Regards Fins repair

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RussellFernandes
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Regards Fins repair

Postby RussellFernandes » Mon Apr 16, 2018 2:25 pm

I recently got a Cylinder Head a lot of fins damaged.. I was just wondering if any one has repaired the fins.. or could advice how to repair them.
I've also attached a pic of the Cylinder Head.

Thanks
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cmfalco
Holder of a Nylon Anorak
Holder of a Nylon Anorak
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Re: Regards Fins repair

Postby cmfalco » Mon Apr 16, 2018 6:28 pm

RussellFernandes wrote:I was just wondering if any one has repaired the fins.. or could advice how to repair them.
As a disclaimer, I've repaired and replaced fins, and I've brazed cast iron, but I've never done both simultaneously. That said, if it were mine I would approach it in the same way as the Al fins I've replaced, although with differences due to the nature of cast iron. However, if you've never done this sort of thing you should find someone with experience because it's not a job for a "first timer."

Cast iron needs to be preheated to quite a high temperature before brazing starts, and then cooled very slowly afterwards. The base of each fin needs to be prepared by grinding with a carbide burr, not with a grinding stone (which embeds impurities), then a fin is built up layer by layer to just over the desired height. It would be best to stop at that point, allow the head to cool (which will take the better part of a day because it has to be well insulated to cool slowly), then grind the braze into the shape of the fin. The reason this is "best" is the next fin will get in the way of access to the previous fin making it more difficult, but not impossible, to sculp it into shape.

However, doing it the best way is also the slowest, since the head would have to be heated again prior to the next fin, and so on, so several fins represent several days of just heating and cooling time. It certainly would be possible to shape the fins after all are finished, and if you have someone else do the brazing for you this is what would have to be done. A die grinder with carbide burrs and a cutoff wheel would be needed. After all of this you'd paint it black and the repair would be invisible to all but the closest inspection by someone who knew where to look.

I should add that the fins could be built up by nickel welding as well. Ni is stronger, but that's not an issue with a fin. Ni rods also are more expensive. Anyway, if someone has experience with Ni welding and insists on doing it that way the end result would be cosmetically just as good as with brazing.

I hope this helps.

RussellFernandes
Posts: 35
Joined: Sat Mar 03, 2018 1:28 pm
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Re: Regards Fins repair

Postby RussellFernandes » Mon Apr 16, 2018 7:35 pm

Thanks cmfalco


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