woody

It seems that some of the first TR77 production run were produced with the same silver/grey frame colour as the MAR. I've not seen this documented anywhere but it's according to people who bought them new at the time who've said they came with the silver/grey frame with green tank and side panels. The more common frame colour was black. The mudguards were an opaque/white colour, no longer available I think, as opposed to solid white. It was the next model, the TR77 Verde that had the green frame and green guards It sounds as though you might have one of those that came with a silver frame, your frame number should start 63 so maybe it's an early number. According to Vitale Ossa the RAL code for the silver is 9006 - or the old 1970s Ford UK colour of Silver Fox is a good match

No holes in a 250 piston

Yes, normal for the 250

They could just be another, later variant of Betor damper rods, all the components are the same as the usual rods, just a different design but they function in the same way. If the forks work as they should there is no need to change them

The Ossa MAR had electronic but when they brought out the TR77 in 1977 (green tank bike) they fitted points to it. They went back to electronic on the TR80 Gripper. Either system will fit all of the trials models so maybe someone replace the elctronic on your bike with the points system, unless you have a TR77 rather than a MAR - engine number will tell you Can't help diagnose an electrical problem but you don't mention trying a different plug. Also possible is the pilot system being blocked or partially blocked in the carb

They're on ebay, however, getting them to sit flat on a curved surface without creases or ripples...... https://www.ebay.co.uk/itm/174995042817?_trkparms=amclksrc%3DITM%26aid%3D1110013%26algo%3DHOMESPLICE.SIMRXI%26ao%3D1%26asc%3D20210125103153%26meid%3Dc8849486c8574ffe98998953bf40daf3%26pid%3D100040%26rk%3D6%26rkt%3D24%26sd%3D174995042801%26itm%3D174995042817%26pmt%3D1%26noa%3D0%26pg%3D2046732%26algv%3DSIMRVIMLRV5WebV1_0&_trksid=p2046732.c100040.m2060&amdata=cksum%3A174995042817c8849486c8574ffe98998953bf40daf3|enc%3AAQAGAAAB8Ea37LkMCFnYSXAHlLtfgVdMp%2Fc6%2FvCY4PRvNQ45qGezsfD%2BSLr4efdblIya0XsZzjKs3%2FR17U21%2FPirmIzvuxeBlfyVuXGO5fPwow4P59GLNbSzyQOp%2BWUiNaHR8uxBfcjU0RdgxtAogbi2oxl2KiYgc0uPR1yvVgaLmmvPgki4DTC0mRU%2BSGODOKOyEXAn5nR9DRk0Uq4FaR%2FdMee4RaHvApGauJdkWOgNGk4UG47YG0ydTtA08SqlghgFsxg0wYLobezhrV9Zb%2FkgRqOeHyTzBrZ6kcbOZ91JYywD7Hpw9dYNtpbD9C9g%2BlIOq8%2FOGr9LVx92tYJzrObJmYLCmIkEC269EUjxZnEnTIdbE0kXpTXRaPZGjAlWyUGACSVBzs4EMUvd0s7CBqMHcZ914uU658eHnVsRarvW69JETaUGooyxozttvidgP15h5QbAnessqpFVeWN4GHQefRoimAumDEhzuoCPO3wS%2BDmh2pA0KJong6zzaG7g29sIzno8wm7ouRLS4h534vgZ%2BmZhPXqePfxCThVYpMKqceQJpVxj9H6OjPOPM7VnlEphqemj%2Fuad5qfcrqj3Uxc1LUZYHbR3zmKqUwV8mKbhlNlKamtd9YHlSjmNMpJw112as4cqOLrxMDlzG2j5DUa6zcQKDP8%3D|ampid%3APL_CLK|clp%3A2046732

You need to put a picture of the part you're referring to as from your description it could be a preload spacer or an oil deflector. Preload spacers are alloy and sit on top of the fork spring under the cap. The oil deflector is steel and pushes up into the bottom of the spring and sits over the top of the damper rod. I'd guess it's the deflector you're asking about Your damper rod is certainly different from any other Sherpa rod I've seen

I had a stator renovated many years ago by Bradford ignitions and it still works, can't remember cost as too long ago but not silly money. I recently had a coil break down and replaced it with one from In Motion which works fine

Wheel bearings just knock out from the inside with a drift but you need to dislodge the spacer tube in order to get a contact with the bearing inner race. If the tube is held tight between the bearings then and won't move then yes, it becomes difficult. Once out you can cut a slot into one or both ends of the spacer so that next time you can get at the innder race through the slot with a thin bar. Or, use a blind bearing puller to pull one out, much easier and quicker. then drift the other one out

If it's properly seized into the the inner bushes you'll have two options to remove it. Engine needs to be removed. Cut through the spindle each end of the swingarm, either with a disc cutter or a saw - obviously you have to be careful to avoid damaging the frame and arm. You can cut through the actual bush to keep away from the frame as they are going to be scrap anyway. Or you can drill dead centre each end of the spindle to depth that takes it inside of the frame and to a diameter just short of the spindle diameter. Now the spindle is 'hollow' a good tap with a hide mallet will break the spindle and the arm is out. Or you can just keep enlarging the drill diameter until the arm just falls out when you've drilled it away to just inside the frame Now you can cut the spindle either side of the engine mount.The spindle rarely seizes in the engine mount and hopefully just slides out. If not you might need a press or more drilling Now you have the swingarm free. Usually it is just the spindle seized in the inner bush that's the problem so the inner bushes should slide out of the outers with no problem, or they can at least be drifted out if stuck. To remove the outer bronze bushes, saw through the length of them on the inside on opposite sides so that they collapse and either fall or tap out. Again, you have to be carefull not to cut into the arm. Pressing them out can be difficult and can distort the arm

The taper referred to is at the top of the tube where it slides into the top yoke, what you see in the picture is normal for the bottom of the tube.

