feetupfun

I was in the same boat as you a couple of years ago. There is probably no need to modify the bike, just keep practising and the sensitivity of the controls will miraculously become exactly right as your brain adjusts. Be patient. It will happen. Yes, a slow action throttle tube can help you adjust. You will find that modern clutches are absolutely fabulous to use once you get used to them. Same for brakes and throttle too. I don't get what you are saying about the clutch lever. You should be able to use one (usually the index) finger with the standard lever and rotate the bar clamp wherever you want.

Dave, there are a few different pistons you can use. The cylinder spacer is to compensate for the different gudgeon pit height of the new piston compared with the TY175 piston (the top surface of the new piston must be at the same height at TDC and BDC as the old piston) A popular choice is to use a TY250 twinshock piston. Another you can use is the KDX220 piston. Another is from a Yamaha Blaster (I think) quadbike. The TY250 piston has a bigger diameter gudgeon pin so would need the pin holes sleeved down. Can't remember about the other pistons re pin diameter. The cylinder will need to be resleeved. The crankcases will need to be machined out to fit the new sleeve OD. I don't know what other people do with the head but mine was machined to suit the new bore diameter. A much easier route for better TY175 trials performance is to take a bit of weight off the flywheel and fit a very thin head gasket. Top end performance can be improved with a bigger carby but at the expense of some low RPM throttle response.

About how the water gets in there- There are many possible routes for water to get inside the crankcase of a Sherco two stroke. You have checked for water leaking from the coolant circuit so scratch that. You don't often wash your bike (me neither) so scratch that. Water can condense out of the air if the inside of the engine is cooler than the dewpoint of the air. Depending on daily temperature swings and the amount of water in the air, it is possible (and in some places very common) for liquid water to build up inside things like fuel tanks and engines. It is why steel fuel tanks rust out so quickly. Water is also a significant component of the products of combustion in petrol engines so no matter how warm your motor gets, when you turn it off, some of the water which is in the form of a gas in the combustion chamber will turn to liquid water as the motor cools down. Being a two stroke, the combustion chamber is usually open to the crankcase with the motor stopped so it gets water in there too. About the oil- Yes mineral based two stroke oil will protect the bearings from rust better than synthetic oil when stored but if you are riding your bike every two weeks it is probably not necessary nor advisible. It would be the sort of thing to do if you were storing the bike for months in a wet climate. Using semi-synthetic oil can be a good compromise for preventing corrosion and minimising engine wear. Thats what I use too. Something else to think about- I hope you are totally sure that the bearings are failing due to corrosion. There is another possible mode of failure that is common in 1970s Bultaco motors that sounds like corrosion failure with the motor running, but when you have a look at the bearings, there are thousands of impressions in the bearing running surfaces caused by tiny particles of hard carbon being squashed between the rolling and fixed elements. Bultaco motors are more susceptible to that mode of failure than many others due to a couple of factors. One is that due to the design, there is no through-flow of fuel-air mixture to keep them cool and clean. Most other bikes have a hole ventilating the space between the bearings and the seal which provides a cooling flow. The other relevant Bultaco design feature is that there can be significant side loading on the main bearing races due to all four bearing seatings having an interference fit. Some people fit a roller bearing on one side to avoid this problem. Its a hunch, but maybe Shercos also suffer from this carbon particle induced damage. If the reason for the short life of your mains is this, then you should use the highest quality full synthetic oil you can get, at the mixing ratio recommended by Sherco, to minimise carbon formation. Using sealed bearings would also provide protection of the surfaces from carbon particles, but you would want to be sure that the grease inside was suitable for the duty.

After-ride easy-to-do sequence to minimise risk of rusty mains: Wash bike Fit a clean and freshly oiled air filter element Run motor enough to warm it up and to blow any free water out the exhaust Pull the starting knob to get it running very rich just before you turn the motor off Plug the exhaust For extreme protection: Before storing, run the bike on 20:1 premix using mineral based two stroke oil and petrol with no ethanol. Store it somewhere with a low relative humidity and minimal daily temperature swings.

