feetupfun

An angle grinder with a 100mm disc will work - I know because that's what I did, and didn't have to take that chain guard off either. The sprocket will pop loose when the disc gets close to the shaft

Replacement sprockets don't have a keyway and work fine so yes, it was overkill to have a key. The swingarm bushes may be rubber isolastic bushings. I have found them in a couple of bikes and got them out by burning the rubber away. This allows you to get the centre bushing out then carefully cutting through the outer steel casing of the bushing with a hacksaw blade. You can replace them with either new isolastic bushings or more conventional steel inner/brass outer bushings

The TY250A when standard has a different rear rim to other TY250 twinshocks. X11 tubeless tyres usually stay on TY250A bead seats. The bead seats on the A model are wide and it is also a wider rim than the later TY250s. The A model is the 434 model. Many other 1970s era tube type rear rims can give problems with X11 tubeless tyres though. The standard KT rear rim is the worst I've had for fitting an X11 tubeless, but if you do what "still trying" says, the X11 will stay on the KT rim bead seats nicely. The IRC tube type rear is fine on any of the old rear rims but where I live it is very hard to buy them, so I buy Michelin X11.

I'm thinking the 247 engine covers changed to being the same as the Cota 348 when the Cota 247 UKR came out but I'm not certain. For the sprocket, if it's on a taper like a 348 sprocket is, use a 100mm disc on an angle grinder. It will fit in there without the disc having to touch anything else. A bigger disc won't. I found that when I got to about 1 mm from the gearbox shaft the remainder of the sprocket sprung apart when a crack formed. For the cylinder nuts, heat them up with an oxy-acetylene welding flame. If you have a steady enough hand you should be able to get each nut very hot without melting any aluminium. You can buy new nuts easily so don't worry about damaging them

Mitas has stiff carcass and low aspect ratio. When they first came out, I bought one, tried it on a modern trials bike for a few minutes and then on a twinshock trials bike for a few minutes and then gave it away. The only place they grip is on a smooth, hard surface

Well done Wufdog. What you've done may be more reliable than the Scorpa version.

Yes. But which one is better and why?

Spares availability is best with Bultaco by a country mile. All the Spanish twinshocks are great to ride but there are big differences in how they feel so you may have a preference depending on what you like a bike to be like to ride. My favourites to ride are any late model Bultaco and the Cota 348

It's very odd for an engine to start from cold without using the starting circuit. This may sound silly but are you sure you know which way the starting lever should be for on and off?

Wow fabulous to see those Homerlite tanks like that Glenn. Thankyou. They are very rare over here. Yes the 124/125 frame is the later style. The earlier style frame design (where the tank fits on) was 10,27,49,80 and part-way through 91/92. While the frame design change that happened during the production of the model 91/92 would probably have required changes to the tank/seat design, that bulge doesn't really fit the changes. Maybe they did make tanks for the models with the horizontal muffler but I'm thinking there would have only been a very small market for it by the time Homerlite started making Sherpa T tanks. If anyone was still riding a M27 or M49 by then, surely they would have converted it to the sloping muffler arrangement (kit campeon). Then again, maybe Bultaco were still selling Lobitos in the UK and Lobitos had horizontal mufflers up until about 1975

If you fit a foam piece around the top frame tube to support the tank it assists holding the tank in place but the main rear attachment is the front end of the seat

I just looked at the parts diagram in the SY250 manual found on The Hell Team web page and it shows no fastener for the clutch actuator arm. All I can see is the actuator arm, the oil seal and two arrows indicating where to put grease. You can look for yourself here: https://www.dropbox.com/sh/11nqsbkutyhwk4i/AACv6HDKAjyWGC4tSl-b-qfpa?preview=Engine-Manual-SY250.pdf

That looks fabulous Carl

Does look nice

I just read the bike log for my hotrod TY175 but no mention of the advance curve. The records are only about testing different combinations of head gasket thickness and the timing of the spark at low RPM.

