straightening a bent engine fin

[DogBunny]

Before and after.

Before and after.
This is something that I have wanted to try for a long time. The patient was an XT500 cylinder head.

I put the head into a 350 degree oven for 15 minutes. The idea was to get the whole thing good and hot and reduce the extreme temperature gradient and thereby reduce the risk of warping the head when I did the spot heating with the hand-held propane torch.
The head is sitting on an extremely high-temp dense refractory fiber board left over from when I used to produce ceramics, but I'm sure a wooden board what have worked.
The heated fin was straightened with simple prying using screwdrivers. The mistake I made was beginning with a thin square shank screwdriver, shown in second pic with the red handle -- the square shank dug in and left marks on the fin. Other than that, the procedure was easy and straightforward.
A little waviness is visible in the second pic. I tried to straighten the waviness with pliers, but that did nothing. If it really had to be perfect, I think this waviness could be eliminated by gentle tapping on the waves with a flat-headed metal drift while the fin was backed up on a metal plate and while everything was still hot from the torch. However, I am quite happy with the result as is. Looks very good from a foot or two away.

This could probably be done on an assembled engine, which is another idea that I have had for a long time. In that case, I would begin by running the engine until it was good and hot before applying the torch flame. Again, the idea would be to reduce having an extreme temperature difference between the whole engine and the spot being treated.

 

[Mailman]

Wow! Color me impressed! I would not have bet that could be successfully done. Aluminum or not, cast parts, especially old castings tend to be very brittle. Well done!

 

[gggGary]

Matches my results with clutch and brake levers, need lots O heat. Haven't done so well with wheels yet, mebbie an oven like you did would get me there.

 

[DogBunny]

I was very pleasantly surprised at how successful this was. Was anticipating the fin snapping at any moment. But, it was surprisingly soft. And, I don't think I got anywhere close to heating the aluminum until it started to "color."
It was doubly surprising because I was "shrinking" metal that had been stretched.
I've followed Gary's lead on straightening levers -- I think they need more heat because they are a lot thicker than a fin.

If I had to do it again, I would have placed a thin piece of flat metal between the screwdriver and the fin to spread the pressure when prying. Near the end, I switched to an extremely stiff putty knife, which accomplished the same thing.

 

[gggGary]

thinking out loud; duckbill vice grips.

 

[59Tebo]

DB,
My first thought was "...don't do it! It'll snap!..." But your results speak for themselves. Nice job! And, yeah, definitely duckbills. Something gradual, and straight. I will keep this procedure in the memory banks!...

 

[kshansen]

thinking out loud; duckbill vice grips.

That's what I was thinking too, have a couple pair of them. They work good for sheetmetal work so I would guess they would be good on the fins. The advantage is they push from both sides and you could leave them clamped on while it cooled down.

 

[xjwmx]

side of a wood chisel would give a nice broad width to push with. is shrinking like it had to a property of aluminum?