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Measure the sag on the fork tubes. The zero position for fork sag is with the front tyre off the ground. Your damper rods are early TY250A (welded-on bottom end). Later TY250 damper rods have the bottom end reduced diameter section made using a swaging process. Yamaha commonly change the design of something but retain the same part number if the two designs are interchangeable. Yamaha didn't make TY250 forks. They were made by Kayaba to Yamaha specs. Kayaba changed the design of TY250 twinshock forks in many ways between the first and the last version but they are functionally the same and the parts are inter-changable.

John Cane has a reference photo on his website showing TY250 fork internals which might help you. https://www.tytrials.com/trailandtrialsuk/cat_88541-Front-Forks.html

Your photo shows TY250A forks apart from the fork spring which is single rate and longer than standard. The standard spring is dual rate, thinner wire, shorter and the ends are tapered on the OD. The spring in your photo looks like what I bought from B&J Racing about 15 years ago to try in a TY250. The B&J set I bought were exactly the right length to use without any preload spacers. In my opinion, the Magical springs provide a superior action for most riders compared to both standard springs and the B&J Racing springs. The parts diagram you said is from "Majesty" is not showing TY250A forks. It is from the TY250 Owners Manual but sadly is not what TY250 forks look like. The TY250 fork diagram from the TY250 parts book also has a few mistakes which can cause confusion. Your forks in your photo look standard except for the fork spring.

If you are using Magical springs with original damper rods, for your weight, 10 weight fork oil should be OK. You didn't mention buying the aluminium damper rods so I'm assuming you are going to use the originals. To start with, set the total Magical spring+spacer length the same as the original spring + spacer length. That will be a few less mm preload than original because your original springs will have sagged a bit over time. For reference, standard A model fork spring free length is 400mm. When you have done that, measure the sag with you aboard and adjust the preload until you get about 60mm sag with you with all your weight on the pegs. Once you have set the preload, go for test rides to see if you want to change to 15 weight oil. Standard TY250 forks have very light damping so I wouldn't go below 10 weight fork oil. If your forks have the drain holes on the sides (early A model) then the standard oil quantity is 175 ml per leg. If your forks have the drain screws at the back (everything after early A model) then the standard oil quantity is 162 ml per leg. The two types of forks have different design (different volume) damper rods.

The cam face can be refinished by welding and machining. The cam end of the pushrod may need to be refinished too. It's meant to be hemispherical. I've seen NOS cams advertised on eBay. Yamaha and EBC and Goodridge are good. Haven't tried Vesrah. Yes milling the grooves is a warping risk but some people do it. I would think you can buy new steel plates from Yamaha if you think there's a problem. I use wet-and-dry paper on mine. I'm still using the original steel plates after four rebores and two new conrod kits.

A lever arm extension reduces how far the plates move apart so can make disengagement worse. Old friction plates can make disengagement worse. If they are more than few years old I would replace them. It usually takes quite a few hours of serious clutch punishment to polish the roughness out of the steel plates. Yes bead blasting is a good thing for the steel plates, as is 120 grit wet-and-dry paper lubricated with kero. Some people mill grooves in them with a milling machine. Anything that helps the air to get in between the plates without bending the plates is a good thing. Is the pressure plate staying parallel with the basket as it moves out? Is the cam face pitted?

The LT ignition wiring from the magneto to the HT coil is usually black coloured. The other wires from the magneto are for lighting and should be insulated from each other and the frame. It doesn't matter how you make the connection for the LT ignition wiring as long as it is secure and electrically insulated from the frame. Bultacos usually have a wiring connector strip near the front downtube but using it is optional. One wire from the kill switch connects to the LT ignition wire. The other kill switch wire connects to the bike earth (frame/motor/stator plate)

One way to help know what year a Rev 3 is, is to count the spokes. The wheels changed from 36 spoke to 32 spoke in about 2005. If it was me buying it, I wouldn't care what year model Rev 3 it is. They are all good to ride. Condition would be the important thing. From the photos it is impossible to know if it is a 200, 250 or 270. The 125 had a different exhaust to the one in the photos.