The one I put on a TY250D motor is a John Cane and I have not bothered putting a timing light on it. I just fitted it with the backing plate in the centre of the slots and the bike ran beautifully. The one I put on my hot rod TY175 is also a John Cane and I did look at the movement of the timing with a strobe but it was so long ago I don't remember details of how it moved. I do remember moving the backing plate to give me timing a bit later than standard at low RPM and that the timing did change as the RPM increased. I'll have a look in my bike log and see if I wrote something in there. A friend fitted a Rex Gaunt ignition on his TY250A recently and I can say that his motor performs pretty similar to my TY250D motor at low to medium RPM but seems to have a bigger hit at medium to high RPM

The fancy modern fork tube coatings are on there to reduce friction, not to protect the tube from crash damage

The cam that the points heel rubs against is normally kept lubricated by a felt wiper. I usually wet the wiper with light oil when I'm servicing the points. If you have good quality points and a working condenser, you probably only need to service the points at intervals of 100 operating hours or so. I've got a few TYs that are still running the original points and condenser and which are still working perfectly. My other TYs that now have electronic ignitions still had the original points and condensers working well when I fitted the electronic ignitions 5 to 10 years ago including one TY175 engine that has been mechanically rebuilt 3 times (due to high run hours) since 1975 but still had the original points when the electronic ignitions went in.

No if the seal leaks as you describe it probably needs replacing. It may have been leaking before you got the bike. If so, it would have lost some of the fork oil via the leaking and once the oil level gets low enough it stops coming out the seal. When you changed the oil, the level was then high enough to be above the seal.

My series 1 M49 Sherpa T uses a triangle muffler with top entry and I suspect it might be the same as would go on your Lobito. I bought a spanish-made aftermarket triangle muffler which looks great and makes it nice and quiet (and was expensive) but takes away a lot of performance. My bike is not road registered. I have repacked the mid muffler and I have used it without the triangle muffler for trials without a complaint. Without the triangle muffler it would probably not pass the inspection for road rego here. I don't know how strict the inspection is in Spain.

Don't worry I've got a set like that on my spares bike. Not pretty

They used rolled plate because that was an economical way to make them. What do you think the expensive modern aftermarket yokes are made from?

Man that sounds a lot of $$$ for those yokes. They are so plain and simple. I know Jared Bates advertised NOS ones about 6 months ago for very low $$$. Jared no longer sells Montesa parts but the person who bought Jared's stock advertises Montesa parts on eBay (USA) Have you looked at the Spanish shops that sell trials bike parts from that era?

metisse while the alloy LH pedal does look nice, the ones I have seen in use and ridden with are not very grippy when wet and I've seen plenty snap when they whack into a rock.

They can drag for a few possible reasons: The plates may not be moving parallel when pushed, although it sounds like you have been pretty careful to avoid this. There can be grooves in the basket fingers that cause the plates to push together if they see any contact. One or more plates may not be perfectly flat, meaning that the axial travel of the pressure plate may not be enough to free the plates from contact due to the increased effective thickness of the bent plate/s. All-steel plates spanish clutches typically have a long engagement because the plates are not quite flat. The original plates are stamped while modern replacement plates are laser cut, so they are flatter. As well as starting out not quite flat, steel plates sometimes distort with use, because they are so thin. the flatness of the plates can be checked on a flat surface like a quality piece of glass or a surface plate if you have one. It's possible that when reassembled, the plates were not put back in the same sequence and position in the basket and the effect of any grooves in the fingers may be now more severe. There may be insufficient axial clearance between the clutch hub and the basket and this may make the problem temperature-sensitive. If the clutch action improved again once the motor cooled down then I would be looking there. Next time you assemble the clutch put some oil on the plates and you won't have to worry about them not having oil. From what you've said i don't think that lack of oil or too heavy an oil is the problem. I use car manual gearbox oil in my Cota 348 clutch casing and it doesn't drag.