Neo I'm with your wife on this one. I've been camping and bushwalking up the top end in summer and it is not the time and place to go trials riding. People are flat out staying conscious just walking slowly in the shade and it only gets slightly cooler at night. David

Chris Maybe the number is actually B440483 and the stamping of the second number was a bit poorly done in which case it would be an Explorer (and the frame will look very much like an MAR). A decent set of photos would be helpful for identifying your bike. I suggest you include photos showing the front mount for the rear mudguard, the wheel rims, the fork sliders and a close-up side view of the swingarm. Regards David

Synthetic oil has a higher film strength than mineral oil at the same temperature so it can generally be used at a lower ratio for the same protection. Synthetic oil creates less visible smoke if used at the same ratio. Using synthetic oil means it will take longer to clog up the exhaust pipe with gunk and form carbon deposits in the exhaust port and inside the head and on the piston crown. An air cooled motor sees a very wide operating temperature range which puts it more at risk of lubrication film failure than a liquid cooled motor. Synthetic two-stroke oil resists film failure due to high temperature better than a mineral oil will. It's not all good though. A fully synthetic oil is not as good at protecting the engine internals (conrod bearings in particular) from corrosion when it is not being ridden. My bikes sometimes don't get a run for months at a time so to provide good corrosion protection I use a semi-synthetic two-stroke oil. I live in a very hot climate and sometimes have problems with motors overheating during the extremes of use (my Cota 348 in particular is prone to heat related problems) so tend to mix my fuel for air cooled two-strokes on the conservative side at 3%. If I lived somewhere cool where motors have an easier life, I would probably use a lower ratio like 2% in my air cooled motors.

Here is a picture of the diode used on Yamaha twinshocks to prevent the motor getting a spark when rotating backwards. This diode is from a 1977 TY250D

Yes 25% oil is too much. It should run fine if you use somewhere between 33:1 (3%) and 50:1 (2%), full synthetic or semi-synthetic. Ideally you should not use two different oils together so either continue to use what is in it already or drain the fuel tank and carby first if using a different oil.

Hi Michael Yes I have ridden both a M92 and a Cota 348 in standard trim recently. I would have said that the 348 responded to throttle input faster than the Sherpa, and the Sherpa had a slightly higher resistance to stalling at extremely low RPM. Are you sure the 348 you rode still had the clutch side flywheel in place? They are easy to remove and some people prefer the bike without it. David

Dave what did you think of the handling and steering of the Miller framed bike compared with your M92?

PeterB Where do you recommend getting one of those DellOrtos from? Thanks David (also from the West Island of NZ)

This may help you with your TY250 cylinder ID. The first TY250 twinshocks (sold here in 1973 and 1974) were called TY250 and had engine and frame numbers that start with 434. These tend to be called TY250A nowadays. The stand is on the frame, the tank is steel, there is a TK carby, the bashplate was fibreglass and they had the bulging engine covers. I suspect the next model was not sold everywhere in the world but here in OZ there is a model that was released in 1975 we call the TY250B that also has an engine number prefix of 434, but the frame number prefix is 493. The B model has an aluminium fuel tank, the stand is on the swingarm and they had a black Mikuni carby. The relevant bit here for you is that while the A and B models both had an engine prefix of 434, the B model cylinder finning goes all the way around the front above the exhaust, while the A model cylinder has a wide gap in the finning there. Later model cylinders (1976, 1977) have full width finning all the way down the cylinder. I've heard annual sales of TY250, 175 and 80 were around 30,000 throughout the mid 1970s.

Hello Felix If you are getting gearbox oil into the crankcase once the motor gets hot, you may have a problem with the vent for either the gearbox or primary drive case. If one of the vents is blocked, there will be pressurisation when the oil gets hot. Bultacos like yours usually have two vents - one for each compartment. The primary drive vent is usually a hole in the filler cap (at the front end of the primary drive casing) and the gearbox vent is usually a hole through the filler plug (located under the carby). The path of the oil leak may well be as Swooshdave found with his bike (through the centre gasket), or it may be through the crank seal or crank seal holder gasket. You may find the leak is not a problem once the pressurisation problem is fixed. David

You should make the electrical connection between the red coil and the frame as good as possible. If that means cleaning the paint off the mounting screws and washers then yes do it. If you have painted the mounting tab for the coil, or if it has a film of rust, it would be a good idea to clean up the mounting tab where the red coil makes contact with it to maximise the quality of the connection.

