feetupfun

M6 x 1.0 is what is on all my Bultacos with mounts like that

Yes that sounds like a good plan. Sounds like you found the source of the noise. Very light scoring is normal to find. If you can feel lines then there is a problem. If it was me I would also clean the rings and ring grooves (using non-caustic paint stripper and a tooth brush) and clean any carbon off the piston crown and exhaust port with either a scotchbrite pad or bead blasting.

Pete88 you didn't ask me but I'll put in my 2c worth 1 for main bearings any discernable movement axially or radially of the flywheel means they need to be replaced. 2 If a ring stays in its groove in any section of the groove rather than moving freely in and out the groove, it is stuck. If there is gum, you will see it. Sticking rings is very commonly seen on two stroke trials bikes. Worn rings are measured by fitting them into the bore squarely between the top of the exhaust port and the head surface and measuring the gap between the ring ends. The pattern of carbon deposits on the walls of the cylinder also is a guide to there being ring sealing problems or not. 3 There should be zero discernable movement up and down of the conrod relative to the big end pin. Slight left-right rocking movement of the top end of the rod is normal. The little end can be inspected with a magnifying glass after cleaning the rollers and pin and the eye of the rod. If there are any visual defects in any of the bearing surfaces the parts should be replaced. It should also have zero discernable movement in the direction of the rod axis but it is normal for the pin/piston to be able to rock slightly in the eye of the rod.

Is that when they went to 32 spokes from 36?

Something fishy here. When USDB magazine did a comparison of all the available trials bikes at some point, they said the SWM was the lightest full-sized trials bike. Maybe it was the TL230 they had and the Jumbo is lots heavier?

Yes that will work with some frames but on many frames (eg Sherpa T and KT250) the wheel is already close to the front downtube or exhaust header with the standard setup.

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.