turbohead

Not a bad touch-up! However, what about the engine while out of the frame? Was it taken apart for an internal "touch-up", too...? (det finns några intressanta fallgropar när det gäller gamla Rotax-motorer)

It still is like before, every bike I have owned and raced over the past decades always have some condensation in the ignition case after a couple of runs. Even a boring ATV has the same kind of interesting, internal water production, like the jap one I use to collect firewood. Of course, there is still a breather attached on such a tool, even today.

Living in another country, with another approach to the current situation, it is hard to comprehend the affects of a more or less total lockdown like in the US. No metal bits to buy makes me sad and lonely....... Being a civil servant, I have been working from my home office since mid March and no change in sight. Apart from doing more video-sessions than ever before, it is not that bad (still not infected, of course...). There is also time for a few hours every day in the workshop, right now restoring an old Atlas Copco Cobra rock drilling machine, very odd solutions in there..... learning new thing about old tech every day. And using an old US Army manual as there are almost no documentation on these things left elsewhere. Looking forward to normal biking, soon!

Looks almost OEM, I hope it sound the way it should, too. Good, old fashioned work (no nasty tricks, like mine...).

If interested, please, have a look at one of the older threads here where I have attached some pics of how it's done to keep the "right look" and have a modern working exhaust.

Magnesium is OK for TIG welding, too. AC/DC, special rods and rather low amps, after cleaning and cleaning again, plus preheating and slow cooling. I case of severe damage, it is the only way out.

If you don't care about the rather specific look of the OEM part, about any mx silencer will work OK.

The Yamaha and Öhlins prototypes were very well built and tried under race conditions for a couple of years, but scrapped as they did not offer any real advantages to make up for the complex system and added weight. Nowadays, traction control systems and other electronic devises can offer almost the same benefits, at least without any weight disadvantage.

HFS is an excellent update for all old bikes, no matter if it is a SWM, Fantic or something else. If you can afford the PRO version, you enter a new era for 35 mm forks....

I must admit my enduro background make me a pretty lousy trials rider, still. Back then, when things got real tricky, speed could save your day if you were good enough and that is very hard to forget or get entirely out of your mind, so nowadays I still ride though sections too quick with too many dabs. Perhaps I should put the blame on my TXR engine and its primary gearing, not myself....? Seriously, you have a point. I'll begin with a 56-60t sprocket and see what that mean to me. Before summer I could even consider taking the engine apart, if things turn out your way. Maybe! (BTW no Telford this year, working a couple of weeks in Africa!)

I am using a swingarm from a later Aprilia TXR bike, as they were more common, at least in northern Europe. No problems to make them fit any '80s SWM bike, just make some spacers between frame and engine, then weld on a pair of shock mounts and a fitting for the rear brake. However, regarding primary gearing, that must be a matter of personal taste from b40rt, as the higher gearing works perfect for me. If not, why go to all the trouble changing clutch basket and so on when you could go for a 56-60t rear sprocket (if you really need to go that slow....)?? ?

I only have a rather low res pdf of this, but hope this may be what you are looking for. SWM 125.pdf

As I wrote above, sound level is (almost) comparable to stock. If you are in sensitive surroundings, don't go for a larger single outlet pipe or mx silencer. Regarding welding, I always use TIG for high stress or vibration exposed welds. You can get decent results using MIG, but the heat affected zone is bigger, the bead process is harder to control in detail, so I play it safe (or use my MIG to fix the parts and then do the actual welding with my TIG). Brazing with a gas torch (or TIG) is an alternative (but take some practice), specially on high alloyed steels.

RIP mr Pickering. Very sad news, indeed. I have been collecting parts and advice for a planned Bantam build over the last year or so and Jim was a goldmine of tips and tricks. As an expert always willing to share his thoughts, he was one of the very few real authorities.

I agree with b40rt on most issues, specially regarding the footrests. Use CrMo plate of the same thickness as the side plates and TIG the bits in place, pre-warm the plates and keep them warm, making the plates and welds cool down slowly (check for any sign of cracks after every ride during the first couple of weeks). However, regarding the midbox and rear silencer, a bit more work than b40rt suggest is well worth the effort. Cut them both up longitudinally with a thin disc and start removing whats inside. Repack the midbox with good hi temp insulation and reweld. Then, cut out everything inside the rear silencer and cut off the rear part as shown. Get a bit of perforated pipe or make one up, to fit between the inlet and a new wall in the rear part. Weld the front part longitudinally and do the same with the rear part. Then, weld the new wall in place in the rear part, as shown. Finally, fit the perforated tube into the front part and fill up with insulation before riveting the two parts together, then paint. I have kept the original twin outlet pipes on this one, but you can also try a bigger single pipe if you like (louder and less back pressure). The silencer shown here is almost as quiet as the original, but is a much better starting point when tuning for better power delivery all through the rev range (porting, ignition timing, carb set up and so on). Of course, you could use any modern mx type silencer instead, but a little visual cheating can be nice, or....?