feetupfun

Nice stand

It's important what "on" means when you are doing the sag. For a trials bike you need to have all your weight on the footpegs. That means no weight on the seat or the handlebars. You can touch the handlebars to stop yourself wobbling, but don't put any up or down force on the grips. If you did that already and got the 1.5 inches of sag shown in the photos, then you have done very well, nothing more to do. The likely reason why you bottomed out on a speed bump is that you were sitting down, well I hope you were sitting down anyway. Trials suspension is tuned for the rider standing on the pegs. When you sit, the sprung weight of the bike is you plus the bike. When you stand on the pegs, the sprung weight is somewhere between being just the bike and the bike plus you, depending on what you legs and body are doing at the time the rear tyre hits the speed bump. If you set a bike up to resist bottoming on things like speed bumps with rider sitting down, the rear suspension will be way too stiff to work properly when you want to use it for trials-type riding.

5mm sag without you on the bike is fine. The sag with you on it is much more important

Original (NOS) replacement sleeves (made by Bultaco) for the popular models have been used up. There are businesses that can make new sleeves. Where I live a new custom made 2 stroke sleeve would be about $500 fitted in your cylinder. There are so many second hand cylinders out there from people parting-out bikes that you can usually buy a replacement cylinder that still has some rebores left in it.

Poor bloke just wants to know what they weigh. I haven't weighed one yet but would put money on it being substantially lighter than a TY175

There is always leakage from high voltage systems. Have a listen to the insulators at a HV transmission cable tower. That crackling and hissing noise is air being ionised (like lightning but on a smaller scale). These get washed with demineralised water to minimise the losses. You can minimise the power losses from your bike's ignition by keeping the HT coil, lead and cap clean and free of any conductive residue. Also check that your plug gap is not too wide and that the conductors inside the cap are in good condition. If you see carbon anywhere in there, it means there has been sparking happening which will reduce the voltage across the plug gap. The HV circuit on a motorbike runs at something like 50,000 volts so even the tiniest bit of leakage can flow through your salty body with great ease and cause damage and discomfort, so don't touch it with the motor running. Some ignitions need the flywheel to rotate at a higher minimum RPM than others to make a decent spark. This means that starting technique can be important.

After I get home from a wet trial, I pump the (tube type) tyres up to about 30 psi with the valve holes at the bottom. This squishes most of the water out of the rim. Then I put the bike on a stand and let the tyres down to flat (remove valve cores) and push the tyre beads off their seats in a few places. In our warm dry climate, the rest of the water inside dries out quite quickly. I also loosen off the magneto cover to let that dry out too.

Whether you should degrease it properly or not before lining it depends on your appetite for risk

Maybe DC's bike was run with a tube in the rear tyre for a while (which would let water in and would be slow to dry out)

Being on the opposite side of the earth, it's the perfect time for me to go to bed

There's no doubt that there are problems with static charge build-up in cars and yes you can buy conductive straps to help discharge the static from a car, but where I live it is thought that car sickness is caused by a conflict between our three bodily balance mechanisms

Yes it's very easy to break a cover like that one. If it does have some sort of sealant sticking it on, then you can try heating the cover where the gasket sits before trying to move it. This could end up very messy, but you could try using a TINY whiff of compressed air via the vent hose. Be ready for flying pieces of clutch cover if you over-do it with the compressed air. A safer but even messier version of this would be to stand the bike back up, completely fill the gearbox with oil and then use a (hand-powered) oil transfer pump to generate a bit of pressure.

I'm starting to get the idea that you are not being entirely serious. First you reckon static electricity causes car sickness and rim corrosion and now you are saying that you have to waterproof your spoke nipples . Mind you it is a fairly entertaining discussion

Yes the WD40 eventually dries and I find it continues to protect the rim from corrosion. As well as for seating tubeless tyres, it's good for protecting tube type rims that fill up with water when you ride a wet trial. I suspect that it wouldn't go well with a natural rubber tube, but I haven't seen one of those for about 40 years

Remove all the screws. Remove the kickstart lever and whatever else might be in the way. Lay the bike over on its right hand side with the cover you are about to take off being parallel with the floor. Carefully ease the cover up a tiny bit and make sure that the gasket stays on one surface or the other, to avoid ripping it. That way you might be able to resuse the gasket. Once the gasket is sorted, remove the cover fully. Oil will drip off it.

You can use WD40 to mount the tyre instead of a water-based lube

Another way for water to get into the gearbox oil is by riding through water

The symptom is water in the gearbox oil. A head gasket leak cannot cause this

There are two clutch covers. The outer one that you have removed is for working on just the clutch. The bigger cover surrounding that cover is the one you need to remove to work on the water pump drive shaft.

Is that the electric works special?

The sliders do not have replaceable bushings. The tubes run against the slider bore directly. Sliders can be machined out and sleeved/bushed. The screw in the bottom is what holds the forks together. The spring clip only retains the seal in the slider. Forks jamming at the bottom of the travel is not usually caused by worn sliders.

The points stay open for a while. The important thing is where the piston is when the points start to open.

You can fit 50 lb Falcon springs to those shockies without modification. They are available as a spare part. 340mm shock length is fine no matter what springs you use on the shocks. So are 350mm shocks. So are 360mm shocks. If you go longer than 360mm shocks you may need to do some metalwork to let the swingarm rotate down far enough. 340mm is probably the ideal length for what you do with the bike. There are many ways to change the spring preload. One way is to take the spring off. You can then move the spring steel clip from one groove to another. This clip is held in place by the top spring retainer so by taking the spring off you can slide the retainer down to expose the clip. You will need a pointy tool to get the clip to move out of the groove. To take the spring off you take the shock off the bike, compress the spring and take out the bottom spring retainer. Another way is with the shock still on the bike. Grip the top end of the spring in one hand and pull it down away from the top spring retainer, slide the retainer down a bit and keep holding against the spring while you move the clip from one groove to another. There is a risk of pinching fingers doing it this way, but it very fast once you get good at it. It is easier doing this with two people. It's quite normal to have to use one of the lower grooves when you use 40 lb springs on Falcons on a TY250. Trials bike suspension is intended to be very soft compared with other types of dirt bike suspension so it works well in sections (low speed with the rider standing and legs forming part of the "suspension"). If you ride a TY250 that is set up to ride trials sitting down and go through a dip at speed, it will bottom out the rear suspension heavily.

No problems with pressure build-up and no vent valves fitted. The oil height is set to give the air spring effect I want when forks have reached normal operating temperature