Repairing Heads and Cases

[graeme]

There's a thread going re a 350 head that's possibly not repairable.

I've had heads and cases welded up to repair broken fins, cracked heads and such.
Any large welding repaires that have been done I have asked that the piece be oven heated before the welding was done. Then let cool slowly before any machining was done to the repaired part.
Question,
How much welding heat or area can be done without softening the casting to a point that it will need re tempering if that is the correct term?
I've seen pictures of a head that Eldert had bath tubed that had a fair amount of fill added to the combustion area.
If the original casting requires tempering or heat soaking to regain the components hardness, how is that done?
I hope this makes sense?

graeme

[double diamond]

Aluminum castings are heat treated to gain strength and hardness. In the heat treating process, the casting is heated to a temperature that is very close to the melting point of the particular alloy, then quenched to rapidly cool. Secondary process of additional heating/cooling cycles are often employed to impart specific qualities to the finished part. Whenever aluminum is heated above about 350 degrees F, it affects the heat treating to some degree. Welding, which by its very nature takes the material beyond melting point, leaves the aluminum in dead soft condition in the heat affected zone. The heat affected zone will extend beyond the actual welding repair depending upon how much of the surrounding area is heated above 350 degrees. Welding cooling fins or even features like intake or exhaust manifolds will result in satisfactory repairs since these are not as dependant upon the mechanical qualities of the material in their function. Also, heating peripheral features will not induce stresses in the part that would be encountered by welding areas in the center of the part such as the combustion chamber. Welding repairs to areas of the cylinder head that will require machining and an interference fit (such as valve guides or valve seats) will result in poor mechanical integrity since the soft material will not maintain the interference fit for long. This is the “by the book” answer. Of course there are many accounts of welding repairs that will apparently defy this information, just depends upon what you want to believe. I’ve never read any accounts of re-heat treating a casting that has been welded, but it seems the process would warp the casting to the point that bearing bores, valve guides and valve seats would all have to be re-machined, let alone not knowing the actual chemical makeup of the alloy such that proper heating to near-melting-point can be achieved. There is a company that specializes in casting repairs: http://www.jandjracingltd.com/Castingrepairs.htm. They appear to be quite experienced in the situation you’re facing; might be worth inquiring with them. A desmo head is a horrible thing to waste. Matt

[joe46ho]

"A Desmo head is a horrible thing to waste"

Amen, and I have never heard of "re-heat treating" Aluminum castings either...Not that it wouldn't have its uses in certain applications...
Before we get too far into this though, can we see some pictures of the head in question ? the better the pictures, the better the feedback will be from people on here that have had castings repaired. As valuable as Desmo single and Bevel twin heads are it would almost have to be broken in half before i would call it "unrepairable" and even then I would probably weld it together, put it on the shelf, and call it Italian art...

Joe

[LaceyDucati]

Hi all
I've had a fair amount of experience repairing and modifying These heads by welding. These castings may well have been heat treated during production, but my experience is that welding them doesn’t effect them to a point that makes them unusable. I have not noticed much change in the machinability after welding so the changes are maybe not as significant as with other alloys. Certainly welding more modern Japanese cases is a different kettle of fish!

There is always an expert who will tell you that you "can't do that" and give you a metallurgy lecture...... But I've not let these people hold me back! Basically you can do nothing and achieve nothing or you can think about it and have a go! With welding you are always going to get distortion and stress, it's just a matter of managing and correcting it as necessary by machining. Pre heating as has be mentioned is must for all but very minor repair, but even then it will limit the chance of stress cracking after cooling or in use. Contrary to the rules I use 5 percent mag wire as I find it gives you a harder material to machine and maintains fits etc. 5 percent silicone the usual wire for castings I have found to give a softer "chewy" weld material. I have carried out the following sort of repairs: exhaust thread repairs, rebuilt "bombed" combustion chambers, welded up guide bosses, filled plug holes after failed repairs, rebuilt valve seat recesses, stitched on broken fins and carried out some fairly radical complete re modelling. I am just listing these to help give you an indication of what is possible if you really want to and you are in the proverbial! Most of the time you have nothing to lose by having a go, or finding someone else to. I must add I'm not a welder and I get away with it!

As for welding fins onto a cylinder, a word of caution. Unless you are just welding at the outside edge for aesthetic purposes, anything else will almost certainly in my experience result in pulling the muff out of round. After welding cylinders they should be checked carefully for distortion and honed true if necessary. An oversize liner will then be necessary to maintain the correct interference.

The following are some pictures showing repairs etc, I'm not good at remembering to take stage pictures, but here are a few.

IMG_2093 (1024x768).jpg

exhaust before3.jpg

IMG_2224 (750x1000).jpg

exhaust after.jpg

IMG_5717 (1000x750).jpg

I may post some further pictures if I find any more relevant.

