feetupfun

Keith Lynas in the USA sells weld-in inserts. I bought one from Keith and had it fitted locally. Yes the Wayne Weedon method is good too

If there were two trials riders of any ability and one of them was required to wear MX boots, the one wearing trials boots would enjoy themselves more

My memory has it slightly different to st pauls. The "Sammy Miller Parts" business was sold to a husband and wife team who commissioned the manufacture of a small batch of new (close to replica) Highboy frames for the TL125/TLR200 motor. They were all sold including one that I've seen that came to Australia. That business later became Feked. I've just remembered the blokes name who bought SM Parts years ago - Richard Jordan

It's fairly dry here and the original zinc plated spokes on trials bikes made in the 1970s are still serviceable 45 years later but do look dowdy. New zinc plate spokes here look good for about 15 years. If you live in a wet area or at the coast they will start to look dull sooner than that. Stainless steel spokes will look great for hundreds of years but how much longer do you think the bike needs to look nice? I use both types, chosen mainly to provide the original look of the particular bike. Most of my Spanish bikes came with stainless spokes so that is what goes back on and all of my Japanese bikes came with zinc plated spokes and that is what goes back on. One Spanish bike came with plain steel (uncoated) spokes and I used stainless spokes on it. If I lived somewhere that it rains a lot or near the coast I would use stainless steel spokes on every wheel rebuild. Maybe you have access to very cheap zinc plated spokes to get your costing of double for stainless, but what I've paid recently is for genuine TY spokes, one wheel costs about $120 while a set of aftermarket stainless spokes for a TY or a Bultaco is between $120 and $180.

To replace the external spring you need to take the magneto cover off. Unless there is something strange about your bike, one end of the external spring hooks over a bolt that sticks out through the casing and the other end goes through a hole in the kick shaft. The head for that same bolt holds a piece in place inside, so don't let the bolt slide inwards while you are replacing the spring

Depends on which kickstart spring you are talking about. There are two. The return spring is external and can be fitted without spiltting the cases. The ratchet spring is internal and requires the cases to be separated.

Would be worth about 500 UK pounds where I live

Looks quite attractive for a bitsa

Slow action throttle requires less force to overcome the return spring. Fast action throttle can be more ergonomic because the rider's wrist does not need to flex out of the ideal position as far. Changing from fast to slow can help new riders adapt more easily to a responsive motor. New riders sometimes buy a trials bike that is not the easiest to learn trials on and changing from fast to slow is much more economical than buying and selling bikes.

TR80 (250) felt OK to me but didn't feel as light to ride as other bikes of that era that I had ridden

There is a bloke on these forums who did a few frames very well a few years ago and I'm sure he will see your posting and reply if he wants to. If you just want the look it is pretty easy to make a TY250 look like a Yamaha-framed Majesty without doing the frame and swingarm mods.

That depends on a couple of things: The "new" cylinder may come with it's own piston. The condition of your existing piston and rings. Do they have enough life left to be worth it? Is the "new" cylinder diameter small enough to be bored to suit your piston? It's likely that a 198 cylinder will have been rebored at least once by now. My own choice would be that if a new piston was available to use as part of an engine rebuild, I would use a new piston to reduce the risk of having to do the job again.

What do you mean here about the Clake?

Sorry Graham yes I was wrong. I've been working on too many engines lately

Standard was 70mm which was 238cc. The earlier "250" Sherpa T engine was 72mm bore standard. Pistons are generally only available in 72+mm sizes now. The 198 and later cylinders can be bored to suit 72+mm pistons without needing a bigger sleeve. One thing that is visually distinctive about the 198 and later "250" Sherpa Ts (198A and 198B) is that they use a metal head gasket instead of the earlier design that had the head seal directly against the cylinder sleeve (so the sleeve on a 198 cylinder does not protrude). The gasket type head design may have first come out on the model preceding the 198 but I don't know for sure. I can do photos of a 198 cylinder and head disassembled if you need it. 198A is the same as 198.

Its based on a 125 Ducati motor

There's an Italjet forum on here with people who know everything about them. In about 10 seconds searching I found someone in the US wrecking an Italjet trials bike like yours and advertising on eBay. I searched ebay using "Italjet Trials" Here is one of the listings from people wrecking one https://www.ebay.com.au/itm/1983-Italjet-T3-350T-Trials-350-Transmission-Lay-Shaft/120688282264?hash=item1c19950a98:g:f~gAAOxybi9Rcr0e

There's a thing called a Clake that uses the left bar lever as a clutch and rear brake that might interest you. I've also often thought that mountain bikes and electric trials bikes with the rear brake on the left handlebar lever had a slight advantage for bike control compared with using one of your feet for the rear brake. As for the having the brakes both work off one lever, it would be a significant handicap when riding trials because the reason they are independent is to provide better bike control. From the sound of your question I'd say that when you have had some more trials riding experience you will appreciate why the brakes are independent.

I avoid needing to use a dial indicator by measuring the advance around the rim of the flywheel. Initially you need to establish where top dead centre is, and you don't need a dial indicator for this. I use a TDC tool which is really just a rod in a guide that screws into the plug hole. Anything that will fit will do the job. Then make a mark 21mm anticlockwise around the rim from top dead centre and use that position for checking the position of the points opening. The TDC tool is marked in mm and some people use this scale to measure piston position BTDC but I don't think this is accurate enough for the job. https://www.inmotiontrials.com/product/tdc-timing-tool-14mm-plug-hole/ If you still feel the need to use a dial indicator but don't want to take the head off, you could take off the exhaust, loosen the carburettor and remove two of the engine mount bolts so you can tilt the engine down at the front and fit the dial indicator.

Maybe it's just coolant that was still sitting in the crankcase after the o rings failed and when you tried starting it after fitting the new o rings, the coolant was blown up out of the crankcase and onto the piston and spark plug

It's time based so the cost depends on how much preparation the operator has to do. If you de-grease and remove paint, silicone, gaskets etc it will save paying someone else to do it. The bloke who does mine cleans external surfaces with bead blast to remove corrosion and ingrained dirt before the vapour blast, which also saves time. I use bead blast if I am going to paint something. The paint sticks better and it costs less. I use vapour blast for things that are going to be left bare like wheel rims, fork yokes and fork sliders

I'm size 45 and "ample" calves. Not Forma boulder. They only just overlap on the calf for me. The old Alpine Stars were OK on my calves but I haven't tried the current stitched-on-sole Alpine Stars

Those two model Sherpa T you mention use a circumferential clamp at the top ends of the fork tubes that is fastened with 6mm bolts. Your Mk4 Lobito was made around the time where some Bultaco models had circumferential top clamps and some models had a cone (tapered) shape to the top end of the fork tubes that fitted into a matching conical hole in the top clamp. For you to be able to interchange fork tubes the fastening method for the top end of both needs to be the same

If you have both bikes why not measure them yourself?

Adding to this topic because of recent interest shown in aftermarket seats for TY250 twinshocks