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repairing broken cooling fin on cylinder
- kenrcruise
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repairing broken cooling fin on cylinder
I had a set of cylinders shipped to me several years ago. Otherwise in good shape, one had a 3/16 x 1 1/2 inch piece of cooling fin break off. I took it to a steel shop and was told it could not be welded.
Can anyone who has successfully done a similar repair advise me of the best way to proceed?
I am considering possibly using an epoxy that can withstand heat. Suggestions?
Ken Cruise
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Re: repairing broken cooling fin on cylinder
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- kenrcruise
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Re: repairing broken cooling fin on cylinder
Regards,
Ken Cruise
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Re: repairing broken cooling fin on cylinder
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Re: repairing broken cooling fin on cylinder
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Re: repairing broken cooling fin on cylinder
Chuck S.
Chuck S
- kenrcruise
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Re: repairing broken cooling fin on cylinder
I will ask a recommended welding shop to braze the broken piece back on. Elsewhere on this site I read of a procedure as follows:
- blasting prior to repair
-paint with high temperature semi-gloss
-heat the cylinder to 400 degrees F and gradually cooling after
Have you had experience along these lines?
Regards,
Ken Cruise
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Re: repairing broken cooling fin on cylinder
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Re: repairing broken cooling fin on cylinder
Ken,- blasting prior to repair
-paint with high temperature semi-gloss
-heat the cylinder to 400 degrees F and gradually cooling after
Apologies for not getting back to you sooner on your question above. I am not an expert welder and have only limited experience welding cast iron. That said I have repaired enough cylinders/heads with broken fins (not aluminum) to have some idea of what works and what doesn't and what's hard and what's easier. Also, I have NO experience with a "Powder Torch" as mentioned above (sounds really interesting!). There are really two parts to repairing a broken fin: either building up the broken area or attaching the broken (or replacement) piece back to the cylinder or head, and then finishing the repair so it will not be noticeable.
For small chips, building up with weld and then grinding/machining the build up area on each side to match the the surrounding fin is pretty straight forward, even on cast iron (make sure the cylinder/head is good and clean (blasting helps here) and very hot before you start. A hand grinder or disk grinder should make easy work of finishing the repair on the flat sides and matching the outer curvature of the rest of the fin(s) because everything is reasonably accessible.
For larger chips or significant breaks, things get a little more complicated. For one, getting a TIG torch into the area to be welded is really hard! There just isn't a lot of room to maneuver in between fins. It's easy to do more damage than good here. Second, cast iron is subject to lots of expansion/contraction when it is heated and cooled. As hot as you can get a cylinder in the oven, the weld pool you create when welding is quite a bit hotter and it is easy to finish a weld on a very thin part only to have a crack form even if you let everything cool very slowly. I have had cast iron cylinders repaired by welding (experts only here), but no one I have ever had do this was willing to "guarantee" they could complete the repair without a crack developing. A few came back with the replacement piece in place, but with a crack in or near the welded area. Good enough to run given there is no real structural requirement here other than to hold the replacement piece in place, but not ideal. Once welded, the flat sides of the repair need to be dressed and depending on how far the weld penetrated, you may "rebreak" the repair as you grind off the excess weld. (Again, welding deep between fins is VERY difficult because of the space requirement.) If the repair is deep into the fins, it can also be difficult to "dress" nicely.
Brazing on the other hand is much lower temperature (less expansion/contraction issues) and the brazing rod simply melts onto the surface and is drawn into the "seam" area between the base fin and the repair piece by capillary action. Preheating and slow cooling are still recommended, but done correctly, other than reblasting or a heavy wire brushing, very little finishing is required because there is almost no surface buildup of brazing material. And again, the structural requirement is minimal.
Probably more than you wanted to know, and just one guy's experience. Keep those worn out and damaged cylinders - they are great for making replacement fin pieces!
Hope that helps.
Chuck S
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