oldjohn

Thank you. Fairly easily fixed.

If by that you mean it's ugly then I'd have to agree. But all I have to do is fit a conventional stay rod and return spring to make it look fine. The areas where I usually ride have lots of long, steep hills and again, the brake is not good. It's bloody brilliant!

Sorry about the long delay in replying but here are a couple of pics. I polished the hub and if you stand back far enough, and it's dark, and you squint a bit it doesn't look that much different from a Bul hub. The backing plate was anchored with a 3mm thick P clip or strap; I'm sure there are neater methods but I didn't want to weld anything or do anything that wasn't easily reversible. The additional arm and spring was added as a temporary measure (about 2 years ago) until I could fit a hairspring to the original arm. I still haven't done this.... The stock Yam brake worked well, but I like to experiment so modified it further. I added an anchor lug (held by the two bolts near the cam in the photo) and removed the pivot pin opposite the cam. The cam now only works against the leading shoe, and this shoe pushes against the second shoe (via a floating bobbin) which in turn bears against the anchor lug. Basically it's just a copy of the servo style drum brake layout that was commonly used in cars. It just needs a very light touch - you can easily lock it up with two fingers on concrete or one finger on dirt. Still it isn't over-touchy and is quite controllable. I'm thinking about trying the same system with a Bul hub (using an iron liner) - this might give decent brakes but still retain the original appearance.

No worries Terry, I've always been happy with the bike and even more so now. It's never let me down even though I ride it nearly every weekend and it's given me a huge amount of pleasure.

