feetupfun

A friend of mines 2001 Rev3 developed what seemed like too much sag on the forks and on investigation he found the spring was broken

may also be restricted tank vent

pretty confusing post there Steve. Head gasket goes at the top of the barrel not the base of the barrel. Or maybe you are talking about problems with both the head and base gaskets?

what year did they have come out?

To save a lot of unnecessary work, before you start pulling it apart you need to work out if it is a fuel or a spark issue. To help with diagnosis, crank seals will not cause a bike to cut out. It will make it run lean when the throttle is in the closed and almost-closed position. Even if the float bowl is clean, and fuel flows from the tank, that does not mean there is not a fuel problem. You should inspect the plug immediately after the failed start attempts to see if it is wet or dry. Sudden cut-outs sounds a lot more like ignition problems. If it starts and runs when cold but cuts out when hot, it is most likely the condenser. If you haven't serviced the points, that can also make the spark less energetic. Also just because you can see a spark when you kick it over with the plug out, does not mean there is a spark when the plug is back in the motor, because the increased pressure in the combustion chamber means that a higher voltage is required for the spark to jump the gap. The colour of the spark can say a lot about the health of the ignition. Pale blue spark is the most energetic and yellow/orange/red is least energetic

For next time, and when you want to tighten it, don't hold the magneto flywheel because you risk twisting the crank out of alignment. Ideal method to undo - use rattle gun Next best method - jam a thick wad of rag in the pinch point of the primary gears For doing it up again - use rag method and a torque wrench, and loctite on the thread

All bikes have play in the drive. They differ only in degree. In trials riding you will ride a lot better by gently using the rear brake against the throttle to provide the fine control you seek. If you are concerned from a mechanical damage viewpoint, I would check the gearbox output shaft spline fit, the swingarm pivot, rear wheel bearings, rear sprocket bolts, clutch inner nut and the primary drive gear nut. Many bikes have a cush drive in the clutch between the drive gear and the basket but the previous respondent says that the Reflex does not. The best way to find where the slop is, is with the bike on a stand and in gear with the motor stopped, rotating the rear wheel back and forwards. When I was a kid and had not been trained in how to ride trials, I went through my TY175 from end to end fixing things to reduce the slop in the drive, even going so far as to fit custom-made cush rubber segments in the clutch instead of the Yamaha items, to reduce the slop. It made absolutely no difference to the way it felt in sections. The first time someone showed me about using the rear brake to avoid the slop, it was a revelation.

yes both seals can be changed without splitting the cases. The primary drive side seal is easy because there is a removable sleeve on the shaft. Buy a new O ring that seals the sleeve to the shaft. For the magneto side I usually use a self tapping screw, or two screws on opposite sides, screwed into the seal and pull carefully on the screw.

Yes they work well. So well I only use one of them on the rear and have never had a problem with the tyre moving. A warning though - they are a bit blunt ended which creates recesses at the ends of the clamp plate that can cause a tube to fail if you use too much pressure seating the tyre.

Rims or rim? Modern fronts are tubed

All the bikes shown in this topic so far have their standard upper shock mounting (ie they are not modified). Yes it seems that there will be too much bending moment in those frame tubes, but it seems to work out just fine in real life

bestrcpilot, I'm interested in building a replica OW10. Are you willing/able to share the blueprints you generated?

There are different rules for twinshock trials bike eligibility in different parts of the world. TLS brakes lie in a grey area in our part of the world for trials, because the only common dirt bikes that had them back in 1982, were MX and enduro bikes that also had monoshock rear suspension, and some people consider that any parts from a bike that was originally a monoshock, should not be allowed in Twinshock Trials. Luckily we are a laid-back lot and don't really care much what forks or brakes are on a Twinshock trials bike, and the rules are suitably vague, so there has not been a protest that I know of. Nice looking bike by the way, especially the graphics and finish on the fuel tank. Also thanks for showing the brake pedal. My Whitlock TY175 frame came without a brake pedal and I am planning to make one that looks correct. What is that kickstart lever off? I'm guessing Yamaha WR200?

you can't get more original than this

Have a look in the topic about Mini Majesty seat/tank Units after your question there. I posted a photo of a full-size Majesty 175 for you

The question is about an odd-looking item on the parts diagram that appears to fit into the cap of the chain oiler

for Scorpa250 - full size Majesty 175 - not red though

Weird hey? Maybe it's a magnet? That cap on my TY250A fell off years ago so I can't check what it does

Here are photos of a friend's bike with a Sammy Miller TY175 seat/tank unit on his TY175 Mini Majesty

I haven't ridden a 4RT since 2005, but would get the Repsol if I was getting a new 4RT. What's strange about that? Where I live the new year models of most brands only come in one or two shipments and most bikes are pre-sold anyway. The only time I have ever had a chance to have a go on a demo bike of a new model was the 4RT when it came out, and the Rev4 250 when it came out. If you wait to ride a mate's new bike of the type you are interested in, there are none left in stock, so you have to wait till the next year's model, and then it will be different anyway. One of my riding friends wanted a Rev4 300 last year and it took about 6 months for him to get it. Is that enough reason to buy a bike without test riding?

Ok just pulled a seal out and measured. The distance from the seal seat to the circlip groove is 12.5mm and the seal is 10.5mm thick

Something sounds fishy with the 15mm dimension in your forks. I would have thought that standard was about 12mm. I will measure some TY250 forks in the morning. Be aware that the circlip is not really essential unless you are going to run with air as the spring. Plenty of times when I've gone to remove the circlip there has still been clearance to the washer that was there when I fitted them - ie the seals have not moved away from their seats in use, and I use anti-sieze on seals so they are easier to get out when I change them. I also run sealed fork caps in my Bultacos that do not have seal retainers and have never had one of them have the seals move either.

It's not unusual to need a few basket cases to make one complete bike. I have a TY250B that is made up from three bikes that were all worse than what you have there in their own way. You can always sell off the excess bits when you have a complete bike, to recover some costs I like that saying Guy

I thought it was common to have a steel backing in TY250 fork seals

your photo shows what looks like the steel innards of a seal with a piece cut out. You say you have tried all methods but did not mention which methods. To loosen the steel "flange", gentle heating of the aluminium slider around the "flange" would be a good idea. After that, a slide hammer with a 90 degree hook on the end of the shaft should get it out without damaging the aluminium. If there was a seal under the "flange" then what you have there is not a standard arrangement. I'm thinking maybe someone replacing the seals previously could only get seals that are thinner than standard, and used the steel part of the old seal as a spacer to make up the difference.