feetupfun

I will be interested to see if you still think it is easy to work on after you get the primary gear off

you've probably sheared the flywheel timing key

I saw the other side via some other photos which were posted on Facebook. I saved the photos and will post them up soon

It's normal for a 4 stroke to have a strong on/off effect with the throttle

My 348 used to have a positive pressure inside the clutch casing. I was never sure that it was a crank seal causing it though because I cleared out the gearbox vent (which was blocked) at the same time that I changed the crank seals.

Despite being Australian, I've successfully interpreted billyt previously and will now have another go: If you ride those three trials with the strange names, the terrain at these trials will suit a trials bike with a fast throttle response

https://www.tyoffroad.co.uk/store/p40/TEMPORARILY_OUT_OF_STOCK.__FOOTREST_LOWERING_KIT_(BOLT-ON)_TO_FIT_HONDA_TLR200._(REF.H025).html

What did the gearbox oil look like?

Not a big deal. A common sight on a trials bike that has ridden a wet trial. I would just fill it with fresh oil. Next time you ride in water it will probably do it again. Sometimes wet oil affects the action of the clutch but if you didn't notice, then I guess yours doesn't get affected.

Easily proven, as I did for myself, by putting a paint marks on the tyre and the rim. Go for a ride starting with a straight valve stem. Look at it after the ride. See valve leaning over and pulled hard against one side of the hole and yet the paint marks are still in alignment. I admit to doubting that this could occur so that's why I did the experiment

Yes the tilting valve stem on a trials wheel is often misdiagnosed as tyre slip. Sometimes fitting a different brand of tube in the same tyre will stop it happening

Sounds like you are thinking of a 5 speed Bultaco engine rather than the Yamaha TY250 motor he is working on.

I love the clutch spring story. It reminded me of when I was working on a TY250 kickstart a couple of years ago. The tiny spring that pushes on the ball went "zing" over my right shoulder at high speed and out the tilta-doorway to somewhere on the rough ground behind my workshop. I looked for about 10 minutes but they are tiny and it would have been coated in dirt so I gave up. A few months later my wife (who knew about the spring incident) gave me a metal detector for my birthday. Well I had a ball finding the most amazing variety of small metal objects out the back of my workshop, but no kickstart spring. I was telling a bloke at work about the spring story and was pleasantly surprised when he later gave me one of those springs that he had ordered along with a swag of other TY parts for a bike he was fixing up. This searching business in a crankcase also reminded me of when I first pulled the cylinder off an OSSA motor. The cylinder studs are usually rusty and if you do it the normal way up there will always be rust particles fall into the crankcase as the cylinder comes free. To avoid this, I hoisted the bike up in the air, upside down, so that when the cylinder moved away from the bottom end, the rust would fall away from the crankcase

I must say I'm impressed with your workmanship, especially the fuel tank. Making stuff yourself is very satisfying. I've wanted to try making an aluminium trials bike tank for a while and seeing yours is motivational. Back on the rules. Over the ditch, we've got a manufacturing date cutoff for "twinshock" bikes (1 Jan 1987) which would be a problem if you wanted to ride that bike competitively over here. Apart from the rules there is always the "pub test". Not sure if this happens in other countries but it definitely is a thing here. Years ago TV reporters doing an opinion piece would posit "what would the man in the street think?" The official legal term is "what would a reasonable person think or do under the circumstances?" But the "pub test" sounds lots better to me because with any luck, she or he will have had a few drinks and be quite prepared to share their thoughts about any topic. I haven't had a drink tonight so I'm probably not the right person to be sprouting off one way or the other.

before you go to the trouble of splitting the cases, try washing the suspected roller out. First degrease the crankcase (so that the steel surfaces aren't sticky) then set up the bottom end with the crankcase mouth facing downwards and with an old bedsheet or something similar suspended loosely underneath and wash the crankcase out with a low pressure water jet (garden hose). If something gets washed out it should get caught by the bedsheet. Spray everything inside the crankcase with WD40 as soon as you are finished to get the water away from the metal. Even easier would be to use a parts washing machine if you have one

