feetupfun

Neither of those are oversize markings so if that's all there is on the crown, then it is likely to be on the standard bore. The safest bet is to have whoever is going to rebore the cylinder measure the bore to advise what the minimum size piston kit is you should get.

I know I've got a spare TY250A lever that is undamaged but like I said, I'm further than Guy so the postage would be expensive. I just looked on eBay and there's one advertised for sale in the US for US$22. There's no way I would sell mine that cheap

I'm still here. What is it you are after?

https://www.yamahaty.com/english/ty125en/elec125en.html

Lorenzo answered about the sleeve gear type that has the sintered bronze bushes. Sounds like that's what you've got

Inspect the gearbox output shaft. It is a short shaft that will have either a pair of sintered bronze bushes or a pair of needle roller bearings inside where it runs on the main gearbox shaft. Both types can wear/fail and cause consequential damage to the gearbox gears due to misalignment (breaks teeth off). Wear in the sintered bush type is very common. Both the shaft surface and the bushes might be worn. I haven't seen a needle roller type fail but it would probably be more spectacular. Check that the kickstart return stop is not bent or burred and has a nice action. This is a fairly common failure point. Also there is supposed to be an aluminium washer on the end of the kickstart shaft. This may be worn out or missing.

I couldn't hear any chirps. Maybe the high frequencies have been lost during the recording. Do you mean the farty noise when you close the throttle? (this is a normal thing)

https://newellmotorcycles.com.au/pages/bultaco-history your frame is a model 150 and your motor is a model 80. Open the link and you will find the years for your frame and motor

It's quite normal for people to ride twinshock bikes in events that don't have a twinshock class

Every second-hand Bultaco I have ever bought has needed to have the crankshaft bearings replaced. They don't last long. There are a few other things inside the motor that may well also need attention. I suggest you use someone who has a good reputation for rebuilding Bultaco motors. There are design quirks that catch people out on their first Bultaco motor rebuild.

My 138 Alpina is the model that followed the 116 and it has a standard-bore 370 Pursang piston in it whatever diameter that is. I don't remember what stamping the cylinder had.

When fully assembled and with the motor stopped, the main gearbox shaft usually needs to be wiggled (by rocking the bike) to allow it to change gears. It looks like you have taken the clutch off. This usually allows the shaft (and the gears on it) to move axially out of their ideal positions, making gear changing harder. The clutch nut holds the shaft in the correct spot.

The benefit of the Rev 3 200 that we bought for my wife (who was a trials learner in the 2000s) is that the throttle response is gentler than the bigger Betas and it is easier to kick over to start than the bigger Betas. There's not much in it though. A 250 is fine for a beginner with a slow action throttle and if necessary the additional options are reduced compression, additional flywheel mass and retarding the ignition.

Yes and I wish I could buy it here. There is no Australian Importer

Jon I'm wondering if the "ELF Indoor Racing Fuel" (which we can get here) is as good as the Aspen (which we can't get here) for people's health because apparently that ELF fuel is designed to reduce the toxicity of the exhaust fumes when indoor racing karts and MX bikes.

Yes lead in petrol was a crazy idea but it was introduced in the 1920s because it was a cheap way to improve the octane rating. It was when leaded petrol was phased out in the 1970s and 80s that some engines developed premature valve seat recession and it was recognised that the lead had been a benefit to the valve seats.

Plenty of people have used a dishwashing machine for engine parts. A dishwasher will make the fins bright but only for a short while because they use a caustic solution which will dissolve some of the aluminium and leave it microscopically rough (open to rapid corrosion). Steam cleaning will not remove the existing oxide. Dry blast will remove the stains and oxide and will leave it microscopically rough (open to rapid corrosion). Vapour blast will clean the fins of oxide and stains and smooths the aluminium surface which greatly reduces the future rate of staining and corrosion.

I think you have described extreme lean fuel/air mixture with throttle slide at idle position. The "choke" is not a choke. It is a fuel circuit that provides a rich fuel/air mixture to help starting a cold motor. When the throttle slide is above the idle position, the starting circuit does not flow. That's why you can ride it around with the "choke" on but with the motor warmed up, it is too fuel/air rich when the throttle is in the idle position. There's a couple of things it could be. Most commonly due to blocked or restricted pilot circuit in the carby. Usually caused by the bike being stored with fuel left in the carby. Possibly due to air being sucked into the motor that is not going through the carby. Commonly due to leaking flywheel side crankshaft seal or at the rubber boot between the carby and the reed cage. Sometimes (very rarely) leaking cylinder base gasket.

The ideal fit of the pin in the piston is such that it has no play when the motor is running. Aluminium expands more with increasing temperature than steel, so piston pins need to have a slight interference fit when at room temperature. For this reason, it's fairly common (in any motorbike engine) that a piston pin may need more than a push with a finger to get them to move at room temperature. Common methods for dealing with this are to either warm up the piston or use a piston pin puller.

That is true if completing the reassembly of the motor with the motor separate to the rest of the bike

I use a socket with the OD machined down to fit onto that nut. Yes a clutch holding tool is required the way you are doing the work, but if you are going to pull a Bultaco motor apart again, consider loosening the shaft nuts with the motor still in the frame and a chain and back wheel in place.

Yes brake was originally on the right but it is very common and easy to convert the late model Sherpa Ts to brake on left to get a better feel. Brake on right used a bowden cable to cross over which dulls the feel. The change to brake on right was around 1975 not 1985. The shocks look like gas Girlings which were a popular aftermarket choice back at the time when this was a new bike. Yes the fork tubes can be rechromed. Also new tubes are available at a comparable cost. If this is a 198B/199B which is what it looks like, it is a very rare bike, and the last Sherpa T model made by Bultaco. As for the year they don't really have a single year because they were produced over a period of a couple of years in the early 1980s when Bultaco was in the final stages of closing down. For parts supply, the best thing to use to identify the bike for the parts supplier are the engine and frame numbers

Not a production bike. I can see Yamaha and Honda parts and a lot of custom work. Frame started as a pressed steel backbone type Honda frame.

I'm quite interested in the development in the design of Bultaco frames, especially Alpinas and Sherpa Ts.

In Australia Yamaha fitted minimalist road rego equipment and gained approval for road registration. I rode my 1996 model until 2002 and absolutely loved it. It was a very capable bike for racing and exploring and was totally reliable. The power curve was amazing (no steps and plenty of go at all revs). With the standard exhaust it was so quiet I had many close up encounters with emus and kangaroos who had not heard me approaching.