feetupfun

Dear Daywen Dating TY twinshock Yamahas is not easy because not all models were sold in all countries. If you post details of the appearance of your bike and where it was originally sold from, you will probably get some useful feedback about your bike. Here in sunny Oztraylia we had four 250cc twinshock models. They were called TY250 1974, TY250B 1975, TY250C 1976 and TY250D 1977-1979. Our TY250 and TY250B both were prefix 434 but were substantially different to each other. Appearance wise, the TY250 was metallic white and yellow. The TY250B was solid white and yellow. The TY250C and D were substantially different to both the TY250 and TY250B but were the same as each other mechanically, differing only in colour and graphics. The C was white and dark blue while the D was pale blue. The TY250C and D share the prefix 493. I could go on all night describing the differences but if you have a bit of a surf around all will be revealed about these and a dfiierent model TY250 twinshock that was sold in Europe with a white tank and a red stripe. Yamaha sold three model TY175s here. The TY175B 1975 and TY175C 1976 were virtually the same apart from the colours and graphics and the TY175JC 1976-1978 was a fully road registerable model that was based on the TY175B/C but with mods to allow it to pass the strict Australian motor vehicle design standards. David Lahey Australia

A good way to start a head moving is to put the piston up near TDC, fill the combustion chamber with oil, refit the spark plug then rock the bike back and forth in top gear. Once it is moving but it is still tight, suspend the bike off the ground a bit by the head and gently bump the bike downwards. Gravity will do the hard work for you.

Yes I have a 4GG TY250Z here in Sunny Queensland, Australia. They were available here in OZ from 1993 to 1995 but very few were sold due to the incredibly high price compared with other contemporary trials bikes. Production was discontinued because Yamaha sold so few of them. The TY250Z has many hand made and imported (into Japan) components which could not be sourced from the Yamaha parts bin so the production cost must have been quite high. There are at least two other TY250Zs still ridden in competition her in Queensland and I know of three others that have been for sale her in Queensland in the past few years. Yes the motor is the same as the Scorpa SY250 except when the change was made to hydraulic clutch on the SY250. This involved modifying the clutch actuating arm so it was a push rather than a pull to suit a slave cylinder. I have seen TY250Zs advertised recently in the UK but not in the USA. They were popular in Japan. As far as I know there is only one of them in Indonesia. Mine was imported second hand from Japan in 1998. It is a 1993 model and I recently took the head off for the first time for a decoke. It didn't even need rings. The head had never been off before. The clutch requires servicing annually to roughen up the steel plates. Spark plugs last more than a year. The TY250Z is great to ride for its age and fantastically reliable compared with modern European Trials bikes or Italian bikes from the same era. I would say it compares with a late model Beta Techno for ease of riding but has better suspension than the Techno. Mine (which is absolutely standard) weighs 83kg which is the same weight as my TY175. The TY250Z feels a bit heavier to ride than the latest crop of trials bikes. If I was to buy a modern bike it would have to be the SY250 because of it having the same motor. If you want more info please email privately. davidlahey at hotkey.net.au

If you are going to the trouble of relining your fibreglass fuel tank, I suggest that you use low viscosity epoxy resin as the liner and buy it from an aircraft or boat repair supplier as previously suggested. The reason for this is that the automobile fuel or "gas" we buy will eventually contain ethanol if not already and polyester resin (which is what fibreglass fuel tanks are normally made of) is affected by ethanol. I'm not actually advising relining with anything unless it is absolutely necessary because it adds weight and can be a bit tricky to get evenly spread inside. Almost any fibreglass tank damage can be fixed by external repair if you take the advice already given on this string. David Lahey Australia

If you are asking about a twin shock Yamaha TY250 clutch, beware of reducing the clamping force because they don't have much margin to begin with. If you are serious about getting a light action, fit aftermarket kevlar (Barnett) plates if available so that you can safely reduce the clamping force by a worthwhile amount without causing slippage. This works wonders on Bultaco Sherpas. I reckon the TY250 twinshock clutch action is quite light if set up and lubricated properly so I haven't bothered modifying any of mine. David Lahey Australia

Falcon Classic shocks are terrific for twinshock trials. I have used them on two of my twinshocks and have never found anything better. David Lahey Queensland Australia

Dear Paul Mac Q1 Is the blue polypropylene tank from a M198 the same as the tank for a M199B? Q2 Where is Bungonia NSW? David Lahey Gladstone QLD Australia

Useful mods for the TY175 are: Use Sammy Miller footpegs. They are a tiny bit lower and further back but the best thing is that they are much larger, providing a much more comfortable ride and better leverage for turns. I will repeat what the previous respondent suggested. Falcon Classic shocks transform wonderfully the way both the TY175 and TY250 handle. Mine have 40 lb springs which are a tad soft for the 83kg rider. Don't make the swingarm longer unless you want to go desert racing. Again retain the standard fork tube location unless desert racing. About 20mm of tube extending through the top clamp is ideal for trials and trail riding. The front end from the TY250 twinshock (larger diameter fork tubes and clamps) fits straight in the TY175 headstock if the rider is exceptionally heavy or picky about fork flex. I find the standard forks to be a bit soft for very heavy landings even with 15wt oil. Increasing the fork spring preload upsets the steering a bit in floaty turns and doesn't have much effect on bottoming anyway. I don't know of alternate springs that are any good. I have tried single rate springs from a TM125 Suzuki set up to provide the same static sag but with a higher spring rate but the standard TY springs were so much better in turns I went back to standard springs. There are aftermarket springs available for the TY250 from B&J Racing in the USA. These work very well in the TY250 forks compared with the standard Yamaha TY250 springs. If you are serious about improving the steering, buy a Mini Majesty frame for the TY175 running gear from Craig Mawlam in the UK. They were made in 1982 and have superior chassis geometry. If you steepen the steering on a Yamaha frame, you may have to redo the exhaust to keep clearance for the front mudguard. The motor can be increased in capacity for more grunt to 205cc with a larger cylinder sleeve. Breathing may be compromised by this ie it may not rev as high as the standard Ty175. Increasing the compression ratio slightly from standard improves pulling power also but requires careful fuel selection and meticulous spark timing maintenance. David Lahey (TY175B fan) Australia

Gaff Yes it is the oil pump cable at the front end of the RH case. The clutch cable is about 1/2 way along the RH case. It is piston port ie no reeds no rotary valve. They run great and are as reliable as an axe. Yes there is a website and forum and there is even someone (in New Zealand) making first rate new otherwise unobtainable parts for these bikes. There are two models KT250A1 and KT250A2. A1 1975. A2 1976. They are the same mechanically but have different paint schemes on the tank and sidecovers. Have a look at the engine and frame numbers if it is important which model it is. The site is: http://members.tripod.com/kawasakiKT/index-4.html David Lahey Australia