feetupfun

Those frames were made at a time when Bultaco frames were starting to be made from chrome moly steel so it might or might not be. Not a problem though because you can successfully weld chrome moly tubing to other common alloy steels and to mild steel. If it was me I would use whatever I could find that was the correct OD, so it looked right. Frame tubes under the engine on a trials bike cop quite a beating so going thicker wall than what you might use if you were trying to make it as light as possible might be a good idea. I would use 2mm wall or thicker. If you want to measure the existing tube thickness, grind part-way through the tube with an angle grinder somewhere in the damaged area.

I would be looking nearby or in the crankcase for the missing needle roller and next time if you warm the piston up, the pin will push out by hand

If it runs OK once you get "above" the flat spot, it's likely to be a problem with the pilot circuit

Wossner and Wiseco TY250 pistons are both a good thing. The piston/bore clearance for a Wiseco will be different to what is in the Yamaha manual. The reason there are lots of standard size genuine Yamaha pistons still available is that it is much more expensive to have a new sleeve fitted compared with a rebore. Now that Wossner make pistons up to 2mm oversize there is even less demand for having TY250 cylinders resleeved. TY250 cylinders last a long time between rebores if they are used for trials and have been looked after. There are still plenty around with the original piston and rings in them. I had a TY250D motor rebored about 11 years ago and used a Wiseco piston and it still going great.

If there is looseness in the fit of the tensioner wheel then it might be precessing (not sure of this is the right word). What I mean is that the tensioner wheel could be wobbling. If it is, then it will wear the bushing rapidly and fail. I would suggest either leaving the tensioner off or buying a new one. I run a M49 without a tensioner since I rebuilt the motor about 4 years ago and have not had a problem. The tensioner probably helps the chain and sprocket teeth last longer than without having one, but there is always the risk of the tensioner failing and causing damage to the casing and clutch. Judging by the number of internally damaged Bultaco clutch casings I have in my collection, having things come apart inside that casing is not uncommon. Your video reminded me of a Bultaco M99 (325cc Alpina) I had when I was a kid. The chain was so worn on it that when the motor idled, the tensioner arm would tap against the inside of the casing.

If you post up the dimensions and a photo of your 123 swingarm, you might find that someone will have a look at their trials bikes to see if the swingarm from something else (other than a 172) will fit.

Whether it's a new fibreglass tank cover or this old fibreglass tank or even an aluminium tank, they all need repairing after damage. If it was me I'd seal it and make it look pretty again and use it. If I had to pay someone to do the work then it would be a harder decision

Yes that's an A model flywheel. The B and later model flywheels have a bigger external steel ring than the A model external steel ring.

OK I'm gonna have one more go before I give up. You don't need to take the head off to find top dead centre. Take the sparkplug out and insert something rigid that will reach the piston crown. There are special tools made just for this job but you can alternatively make something up. It is called a top dead centre tool if you want to go looking on the internet. It doesn't even need to have a measuring scale or a dial indicator because you can determine the amount of advance in mm around the flywheel rim using geometry, and I have told you already the distance is 21 mm. You just need to mark TDC on your flywheel so it lines up with something on the casing and measure 21mm anticlockwise from there and make a mark. The only important things about the points is that they start opening when the piston is at the timing mark, they conduct electricity when they are touching and when they are fully open, the gap is not too big or too small. To make a simple tool to show clearly whether the points are open or closed, use the points as a switch/contactor in a low voltage DC circuit that includes a DC supply and a light bulb. When the points are touching, the light will be bright. When the points are not touching, the bulb will glow less brightly. Disconnect the points wire from the HT coil before you start. It is at this disconnection point that I connect one side of my DC supply, if I am using the bulb method. The other side of the DC supply goes to somewhere on the motor casing. The light bulb method is popular, as is using a cigarette paper between the points or using a buzzer or using a volt meter or using direct visual observation of the points. They all work

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