feetupfun

Yes as Andy.T said, I replaced the rubber elements in my TY175B cush drive in the late 1970s when I noticed there was a bit of slack there and thought it might affect the way the power was delivered. It took quite a bit of work, having to make new rivets and cush elements. I didn't notice any change in the way the motor felt and reckon I just wasted my time by working on it. I still ride that same bike and the clutch basket cush drive is still going fine. Of course if for some reason the rubber elements were allowing metal-to-metal contact they should be replaced.

The sleeve was made from a GS1000 sleeve The piston was from a kit that converted the DT200/WR200 to 230cc

corrosion in the cooling circuit

Australian design regulations for road-registerable motor bikes require the side stand to be self-retracting. I assume it is the same in many other countries. Aparrently there were a significant number of deaths and injuries around the world attributable to people riding (road bikes) with the side stand still down so all road-registerable bikes require it. Until now I didn't realise it was a "feature" on new trials bikes. It is very unusual to road-register trials bikes here so the trials bike importers probably nobble this "feature" before we see them.

On the same issue, I suspect that fitting a wider rim will make a competition trials tyre work less well on trials terrain than it would on the standard width rim If it was being used on a Dirt Track racing bike (a slider) there might be an improvement by fitting a wider rim.

The increased width of the bigger rim will be no problem as far as clearance goes. I know this because I fitted my M138 Alpina with a Pursang rear wheel (which have a much wider rim than Alpinas and Sherpa Ts come with)and it made no difference to the clearance to the swingarm, exhaust and chain. The width of the tyre is the critical dimension - not the rim.

I think that for such a big 428 sprocket you will not find one ready-made for an early Alpina hub available on-line. The Aussie Talon importer sells 428 and 520 rear blanks made from aluminium alloy for reasonable prices so I imagine you should be able to get a blank from Talon direct or from someone nearer you who sells them.

I bought new Alpine Stars just before christmas and have not had any problems getting used to them. I had SIDIs previously. The sole is more grippy on the footpegs than the SIDIs but they feel very similar otherwise to me when riding. The SIDIs were easier to walk in but I have no problems walking in the new ones and it is probably only different because the SIDIs were at the end of their life.

The reproduction type looks good but is more prone to breaking. The genuine is more expensive but has the same (good) bending properties as what came new on the bike. Don Newell in Brisbane sells the genuine type as do many other suppliers.

I usually ask the seller to email some more photos in that situation

Someone in the UK was chasing TY250 engine covers on this forum a few months ago. Here is a magneto cover on eBay in Australia. Same seller has also listed an oil pump cover. http://cgi.ebay.com.au/Yamaha-TY-250-Ignition-Cover-/270732172495?pt=AU_Motorcycle_Parts_Accessories&hash=item3f08e51ccf

Photos of TY175, TY250 and KT250 illustrating fork tube angular offset http://www.trials.com.au/content/index.php?option=com_wrapper&view=wrapper&Itemid=42 In case that link does not work for you, the posting is in the Technical Help forum of trials.com.au

It is bedtime now but I will endeavour to take some photos tomorrow evening

Gav the ideal upper shockie mount location will depend on what the extended and compressed lengths are for the shockies you are planning to fit, and the leverage ratio you are intending to achieve - so there no one correct location that is ideal for every rider and every shockie. There are limitations for rear axle travel with standard TY250 frames/swingarms, but these can be overcome if the brake pedal pivot mount is moved or if the rear subframe is bent upwards or cut off, or the swingarm length increased. As far as the shock mount design goes, I will take a close up photo tonight to illustrate the way I did one bike. I can't seem to upload photos to this forum tonight so will send you the photos via the email address you posted at the top email sent

maybe you are measuring something different to what we are talking about? I can take a photo and post it up if required to remove any confusion. It is the fork tubes that are set non-parallel to the steering axis

I think you will find the OD of the standard sleeve prevents going above 70mm bore (it sounded to me like you were asking about boring the standard sleeve bigger). Bigger bores than 70mm are possible but only with a bigger OD resleeve and the maximum OD of the sleeve is limited by the location of the cylinder studs. My TY175 is 72.5mm (bigger sleeve fitted) and the sleeve is very thin. If money is no object then 72.5mm bore is possible but a 70mm bore would be much less labour cost.

The rear Bridgestone trials tyres I have seen are not competition trials tyres but do have a block pattern like a real trials tyre. They have a rounded profile, cross plies and have stiff sidewalls. Conpetition trials tyres have a square profile, radial plies and flexible sidewalls. Bridgestone trials tyres would probably be good on a bike that was never going to leave the bitumen. Bridgestone trials tyres are very much like the rear tyre that would have come standard on the TY250. Since then there has been 35 years of competition trials tyre development.

It has a centrifugal clutch and there is a manual hydraulic override operated by the LH handlebar lever that acts against the centrifugal engagement mechanism. The manual clutch feels and acts just like a normal bike clutch, but it can only drive above a certain motor RPM. It is a pretty clever set-up if you don't want to have be kickstarting your kid's bike all day (it stops the kid from stalling the motor), but the kid can use the manual clutch just like a normal clutch if they want to.

Ben you have just discovered another reason not to fit a Pirelli MT43 on a 348. This is a common problem with tubeless tyres. I have seen a work-around for this problem - four tyre clamps equispaced around the rim. Another person kept the pressure above 8psi to keep the tyre on the rim.

Maybe Montesa designers were concerned that the taper might be damaged if the sprocket rotated relative to the shaft as the retaining nut was being tightened.

Sorry to disagree with previous poster but 360mm shocks have same travel as 340mm shocks Also disagree re advisability of sliding fork tubes down to top clamp - it makes the steering feel worse Recommend 340mm shocks and standard position for fork tubes

For riding dry rocks it is the age of the tyre that is important, not how much tread depth is left. Most of my tyres go hard (and useless) long before they wear down much. If your tyres are worn but still soft, they are fine for dry rock riding. If you ride wet slimy rocks, the only tyre that works is a tyre with sharp edges. You haven't said the condition of the shockies but I would say if the shocks still move freely and have damping, you will get a bigger improvement with new tyres.

The round barrel 250 (M27,M49,M80) motor is quite soft at extreme low RPM but makes reasonable power everywhere above extreme low RPM The later 250 (square barrel 238cc) makes good power (for a 238) rignt down to extreme low RPM but is not as strong at the upper end as the round barrel. In trials use the later motor is easier to live with in modern twinshock events, while the round barrel motor is a very nice motor for more open sections and trail riding.

Our AVGAS has an SG that is quite different to car petrol from the bowser (AVGAS is less dense) and this can cause problems with carburetion when switching from one fuel type to another, particularly with bikes that have the carby leaned forwards a long way, like on Betas. AVGAS is fantastically stable fuel but is not permitted in sanctioned competitions. Luckily most service stations where I live still sell ethanol-free 98RON unleaded which works quite well in trials bikes.