feetupfun

One way to judge piston ring seal without pulling much apart is to inspect the cylinder wall via the exhaust port or the plug hole, looking for dark areas (carbon). Carbon on the walls indicates piston ring blowby. Be aware that trials two strokes nowadays commonly suffer from having the rings stuck in their grooves by gum and carbon. This can happen quite quickly depending on how the bike is ridden, the type of premix oil and how well the bike is jetted.

TRS sells electric start 250 and 300 two strokes and they are very popular.

The ball and spring can be installed or removed with the engine assembled

You can use the TY175 head or the DT175 head. If you use a DT175 head, the compression ratio will be higher but you may need to trim the head fins for exhaust pipe clearance. You can mount a clutch cable holder on the engine casing or on the bottom cylinder fin. The DT175 cylinder fins will not interfere with anything physically. Trim them if retaining the original TY appearance is important to you.

DT175 1974,75,76,77 (DT175 ABCD models) cylinder will fit and function well but has different finning outline to TY175. I have not tried or measured up a CT1,2,3 cylinder.

Which brake plate is standard/correct depends on which hub is on your model 92. Also, they might both function OK. Can you do photos of the hub showing the brake drum and an external view showing the finning and both spoke flanges?

Here's the OSSA cush drive puller photo

Yes, quite impossible. "Fingers" on a puller made to fit in there are not strong enough for the job by a large margin. The puller needs to pull on the whole surface. The Montesa primary drive crankshaft gear of the same era as the OSSA cush drive is also on a taper and is also impossible to get off with a universal puller so it is not just OSSA who did this back in the day. I'll post a photo up later when my cloud storage is talking to me

200 Euros labour plus parts sounds quite reasonable to me and even cheap if they have to source or make a special puller. Do they know what's involved?

Yes it's not easy but are you saying you can't find where to buy the special puller from?

Triad, if the primary drive crankshaft sprocket has a cush drive, then it is an easy job to change the crankshaft seal, but you need to buy a special puller for the cush drive. These pullers are available from vintage OSSA parts suppliers in the UK and USA. Buy a primary drive cover gasket and crank seal holder gasket while you are at it.

Non-powerjet. If you want an OKO, the model is K-100 and people usually run a 26mm or 28mm

While it's probably OK to leave fuel in it, it would be kinder to the tank liner to store the tank dry over winter. Nowadays after a ride, I drain and dry out my lined fibreglass tanks if it will be more than a few weeks until the next ride. My oldest epoxy tank liner is about 20 years old now. For the first 15 years I left that one with fuel in between rides and it gradually changed from honey colour to dark brown over the 15 years. After I noticed this happening I started draining it between rides and now at 20 years it is still working fine. It may still have been OK if I had continued leaving fuel in it, but the colour change made me wonder if it was being gradually damaged structurally. For info, Caswell liner is epoxy resin

If you are using the Explorer exhaust system, there is no advantage in using anything bigger than the 27mm AMAL. The Pioneer uses a bigger carby because it sucks a lot of air when it is on the pipe. The Explorer exhaust will mean that the Pioneer motor will suck about the same amount of air as an Explorer motor at full power.

When you have finished riding, turn the tap off and run the fuel level down in the float bowl before you stop the motor. Otherwise the evaporating fuel can make the float needle sticky. You may even have a passing fuel tap which could exacerbate this effect by allowing lots of premix to evaporate between rides. As for the lanyard killswitch, it can be wired in parallel with the standard kill button/switch, so the standard kill button/switch can stay. Maybe post a photo showing the "actual" slide switch you are asking about