feetupfun

The chamber in the photos has not been opened for cleanout previously. On something like a Bultaco trials bike, cutting out a flap or hatch and butt welding it back works well because there is a lot of space between the wall of the chamber and the cylindrical mesh tube inside, and the tube is only held at the ends. On a TY chamber that technique does not work well because the internal perforated mesh is attached by welding to the outer wall very closely in many places. If you want to clean it mechanically (and I'm not suggesting that is a good idea) you need to cut the chamber in half lengthways, cut out the perforated mesh, fit the packing, weld back the mesh then weld up the chamber. I recommend burning the chamber clean. Keep it at or below red heat. Some people use a wood fire. I use either a large LPG (Propane) torch or an oxygen-acetylene torch. It should take about 10-20 minutes to do.

If it was me I'd burn it out. If you are dead-set keen to keep the packing intact, try the hot tub first. Your locations 1 and 2 would allow you to fix only the areas where the holes are cut. The chamber has to be cut in half and remove the perforated mesh to do the job properly

Sounds like the casing has pressure inside for some reason. Maybe the vent is blocked and when the motor warms up due to expansion of the gas inside it generates pressure that is not being relieved. Could also be a drive side crank seal leaking.

The main chamber has packing too. It is a thinnish layer between the outer wall and a layer of perforated steel mesh that follows the shape of the outside. It doesn't actually make much difference to the sound if the packing is functional (dry) or gooey or absent, but it is certainly a lot lighter if it is not gooey. If you heat the main chamber to a high enough temperature, the packing will change from being a fibrous mineral cloth to a glassy viscous liquid. If you do it right, the molten glassy material will flow out of the chamber. If you are someone who is fastidious enough to want to completely restore the main chamber to original performance, it is possible to cut it apart, remove the perforated metal, remove the gooed up packing and fit new packing and weld everything back together again. There are photos somewhere in the forums of how someone cut theirs apart and rebuilt it.

The thing that looks like a wagon wheel is the swirler part of the spark arrestor. It causes the exhaust gas to accelerate and spin. By making the exhaust gas spin as it moves rearwards, carbon particles (sparks) are caused to move outwards and become trapped on the outside of the inner tube, while the gas flows through the inner pipe. The wagon wheel looking thing is made from cast aluminium and will melt if it gets hot enough. The second zone of the end muffler is the muffler and to quieten the exhaust, requires the mesh to be clean and to have dry muffler packing around the outside of the mesh.

The double-chamber muffler looks interesting. How does it work?

Standard TY250A end muffler has a cast aluminium swirler inside that is part of the patented "Yamaha-Krizman" spark arrestor mechanism. If you burn this muffler out, the swirler usually melts and the motor then runs much better

The usual technique to avoid wasting money is to get the person doing the re-boring to measure the cylinder and tell you which oversize piston kit to get before you order the piston kit

Your best bet is to either ask on this forum or phone a Bultaco parts shop. There are thousands of people who know Bultaco Sherpa Ts intimately. Many of them look at this forum. There is no compiled cross-reference of model parts to refer to. The parts don't come with the part number marked on them. They did come in packaging that had the part numbers. Some parts changed during the production of a single model designation. There were some years when more than one model of 325/350 Sherpa T was released. Some models were sold for more than a year. Some parts were unchanged on subsequent models. You have a common model that will not be hard to sort out.

I'm guessing its the fuel tank vent hose. Being fairly elaborate-looking I'd say that it comes with the bike to enable it to be sold in some countries that require a one-way valve in the vent hose for emissions laws compliance. Does it have a vacuum operated fuel tap? Some bikes have a fuel tap that opens automatically when the engine is running and this could be the hose for that. Maybe it's the coolant system vent hose.

They are about $20 from Wiseco sellers

In 2010 I said they fitted perfectly. That means I didn't have to alter the piston or the cylinder or the crankcase or adjust the ring end gaps to be able to use it. One engine was a TY250B and the other was a TY250D. I haven't fitted any Wisecos in TY250 motors since then. I'm eventually going to re-bore my TY250A which is still on the original piston and rings, because I just rode a friends TY250A which had a fresh rebore and mine is a bit down on power compared to his, which usually means worn rings, especially if they are 44 years old like mine are. I'm thinking of using a Wossner piston kit this time. I'm not interested in just fitting new rings.

