Straigtening bent front cylinder head fins

elefantrider

elefantrider

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I have a rare head with bent front fins caused by a previous owner not following the manuals correct removal instruction.
Interested to see if people on here have had good luck straigthening front fins without breaking them and what technique/tools did you use?
 
elefantrider said:
I have a rare head with bent front fins caused by a previous owner not following the manuals correct removal instruction.
Interested to see if people on here have had good luck straigthening front fins without breaking them and what technique/tools did you use?
Click to expand...
Elefant,
Jim Comstock straightened out a fin on mine without breaking it. I have no idea how he did this but it can be done.
Mike
 
elefantrider said:
I have a rare head with bent front fins caused by a previous owner not following the manuals correct removal instruction.
Interested to see if people on here have had good luck straigthening front fins without breaking them and what technique/tools did you use?
Click to expand...
Luck has nothing to do with it. They can be straightened. Seek the services of a TALENTED fabricator.
 
I've talked with a couple of talented guys who have had them break while attempting to straighten.

I really don't like looking at front bent fins. Am thinking heat and using something like this.


Straigtening bent front cylinder head fins
 
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Tricky stuff .
I have an 850 head with a welded back on piece of fin , where I assume the head was dropped on a floor by the previous owner .
It's a good weld , then it was filed down on both sides of the weld . You can barely notice it .
 
SteveBorland said:
I was always told to use a bar of soap - apply to the part to be bent (or de-bent), then heat up until the soap turns black then go for it.
Works with brake & clutch levers, never tried with a head fin though.
Click to expand...
Taught the same thing when learning to weld : also , for Ally TIG welding, when pre-heating-(-but basic-) - spit on it and when it sizzles it’s good to go…🤞
 
SteveBorland said:
I was always told to use a bar of soap - apply to the part to be bent (or de-bent), then heat up until the soap turns black then go for it.
Works with brake & clutch levers, never tried with a head fin though.
Click to expand...
Well here’s a strange-but-true story…

I once straightened a brake lever on my GSXR750.

It worked fine all summer.

Then one very frosty morning in winter I backed the bike out of the shed, over a ‘bump’ at the door and back onto the concrete. I laid it on its side stand with a bit of an accident ‘jolt’ and turned to shut the shed door etc.

I heard a tinkling sound behind me. The bloody brake lever had broken in two and fallen on the floor.

It obviously had a crack that had gotten weaker and the frost and the jolting had finished it off.

Naturally, I was horrified at what cudda happened !

I don’t straighten alloy brake levers any more…
 
elefantrider said:
I've talked with a couple of talented guys who have had them break while attempting to straighten.

I really don't like looking at front bent fins. Am thinking heat and using something like this.


Straigtening bent front cylinder head fins
Click to expand...
Find somebody that knows what they are doing
But If you attempt it yourself use a piece of wood
And as you heat the fin rub the wood periodically until it leaves a black mark
Then give it a slight tweak
Then heat again and repeat until straight
There are other ways to get the correct temperature including using soap etc but this works for me
 
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Never tried to straighten fins on a Norton head but have straightened them on Guzzi heads and barrels. I preheated in my oven and then used oak billiard table shims between the fins to stress the fins in the way they needed to go. I would preheat the part, tap the wedges in, heat the part some more and then allow to cool. I did this over several days to avoid putting a high stress on any fin. IMHO the secret is to move the al at a fairly hot temperature a little at a time, thus it is less likely to crack. I had several fins that were collapsed on each other and succeeded in straightening them so you can not tell now.
 
Hi I have straighten a few aluminum fins on my Manx head and barrel, also the fins on a Triumph T100r, as well as the fins on my TR250 Suzuki barrels, also straighten the handle bars on my Kawasaki ZX10 after a high speed get off, none of them have ever failed, yet :eek:.You just need to be slow and don't over do it, when you heat you need to wait till you can feel it move, under a light force, don't try to do it in one go, just do it easy but controlled. Ok forgot the Commando it had a broken fin and bent fins.
Another thing I was taught while at welding school was to coat the aluminum with soot from a carburising flame form an oxy set, heat till the the soot burns off and ready to weld or bend.
Burgs
 
Fast Eddie said:
Well here’s a strange-but-true story…

I once straightened a brake lever on my GSXR750.

It worked fine all summer.

Then one very frosty morning in winter I backed the bike out of the shed, over a ‘bump’ at the door and back onto the concrete. I laid it on its side stand with a bit of an accident ‘jolt’ and turned to shut the shed door etc.

I heard a tinkling sound behind me. The bloody brake lever had broken in two and fallen on the floor.

It obviously had a crack that had gotten weaker and the frost and the jolting had finished it off.

Naturally, I was horrified at what cudda happened !

I don’t straighten alloy brake levers any more…
Click to expand...
Ah, that's why God never intended bikers to ride in winter you see... :)
 

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