Well there's been some progress... I'd been thinking it'd be nice to try some longer shocks to see what effect it had on steering, but didn't want to spend a lot of money on good shocks without knowing the effect of the change in length, so thought I'd buy some cheap, longer Chinese shocks. If the extra length turned out to be a step backwards I wouldn't have lost much money but if it turned out to work well I could then buy something decent in the same length. Anyhow, I bought a set of GX Motors shocks, 365mm long, from eBay. These actually don't look too bad on paper - for a start they have a longer stroke than most of the other Chinese jobs, a fraction longer than the old Betor experts I used previously. Many of the Chinese shocks use the same short body and adjust the eye-to-eye length by using a longer rod-end mount. So many of them end up with a shorter travel than you'd expect. The GXMotors shocks have a reasonable travel length and they also use a 12mm rod which should make them a fair bit stronger than the somewhat flimsy Betors. I was expecting them - as a "budget" shock - to be underdamped and if so that'd be fine - I liked the old Betors best when they'd lost a lot of their damping effect. That's not how they turned out however... The ones I bought were listed as being suitable for an early 125 Elsinore and I thought they wouldn't be a bad match with the Sherpa as they both have similar weights. The reality turned out to be somewhat different when I got the shocks - there's no way these would have worked at all on an old CR125. For a start they were fitted with a pair of the heaviest springs I've ever encountered - they'd be too heavy for a Harley (seriously), but they might work on the rear axle of a Mack truck carrying the Queen Mary. They were so stiff I had to use a spring compressor to get them off and then modify the shocks to allow the old Betor springs to be fitted. The damping was odd too. Rebound damping was fairly normal, maybe just a tad heavy. But the compression damping was like nothing I've ever experienced. Pushing down slowly they behaved fairly normally apart from overly heavy damping. But if you tried to compress them quickly they'd virtually lock solid - they didn't just slow up, they stopped. I found you'd get one quick compression stroke before they locked, and if I bounced on the seat (stationary) several times there was very little movement at all. Weird. But I fitted them anyway just to see how they'd go when actually riding. How they went was just like a rigid frame - they were basically hydraulically locked. But I wanted to keep riding so I took the shocks off and refit them upside-down. Being old-style double-tube shocks I thought that this would stop the damping from working altogether and at least I'd get some movement back so I could ride for the rest of the afternoon. I got a pleasant surprise though: the compression damping did in fact go away but the rebound damping continued to work to some extent. Riding the bike I found the semi-disabled shocks to be actually not bad - pretty bloody good in fact. The bike rode nicely, traction seemed largely unaffected but there was a tendency for the rear end to kick up over logs and ledges. Although the bike was now obviously underdamped I was now convinced that damping quite a bit lighter than the old Betor Experts was what I wanted. What about the extra length? It did feel just a little less prone to pushing the front in a very tight turn, though the difference was small and possibly just imaginary. Still, I thought it felt a little better and certainly no worse, so decided to stick with the same length when I bought the "good" shocks. I actually rode with the upside-down Chinese shocks for a while before ordering the new ones. I wanted something not too expensive, rebuildable and with light damping, and eventually settled on some Falcons with the Superlight damping option and springs as per Falcons recommendation for my bike and weight. They arrived quickly after ordering (considering the shipping to Australia) so I fitted them and took the bike out to my usual practice area for testing. My first impression was that they were perhaps just a tad overdamped even with the Superlight option, but even so they were very, very good. Falcon advise that it takes a little while for the new shocks to break in and free up, and that's exactly what I found. After a few hours they felt damn near perfect. Traction over rocks and roots and so on was very noticeably improved, and the tendency for the rear to kick up over logs and rock ledges disappeared completely. It felt weird at first riding over bigger logs (for me anything over 500mm is big) on the back wheel and being able to feel the rear wheel roll over the top and down the other side. I could hit things like this quite hard without the tyre being kicked clear of the obstacle, and while the bike felt less "lively" it was certainly more stable and composed over the really rough stuff. After a while I noticed I was riding slightly differently, with more weight over the front. Like most people I guess, I unconsciously position myself to put the weight where it's needed - to the back for more traction, or more forwards to keep from pushing the front out. It seems that the improvement in traction was allowing me to keep more weight over the front and this helped with steering. In short, I'm delighted with these shocks and surprised at how much they have changed the feel of the bike. With the old Betors I always felt that the front suspension worked better than the rear but now I feel that the forks could stand some tuning... So, was the exercise worth it, and what did I learn? Yes I think it was worth it. I can't say the extra length makes a big difference but I think it's a tad better than before. I think it is just a tiny bit easier in very tight turns. My gut feeling from the start was that quite light damping was the way to go, and that turned out to be true for me. If you come from a background of motocross or enduro riding then you need to forget everything you already know about suspension. A trials bike wants springing and damping that would be impossibly light for an enduro bike. I guess the low speeds, light weights and baggy underinflated tyres make the difference. The spring rate recommended by Falcon turned out to be spot-on. The experiments with the cheap ebay shocks helped guide me with damping. The old Betors were overdamped, the ebays were grossly overdamped when the right way up and underdamped when upside down. I concluded that being slightly underdamped was better than being overdamped. As it turned out the Superlight Falcons were ideal for me and I certainly wouldn't hesitate to buy another set. But keep in mind I'm not an expert rider and that others may have different preferences. Top pic is Falcon, bottom is eBay cheapies. Apologies for the long post.

There's something wrong if the seal housings are fully seated yet the crank is still off-centre. There should be very little crank end-float with the housings fitted and a standard case gasket fitted. With a cold engine 0.5mm is plenty and you wouldn't want much more than 1mm. You certainly shouldn't need to be tapping it with a hammer and it shouldn't even be getting close to rubbing on one side. If it's that far off centre there's something very wrong - incorrect seal housings perhaps, or gaskets behind the seal housing instead of just the o-ring, or maybe the housings simply aren't seated fully. You can check this with a thin feeler gauge (say .002") but be careful jacking things around with the seal housing bolts - the housings are a bit fragile. If the crank end float is excessive or it's off-centre you may have to shim or machine the housings but unless you have some oddball or mismatched parts it shouldn't be necessary.

The crank is located by the seal housings. If the housings aren't fitted the crank can slide up against one side. Once you fit the housings the crank should be centered.

