feetupfun

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.

If the triples are straight you can't get enough steering lock without the tubes hitting the frame

regarding achieving the ideal offset. yes it can be done with parallel offset or axle ahead of fork tube centreline, but the lowest mass moment of inertia without having the axle way forward of the line of the tubes comes with a combination of angular offset at clamps and minimising the absolute offset at the clamps.

I thought I said that already

There are a few reasons for the forks being not parallel with the steering head on many bikes (not just twinshocks) It is a way to provide the ideal steering trail without having to have the axle set forwards of the centreline of the fork tube axes (manufacturer may be limited to one fork leg design) It allows for the steering geometry to be closer to ideal through the suspension travel of the forks It reduces the mass moment of inertia of the front end compared with having the same forks but fitted into parallel triple clamps. This is due to the tubes being closer to the steering head axis (for a manufacturer stuck with using in-line axle forks) I can't see it making any difference to steering geometry at full lock

Somewhere between 5 minutes and 30 years depending on how well the bike is maintained, how it is ridden and how frequently it is ridden No a pressure test will not tell you if the piston is worn and neither will it indicate the ring condition unless they are so worn it will barely run. Piston, ring and cylinder wear can be physically measured with the top end apart. Someone with mechanical aptitude and experience with your model of bike will probably be able to judge how worn the rings are when kicking it over and riding it. Similar with the level of noise generated by the piston when hot and cold.

I recommend 340mm and leaving the fork tubes 20mm above the top clamp. Dropping the tubes down makes the steering feel terrible even with 360mm shocks (the 360mm shocks and tubes dropped to level with top clamp means that the standard steering angle is retained but the trail is different to original). It also increases the flexing of the forks. It's personal though and I do know people who reckon that the increased ground clearance is worth the loss in steering quality.

Mike I will work out what it would cost to buy the same product from Germany because I have not tried before but I suspect it will be more expensive from Germany because: 1 Germany is not near Australia 2 Postage from the USA to Australia is generally much cheaper than postage from the EU 3 I don't pay customs duty or VAT or GST from either the EU or the USA David

the tytrials unit works well and was easy to fit. The only difference I noticed was that there seems to be less variation between the strength of individual power pulses at extreme low RPM. I have not tried the others.

Magura assemblies from resellers in the US for about $70 a pair Suzuki RM80X assemblies for about $50 each from Suzuki shops Both are quite crash resistant. I use the Suzuki levers on my 1970s jap trials bikes because they look right, and AMALs on my Spanish trials bikes. If I had a 1980s trials bike I would use the Maguras.

Full synthetic gives the lesser amount of smoke, lubricates best under extreme conditions (pressure and temperature), causes less carbon build-up in the combustion zone, tends to create less ring gumming issues Semi synthetic is not quite as good as synthetic in all those areas, but protects the steel items inside the motor (conrod bearings especially) from corrosion better than synthetic while the bike is not being ridden.

The right height is whatever you think works best. Moving them up or down changes the steering angle, steering trail, wheelbase, ground clearance and how much they flex around. The standard height from the factory is 20mm protrusion above the top clamp.

Ideal gearing is a difficult subject because it is a personal taste thing. When I started riding my 348, I thought the standard gearing on it was too high, and fitted a rear sprocket with 39 teeth (33 is standard) but the motor was not running very well (AMAL problems). Once I got the motor running well, I found that the bike felt too slow in first gear in sections and second was too fast. I then put a standard rear sprocket on and it is wonderful to ride. The front sprocket was standard size all along. If you buy a Pirelli and use it till it wears out, you will be regretting your decision for a long time. They take an amazingly long time to wear out but are quite stiff in the sidewalls and are scary on wet rocks. Michelin or IRC tube-type rears are really the only decent rear tyres for that rim. For performance the IRC is better but is more sensitive to tyre pressure than the Michelin. Michelin used to sell a very good tube-type rear but the current Michelin tube-type is not as good.

Only the hearts and wallets of many Twinshock riders around the world. Same for the Honda TLR250, which also didn't win any world titles

Mike you can buy them from Don Newell in Brisbane, Queensland (advertises in VMX magazine). I think they (Falcon) only answer the phone after lunch (their time) so it might be good to try early in the morning NZ time.

All of the twinshock TY250 models have interchangable forks ie same travel, length, diameter and mudguard, brake arm and axle attachments. There are minor differences between them but nothing that stops any model forks fitting any model bike.

A TY250 piston can be used to get the motor to about 190cc, but it is not as simple as boring the hole bigger because the gudgeon pins are different diameters and the cylinder requires a bigger OD sleeve

If you can see a gap when holding a straight-edge against the tube, it is bent Whether it can be straightened depends on how badly bent it is and if there are any creases or is it bent into a gentle curve. Another test is to hold the slider still (by carefully clamping it to something solid) and rotate the tube. You will see any run-out as the tube rotates. Are you sure only one is bent? I would be having a close look at the other one while the front end is apart. You should also check for bending/twisting of the triple clamps.

Frame and tank look like Pinky. Pinky did not have a tank cover. No idea what the seat it from

If bogging means the motor dies as the throttle is opened, it may be a blocked or partially blocked pilot jet (lean mixture as throttle opened). dombush's choke test will test this possibility

Only the very first and last models of the Alpina are close in design to the Sherpa T of the same year. Even those Alpina models are not as good as the Sherpa T of the same year to ride in sections. The differences vary from model to model, but the Alpina is generally inferior to the Sherpa T in that the hubs are heavier, the steering trail is too great (most Alpinas use Pursang triple clamps), the wheelbase is too long, the tanks are bulky, some frames are heavier (more frame elements) and the gearbox ratios are too far apart in the lower gears (1,2,3) and too close together (3,4,5). Having said all that, any Alpina is a better bike for trials-type riding than any MX based bike of the same era. In comparison with the Alpina, the OSSA Explorer and Montesa Cota Trail models are much more easily made into capable twinshock trials bikes.

Hi Jon I read your posting on the Aussie trials site. You helped bob1 with your reply and I did not see a question in your posting to answer so didn't reply. There are only a few hundred Twinshock trials riders in Australia and only a few active twinshock trials forum members so don't expect to be knocked over with replies to postings on the subject. For people wanting to buy second-hand TY twinshock parts from Australia, I suggest you look at eBay.com.au because they do come up for sale (it is a different website to eBay.co.uk) The availability of TY250 magneto covers is probably no better here than in the UK, because they suffer internal corrosion and rock damage. Ty250BCDE clutch covers corrode inside the oil pump compartment. I recently bought a TY175 bottom end (with clutch cover) and a TY175 magneto cover via aussie eBay for reasonable $$ and there have been lots of TY250s suitable for parts for sale and also individual TY250 parts for sale. If someone from overseas wants to buy some particular TY parts from OZ, I am happy to help with the logistics if I can. The Yamahas that have the clutch cover without the oil pump compartment that can be used on the TY175 are YZ125ABCXDEF and IT175DEF. DT125 and DT175 clutch covers can be used but look pretty bad and are lots heavier. I don't know of any other Yamaha motor that has a clutch cover that will fit a TY250 but would like to try a DT2 or DT3 clutch cover as I think they might fit.