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Bent fin straightening

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K2-K6:
The key to it is putting heat into the bend site, without which it won't move but crack instead.

No good just warming it up, resistance of the casting to heat can easily take possibly the maximum range there around exhaust port. You'll need to be above that to get any reliable effect.

Practice on something expendable as I've suggested above, you'll feel it go very easily when enough heat is there. As noted, it feels like Plasticine when it moves.

Blow torch with tbe blue tip of flame directly on the bend is needed. It'll dissipate almost as fast as you put it into the metal though, hence holding a lever on it while you heat to feel it move.

If you heat it and then remove the heat to bend it, then it'll cool sufficiently for it to crack. You've effectively got to do this "live"  blow torch is safe, you'd need more care with an oxy-acetelyne torch.

Grewth:
Thanks for the advice  !
One thing worries me,  I don't like the idea of heating up one end of the head while the other end is relatively cold.
I'm thinking that maybe this could cause the head to warp and the head gasket to blow.
I'm wondering if it would be better to remove the head and get all of it good and hot, before directing extra heat at the offending bent fins.
On the other hand,  with the head in situ, all the holding down studs are fighting warpage.
Damned if you do, Damned if you don't  ?
Maybe I'm over thinking this ?

Oddjob:
I'd say so.

DomP:
Id be interested to see how this goes, as I said I chickened out but if yours goes well I may give it a go.

K2-K6:

--- Quote from: Grewth on May 31, 2025, 12:47:34 PM ---Thanks for the advice  !
One thing worries me,  I don't like the idea of heating up one end of the head while the other end is relatively cold.
I'm thinking that maybe this could cause the head to warp and the head gasket to blow.
I'm wondering if it would be better to remove the head and get all of it good and hot, before directing extra heat at the offending bent fins.
On the other hand,  with the head in situ, all the holding down studs are fighting warpage.
Damned if you do, Damned if you don't  ?
Maybe I'm over thinking this ?

--- End quote ---

Apologies, forgot to write an answer to this.

It's effectively safe as you'll just not generate anything like enough heat to affect  it. It is more stable when clamped though rather than removed.

To clarify, using a small blow torch like a plumber's kit, you'll need to play the hottest part of blue tip right onto the "crease" line to have any effect.  Just gently leaning on the lever while doing that will show if there's enough heat to move it. Then it will go easily.

If it doesn't feel like that, plasticine/ pastry feel, then there's no point applying more force else it will definitely snap off. It defines itself, going if enough heat, leave it alone if it doesn't move easily.  More complex to put into words than the reality of doing it  :)

As I've indicated, any bit of scrap aluminum held in a vice with heat on it will give a reasonable feel for what you're after without risk. At least it'll let you make a decision before committed to the fins.

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