Probably, I've run 70s trials bikes including Sherpas for years, they run fine on premium fuel. I use V-power

Although I said I don't know about Avgas on your other post in terms of actual use, I do know it contains lead and therefore isn't allowed in trials as only unleaded is allowed (obviously no testing is done so no-one is going to know) However, you really don't need 100 octane fuel for a Sherpa, it runs fine on premium or super fuel. However, I'd avoid E10 due to the increased ethanol which could damage your tank if it's fibreglass (as you have a model M150 it could be an alloy tank) Just stick to premium fuel from the main brands as it contains little to no ethanol Trials engines, from that era especially, are low compression ratio which spend hardly any time on full throttle in comparison to road racing or motocross

The engine is dated in the same way, as from the factory the engine and frame numbers matched, apart from the letter prefix, so your engine is from a 1971/72 bike. There is no difference in performance between this engine and the original engine. Apart from the clutch cover they look the same. There are however a few internal mechanical differences so it is important you give the engine number when ordering parts I don't know about Avgas

The practical advantage of the flanged tubeless rim is that eliminates the possibility of losing air through the spokes which can happen on normal tubeless rims if the seal isn't good (I use silicon sealer instead of a rubber band, the type used on aluminium window frames) However, with some tyres either type can leak from the tyre bead so flangeless doesn't 100% guarantee that a tyre won't deflate slowly over days/weeks Others like them because of appearance which is just personal choice The problem lacing to a Bultaco hub is the length of the spokes on the sprocket side can be a problem. I've seen Fantics with them so it can be done. I think though that they are hard to find now. If you buy a used rim make sure you see it first as they can corrode on the inside so if there is a tyre fitted you won't see it, as outwardly they look fine

There is shortage of IRC, next batch is due at the end of the month. There's a shortage of most tyres at the moment it seems

It's the stroke

They're usually quite tight, helps to warm the piston and it should push out. You can also tap them out but you need to suppoprt the piston so that it doesn't get damaged against the studs and also that lateral force isn't imposed on the rod You can also buy universal pin removal tools which are quite cheap

You won't find the 70 number prefix on the ID listings as it is one of the few number prefixes that doesn't appear for some reason. The Verde 250 is usually a 72 prefix but there were some with 70. The MAR colours disappeared in '76

It's a TR77 Verde which would originally have green frame, tank and guards, not uncommon to find later bikes painted in the MAR colour scheme. If you google Ossa TR77 Verde you'll see images

Yes, it's suitable for that engine

I don't think any record of this will exist, given the small amount made they were probably all assembled around the same time anyway. From what I remember the only variances are bottom fork legs with one or two seals and some not being drilled for pinch bolts on the brake side. A bracket on the down tube on some, triangular alloy head steady on some and a mix of alloy or steel brake and clutch arms. All this can app;y to both 340 and 250 though. As mentioned above some 340 escaped with tapered forks, not sure whether this happened on the 250 as well. Some, maybe all 250 had a small Pursang type weight on the crank, clutch side but still with single row chain, not duplex (mine is like this) Then there are the half dozen that were 6 speed for France - I know this is a big debate as to whether it happened or not, someone has posted on facebook with pictures that they have one. It isn't hard (for a machinist) to adapt a 5 speed case to take the 6 speed cluster, so no reason it couldn't have happened at the factory, or they could have used 250 Frontera 6 speed cases. I have a 199B that has a 5 speed casing modified to take the 6 speed gears

On the model M92, the exhaust does run close to the tank but obviously shouldn't touch. The header pipe slides into the silencer. It may be that it isn't pushed in far enough which is causing it to sit at the wrong angle and slope upwards towards the tank. The silencer has a fixed bracket for attaching to the engine mount so unless that has been altered the silencer can't be mounted incorrectly. From what I can see of the silencer it looks to be the correct one Take the header off, slacken the silencer bolt and refit the header without the rubber and ensure it is pushed fully home into the silencer and see if it sits correctly. If the header is the correct one it should do. If it still touches it's possible the front pipe has been altered or is the wrong one, although it looks the correct one, just painted black, as mentioned above it would be chrome originally. A picture showing the full exhaust would be better. Picture below is a model 92, you can see how close the exhaust is and the angle it should sit at

So we're back to the Talmag again, one trial from many, as other events allow modified bikes so give it a rest banging on about rules you know nothing about and cheating riders. The Talmag has no specials class, all of the bikes should conform to their original spec. Those that don't shouldn't be accepted. That is up to the club. They obviously choose to accept modified bikes and have done for years. No it is not cheating as it is all in the open, everyone can see it, nothing hidden. No-one claims to ride something it isn't. If someone entered on a bike that looked every inch original, claimed it to be original but had hidden or disguised modified parts to gain advantage, then that is cheating. That isn't what happens though is it

I've just been ordering some gaskets from Showe Performance in Stourbridge and noticed they also stock a large selection of of reed petals - may be worth a try if you measure yours, see if they have a match