Straightening Bent Fins?

[mx250]

Straightening Bent Fins?

Has anyone Straightened Bent Fins on an MX250, or similar?

I have 2 fins bent, one on the head and another on the barrel, both very slight, 2-3mm. There's no pressing reason other than looks but can they be straighten easily and with minimal risk of snapping?

The Yammy alloy seem very pliable, some barrels, e.g. the Monty, I wouldn't even try as the allot seems too brittle. Has anyone had any experience? Got any advice?

[YZ360A]

Yes small timber wedges a few of them and you will have to move them around to suit from side to side of the fins.
Some you may have to leave in certain spots to rebend bent section back into place. 

And tap slowly slowly.

Adam

[LWC82PE]

YES easy done. i use a oxy/acet flame and very carefully heat the fins up then use pliers or something to bend the fin back. you have to be real carefull as alloy wont go red so you cant see how hot it is. you will get the hang of it though. practice heating alloy up by using a bit of scrap first so you get the idea of how much heat is enough. although ive never dont it, if your not carefull you can stuff things up and make a mess pretty easily with too much heat and the fin can just melt right away. ive had some really badly bent fins on TS barrells and i fixed them up really well

[firko]

I haven't done an MX 250 but I straightened some RT1 fins recently using a combination of the above methods. I used the wedges as Adam suggested they were made from steel. I also applied a small bit of heat using my butane soldering torch rather than the oxy. It worked perfectly and I'm about to straighten a couple of fins on my Ducati the same way.

[paul]

weve just done some on a maico barrel  same method  heat ,wedges  gently gently no worries

[maicomc490t]

As any Maico guy knows the fins were either prebent at the factory or they sort of curl up over time all by themeselves?

Owning a few of the beasts from West Germany that I do, I have developed a flair for fin straightening and offer my tips but use them at your own risk, lol!

Before you even start thoroughly degrease and pressure wash the barrel to minimise all the drool causing problems and once clean check for cracks on the affected fins. There is no point attempting to straighen a half broken fin unless it is welded back together at the fracture site or the whole thing most likely will end on the deck.

To ensure you have a firm grip on the barrel I clamp a slab of 4 x 2 timber into the vise and then clamp the barrel onto it using sash clamps. Of course if you don't have a vice the timber can be clamped to anything you like so long as the whole deal is secure.

Using an old tyre lever GENTLY apply a GENTLE load under the bent fin while CAREFULLY applying heat over the bent section of the fin/s concerned on the opposite face. You will feel the lever starting to have an affect as you apply the heat as the fin softens. At this stage don't over do it and apply heat to the areas that are bent only. The fin will generally behave like plasticine and go right back to it's origin undamaged position.

I use oxy because its easy to get good heat in quickly and set a neutral flame that is not burning too agressively. Firkos suggestion of butane makes a lot of sense as well (see below). It's cooler and most importantly most guys at least have an LPG set up.

With some practise you will soon do it like a pro but remember that the cone of the oxy flame is burning at around 3000 degrees C while aluminium begins to melt at approx 650 degrees C - you don't have to be a rocket scientist to know what an overzealous application of heat will do to you cylinder so just go SLOW.

Hope this helps a little,

See you at the back of the pack in 08