feetupfun

Montesa Cota 247, 348 and 349 also drive the primary gear with a taper

If its sustained riding - like along a road - that you are talking about then the cause might be poor tank tank venting creating a slight vacuum in the fuel tank

John what is that light coloured thing visible through the bearing hole?

TY175 does have a weakness in the design of the return stop peg on the shaft. It can slip around on the shaft. Common problem. If it has slipped, work out where it should sit, move it back and weld or bronze weld it in position. The original design is a press fit that can slip if the kickstart is allowed to slam against the return stop. If that has gone wrong, you are lucky not to have holed the clutch casing Before you start pulling it apart though, a TY175 kickstart that is working correctly engages when the lever is horizontal (about level with the footpeg) They also develop looseness in the knuckle joint which causes the end of the lever to be lower

electronic ignition supplier should tell you what gap to use, but there will be no harm done using 0.4mm. I use 1.0mm plug gap on my bikes that have modern aftermarket electronic ignitions.

A local engine rebuilder here makes replacement crankshaft halves as an alternative to the build-up/grind back technique. Both will work

Probably depends on who does the welding, but the ones I've seen done with welded nuts still work fine.

You can get aluminium nuts welded to the WES and fit the standard heat shield. I think this looks great

There are different width 520 size chains depending on brand and if they are non-sealed, o ring or x ring What size front sprocket is it? A photo showing where it rubs might help solve your mystery

The reason that there is still a throttle cable but no cable for the clutch or brakes is simple; The brakes and clutch provide extremely important feedback through the controls. For the brakes the feedback is pressure variation under the foot or against the lever. The important feedback from the clutch is the accuracy with which the rider can feel the point of engagement which is marked by a rapid reduction in lever pressure as felt by the riders fingers. With both these systems, feedback is better with hydraulics. In the case of the throttle cable, the only feedback is from compressing the slide return spring. The force from the spring is only there to overcome friction so the throttle self-closes. In the quest for better emissions, reliability and performance, the future of two stroke trials bikes includes electronic fuel injection and this will consign the humble throttle cable to oblivion. Maybe not next year or the year after, but eventually it will

the standard number for getting to world class level in any sport or endeavour that requires brain and body coordination is 3000hours of practice, so it pays to start at a young age and do lots of it every day

The OKO carby also goes well on the 325 Bultaco Sherpa T

I will have a go at translating Dabsterese into Aussie English "Guys, admit that you are wrong. The reason people reline Bultaco hubs is because the chrome lining fails. If we didn't have to reline Bultaco hubs the discussion would not have begun"

Note that Moto GP use carbon fibre composite discs in fine conditions (carbon fibre only works while it is hot) and ferrous discs when it is a wet race. What racing vehicles use is not of much relevance to trials bike brakes I would say

The signal-to-noise ratio (for the communications between the clutch, the brakes and the brain of the trials rider) is better with hydraulic discs and clutch than with cables, so hydraulics provide a performance advantage. Hydraulics and disc brakes go hand in hand. Cable disc brakes provide poor communication in comparison, as do hydraulic drum brakes. Please don't use street car justification for something on a trials bike. On street cars the signal-to-noise ratio of the clutch is not particularly important, so if a (cheaper, more reliable) cable can be used for the design, it will be. People want to buy the trials bike that maximises their chance at winning. The proof of this is that so many people keep buying the latest and greatest, and are willing to lose $$$ on depreciation each year, rather than keeping riding the one bike until it is uneconomical to maintain.

I have Marzocchi Strada shockies on a twinshock enduro bike and while they are OK for that, they have the wrong damping pattern for trials. Those Marzocchis that came off your Fantic may have been OK when they were working, but to fix them would probably cost more than buying a new, decent set of modern trials shocks

The chain is supposed to be very close to the shock spring. If you move the sprocket teeth towards the centre of the bike, the chain will then be misaligned. Most people space the shock out a little at the bottom mount with a washer to give more chain clearance. The problem comes about because modern shocks have bigger diameter springs than what the bike was designed for

I like the look of drum brake wheels, just like I like the look of the motorbikes they come on. Not many things mar my enjoyment of the aesthetic appeal of a motorbike, as much an old bike that someone has retrofitted a disc brake to I also think that a well set-up old trials bike can feel absolutely wonderful to ride, despite it being so different to a modern trials bike

I think you might have got more response initially with a different heading. I read the heading a different way to what you seem to have intended people to read it, and didn't even open the posting until you replied to yourself

On the sprocket side there is a spacer with a steel disc. The steel disc protects the bearing dust seal. The bearing dust seal runs on the OD of said spacer TY250 twinshock does have another spacer that sits inside the chain adjuster cam and inside the swingarm plate. If someone has fitted TY175 chain adjuster cams, your axle will appear to be too long, and the axle will be able to flop up and down in the swingarm slot when the nut is loose. If you post up a picture it should be obvious to any TY250 owner what is wrong or missing on your bike

Paul if you have a Bultaco with pin-type spring retainers, don't try and use anything but standard plates because it will be impossible to get the pressure plate load right otherwise. You should be able to buy a second-hand later model clutch with nut and stud spring retainers if you want to take advantage of the plates with friction material on them on your 325

The reason why four plates, may be that they are thicker and only four will fit in the basket. That is the usual case with plates with friction material bonded on. If you make the metal part of the friction plate too thin, the tangs dig into the basket fingers, so it is unavoidable that plates with friction material added will be thicker than the standard steel plates The reason why you can get away with replacing five steel plates with four plates with friction material on them, is that the friction generated per plate is greater with the friction material. If you can fit five of the new plates in there without the spring nuts hitting the clutch cover, or the stack being too deep for the basket, then use 5 plates and enjoy a lower lever pull force. When setting the pressure plate spring preload, set the spring load only just high enough to stop it slipping at full power in top gear (top gear puts the greatest torque on the clutch). You can get pretty close to the ideal setting in the workshop by increasing the spring preload until the kickstart is just able to get the motor over compression. As well as this basic setup, there lots of other things that can be done to reduce clutch lever pull force on a Bultaco. Here are a few: Fit roller bearings to the clutch camshaft Choose a leverage ratio that maximises the mechanical advantage between your hand and the clutch pushrod, yet still moves the pushrod far enough to completely disengage the clutch Use a high quality cable Use a high quality lever Route the cable to minimise friction Lube the cable Service the camshaft Set the cable and pushrod adjustments so that the clutch arm is at 90 degrees just as the full load of the pressure plate is achieved Fit a hydraulic clutch with slave that bears directly onto the pushrod The powerful versions of the 5 speed motor like a 370 Frontera will always have a heavier clutch pull than any of the 250c Trials and Alpina motors need to have. Even a completely standard clutch setup on a 250 Sherpa T can be made to be a one-finger operation, and the 325 trials motor can be made almost as light, but to cope with the power of a Pursang/Frontera going through the same design clutch, will require more force on the pressure plate, or more elaborate methods, to reduce lever pull down to single finger levels.

It depends on how much the motor has been hotted-up, and the riding technique and standard of the rider. I have a fairly-well hotted up 205cc motor in one of my TY175s and there is no way I would want to reduce the flywheel weight from standard, but on another TY175 with standard performance motor I think the little bit of lightening it has had has helped it. There is no one perfect flywheel weight for any motor, because flywheel effect is a trade-off and everyone rides using different technique

its commonplace nowadays to be able to buy (Wossner) pistons up to 2.0mm bigger than standard and generally do not need a bigger OD sleeve