feetupfun

Totally agree with Woody comments and suggest you have a ride of one before you go ahead. If you can't find one to test ride, that should tell you something The TY250 head will be the wrong shape inside because the bore diameter is different. It may also need machining to get the compression ratio right. The different model TY250 cylinders can be identified externally. If after all the advice, you still want to ride something with too much capacity, did you know you can make a 360cc TY250 motor? You can use an RT2 or RT3 or DT360 cylinder, head and conrod and lengthen the stroke. The downside is that it needs more machining of the crankcases than the 320/340 motor due to the stroke and conrod differences, and will not fit in a Yamaha based frame Majesty due to the extra height of the cylinder and head. It also needs a flywheel approximating the weight of a Volkswagen Beetle to make it rideable

Maybe it's just my eyes but in the lower photo it looks like the steel cylinder that the plastic anti-bottoming cone fits into is on upside down, because I think I can see a short recess inside the end of it. I think the end with the recess should face up not down. If the cylinder is the right way around, you should be able to slide the whole plastic cone into the cylinder.

centre of clevis pin hole to far end of threaded section 411mm threaded section 70mm

Twinshock or mono TY250?

I bet that magneto cover would not fit on the inner cases of a YZ

The bike with the dell orto carby that Craig is sitting on has a cylinder which displays a part number in the casting, which identifies it as originating from a TY250B The engine inner cases and engine covers on that same bike look they are from a 1970s Yamaha works motor that Mick Andrews used The kickstart lever on that same bike is TY175

There are a few different bikes shown in this forum string. Please say which bike you are referring to when you post as it is getting to be quite confusing

That was a Kato 175 replica owned by Craig Mawlam

If you want to stay around 250cc, then get the bore measured by the person who will be reboring it. They will tell you from that what size oversize piston to buy. You should always get the smallest oversize that will clean up the bore, so you then have more options for the next rebore. If you want a bigger displacement, you can get pistons up to 2.0mm (0.080") above standard diameter off the shelf made by Wossner, which increases the capacity. TY250 motors can also be made 320cc but this is a lot more expensive because there is a new sleeve and more machining required, and rejetting, and a heavier flywheel

Bushfires one corner, cyclones and flooding in another. Jon I hope your brothers place is going to be OK

http://www.trialscentral.com/forums/topic/48320-oil-mixture/page__st__75

so clean it's virtually invisible

Here is the sprocket spacer with the extra wheel bearing in it http://www.francetri...-sprocket-.html

and how worn it is on that bore

the heat produced would need to be rejected so an oil cooler would need to fit in somewhere, maybe a second coil in the engine radiator tank, but it adds a considerable amount of extra weight compared with what is there now The next stage from this would be hydraulic drive to the rear wheel, incorporating braking in the hydraulics (like on a zero-turn lawnmower)

a few years ago there was five to choose from: Scorpa 250, Scorpa 125, Sherco 320, Beta 250/300 and Honda Montesa 4RT, and Gas Gas had a prototype side valve 4 stroke

He was 9 when he started riding the GasGas, and we changed because the OSET was very difficult to ride in sand and water-worn stone creek beds, a function of the small diameter wheels and very short travel suspension on the 2007 model OSET 16. He was quite small for a 9 year old and could still fit the OSET OK as far as size goes when he was 9. He is 12 now and about the size of an average 9 year old and the GG50 is perfect for him. Yes the GG50 has a lot more power than the 24V OSET and it has very good suspension. The only riding drawback I found with the GG50 is that they come fitted with tyres that are not really trials tyres. They are commonly replaced with Cheng Shin tyres. As far as clutches go, the GG50 has a clutch that can be made to work as a centrifugal clutch and/or as a manual clutch. As they come standard they are auto clutch with manual override, and if you take the springs off the centrifugal weights, it becomes a manual-only clutch. For those people saying how good TY80s are, I agree.My son also rides a TY80. If we are going on a trail ride, or competing in a classic trial, he chooses the TY80 and when he is competing in a modern trial he usually chooses the GasGas 50

