feetupfun

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

OEM VM26 from DT175 works. Haven't tried a VM24, didn't even know they made one

I usually use no washers but do use loctite. The reason I don't use the washers is that I fear that a piece might come loose and cause damage

Sometimes people use Loctite on the threads of the bottom screws, and a rattle gun will not undo them using the inertia of the damper rod alone - the damper rod needs to be held stationary

I rebushed a TY175 basket that was pretty sloppy and used punched-out discs of insertion rubber (the discs are round in the TY175) and made new rivets. It got rid of the sloppiness but didn't make the slightest difference to the way the bike went. That was 35 years ago and those discs of insertion rubber are still going strong

manufacturers don't grease them properly when the bikes are assembled

Fuel tank is IT Yamaha 1977/78 It's a TY250 frame and they never had tubes under the engine and the original A model bashplate was rubbish It looks complete enough to me to be resurrected for trials use here in Australia It has a TY250 B model carby The motor and frame look like A model A model frame and motor should have numbers that start with 434 I'm intrigued with the extra bolts through the frame plate where the swingarm pivot attaches on the RH side of the bike

http://www.mijossi.com/3ty/bibliographie.html

The effective length (the distance between the spring seats) of the spring guide/spacer is 123mm. The steel section is 24mm OD. The plastic spring seat is 23.8mm OD. The peg on the plastic spring seat that goes inside the spring is 15.5mm OD. The hole through the middle of the plastic spring seat is 12mm. The four holes in the necked-in section of the steel bit are 5.5mm diameter. The steel that the spacer is made of is 1mm thick. The opposite end to the plastic piece is formed inwards about 3mm to make a flat spring seat The oil deflector is also formed from 1mm thick steel. The OD of the cup section that goes inside the top spring is 16.3mm. The cup section is 52.5mm long and has a single 1.75mm hole in the side near the bottom. The original long spring is a slightly smaller OD on the bottom end to the top end, and the oil deflector will only fit in the bigger end. I am yet to work out why the arrangement for the springs in these forks is so elaborate compared to every other set of 1970s forks I have worked on. I will leave the springs out for a while in case you have any more questions

I thought you might ask that so I left them on the bench last night and will measure this weekend

I have posted a photo of the fork spring assembly to the Trials Australia forum topic "Basket Cases", at the bottom of page 64, because I couldn't get it to upload to Trials Central http://www.trials.com.au/forum/viewtopic.php?f=16&t=4785&p=36482#p36482

I can take photos of the parts laid out in sequence if you need it

There is meant to be a spacer between the two springs, and an oil deflector. So from the bottom it is damper rod, then spring, then spacer, then other spring, then oil deflector, then cap. If you have some TY250 springs handy they work just fine in there with a spacer sized to give about 20 to 25mm preload. If you want to retain the venting on the caps, you will need some sort of oil deflector. I use TY250 (unvented) caps on my KT forks

also consider that the quality of the frame earthing for the motor casings and the HT coil may have been affected by your restoration

Dont just blow out the jets. Remove the pilot jet and look through it and clean it until it is clear. Your symptoms sound like a blocked pilot jet. They commonly block up from either a particle or from gunk if you let premix dry out in the float bowl between rides

as for your other question about the lack of a circlip above the seals, that is quite normal for those forks. The friction fit of the seals in the fork bottom section is all that is needed