feetupfun

MT13 Pirelli was certainly the hot ticket when I was a kid (late 1970s). My memory tells me that the other proper trials tyres at the time were either Avon or Dunlop

There is no law against using a roller. I've seen plenty of twinshocks with a roller on the tensioner arm instead of a slider. Whatever rocks your boat.

Wet trial = heat up brakes after trial before loading bike into transporter to get drum surfaces as dry as possible. When I get home, clean external mud off bike then take wheels out and dry brake parts fully. Then some time before the next ride, service the brakes

Wossner make 2.0mm oversize for TY175 and are good quality

still trying, you have ignored the friction at the interface between the cam and the rubbing plate and this friction causes loss of feel that gets progressively worse as the angle increases, and as guys says, jamming on of the brakes at higher angles. The best feel and strong braking is achieved by matching the shoes to the drum and minimising the cam angle. Depending on the cam width, 3 to 5 degrees cam angle is usually enough to provide a suitable working clearance for the shoes

Yes I'm 57 and same problem here. To see well when riding trials I have had a set of single focus (distance) lens glasses made and they are really great for riding trials. Only problem is I cant see clearly up close so using a smart phone or fiddling with carby jets is not on. I also had bifocals made with only a tiny bottom lens but I didn't like them anywhere near as much as the single focus pair for trials riding

Discs can be severely heated and not affect the hub, but if you heated up a drum to the temperature that people heat discs to to water-quench-clean them, the bearings would fall out and the grease would catch fire, and if you have a Bultaco hub with the replacement steel or cast iron liner fitted, the liner would probably fall out

It should clean out of the engine pretty fast without doing any special washing out. I had a two stroke lawnmower that had the tank accidentally filled with diesel and the person borrowing it attempted to start it (until they broke the starter mechanism). I fixed the starter, drained the tank and carby and put premix in the tank. It started up fine but the exhaust fumes smelled terrible for the first few minutes

I think that is the one Tim has seen but he might not have noticed that every second page is in English

5kg sounds fairly optimistic for an engine

as bigshiney bike says, but the crankshaft drive gear is on a taper, not a press fit

Pretty sure there is a Haynes workshop manual for TY175

I reckon that Yamaha just want to have their livery on show wherever possible. Back when they were selling motors to Scorpa for use in Scorpa trials bikes, the bikes that the Yamaha sponsored riders rode in Japan were Scorpas but decorated as Yamahas. Now that Scorpa trials bikes no longer have Yamaha motors, Yamaha can make a semi-works trials bike any way they want and decorate it as a Yamaha and vive la difference. It's not as if they are going to redecorate a Honda 4RT in Yamaha livery. I just wish that Yamaha would (once again) make a decent production trials bike and sell it internationally.

Yes the replica KT bars are about an inch higher than modern 6" Renthals. The bars on my M49 in this photo are a bit higher again than the replica KT bars and were custom made from thick-walled 7/8" structural aluminium tube to replicate the shape of the bars that people rode with on these bikes when they were new. The bars provide very nice ergonomics on this bike for me (5' 10") with the footpegs in the original location

I've just noticed that your bike appears to have shockies that are quite a bit longer than most people use on that bike, which would be contributing to your neck discomfort because the rear of the bike (including the footpegs) will be higher than normal

Because the bar clamps are now so much higher than standard, you have created a severe limitation for how far you can get your upper body forwards. This is one of the reasons Fat bars (that have no cross-brace) are popular. I see you have bars with no brace already, but you could improve your chest clearance and still have the extremely high bar-end position by having custom bars made that have a higher rise. You look quite tall, so could probably benefit from lowering the footpegs which would allow a less extreme bar end height and still have a comfortable neck angle.

Bultaco brake pedals don't usually have a return spring on the pedal, or the rod, or the cable, but there is no good reason not to fit one if you want to. If its the hole I'm thinking of it's for the brake light switch actuating link/spring. Some rear brake light switches mount on the swingarm and some mount to the frame above the swingarm pivot

It's standard thread direction

If you measure up a set of modern footpegs you will see that there is not enough space to fit them between the bike frame and the kickstart lever. Options for using modern pegs include: A device/method (locking pin, wire hook) that holds the peg up while you kick (popular) Lift the peg to let the kick lever go past it, kick start the motor, then let the lever retract past the peg. If you have a suitably light return spring on the peg this works fine. The kickstart doesn't engage until it is at peg level anyway (popular) Don't use a RH footpeg spring and keep the pivot action free. The peg will stay up if you lean the bike a bit too the left as you kick (popular but not legal in some places that require spring-return pegs) Reshape the kickstart lever to clear the peg end (not recommended due to the kickstart lever knuckle already being a bit flimsy and this method puts extra load on the knuckle)

The Yamaha Ty175 clutch cable works very well

Sherpa T rims are not meant to be central to the spoke flanges on the hubs, but sometimes are respoked centrally, which puts the tyres off-centre

Yes they are a bit zippy I think on watercooled bikes people sometimes use two base gaskets instead of one base gasket to reduce the compression ratio if needed. Yes it changes the port timing too but that is what I've heard. 3mm spacer under the head would be way too much anyway. I would think 0.5mm to 1mm would make a noticeable difference to compression ratio

Guy, young riders who ride twinshocks set a faster idle than you or I would usually have and they use the clutch almost everywhere so it is not really a "bike" thing, more of a "rider" thing when or if to use the clutch. I confess to using the clutch sometimes on my old trials bikes

If the sleeve is big enough to be touching the 8mm cylinder studs and is concentric with the PCD of the studs, then you should be able to go to 72.5mm bore

If you post a photo of the piston and the important dimensions of the piston it will make identification more likely