feetupfun

I've found that buying incomplete bikes is OK but you can usually benefit by buying a few of the same or similar type to allow making up one complete bike. Buying missing parts from someone selling individual parts can get very expensive

Standard TY twinshock front ends provide excellent steering for trials

It can go the other way if the bike has a head-on crash into something!

The setting of the points can be done with little effort by using a 12v battery and a 12v incandescent light bulb. Apply the 12v DC across the points and you will see a large change in brightness of the light as the points open and close. Yes a digital ohm meter would turn the job into a nightmare, unless you disconnect the condenser first, which is why people use a light bulb or a buzzer. Fuel vapour can cause deposits on the faces of the points. Pitting of the points faces is usually due to poor condenser performance. A good test for the condenser is to look through the little hole in the flywheel with the motor running. If it is a bit like fireworks night inside there, then the condenser is not working well. Even with a good condenser there will be a little bit of sparking. I use 21mm BTDC measured on the rim of the flywheel for my timing mark. The air bleed screw should be somewhere between 1 and 3 turns out from fully in. The actual position of the screw is chosen to provide the nicest firing pattern at idle. The idle speed should be done by moving the throttle slide bottom stop. If the idle firing pattern cannot be made nice within the range I mentioned for the bleed screw, then there is still something wrong. Your air leakage at the LH crank seal sounds like it was very bad. Leakage there first becomes noticeable in the way the motor runs when there is a tiny oily witness at the outer lip. You should be able to tell which way the stator plate goes on by the run of the wiring. TY250s have the points in front of the crankshaft. If you still have any doubts about your setup, take the flywheel off again and take some photos. It won't hurt anything to run it a bit retarded if you are taking it easy, and it will reduce the likelyhood of kickback

Excellent and thank-you agent99. The photos are lovely and the sound of 99 saying "Oh Max" is something I always enjoy remembering

Standard points on Yamahas normally last decades in trials use. Two of my TY250s still have the original points and condensers and still work perfectly. I wouldn't worry that your stator coil looks different to the photos in the B manual. A and later models ignitions all work great if they are undamaged and set right. Post up a photo if you still think yours isn't standard. Yes the diode was an improvement that came in with the B model. Having one will not stop the motor kicking back when you are starting it because a diode will only stop the ignition making a spark if the engine is rotating backwards and a kickback happens when the motor is rotating forwards (too slowly). Good that you set a timing mark on the flywheel. It makes it easier to set the timing compared with a gauge measuring piston position through the sparkplug hole. Your Yamaha shop led you astray if they said that the timing wasn't critical. The timing is critical but the points gap is not critical. On a Yamaha you change the gap to achieve the right timing. Yes you can do it through that little hole. Set the clamping screw so it holds the points in place but not too tight that you can't move them to get the adjustment right. Once it is right then fully tighten the clamping screw. The points should begin to open at the timing mark with the motor being turned in the running direction. To tell exactly when they are opening you can use your eyes and a torch, or a timing buzzer or a timing light. I usually set them with a buzzer, then run the engine and use a timing strobe on the timing mark to confirm that it is right. The ignition should work fine with a gap anywhere between 0.2 mm and 0.5 mm. I know Yamaha recommend a narrower range. When you do buy points and condenser, don't buy cheap stuff or an old condenser. Also you can mount the condenser up near the HT coil and it will still work OK. That way the condenser will not get as hot. The only workshop manual I know of for the A model is the owners manual and they do come up for sale. There are two parts manuals. One is just A model and the other is for A and B models. They also come up for sale now and then. The A motor is the same in many ways to the B. The place most people get tricked up when working on A models is that the clutch and primary drive is different to the B and later. There is nothing wrong with the A design it is just what Yamaha had in all their dirt bike engines at the time and the B is a later design. If you are serious about getting rid of the kickback, you can fit a modern aftermarket ignition that has an advance curve. This gives you much less chance of a kickback at kicking speed.

10mm freeplay is about right for a new chain. The whirring noise on your video clip as the motor returns to idle does sound a bit unusual.