I've always viewed the whole "hold-the-brakes-on-while-you-nip-up-the-axle" routine with extreme scepticism. I mean, if everything is in good condition you're going to have what, maybe 2 thou clearance between the backing plate bore and the axle - not enough to allow any significant movement. Likewise, if everything is in good condition you'll have nice square faces on the backing plate, the sleeve in the fork slider and the bearing spacers, so that when you tighten the axle everything pulls up squarely and securely with no scope at all for movement. But if things are so worn that you have to play these mickey-mouse games upon reassembly then I think some work to restore proper fits is in order. There simply shouldn't be any possibility of the backing plate being out of alignment once the axle is tightened.

If I won 20 million in the lottery I'd spend half on coke and hookers. The other half I'd probably just waste...

A source of material for cast iron drum sleeves is cylinder liners for diesel engines. If you know someone in the engine reconditioning business they may be able to get you an old liner from a larger diesel that you could use, but even new liners aren't that expensive and one cylinder sleeve will have enough material to line a few drums.

There are a few methods. One is to have the shoes radius ground by your local brake place to match the drum diameter. Another is to chuck the backing plate with shoes attached in a lathe and turn the linings down to match the drum. You need to have the shoes shimmed out a little from the cam when you do this. Yet another old-school method was to chalk the surface of the drum then spin the wheel and apply the brakes. The chalk shows where the high and low spots are so you can then file the high spots down. If you repeat the process enough times you'll eventually get a pretty good fit. But I've found that no matter what method you use it still takes quite a few hours of riding time to really bed them in properly on the bike. They generally improve quite a lot once they're fully bedded in. My highly unscientific testing process consisted of riding on my concrete driveway and seeing how much pressure it took to lock up the front wheel (sitting down). I could never really get the Bul brake to fully lock even squeezing hard with four fingers. With the modified Yam brake I can lock it with two.

I'll put up a photo or two later. I couldn't get bearings that fit the Sherpa axle directly so ended up using ones with a bigger ID with stepped spacers that sleeve the ID down to the axle.

Agree, the main problem seems to be the chrome drum lining used on the later bikes, along with the grey cardboard that most manufacturers pass off as lining material these days. I'm not suggesting that we return to carcinogenic lining materials but I've never found the grey stuff to perform very well in any application. Even with the Yamaha brake, it didn't achieve full power until I fitted a set of NOS factory linings - none of the aftermarket shoes came close.

125mm, if its the same as the slightly earlier Sherpas. I got so fed up with the front brake on my 199 I ended up replacing it with a Yamaha DT/MX/YZ/IT hub. I stripped the paint off and polished it so it looks sorta-kinda like the original, but now I can stand the bike on its nose with one or two fingers; something I could never get the Bul brake to do.

Wash the big end out and dry it with air then give it a squirt of WD40 or similar - if it's full of gluggy oil you won't feel the wear so clearly. Sit the crank on the bench and position the rod so that it's at or near the TDC position. Hold the rod between the thumb and forefingers of both hands, near the bottom of the rod so your hands are resting on the crank. Push the rod up and down and feel for any play in the bearing. Take your time doing this; if the rod isn't held perfectly perpendicular to the crankpin (looking from the front or rear) you won't feel any wear that's present. If you don't feel any vertical movement and the rod turns smoothly without any perceptible roughness and there's no sign of heat (like blueing) on the big end it's good to go. Don't forget to oil it before buttoning up the top end. Check the surface of the little end bore for wear and pitting while you're at it. The method I use is to fit the bearings to the crank first; they need to go right up against the shoulder. Warming the cases lets the bearings go in easily (there's a whole thread on this procedure here - everyone has their own preferred method) and a little oil on the case bores helps too. The seal retainers locate the bearings (and the crank) axially in the cases so that the crank is centred and nothing rubs. Replace the crank seals and o rings while you're at it.