Bent fin straightening

[Grewth]

Don't you just hate bodgers ?
Today I have drilled out the sheared off exhaust port stud that was holding me up.
Now ordered a M8 Helicoil kit which should get me sorted.
It's given me a chance to take a really close look at the head.
Obviously one of the previous owners was some species of Primate,  possibly a Gorilla.
Anyone got any tricks or tips for straightening bent fins without breaking them ?
I think that they're probably going to have to stay bent until the head has to come off. [ Guests cannot view attachments ] [ Guests cannot view attachments ]

[K2-K6]

One successful way (there aren't many) to re-bend aluminium alloy components is to heat locally while applying leverage.

If you can get a small flat lever in there (like an old bicycle one, thin and spoon shaped end) to get reasonably secure purchase, then use a blow torch to heat directly where the  bend is sighted, they will usually move.

You don't need much force else it'll snap. More feel by pressing on the lever and you'll feel it "yeald" as heat gets to threshold.  Its quite safe to try, if it doesn't move its not hot enough so don't lean on it like that.

I've always bent clutch and brake levers back to shape like this, in a vice with ring spanner over lever, play the heat on until you feel it go. It's genuinely very low force when you feel it moving though.

You could try for feel if you've an old lever to gently test the process and get your eye in before the critical fins. It is very gentle though to emphasise that, not much force but bring the heat up until it starts to "plasticine" and go where you need it.

[Nurse Julie]

Gentle heat and a wedge shaped piece of wood will help. But, old alloy is brittle and the fin may still break as those bent angles are quite acute.

[DomP]

I chickened out and left mine as a sign of a lived life and added character

[Oddjob]

I’d need to fix that, it would bug the hell out of me. I’ve straightened alloy and it’s doable, just don’t rush it.

[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]

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 ?

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.

[Grewth]

Thanks for that  !
At present I've got a full 13Kg bottle of propane,  and a roofers torch.
I bought that to remove the steering relay from a series Land Rover.
Maybe I'll need a smaller torch for motorcycle fins ?
Today I extracted the engine from the rust bucket CB750F2
Plenty to go at there, and then I've got the mystery of the K0 to K6 type exhaust manifold stubs.
Presumably fitted to accommodate the rotten 4 into 1 pipe that was fitted. [ Guests cannot view attachments ]

[DomP]

I'd get a mapp gas torch from Toolstation, runs hotter, mine came with three different jets with varying patterns which I use for plumbing in kitchens and bathrooms.