Broke a small corner of a cooling fin clean off

[RubNDub]

Oops. Got a little handsy while cleaning up my 1200's heads, and about a half-an-oreo sized corner of one of the cooling fins broke off.

It's a clean break, so surely I can weld the corner it back on. But from what I vaguely recall, it's probably ill-advised to "just weld it back on".

The fins (and head I guess) are cast-iron, right? So I'll need to pre-heat the pieces, and then do I need to run a specific type of wire in the mig? Sprinkle it with magic dust? Hum a prayer? Did I forget anything?

Would be nice to try and get that "stipled" cast iron look back on the seam too - if anyone knows of some clever tricks to make the weld look tidy?


Thanks for the advice!

[V8Nate]

I would say that one small oreo sized fin being broke of wouldn't hurt anything to stay missing. Im sure trying to weld it back on would be more work than its worth.

[RubNDub]

Hey Nate,

I tend to agree with you: The performance loss will likely be minimal. It just sticks out like a sore thumb. I'm not adverse to time spent provided I can do a reasonably good job.

[SCOTTRODS]

Leave it alone or take it to an Aerospace welder who has all the goodies to work with. There are little flap pieces (with anvils) available to "shot peen" the metal back to appearance sort of, but not so much for appearance, but for metal integrity and heat dissipation (all the little dings make for a larger actual transfer surface for heat to dissipate). I believe you might be able to shot peen with a blasting rig as well, but you have a bit more investing to do to get to that level... on the order of 10's of thousands of dollars... where the little flap peening things are a few bucks each (say 10-15 bucks or so... may be cheaper). They go in a die grinder, which if you are welding stuff... I kind of suspect you have a die grinder.

[RubNDub]

Asked around a bit more. It sounds like pre-heat isn't strictly needed given the thickness and application. Prep work (v-groove the pieces), cleaning and then straight to MIG. Slow cool-down was still emphasized.

ENiFe-CI aka "Nickel 55" welding wire was suggested, as the coefficient of expansion is a close match for cast-iron.

I also found this: https://www.mig-welding.co.uk/cast-iron.htm

The stippling can be probably be "simulated" with a ball end or other small carbide bit off a dremel I'm thinking High-temp paint for either all the fins, or just the section welded (with a good match) could work.

[Bruce2]

All VW cylinder heads are aluminum.

[RubNDub]

Bruce,

Is this in the specs anywhere? I simply assumed they were cast iron based on the "look"...

I would have expected aluminum to be too soft - given the forces from the valve springs and whatnot.

I'll pull out the shop manual to see if I can find any material specs.

Thanks

[Bad Bob]

4043 filler rod is used on aluminum castings (TIG). It’s also available in small spools for MIG.

[SCOTTRODS]

The stippling can be probably be "simulated" with a ball end or other small carbide bit off a dremel I'm thinking High-temp paint for either all the fins, or just the section welded (with a good match) could work.

Again, the "stippling" effect is for two reasons. One is to Strengthen the metal or surface harden it.(I may have the specific process wrong, but I stated it better above by Saying the metal's integrity)
The other reason is to create more surface area to dissipate heat. A dremel will defeat the Metal's integrity but likely *will* give you more surface area. It should not be based on appearance, but function.A dremel also removes some of the metal and may actually weaken the area and cause issues with hot spots... But this is your baby... if it's only about appearance, then dremel on.
Flap peening is an art in itself and requires the ability to test the flap application to an Almen Strip to identify the amount of peening needed and also to help set up the dremel/die grinder speed (which is critical to the correct peening procedure) Almen strips are a specific metal and thickness of it, that will curve due to the peening, at a specific speed for a specific time measured... Aircraft stuff. It's really not hard, but you can simulate the process without specificity to get a relatively close function and appearance al in one. The peening flaps are available as are the tools and Almen Strips. But I would likely get a flow control and put it in my air line and regulate the speed of my die grinder with it until I felt comfortable with the results on a test piece (I have some older heads sitting around still... they'd be perfect). Looking into flap peening strips just now, The little flaps are about 40-50 dollars apiece. that's a little piece about 9/16" x 1.25" with little peening balls affixed to the two opposite sides for clockwise rotation both sides hit the surface with peening balls. Anvils are pretty cheap or even something you could make at home if you have some materials and patience. Pack of 10 flaps = 400 plus dollars... not cheap in bulk.

[RubNDub]

Again, the "stippling" effect is for two reasons. One is to Strengthen the metal or surface harden it.(I may have the specific process wrong, but I stated it better above by Saying the metal's integrity)
The other reason is to create more surface area to dissipate heat. A dremel will defeat the Metal's integrity but likely *will* give you more surface area. It should not be based on appearance, but function.A dremel also removes some of the metal and may actually weaken the area and cause issues with hot spots... But this is your baby... if it's only about appearance, then dremel on.

Sure, a coarse surface means more surface area, means better cooling - similar to a sponge or porous rock. Makes sense.

What do you think of forgoing any messing around with a dremel or similar, and simply making a basic repair, and then painting the fins and other case components?

It seems like a lot of motorcycle enthusiasts do this, and I recall having seen some Indian and Harley motorcycles coming from the factory with the barrel fins painted.

Are the considerations different because the VW engine is in an enclosed space (less airflow than an expose motorcycle engine, say), or could painting be a good "middle ground"? I've seen a lot of good looking paint jobs done this way, but if it's going to put the engine at risk because it's going to drastically impede the engines ability to keep itself cool, I want to know.

[Bruce2]

What do you think of forgoing any messing around with a dremel or similar, and simply making a basic repair, and then painting the fins and other case components?

Just ignore all that "stippling" nonsense. On your repair it won't amount to anything more than a fart in a hurricane.
Get someone who knows how to weld aluminum and ask them to weld the fin back on. Don't worry about anything else. The alloy doesn't matter. Do not paint the cylinder head!!
Fix it and move on to the next project.

[SCOTTRODS]

when this thread was proposed it sounded like RubNdub wanted to do things as correct and solid as possible... Just putting the info out there in case someone else reads this thread and might get some in depth ideas on how to make the most correct repairs. The best will always be the best... just a patch will often do the job with minimally notable difference (in this case I agree with Bruce, but was offering up the more proper ways to do it for those who may be interested)

As far as paint is concerned... not a great idea unless it's a heat dispersant coating or something that doesn't cover the surface without the benefits of open air metal to air heat transfer. There are several makers of the proper products for that as well, but I'm seeing a trend on this and will not bother to go into heat dissipation coatings. Like I said beefore... It's your car... Your repair... and as Bob hoover used to say "You're the mechanic".