Repair of broken fins on cylinder head

good luck mate. i await your results with bated breath. hope it works.

I bought a Lumiweld kit many years ago and found it the answer to all sorts of problem that I encountered when rebuilding a number of Nortons. There is a similar version around called Technoweld and probably some other brands as well.

I successfully used my kit to mend broken alloy brake and clutch levers, brake shoes where the spring hook had broken off but mostly for building up stripped threads in the crankcases and gearbox casings before retapping back to original size.

This low temperature welding process does have its limitations and I did find a few times that my plans for a quick fix went terribly wrong. The first big disaster was trying to build up a stripped thread on a 389 carb top. The carb just melted. Another non-event was trying to replace the mudguard stay boss on the bottom of a fork leg. The hot welding material just ran everywhere and burned holes in my bench top and boots. It is very difficult to build upinto a lump for shaping like you can with arc welding.

However, I was able to do exactly what you are attempting ie. mend two broken fins on a cylinder head. I first bought an old knackered head for a couple of quid to saw up for spare parts. The good head was then prepared by sawing and filing to give straight but angled edges reading for welding. The replacement fin pieces were also cut so that the joining edge was straight and also had a slight angle so that when mated up there was a small valley for the alloy weld to sit in before it solidified. Onceeach weld had cooled a lot of filing made the finish quite acceptable. Drawbacks of this processare- the joining material goes dark with ageing.You can not weld close tothe exhaust ports asnew joints will melt again when the enginegets hot.

I also found that plenty of spare rods were needed for each repair. Get at least 10 more as you will find they melt away very quickly. You must use a stainless steel brush to clean up parts before welding and preheating bits in a very hotoven will save a lot of expensive blow-torch gas. Have some form of container to catch any alloy welding drips otherwise you will find that splashes tend to stick to every other fin and are very hard to remove.

This is a classic 'practice makes perfect' activity. Good Luck!

Phil Hannam

Hi, I did as you and bought a `Lumiweld` kit from Frosts, I practised on a couple of scrap bits of ally over the bench and found that, with perseverence, I was able to weld with the kit; the more you practise, the better it gets. BUT when I came to attempting the big stuff, ie an inner primary chaincase off a Mk111, I placed the part in the oven to pre heat it, thinking that would save time, effort and butane gas for my `camping gaz` blowlampbut I too found that the big parts drain away heat faster than you can put it in, and I eventually gave up and took the chaincase to an ally welder.

In conclusion my impression is that Lumiweld and other kits of the same type are fine for small parts but no good for large items that cannot be temperature controlled effectively.

So, there you have it!

Ken & Paul

You have both discovered that the big fixes are never as easy as repairing small bits and pieces. For items such as levers and brake shoes I found a single torch was ample but anything much bigger needed not only serious pre-heating but an extra torch or two to keep the heat level high enough to weld pieces up.

On my Commando crankcase andouter primary cover I had a big Paraffin blowlamp on max power heating each item from behind. Even then, I sometimes had to use 2 other gas torches to help get the heat level up enough to melt the rods. It did work but I had to be careful as the Paraffin residue tended to taint the welding area.

For fixing my cylinder head fins I made up a small oven from old bricks to help keep the heat in one area anddiminish the problem of dissipation.This time I had the use of a king-size gas torch with its head on a flexiblehose. This was positioned through a small hole in the brick wall and aimed at an area just under the fins. The head was pre-heated in the oven at 250*C for an hour before placing inmy DIYbrick oven.

Even using thick welding gloves did not prevent my fingers from cooking once I had all 3 torches burning and aimed at the head. Scratching at the welding, with the stainless steel rod,to release the oxide was very difficult but I did get a result that was good enough to file into shape once everthing had cooled. Two hours later!!!

However, I would not try this repair in the same way again. The reason being, firstly all the torches got too hot to hold,which meant that they were close to going bang! Secondly, I lost hair and foreheadskin from my bonce and burnt my fingers quite badly despite the gloves. Finally, I managed to get through about £10 worth of alloy welding rods. The local Mr Fixit only charges £5 an inch for his Alloy weldingand common sense said that getting twofins welded back in placeby him, would always be cheaper than a new garage or a funeral.

Previously wrote:

As part of my ongoing Commando restoration I am now tackling the engine, which needs alot of workdoing to it. One job I have been trying to resolve is the cylinder head which is a complete mess. Initially I did not think it was repairable but good used heads just dont seem available unless you have silly money. Firstly there are four broken fins the worst being the two topfront fins between the exhaust ports. I have had a couple of quotes for repairs but these seem very expensive, if indeed they can be done at all. So I have dicided to have a go myself. As the broken peices were not with the bike when I bought it I have had to fabricate them from anobsoletealuminium PCB enclosure I acquired from work. Ifirst made a template from card and then cut and filed the aluminium piece to the same shape as the template.Instead of trying to fit and weld the fin against the broken peice I decided to fit the new piece on top of the broken fin. My original idea was to drill and tap intowhats leftof the broken fins and thenscrew the new fins on top of the broken fins. However I have come across a product called 'Lumiweld', thisis amethod more akin tosoldering or brazing rather than welding. I got the kit from Frost Autos for about £20 inc post. The kit consists of five rods, cleaning brush and an abraiding rod. All thats required is a butane torch to get the work to temp and apply the rod like solder. Has anyone used this product to do similar work? and have you got any tips?

I will keep you posted as I get on and pass on any tips I may have. I dont know if I will succeed but I'm going to give it my best shot, after all I have nothing to lose in trying.

hello pual Please not not mess about with lumweld its RUBBISH send it back to Frost and get money back The only way Is to Have it welded By TIG welding As Alloy Is very trick to weld you have too be very skilled need to weld it with TIG welded thats why its expensive if you try doing it your self you will end up ruinging the cylinder head all to gether So Stop MESSING About Get Done right with the guys who have got the know how ? OR buy a aother Cylinder Head Yours Anna J Dixon