Heating a cylinder head

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laurentdom

laurentdom

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Hi All,

I've found a very good welder to repair 3 broken fins near the right exhaust port, but he is not experienced with our vintage motorcycles. After a test on the donor head, he tells me that to avoid tiny cracks around the welding area, he will have to heat the whole head up to 300 Celsius degrees.
I'm a bit concerned about the impact on the valve seats and valve guides. Will they stay properly located?
The welder told me that he would prefer working on a nude head (i.e. without the valves and rockers etc.) but what I plan to do if I go this way is to leave the 4 valves in place so that they keep the valve seats under pressure and the valve guides in place.

Thanks for your thoughts about that.

Laurent
 
I'm no expert on this but 300C seems way too hot. To change guides, the workshop manual say 150-200C and from experience they come out and go in pretty easy at 150C. I've never changed seats but in reading about changing them in aluminum heads, it appears that 225-250C is enough for them to fall out. I would ask him to do 100C and if he can't do that, I would keep looking for a welder.
 
Whenever I weld fins back on I just heat the head a little
Then weld the fins back on or more usually I grow new ones
Never given a thought to the temperature
I think your welder may be over thinking it
 
Many thanks to you all for those quite helpful infos.

I'll ask him to follow your advices. Furthermore, the crack created by the test is located between the weld and the N° 7 nut hole in the fins which -to me- is far more risky than where the repair is to be made.

Cheers,

L.
 
Have you spoken to Bruno Perlinski in Lille?

Not on your doorstep I know, 800 km, but very experienced with Nortons!

If nothing else, he will tell you the correct pre-heat temperature for the task!

I will need to make the 450 km journey from here this autumn for fuel tank and frame work!
 
baz said:
Whenever I weld fins back on I just heat the head a little
Then weld the fins back on or more usually I grow new ones
Never given a thought to the temperature
I think your welder may be over thinking it
Click to expand...
Sounds a bit more like the guidance for welding a cast iron head?
 
SteveA said:
Sounds a bit more like the guidance for welding a cast iron head?
Click to expand...
Here's a combat head I've just welded, not finished yet
But when finished it'll be blasted
 

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baz said:
Here's a combat head I've just welded, not finished yet
But when finished it'll be blasted
Click to expand...
Coming along nicely.

I meant the preheating to 300C as per the OP's welder.

Isn't that more what you might do with an iron head?
 
SteveA said:
Coming along nicely.

I meant the preheating to 300C as per the OP's welder.

Isn't that more what you might do with an iron head?
Click to expand...
With an iron head I would heat it until I felt it was right
But no Idea what temperature that'd be I'm a bit to old school for that
But with cast iron I would tap it with a blunted chipping hammer and then wrap it in an asbestos blanket as it cools
 
Normal pre-heat temperatures for aluminum welding are 200 to 250 F, NOT C. 300 C (572 F) will definitely affect the heat treatment of many aluminum alloys. Lincoln Electric recommends a maximum of 230 F for aluminum pre-heat. Hobart and others recommend a maximum of 250 F, but no one that I know of calls for anything near 300 C.

On another note, repairs for a broken top fin at the front frequently have a problem with cracking around the holes for the 5/16" studs and nuts. I'm not sure why, but I've encountered that several times, most recently on a 750 head I'm currently working on. Pre-heating, use of the right alloy rod and patch material, and a series of short welds instead of a continuous bead seem to help, but that area really likes to crack.

Ken
 
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Thanks Gents for your tips and improving my knowledge of alloy welding (not that difficult, starting from zero!).

I will ask him to pre-heat the head at about 100°C, no more, and keep you all updated of the results.
 
@laurentdom

Without seeing pictures of the damaged area it's difficult to give a valid statement or suggestion.
I'm an ex tig weldor and certified IWE, having welded (as well as cast (tig brazing)heads) aluminum heads on plenty occasions and usually 90-130 C are more than sufficient for preheating.
With modern amplitude variable (not Just Phase percentage) professional (thus approx 300Amps) Inverters there is in some instances not even a need to preheat.
Never hurts though to conduct the welds with reasonable tack welds first coming in from both sides and depending on the weld length in pilgrim steps.
By far more important is that the proper filler gets selected, most of the time 4043 or 4047

Kind regards

Christian
 
Heli arc aluminum, no preheat.
Preheat cast iron, weld, cool slowly.
 
@wot

Helium is not very common in Europe besides in rather specialized welding shops.
For cast there are several methods recommended by the AWS although I prefer TIG brazing for reduced risk of tensions and cracking.

Kind regards Christian
 
Heliarc is an old term for TIG welding. When TIG welding was first developed, helium was used as the shielding gas. The term Helicarc is occasionally used as a generic term meaning TIG welding, even when the shielding gas is not helium.
 
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Job done and well done! First test ride today.

Considering your comments, the welder decided not to pre-heat the head.
He started to TIG-weld the lowest one where the bubbles you can see are typical of a poor alloy /casting quality as he told me.

Bad link removed

I plan to trim a bit the welds during the winter break (He recommended to use the lowest speed with a Dremmel to minimize the vibrations and induced risks of cracks).

Thks again for your support.
 
Last edited by a moderator:
laurentdom said:
Job done and well done! First test ride today.

Considering your comments, the welder decided not to pre-heat the head.
He started to TIG-weld the lowest one where the bubbles you can see are typical of a poor alloy /casting quality as he told me.
Click to expand...
Bad link removed
laurentdom said:
I plan to trim a bit the welds during the winter break (He recommended to use the lowest speed with a Dremmel to minimize the vibrations and induced risks of cracks).

Thks again for your support.
Click to expand...
Bubbling is a common problem in welding Commando heads. I've had the same sort of comments from a very good welder I used to go to, before I had my own TIG outfit. I don't know if it is the alloy or casting quality, or just all oil absorbed into the porosity of the castings. The usual solution seems to be just to keep burning out the contaminants, but that gets old pretty fast. But then I'm not a professional welder, so maybe it's my technique too. It really shows up in trying to weld in the combustion chambers. Might be all that baked in carbon. If anyone has a solution, I'd sure like to hear it.

Ken
 
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