Here's a listing that says that TL250 forks seals are 33x46x11 which also fits KX65 and RM65. If that's right you could buy them at a Suzuki or kawasaki dealer. If it was me I would measure the seals myself first https://www.ebay.com.au/i/292664478254?chn=ps

Sometimes you will need to buy from overseas. When I do that, I choose a place that has as many things that I need as possible to minimise the overall freight cost, especially on bulky things like mudguards and sidecovers. For fork seals try MXstore at the Gold Coast or work out what modern bike uses the same size seals and buy them from the dealer. It's very likely to have a size that is still being used in something. What size are they? As for fork scrapers I've seen some at a good price in Thailand, maybe not TL250 size. Be aware that they sold most TL250s in North America and Australia so the usual good places for old trials bike parts (UK and Spain and France) may not have much.

I lowered the pegs on this bike a while ago and was not happy with the amount of free travel for the standard brake pedal once it was adjusted downwards to suit the new footpeg height. I made a couple of experiments first to make sure the shape was going to be right and finished the final product today. I'm getting the bike ready for a friend to ride at our upcoming state Twinshock Titles.

I've bought some modern PPP guards and headlight for my Alpina and can vouch for the quality

OK I looked at the "Happy New Year" posting and 86 and 99's bikes do look fabulous. Being quite a fan of Get Smart, I'm now really keen on seeing photos of 86 and 99 and hearing 99 say breathily "Oh Max" as Max rides past

Be careful if you don't rebore it because some (most) new pistons have an L shaped top ring which means that the top edge of the top ring travels right to the top of the cylinder. If you have the original TY250 piston in it, it will have "square" rings and being set down the piston a bit, these rings don't travel right to the top of the cylinder. If there is even a microscopic lip in the bore at the top end of the travel of the old rings, this lip will cause problems for a piston that has a top L ring. If it didn't rattle much before you pulled it apart, it might be worth just fitting new rings to that piston. If you do, make sure that you are getting A model rings for an A model piston. B model and later TY250s came with L ring pistons so their rings will not fit your piston (if yours is the type with square rings) Comparison photo

I've used 660 a few times over the years in bigger stuff and not had problems getting things apart again as long as you can heat them up, which softens the loctite. Your application would be fine but keep the 666 confined to the parallel shaft and the key and keyway

Thanks Guy. I actually rode it in a race (an enduro sprint for vintage bikes) recently and it was fabulous to ride. It was the first decent ride I've had on it after transforming it from a basket case.

Well the mount is not as pristine as I had thought, but looks like it is still the original shape

OK photo time

Excellent thanks and you are welcome to try out my bikes. Yes I'm coming down and planning to ride Open Twinshock blue line

It's because the motor on a motorbike rotates a lot faster than the ideal rotation rate for a bicycle pedal crank

I recently bought a set of magicals springs for TY250 forks. They are dual rate of a similar design to the standard TY250 springs. On the magicals, the first rate is a bit stiffer than standard springs and the second rate comes in earlier in the stroke than the second rate on the standard springs. I found the magicals springs made otherwise standard TY250 and KT250 forks feel even more under-damped. Very good in combination with Majesty damper rods though which provide more damping. Rod after reading your last post I was wondering did you check how good was the piston/bore sealing in your Marzocchi forks. Yours may have a ring for all I know - I haven't worked on Marzocchis from a 240 Fantic, but Betors from the same era have sealing rings on the damper rod pistons. I'll be very interested in what you find with the HFS setup.

It's not a flat bracket so you will need more than a tracing to replicate it exactly. I have a TY175 frame that is undamaged if you want photos. I'm assuming yours is the competition frame because they are the ones with the weak bracket. There are other 1976 model TY175s that have a much more substantial bracket. The frame type I'm thinking you have is frame number prefix 525

Seems to be a very common mod to the 123

Mikr do you have tyres for your 123?

You can put it back in no matter where the shift drum is sitting. All that thing does is hold the shift drum in the positions that suit where each gear is correctly engaged. Your photo appears to show a dip where the plunger goes. If there is a dip there it means that the drum position is right to have the gearbox in a gear. If there was a bump in line with where the plunger goes, the shift drum would either rotate as you fit the plunger until the plunger goes into a dip, or the spring under the plunger would compress with the shift drum staying still. In the second case as soon as you do anything that moves the gearbox shaft, the drum will rotate and the plunger will slide into a dip and stay there until you shift gears with the shift mechanism.

Looks fairly normal for that seat