An excellent outcome

The "American" stator coil and the "European" stator coil are probably the same item and the difference in resistance values you are seeing in the reference material is probably a typographic/transcription/translation error. I have looked at my reference sources for that resistance value and found the same error as you found. If it was me I would just rewind it with the same number of turns, using the closest wire diameter I could find to the original. The resistance value of the stator winding is not a critical value. It is provided in workshop manuals for fault-finding purposes.

There should be a circlip on the shifter shaft on the left side of the motor. The circlip bears against the shifter shaft oil seal and prevents the shifter shaft from moving towards the right. It may not be immediately visible because it may be concealed inside a plastic roller/wheel that protects the shifter shaft from the chain rubbing.

Maybe one of the gudgeon pin clips came loose and put a big groove in the bore and it needed a 2.0 mm oversize re-bore to clean up the bore so they could keep riding it?

0.015" is good. 0.15" is way too much.

Nice to see. I have one for the same reason you mentioned.

The OSET 24 is smaller than an adult size trials bike so is not as comfortable to ride for an adult-sized person as an adult-sized electric trials bike is. Electric Motion trials bikes and free-ride bikes are adult sized and are popular. Google "electric motion trials" or "EM trials"

When a frame becomes pushed out of shape by riding, like in those photos, I take the motor out to make it easy to push it back into shape.

I'm always interested in the way Bultaco changed things on some models without changing the model number. The model numbers that had the most changes are the most interesting to me. I have a fair handle on the changes through model 49 and through model 91/92 but not the others. I'm rebuilding a model 85 at the moment so am particularly interested in knowing at what production numbers the model 85 changes happened? I'm most interested in when the footpeg mounts became welded on, the swingarm pivot nuts were recessed into the frame, the steering security lock was fitted, the chain tensioner became rearward-facing and the chain oiler was incorporated. I only have two model 85s to refer to, one in the 2000s and one in the 5000s, so I'm hoping others can reveal what is on their model 85s. I've seen the sales brochure for model 85 Alpina and that bike has bolt-on footpeg mounts so I assume that bike was early in model 85. My model 85 in the 2000s has welded-on footpeg mounts and recessed swingarm pivot nuts, forward facing chain tensioner, no steering security lock and no chain oiler. My model 85 in the 5000s has welded-on footpeg mounts, rearward chain tensioner, steering security lock and chain oiler I figure that the footpeg mounts became welded-on type at the same time that the swingarm pivot nuts were recessed.

The tank/seat is from the first series of Alpinas (models 85/97/98/99). Being a model 97 (Alpina) frame it will have an identical frame and front end and wheels to the series 2 model 80 Sherpa T. The model 85 internal Alpina gear ratios will be a bit of a pain for trials use because you'll need a very large rear sprocket to get first gear slow enough.

Two stroke trials bikes ridden in trials type riding go well with a 5 or 6 heat range plug (NGK heat range numbering). If the two stroke trials bike is used for sustained/continuous riding, like along a road or at the beach, or in desert sand, or trail riding that involves long climbs, a 7 or 8 heat range plug will work better.

What point are you getting stuck at? Are you having trouble getting a good connection between the drift and the bearing inner? Is one bearing any easier to connect with than the other? If heating didn't help, then whatever they used is probably not loctite so may be an epoxy. If it is epoxy then the aluminium will probably melt before the epoxy burns. In the worst case you can remove bearings with grinding tools. Maybe post some photos up

While the one in you photo may well be a one-piece forging, if you were to make one starting with a standard lever, the bush at the top end could be welded on.

Yes you have the dish the correct way. Yes 13/55 is a good choice for competition riding.

The type with the sliding bar shown by MikeS300 could be easily made by modifying a standard kickstart lever, but it doesn't move the top end of the lever out of the way of your shin any better than the standard lever. I feel that a lever that swivels at the bottom (like a Beta lever) would provide better leg clearance.

27 mm x 1 mm left hand