Oh yeah - gold rims are fantastic

I posted a photo when I did it years ago but finding that might prove difficult and I'm not ready to pull the tyre off just yet to take another photo. Maybe I can describe it better. If that doesn't work I'll do a sketch. The bike is on a stand with the rear wheel fitted, but with no tyre fitted to the rim and no chain on the sprockets. I cut a circumferential groove in each bead seat with an angle grinder fitted with a 2mm wide cutting disc. I spun the wheel by hand to start it spinning then started cutting and this kept the wheel spinning. I cut one groove about 2mm deep in each of the bead seats. The rubber on the surface of the tyre beads deforms into these grooves once the beads are up on the seats (40psi and WD40 to seat the beads). This keying effect prevents the tyre bead from slipping sideways back off the bead seats when the pressure is let down for riding. Yes there is a tube in there - it is a TY250D tube type rim and a Michelin X11 "tubeless" tyre

A modern Sherco/Scorpa branded as a Yamaha is a quite appealing idea to me. When the Scorpa SY250 came out in about 1999 or 2000 I remember seeing a photo of one in Japan painted up as a Yamaha and went along to the local Yamaha shop with a photo of it and asked when I could buy one of them (I knew what it was). They said you can only buy one from the Scorpa importer and it will be decorated as a Scorpa. I never bought an SY250, despite it having the Yamaha motor. I don't think the trials bike marketing people realize the pulling power of the popular and well-respected brands (like Yamaha) for old blokes like me.

Tubeless Dunlops and 1970s Akront rims are not a happy combination. Wider (2.15) tube type rims do work better with tubeless tyres but the fundamental problem is that the bead seats in those Akront rims is too narrow. It's very likely that you will be able to reuse the spokes so give the wider rim a go and if the Dunlop still won't stay on, then use a tubliss. I did an experiment that probably not many people would want to do, but it has worked for me. I wanted to see if I could get a tubeless tyre to stay on a narrow tube-type rim (TY250D rear rim) by cutting a groove in the bead seat for the tubeless tyre bead to key into. I did the experiment about 3 years ago and it has worked a treat. The new X11 Michelin tubeless tyre I fitted (with no tyre clamps) to the TY250D rim has never popped off the rim or slipped and is now almost worn out. I also bought a tubliss at the same time, expecting to need it, but it is still on my shelf

First thing I noticed when I found your KT, still trying, was that it only has one shock!! Hard to be a twinshock without two shocks, or maybe it's just an optical illusion there is another one on the other side of the muffler (out of view) Very interesting design and yes it sure makes the motor look big

I love experimenting with twinshocks too so know where you are coming from. I'm currently making (probably less drastic) changes to a KT and would love to see photos of your "KT". I'll go looking in the "projects" section About your specifying non-progressive rear suspension, if that was an actual rule then the early 1980s OSSA gripper would be excluded, because it has positive rate rear suspension geometry. Also the Godden Majesty 250/320 has negative rate rear suspension geometry so not having progressive geometry is probably not something that could be used in any rules without excluding some completely standard twinshocks. With the brakes there are lots of standard twinshocks including the KT that have a rod actuation for the rear brake so probably shouldn't make cables compulsory for brakes.

A small amount of thin anti-seize compound on both the thread that goes into the cylinder and the thread that goes through the head. When you tension the head nuts to the correct torque, the force on the threads prevents either of them from undoing. You should be able to work out which end is which by measuring the lengths of the holes through the head. Usually the end of a stud that is threaded into aluminium is longer than the end that has a steel nut, because aluminium is softer than steel.

You can also buy zinc-plated spoke kits made in Thailand. That's what I've used on my KT

Having seen what goes into re-sleeving a two-stroke cylinder and doing some of the process myself, I consider that $500 is good value for that job. Buy the material Machine out the old sleeve Machine the OD and flange of the new sleeve and rough out the bore Mark out the holes for the ports Cut the ports Fit the sleeve (shrink fit) Finish machining the top and bottom ends of the sleeve. Finish the ports to size (porting tool) Bore the cylinder to suit the piston Chamfer the port edges In my case it was done to make a big-bore cylinder. It would have been far cheaper for me to buy a second hand standard cylinder but that was not the goal