinions on beat way to repair/replace cylinder fins

The machine shop I'm now part time at employees a main welder who has some crazy certifications related to various welding techniques and material.We have mig,tig,arc,oxy,and also do a fair amount of silver solder work.He is truly one of the most skilled welders I've had the pleasure of knowing.He builds low boy semi trailers,etc.,etc. and is a whiz at welding cast.
Any way I need to fix some broken fins on a 45 cylinder.I have extra cylinders I can rob fins from as they aren't good for much else.I'm hoping someone with actual first hand experience can suggest the best type of welder to use,the best welding rod,tig wire,etc.,or should I have him melt pieces of extra fins to use for the welds so the filler for the welds is the same as the cylinders.He's welded more cast then I can remember over the last 15 years or so.Having said that on such a small area should I have him preheat his work are as well as wrap the cylinders in welding blankets to slowly cool them.I'm asking here on the board as collectively the members know more then my employee on what works best for motorcycle cylinders.I build a bike every other year or so there but my bikes are the only ones they take time to fabricate parts for as it's a very busy shop and a money losing proposition to work on bikes.

I'm far from being a professional welder but silver brazing worked for me when I fixed a missing fin on my UL iron head - but everything must be REALLY clean, otherwise it will peel at the interface. If done well it would be very difficult
to tell where it was repaired. Preheat and allow gradual cooling. Maybe you should let your co-worker do this for you, since he is a welder. Good luck.
Karl.

My co-worker Roland is definitely going to be doing the welding I have him do all my critical welding.The crew trades work back and forth for one another and I just wanted to see what I was asking of him before I actually asked.On the silver solder I know he likes to use it a lot.I have several decent sized repairs to make.Should I bevel the edges of the fins where they will be welded together?What's the trick to welding both the top and bottom side of each fin?I know a quiz here but I plan to talk to him tomorrow about it.I think I've read somewhere,possibly on Matt Olsen's blog to weld on over sized pieces of fin scraps then machine them to match the surrounding fins.And lastly when I weld I usually blast the surface clean then wash the area with acetone.Does that sound acceptable to you?Thanks I feel a little better about having him do it now.I weld but have zero skill compared to him.He's even qualified to weld underwater,we're lucky to have him for only $32.00 per hour..........

I have never had a fin replaced with a donor piece that didn't turn out obvious as a repair, even when it was the original fin.

However, fins built up bead by bead and then carved to shape can be virtually un-detectable.

FIN.jpg

And they transfer heat properly, too.

Most pro welders prefer silicon bronze filler for cast iron, but occasionally only nickel will stick.
Since I am not a pro welder, I had tremendous success with old piston rings for filler!

....Cotten

Thank you Cotten your advice is highly appreciated and I'll pass the info along.To be honest I know he knows how to weld cast as well as anyone so I'm sure he has a "method" he uses.He is very highly skilled I just haven't even mentioned a word about this project to him yet.As I've been with the owner a long time the welder would do the job no matter how much work was involved if I told him I needed it done.I consider him a friend as well as a coworker so I tapped into this sites knowledge base for the details before deciding if I'd mention the job to him or not dependent on how labor intensive it was going to be.Thank you again..............

TIG WITH STAINLESS ROD

another vote for Cotten's method, with the proviso that grinding the back of the repair, or both sides if it's an intermediate fin, to get a good cosmetic finish is an awkward, time-consuming job.

It's perfectly do-able, but slow. I've had engine parts which have used it for quick-and-dirty repairs on racing engines where people tend to worry less about finish and more about producing a durable repair and covering it with matt black paint.

Whatever method your welder is comfortable with will work. I use weld build up method that was taught to me by someone that has used it successfully for years on very old vintage restos. It's the finish work that that makes the big difference. I use a 4 1/2" grinder with the wheel guard removed to get more ease of use. I wear heavy leather gloves to guard against kickback. I use a wheel to rough in and then I use several thin cutoff wheels stacked on the arbor, which gives some flex for the next step. After its all shaped I sand blast that area to even it out, then I glass bead all over or use coarse walnut shell, depending what finish I'm looking for. I like the look of the steel shot finish that Cotton uses. I'm going to try that.

"Whizzer " wheels turned slow are the key to carving the sides of fins.

Shaping the curve and edges is a matter of a big bastard file filled with pooltable chalk.
Character for the edges is added before shot-peening by beating with a coarse stone on a stick:

UNPOLISH.jpg

Bead or ALOX blasting after shot-peening provides a mill profile for enamel adherence.

Hard fillers like nickel or stainless take three or four times as much effort to carve as silicon bronze or cast iron filler.
But occasionally that's all that will stick to some castings (like '30 Chief heads.)

.....Cotten

Cotton, Thanks for sharing your methods. I now have some new stuff to try. To get the edges I have used coarse paper and a small rubber mallet.

Beachdog!

I found that beating upon abrasives tended to embed them;
Stones don't so much, and you can 'distress' much deeper, but you really have to vary your pattern on broad surfaces.

The pointy one is great for carburetors.

.....Cotten

Cotton,
You're right. I end up having to remove the embedded grit with a stainless brush, then a light blasting. Thanks again for sharing your secrets. I always pay attention to your words because you are not just a thinker, but you actually do stuff.