Clutch Casing Warped

[d250b]

Hi All,

Having had a welding repair done successfully to the clutch casing on my M190 Sherpa a wee while ago I undertook to get the same thing done on my new project (M121 Pursang). (Bultaco fetish? )

Unfortunately the alloy on the Pursang behaved rather badly; I understand that some of the alloys can be a bit porous and absorb oil over the years and this flares up and makes a mess of the weld?

Anyway the welding proved problematic and it was a much bigger job than it should have been. It appears that the heat has warped the edge of the casing and as you can see from the photo I now have a small gap, probably about 1mm deep and 5-6cm long on the bottom of the casing. I've had it on the bike with a new gasket and plenty blue gasket sealant but she leaks....so I'm really disappointed.

Just wanted to get some opinions on the extent of the problem; can this be remedied by putting the casing on a flat surface on a big sheet of emery paper and rubbing down/is there another solution/or is it knackered?? Would value some opinion/advice.

(Apologies if its not the done thing to ask about a scrambler in here but there doesn't seem to be the level of information out there about Pursangs as there is on the Sherpa or a source of knowledge anything like there is on this forum. Is there anyone else out there who has a Pursang in their Bultaco stable??)

Cheers

D

[bisby]

You could try some J B weld 2 pack adhesive, it sets hard and can be filed down.

Or have a bead of alloy weld put on edge but if you have had problems welding this may not be the best way?

[wherry]

Yup you could build it up with a 2-pack filler as above or maybe try Lumiweld. I must admit I haven't heard much at all about Lumiweld for quite a few years now but it still exists according to Google. We used to use it during vintage car restorations years ago. It's a low temperature 'welding' product.

[dadof2]

Agree with Bisby.

I would not try luminweld or its equivalent from ESAB, needs a fair bit of skill and is difficult on edges.

I would build up weld on the edge with TIG. If you use JB weld (which will work) scrape a small groove along the centre of the gasket face to help key it in place.

To flatten a gasket face I initially file it then use grinding paste on a sheet of plate glass.

If you can't find anyone in tour area who is a good TIG welder you could try Tony Baker on 01768 881 653. He is not far from Nord View where the world round is held

[2stroke4stroke]

I would expect a good bead of silicon seal between the faces to keep that oiltight.

[guys]

aluminium castings can contain impurities, which can make welding them a precarious job.

I would use something like this as some others already mentioned. The risk of it going bad is far less compared to welding.

I've used it to seal a crack in the clutch casing of my 159.

http://www.loctiteproducts.com/p/epxy_weld_t/overview/Loctite-Epoxy-Weld-Bonding-Compound.htm

Edited January 22, 2015 by guys

[lbhbul]

I would guess that the wet or dry paper fixed to a nice flat surface & lots of elbow

grease is a for sure way to get it flat.

A way of repairing Bull cases that has worked forever is a clean inside surface,roughed

up well, & a polyester resin & glass patch in place of welding when possible.

Wont fix your problem very well now, but in the future.

Larry

[pschrauber]

I had similar problems with my Bultaco both side cases had cracks, due to hits through rocks, here the clutch side from inside:

The welding was a nightmare ... as mentioned due to oil which came up during welding, anyway got a homogeneous metal layer again but not nice looking surface, still the logo hat some break outs ... here the rotor side:

Then I decided to tried out 2K metal modelling masses which is heat resistant up to 300°C. That stuff is mixed together is for around 5 minutes soft like clay then hardens quickly as hard as Aluminium. Th allied masses can be milled, grinded like metal. I could reform the missing parts and then mill grind excessive material away.

A second rotor side case had a bigger break out at the rear under the clutch mechanism:

I could remodel the missing parts with this stuff very well:

After the paint job they looked very well again.

I would recommend this - we call it "Knetmetall" - its btw. very price worthy ... you only should know in advance how much you need and

don't apply too much it is as difficult to process as metal. A rough underground - as already mentioned - is also important.

[twinnshock]

In my humble oppinion trying to bung the gap with various goo's just does not work. Provided the warp is not to big I would mount the cover on a milling machine and skim the face flat. You have to be carefull not to remove to much material as clutch clearance is not great. You should have on the M121 an earlier style cover that has a bit more clearance than the later shape. Quite interesting or challenging setting up and clamping but I have done this and it works. I might be biased as I have a milling machine in the garage.

And yes I have a Pursang in the shed. Based on the frame and engine number the 20th M120 built. So a genuine pre 74 bike.

Stuart

[paulc76]

In my humble oppinion trying to bung the gap with various goo's just does not work. Provided the warp is not to big I would mount the cover on a milling machine and skim the face flat. You have to be carefull not to remove to much material as clutch clearance is not great. You should have on the M121 an earlier style cover that has a bit more clearance than the later shape. Quite interesting or challenging setting up and clamping but I have done this and it works. I might be biased as I have a milling machine in the garage.

And yes I have a Pursang in the shed. Based on the frame and engine number the 20th M120 built. So a genuine pre 74 bike.

Stuart

agreed or lap it out laborious but worth it

[paulc76]

4047 filler rod can be better than the usual 4043 no use now but maybe in the future

[lbhbul]

Agree with milling,but as noted difficult to set up.

I made the mistake of having one welded (only because of polished 151 case) now we have messed up threads

for clutch adjustment plug! Luckily have a mill & lathe so can fix this mess (hardheaded).

So I wont weld anymore, to many covers to be had out there.

Fix the black covers as Patrik shows.

Larry

[dadof2]

To clean an aluminium case before welding, cut out the areas where weld metal is to be deposited then soak it in hot potassium alum solution overnight. Remove any non aluminium parts first.

For cutting out do not grind, use carbide burrs in a drill, dremmel or die grinder.

Edit - What I used to do was put car body filler on these vulnerable case areas before I rode the bike. It stops the damage happening and you just burn it off with a blowtorch and wire brush when its time to sell the bike.

Edited January 22, 2015 by dadof2

[sherpa325]

Trying to repair that gap by welding will create more problems than it solves, I would glue some sheets of various grades of emery paper as well as wet & dry to a flat surface[glass is great] and then work the case over the varying grades until it is flat. I am pretty sure there is enough clearance for the clutch. Worst case scenario you may have to make your own gasket out of thicker gasket paper to compensate, but I doubt it.

Cheers Greg

PS I have had all sorts of Bultaco aluminium alloy parts welded without any problems, the welders usually comment on the good quality of the alloy used.

[ask greeves]

To repair this sort of problem, it's important to firstly understand whats happened. My humble opinion is that during the welding process, that particular area, got so hot as to drop (wether inwards or outwards) out of true, depending wether it was welded from the inside or outside. We don't have a photo, looking at the area from inside the machined surface, so could be either ( drop in or drop out). I would put the job on its machined surface onto a nice thick steel flat surface (steel surface plate or similar) and heat the case approx an inch above the dodgy area...and let gravity and maybe a few gentle knocks just above where its being heated. I know this sounds drastic and there's many if's and but's, heat it to much and the aluminium will melt and the difference between making the metal malible and melting is neglible. This might get the job somewhere near, for repairing the machined surface, to accept a gasket that doesn't leak.