feetupfun

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

you should be able to change the condenser on a Ty175 without taking any stator coils off or taking the stator backing plate off the bike When you spun the motor with the drill and got 3.5V AC, did you have a sparkplug connected between HT and earth, and what RPM did you spin it at? You used a term for what you did to the killswitch that I thought I had better ask about. Did you bypass it or did you disconnect it? For what it is worth the most common loss-of-spark issues with TY175s are caused by (in no particular order) Worn main bearings Not enough points gap Dirty or wet or stuck or worn points Failed condenser Broken or cracked points or condenser wire Broken or cracked LT wiring Sheared flywheel timing positioning key Failed stator winding insulation (the last few inches) causing a leak to earth Less common: Loose stator coil mounting screws Magnets rubbing on coil laminations Repaint of frame causing poor earths of motor casings or HT coil Pinched or rubbed through insulation on killswitch or LT wiring Faulty HT plug cap

HDPE

for the adjustment problem: you didn't mention the ball between the pushrod and the mushroom rod. They can fall out unnoticed while you work on the clutch for the heavy action: inspect the camshaft for wear where the rod end rubs you might have been sold springs that fit, but are stiffer than TY175 springs. A lot of Yamaha models use similar but stiffer springs. Try the old springs lube the cable Because you have a combination of heavy action and lack of adjustment, it is also possible that you have too much plate stack height. Compare the thickness and quantity of the old plates with the new plates

Two strokes don't usually have oil filters

I think you want bigger front sprocket not smaller

As for the question of there being a need to remove mass from both ends of the shaft, it makes no difference to flywheel effect which end of the crankshaft the mass is removed from. It will however cause the bike to balance a tiny bit off vertical if you only remove mass from one end of the crankshaft

If you really want to, it is possible to calculate how much a difference a given change in flywheel arrangement will make to the total "flywheel effect". This will involve working out the total flywheel effect for the crankshaft (all 5 flywheels in the case of a Sherpa T) and the clutch and comparing it with the calculated flywheel effect after making the proposed changes. In the case of the machined-down drive side flywheels in taff_d's photo, I suggest if someone wants to reduce the flywheel effect, only machine the wheels narrower rather than reduce both their width and diameter. This will give you a much bigger (gravity) weight loss for a given reduction in flywheel effect.

I think there are new aftermarket tubes available from the US and the price is pretty much the same as getting the originals redone. Those tubes on Greg's bike came from a different bike that had 30mm tubes. From memory they might be from a CR80. I have seen other TY175s with shortened tubes from 80cc MX bikes. Early DT100,125 and 175 and early Yamaha AG bikes had 30mm tubes too, but because they are just as old as TY175 tubes it is rare to find good ones. Last time I had a set done (in Brisbane) they were $150 per tube plus postage, but it has probably gone up since then

If your "new" condenser is from 40 years old stock then it may have failed due to age. I use "recently-made" condensers and fit them externally. Another possibility is that you have not fixed the root cause by fitting a new condenser. There are lots of possible causes for an intermittent ignition problem Depending on your attitude to life, there are lots of options for how to get your bike reliable. Some people love to fault-find logically, some people like to have a completely original bike, some people want to spend the least amount of money possible, some people like to take a random approach changing things here and there and some like to minimise their stress levels. Modern electronic ignitions are very popular for good reason

My friends bike (175cc with the shorter extension (35mm I think) and 5mm lower axle slot) has the standard frame loop and feels lovely to ride, slightly more stable than standard. I'll see if I can find a photo of his bike Mine is 205cc and 45mm extension and is also very nice (more stable than standard) Photo of friends bike attached. Note his bike has non-standard fork tubes (much longer than standard)