Here's another ventilation hole I found in a M85 frame. The wasp thought it was just perfect

lorenzo I just checked a couple of M85s for the hole in the underside of the rear loop and they both had the hole you described. My thought is that hole in the M85 frame rear loop is for ventilation to avoid problems with internal pressure during the welding process. It looks similar to the holes required for tubular structures to be safely hot-dip galvanised.

Might be the military version Sherpa T with a gun-rack (joke) They did make a Sherpa T model that had a dual (long) seat. What was your frame number prefix again? I think the dual seat Sherpa T model was prefix 221 and it would have had a seat like a model 212/213 Alpina

Those frames were made at a time when Bultaco frames were starting to be made from chrome moly steel so it might or might not be. Not a problem though because you can successfully weld chrome moly tubing to other common alloy steels and to mild steel. If it was me I would use whatever I could find that was the correct OD, so it looked right. Frame tubes under the engine on a trials bike cop quite a beating so going thicker wall than what you might use if you were trying to make it as light as possible might be a good idea. I would use 2mm wall or thicker. If you want to measure the existing tube thickness, grind part-way through the tube with an angle grinder somewhere in the damaged area.

I would be looking nearby or in the crankcase for the missing needle roller and next time if you warm the piston up, the pin will push out by hand

If it runs OK once you get "above" the flat spot, it's likely to be a problem with the pilot circuit

Wossner and Wiseco TY250 pistons are both a good thing. The piston/bore clearance for a Wiseco will be different to what is in the Yamaha manual. The reason there are lots of standard size genuine Yamaha pistons still available is that it is much more expensive to have a new sleeve fitted compared with a rebore. Now that Wossner make pistons up to 2mm oversize there is even less demand for having TY250 cylinders resleeved. TY250 cylinders last a long time between rebores if they are used for trials and have been looked after. There are still plenty around with the original piston and rings in them. I had a TY250D motor rebored about 11 years ago and used a Wiseco piston and it still going great.

If there is looseness in the fit of the tensioner wheel then it might be precessing (not sure of this is the right word). What I mean is that the tensioner wheel could be wobbling. If it is, then it will wear the bushing rapidly and fail. I would suggest either leaving the tensioner off or buying a new one. I run a M49 without a tensioner since I rebuilt the motor about 4 years ago and have not had a problem. The tensioner probably helps the chain and sprocket teeth last longer than without having one, but there is always the risk of the tensioner failing and causing damage to the casing and clutch. Judging by the number of internally damaged Bultaco clutch casings I have in my collection, having things come apart inside that casing is not uncommon. Your video reminded me of a Bultaco M99 (325cc Alpina) I had when I was a kid. The chain was so worn on it that when the motor idled, the tensioner arm would tap against the inside of the casing.

If you post up the dimensions and a photo of your 123 swingarm, you might find that someone will have a look at their trials bikes to see if the swingarm from something else (other than a 172) will fit.

Whether it's a new fibreglass tank cover or this old fibreglass tank or even an aluminium tank, they all need repairing after damage. If it was me I'd seal it and make it look pretty again and use it. If I had to pay someone to do the work then it would be a harder decision

Yes that's an A model flywheel. The B and later model flywheels have a bigger external steel ring than the A model external steel ring.

OK I'm gonna have one more go before I give up. You don't need to take the head off to find top dead centre. Take the sparkplug out and insert something rigid that will reach the piston crown. There are special tools made just for this job but you can alternatively make something up. It is called a top dead centre tool if you want to go looking on the internet. It doesn't even need to have a measuring scale or a dial indicator because you can determine the amount of advance in mm around the flywheel rim using geometry, and I have told you already the distance is 21 mm. You just need to mark TDC on your flywheel so it lines up with something on the casing and measure 21mm anticlockwise from there and make a mark. The only important things about the points is that they start opening when the piston is at the timing mark, they conduct electricity when they are touching and when they are fully open, the gap is not too big or too small. To make a simple tool to show clearly whether the points are open or closed, use the points as a switch/contactor in a low voltage DC circuit that includes a DC supply and a light bulb. When the points are touching, the light will be bright. When the points are not touching, the bulb will glow less brightly. Disconnect the points wire from the HT coil before you start. It is at this disconnection point that I connect one side of my DC supply, if I am using the bulb method. The other side of the DC supply goes to somewhere on the motor casing. The light bulb method is popular, as is using a cigarette paper between the points or using a buzzer or using a volt meter or using direct visual observation of the points. They all work