I fitted Boyesen reeds to a TY250D twinshock motor at the same time as it getting a rebore. It needed the air screw adjustment changed to get the jetting right again. I cannot feel any difference in performance or response riding that bike compared with another bike I have with a recently rebored TY250B motor fitted with standard Yamaha reeds. Both motors are standard except for both having their flywheels lightened the same amount. A riding friend fitted Boyesen reeds and a reed case spacer to his TY175C at the same time as a rebore. He could not attribute any performance improvement to the reeds or the spacer.

I can remember my Dad suspending a whole Norton 16H by the barrel when I was a kid. The idea was that the weight of the bike would keep the piston/cylinder sticking issue under load continuously. Soaking in penetrene and a hit on the piston crown every day with a wooden drift got it moving after about 4 weeks - lots of patience there. The 16H had been parked beside a sand track through the dunes at the back of a beach for about 20 years (with the oil tank lid open)

My (1976 Oceania) TY250 has an ignition diode, but it is a solid black object about 5mm square and 20mm long, in the ignition wire between the points and the HT coil and is located near the carby. The object on that European TY250 in the photo looks to me like a power resistor used to reduce the current to the battery when the lights are not being used, or in the case of the bike not having a battery, to reduce the voltage to the lights.

If you want to work out if your tyre is a tubeless type or a tube type, read the writing on the tyre wall. It should say "tube type" or "tubeless"

The timing does not have to be wrong for the motor to run backwards. With the timing set perfectly for running in the normal direction, a TY175 will also run backwards. It will be less responsive and less powerful than when running forwards because the timing will be retarded compared with ideal. Although it is possible to get one with good timing running backwards by half-hearted kicking, if it happens frequently, the timing is probably too far advanced.

Hi Copemech Yes we can buy Notoil here in OZ. The local Yamaha dealer gave me a sample pack to try for feedback a few years ago. I found it works well when freshly applied, but dries out much faster than the normal air filter oils. Yes it's more convienient and probably more environmentally friendly, but if a bike only get ridden once in a while, then you need to do the air filter service close to when you want to ride, rather than servicing it at the most convienient time. David

No. WD40 is not sticky enough to trap the dust particles, and will dry out quickly. There are oils made especially for the foam type air filters commonly used in off-road vehicles and you should be able to import some of this oil from wherever you bought your Gas Gas or a local motorcycle shop in China. It is just called "filter oil for foam air filters" and there are many brands. If you can't wait to ride your bike till you get proper air filter oil, use the same oil that you are going to use to mix with the petrol to make your fuel. It will slowly move out of the foam by gravity but if you reoil the filter frequently it works OK. For whatever oil you use, make sure all the foam is coated with oil and that you have squeezed all the free oil from the filter before you install it. Foam not fully coated = dust gets in engine = motor wrecked Too much oil = carburettor affected by oil flowing down from filter

Dave I think I have worked out what is going on with Woody complaining about Michelin tube type rears - there were/are two types of Michelin tube-type rear trials tyres. The one I used successfully for years and would still buy if I could get them is the X11 tube type. They are/were terrific to use but became more and more difficult to buy here, being imported only twice per year, and the flat track racers snapping up most of them. About two years ago I heard that Michelin were developing a tyre that will fit both tubeless and tube type rims, but in searching for them, I discovered that Michelin also make a tyre that looks just like a proper trials tyre, but is not a radial and is not called X11 tube type. I don't remember what it is called exactly, but I have seen one on a M198 and saw enough to know that it is pretty useless for trials competition. David

Assuming you mean Godden Majesty frame for TY175 motor Early 1980s Appears to be the same angle as standard Yamaha TY250 and Godden 250/320 frame. Only know for sure that the wheelbase is longer than the TY175. Suspect it is the same as Godden 250/320 which is 25mm longer than TY250.

Cota 200s are nice to ride and relatively light. Montesas of the twinshock era are generally well designed competition machines that won many titles at a high level in their time. The Cota 200 kickstart mechanism has a weakness and the supply of genuine parts to fix it when it breaks have been used up. I haven't heard of anyone making replacement parts yet. The weakness with the kickstart is a design issue that is shared with a few models that use the same mechanism (mainly Cota models 172, 200 and 242). There are design weaknesses with all bikes, including Jap bikes. Other Montesa Cota models have different weaknesses. Maybe you could do a bit of searching on the forums on this website to learn more about twinshock Montesas.