feetupfun

Thanks. I had just cleaned them for a photo session for a virtual classic bike show.

Snap! You have great taste in motorbikes

They are the same basic layout as every other motor of the era but there are features that some people haven't come across before. Here are some things that spring to mind: The conrod is held centred on the crankpin by spacers on the gudgeon pin. The primary drive crankhaft gear is mounted on a taper which needs a special puller to remove without damaging the teeth. The cylinder is held on with 7mm internal hex nuts. The positioning (and side play) of the crankshaft is set using shims behind the crank seal carriers. The kickstart travel stop is a weak design and very commonly broken which allows dust and water into the magneto casing. Take note of how the shift mechanism is set up before you pull it apart. Yes the side play and positioning of the gearbox shafts is important but if you use the same shims in the same spots and use the same thickness centre gasket 0.5mm it will probably be fine. Pistons are very expensive.

The ideal footpeg position depends on a lot of things and you won't be able to know for sure until you have test ridden it so yes bolt-on adjustable position pegs are the go for an experimental bike like yours. For a starting point, I'd mount the pegs so that the middle of the peg platform is in line with the front end of the tyre tread with the axle at mid slot.

Generally a trials swingarm should be as long as possible yet still achieve the wheelbase that you want. For a bike with something like your B250 engine (an engine that is long from front to back) you will probably end up with as short a swingarm as will fit an 18" trials tyre and the wheelbase will still be on the long side of ideal.

For comparison, this is a standard Kawasaki KT250 front end. I chose this photo because this bike has the most steering angle of any of my bikes.

Excellent. Thank you. That is fairly serious steer angle

90 degrees is an awesome design target. If you've got it, flaunt it. I'd love to see a photo.

Maybe try googling Leonelli instead of Lionelli. Have you looked in the owners manual for your bike?

The SWM Jumbo came with 38mm forks

I'm still working and may not even get any time off due to working at a power station. Plenty of things I'm ready to do in the workshop, mostly involving 1970s trials bikes

and if I could source IRC I would use IRC also. They are both very good.

People (including me) fit Tubeless X11 Michelins on Tube Type rims.

Who cares what people do on ebay? Isn't there a for sale section here on Trials Central? That would be a pretty good spot. There's also the various facebook Montesa pages which are 100% Montesa enthusiasts

depends where you compete

The threaded holes in the hub normally go all the way through so maybe there is just some crud in the holes stopping the bolts going all the way in. If that is the problem and you don't want to clean out the holes, you could fit some 8mm washers under the bolt heads or buy some shorter bolts..

The TY250Z motor is based on an early 1990s YZ250 motor. The TY250 air cooled mono motor is based on an early 1980s YZ250 motor. They started with a clean sheet of paper for the TY250Z but did use the pinky front wheel.

There is a plastic toolbox that sits in the space but none of mine still have it

I had an aluminium tank that had developed a line of corrosion holes in the bottom of one side which were in conjunction with the gum that forms when modern fuel is allowed to evaporate in-situ. The corrosion holes were under the gum. I suspect that there may have been some water also present during the hole-forming process but by the time I got the tank it was dry and just had the gum and the holes. If you don't allow things like that to happen to the tank, aluminium is one of the best (longest-lasting and lightweight) materials for a fuel tank. I've seen zero corrosion damage on any other aluminium trials bike fuel tank.

nothing there on either of mine

its a right hand thread

There is nothing stopping you fitting the new outside bush further in from the end

What is the problem with the bush going right to the end? One thing I do know is that I couldn't source the right size bushes for a M85 sleeve gear last year so I bought bushing material with a smaller ID and bored it to size once it was in place in the sleeve gear. Haven't tried the motor yet. I've always wondered why some 5 speed motors have needle roller bearings there and some have sleeves.

Yes

Yes the top bend is made from a pre-formed exhaust pipe bend. They come in various diameters and one size is smaller than TY250 and the next size up is slightly bigger than TY250