Straightening fins

[Seamus]

Anyone tried this? I have a set of barrels that have a few bent fins. I would like toi use these, but would prefer to straighten the fins before doing so.
I was thinking of heating them with a hot air blower (used for paint stripping, soldering etc) and then using a clamp to pull them into position. What's the chances of this working?

Anyone with a better idea?

Cheers

Seamus

[UKROBK7]

I used to anneal sheet aluminium by rubbing soap onto it and heating it up.  As soon as the soap turns black stop heating and let it cool down completely.  The sheet should then be annealed and easier to bend.  Whether this works on cast alloy I don't know - could do with trying it out on a cheap scrap head first

[Seamus]

Thanks, that could be useful information. I guess you used ordinary hand soap.

Unfortunately, I don't have a spare head or anything else to play with. I am not too sure of the grade of aluminium used by Honda, but I would not be surprised if it was an alloy of some sort made as cheaply as possible.

[K2-K6]

I think it's true to say that most castings don't take very well to being bent.

Sheet alloy is effectively forged (rolled through a mill to get down to required thickness) this gives it very different properties to cast when bending.

It's true what UKROB says that you don't want to heat it too high as it doesn't change colour like steel, so hard to judge how much heat you've got in it hence the soap as a signal.

I would say you've got to use more of a blow torch temp to get near effecting any changes.

Done quite a few reforming of motocross alloy levers using heat before (believed the good ones are forged) and they bend back easily. The method I use is to get some leverage in place and lean on it a little, then apply heat to local area and you can feel it start to yeald as the heat comes up. Heat needs to be aimed at the bend point.

Go REALLY carefully at it and just move it very small amounts if it yealds, leave to cool a little between attempts to avoid too much localised heat build up.

Clean it first and inspect for any cracks, if they are there it would probably snap at this point with most methods.

[Honda Brat]

depends on how bad they are bent?  I am in the process of doing a complete re-build on a CB500/4 engine.  I have/had some snapped fins and also some bent fins on both the head and barrel, the ones that were snapped I feathered in with a flap wheel, a dremel and hard work and the fins that were bent I used the shank of a large size screwdriver, almost the same size as the space in between the fins and tapped it through the bent fins until they were straight, no cracks no problems, once they have been vapour blasted the barrel will get a fresh lick of paint and fingers crossed once everything is buttoned up and in place you won't notice.

I did this on my Harley motor when I tore that down, same principal and no bother.