Your brain and body will adapt to any clutch in time. Also bear in mind that a 2002 Sherco 290 is great for blasting up things but not the easiest motor to manage in technical riding. If you are OK with your clutch control in technical stuff when fresh but have problems later on in a riding session, then your clutch pull muscles need more conditioning You can also test other people's clutch pull to judge if yours is unusually heavy Unless you have unusually small hands or very thick fingers, then standard levers will be fine

my son went from an OSET 16 to a 2010 model GG50 (in 2010). There have been a few minor problems with the GG but it is a strong performer with great suspension and brakes. We live and ride in a hot place. A friend's child rode a Beta 50 auto for a few years and the way the motor used to overheat and carry on did not impress me. We chose the GG because it is water-cooled with a thermo fan and copes very well with our climate. I can list the little problems we have had with the GG50 if you want

near the bottom on this page http://tyoffroad.weebly.com/restoration.html

I rode with a Leonelli lanyard for my last four or so trials in 2013, to get ready for the 2014 season (they are now compulsory for all trials riders at Motorcycling Australia events). In 40 years riding trials, it was the first time I had ever used one. I had no problems with accidental activation or missing lanyard. Holding it under your thumb as Paul suggested is a good idea. I did try and move my left hand off the bars a few times to do something while stopped, but the strong magnet in the Leonelli lanyard meant that I felt resistance to lifting my hand so didn't pull the magnet off. I have had many crashes in trials where a lanyard would have made for a better outcome. I reckon the benefits of a good quality lanyard switch outweigh the risk of negative outcomes by a huge margin.

Its the rings and bore surface that need running in - not the piston. A lot of heat is generated by the friction of rings on a fresh bore so the main thing is to only run the motor until the cylinder gets hot, then let it cool down. If you get it too hot, the rings and bore can be damaged. On the first run it might only take 1 minute to get hot. With each successive run, the time it takes to get hot will be longer. I judge that the cylinder is hot when I wipe a wet finger on a fin and the water/saliva sizzles. If you have an infra red thermometer, 110 degrees C is about right. Use a fuel mix that has a lot of oil in it to reduce the risk of damaging the rings or bore. I use 20:1 semi-synthetic for the initial runs. If you use full synthetic oil it will take more running time to bed the rings in. After the first few runs, the heatup rate will be slow enough that you can ride it gently for a short while before it gets to water sizzle temperature. When you notice that it is taking a normal time duration to warm up the motor, the rings will have been run in. I find that new rings on a fresh bore usually takes 5 to 8 runs to bed in.

A useful tip for setting the clutch spring preload: Fit the plates and pressure plate with a coating of oil on them Set the free play for the push rod Set the clutch spring preload so that there is just enough drive through the clutch that you can kick it over compression with the kickstart without the clutch slipping That will get it very close to perfect before you take it for a cover-less test ride. The last two bikes I did, did not require any further adjustment after using the kickstart test method to set the spring preload (M49 Sherpa T with Barnett plates and M138 (350) Alpina with Bultaco plates)

As well as fixing the hub and basket, I would be fitting a set of Barnett plates. They are flat and because they use friction material, you can run with less clutch spring preload without slipping. You would have noticed that even the flattest standard plates have high and low spots. If you compare the Bultaco plates with the steel plates in many other bike clutches, you will see that the Bultaco contact pattern is on the inferior end of the quality scale. I have seen standard Bultaco plates ground flat on a surface grinder, which improves the contact area, but reduces the thickness of each plate so makes them even more likely to put grooves in the basket fingers and the hub splines.

a word of warning about flexible sealant liners - if you use one of these liners then suffer structural damage to the tank, the liner makes it much harder to repair the tank (fibreglass, steel or aluminium tanks). In the case of metal tanks, you can't use any process that involves heating for the repair. In the case of damaged fibreglass, the repair will be complicated by having the internal flexible coating. For fibreglass tanks like yours I recommend lining with either petrol-resistant polyester resin, or with epoxy resin. They are available in a viscosity grade suitable for lining our tanks using gravity to spread a thin layer over the internal surface. I've successfully lined many 1960s and 1970s Spanish fuel tanks with epoxy. I originally started lining them because the fibreglass was in poor condition internally and I was worried about possible petrol leakage damaging the paint scheme I was about to apply. That was quite a while ago now. The new components in our petrol are now another good reason for lining them with epoxy. I use this stuff bought from our local boat shop http://www.westsystem.com/ss/