Hope this helps

Nigel

[graeme]

This is a matched pair of very late DM450D cases that have (I assume) been sitting on a concrete floor for a long time.
The left case has some holes and a lot of pit craters that don't go right through.
The rest of the case is in good order.



This is the main reason I asked the original questions regarding welding.
Thanks for your answers.

Graeme

[Thevin]

Hi all
I've had a fair amount of experience repairing and modifying These heads by welding. These castings may well have been heat treated during production, but my experience is that welding them doesn’t effect them to a point that makes them unusable. I have not noticed much change in the machinability after welding so the changes are maybe not as significant as with other alloys. Certainly welding more modern Japanese cases is a different kettle of fish!

There is always an expert who will tell you that you "can't do that" and give you a metallurgy lecture...... But I've not let these people hold me back! Basically you can do nothing and achieve nothing or you can think about it and have a go! With welding you are always going to get distortion and stress, it's just a matter of managing and correcting it as necessary by machining. Pre heating as has be mentioned is must for all but very minor repair, but even then it will limit the chance of stress cracking after cooling or in use. Contrary to the rules I use 5 percent mag wire as I find it gives you a harder material to machine and maintains fits etc. 5 percent silicone the usual wire for castings I have found to give a softer "chewy" weld material. I have carried out the following sort of repairs: exhaust thread repairs, rebuilt "bombed" combustion chambers, welded up guide bosses, filled plug holes after failed repairs, rebuilt valve seat recesses, stitched on broken fins and carried out some fairly radical complete re modelling. I am just listing these to help give you an indication of what is possible if you really want to and you are in the proverbial! Most of the time you have nothing to lose by having a go, or finding someone else to. I must add I'm not a welder and I get away with it!

As for welding fins onto a cylinder, a word of caution. Unless you are just welding at the outside edge for aesthetic purposes, anything else will almost certainly in my experience result in pulling the muff out of round. After welding cylinders they should be checked carefully for distortion and honed true if necessary. An oversize liner will then be necessary to maintain the correct interference.

The following are some pictures showing repairs etc, I'm not good at remembering to take stage pictures, but here are a few.

IMG_2093 (1024x768).jpg

exhaust before3.jpg

IMG_2224 (750x1000).jpg

exhaust after.jpg

IMG_5717 (1000x750).jpg

I may post some further pictures if I find any more relevant.

Hope this helps

Nigel

That's some nice work...

[LaceyDucati]

Graeme

I think as you say this damage occurs from sitting on a damp floor. Casings are a bit tricky, personally I would just aqua blast the cases and live with them. I've seen them like this and on the inside as well, you are never going to make them look perfect again and trying to by welding will lead to a lot of distortion. Small localised repairs are all okay on cases, but beyond that distortion is a real problem. Being thin wall they will pull even with preheating and clamping. As these cases are not unusable you could end up worse off trying to tart them up. If they leak the odd hole hole sealing wouldn’t be a problem.

It is possible to mix and match casing halves with a bit of machining. The cases were machined as individual components on multi spindle machines and until a pair were put together at the factory after this process, they were not a matched pair. They then machined the cylinder mounting face, bore, etc for the cylinder to locate and after this the casings became a pair and were marked accordingly underneath. Therefore if you put together an unmatched pair you will find steps on the cylinder mounting face and in the bore. If you then skim the bore and face true to the mains and average out any other errors you will end up with a usable pair. I've done this on race bikes and even fitted a right hand 4 speed casing to a left hand 5 speed casing. In racing the left hand cases can occasionally split through the mains and right hand cases can be badly wrecked by chain failures on flogged scramblers etc. Therefore matching halves is a great way of resurrecting otherwise scrap cases.

Finding a left hand 450 casing might be difficult as they are sought after for racing. All cases are getting rare these days, therefore until someone stumps up to make some more, we should all be as sympathetic and as careful as possible! Hence why I seek otherwise scrap heads to start race heads.

Best Wishes

[graeme]

Hello Nigel,
Good advice, I'll just have the holes welded and leave the rest alone.
What happened to the factory molds? Do they still exist?

Graeme

[Sam]

I have welded many two stroke heads to change the combustion chamber shape without any problems,I have also rescued a set of BSA B50 cases where the rod broke taking out the front engine mount on one half. I had a spare B25 case which the missing part was cut out then matched to the B50 case and pre heated being a thick part and welded.

Looking at your cases Graeme I would recon the perosity would be deep into the alloy and would give a poor/contaminated weld, if you do attempt to have them repaired bolt the cases together prior to attempting the repair this will help reduce warping.
p.s. that was done to the BSA cases before I welded the mount in place