feetupfun

It could be something as simple as the rim not being centered (spokes adjustment) and you can measure that. Don't measure from the tyre, measure from the edge of the rim to the fork slider on both sides. No matter what hub or yokes you have, the rim needs to be equidistant from the sliders and mudguard brackets. If you are still worried if it is standard or not, post up a photo of your front end and you will soon find out.

Its fairly normal for 1970s Montesa 247 and 348 clutches to shriek and squeal if the oil is too light. If you want it quiet and smooth you will need something heavier than ATF. I run Castrol VMX80 in my 348 clutch and it is silky and quiet and doesn't drag or slip. No I don't know of anyone selling new, genuine clutch plates for a 123. I'm sure Peter Schoene could get you some. I bought some 1970s Honda CR125 friction plates years ago to try in my 348 but have not got around to it. They will fit the 348 basket but from memory only drive on half the number of tangs. I've not worked on 123s or 172s so don't know if they run different plates to the 200/247/348/349. As for internal adjustment, there is an adjustment on 247s and 348s that works by choosing from various length brass plungers that bear on the three-legged spider. You could also adjust it by using different thickness gaskets on the clutch cover. Again I don't know what is in a 123. You can buy reprints of owners manuals from Southwest Montesa in the USA

Hi Andrew and welcome from another Aussie. You aren't the first person to wonder why things were done some weird way on an old Spanish trials bike. They are like a treasure trove of entertaining design features. Sorry I can't help with the Cota 172 oil quantity but I'm sure that someone can and owners manuals are available if you are stuck. About oil level checking, there are not many old spanish trials bikes with that facility and not all of them even have a filler plug.

I've got an unmolested early 434 model motor (never even had the cylinder head off) that I can take photos of, but I suspect that there are actually two different cylinders that came on the first model TY250 so that might be what is causing confusion. One type has a circular un-finned section above the exhaust port. Is that the type of cylinder you have?

Yes they work well on a trials bike and while they may not meet the rules in some places, no-one has objected to people using them in competition where I live. I wanted to run one on my Alpina but the local KTM dealer wasn't able to supply them. The people I know who do run them on their trials bikes have sourced them from KTM dealers who took them off Freerides at their customer's request.

The Yamaha heat shield fitted after straightening the curve and elongating two of the holes. Since I bought mine the design has changed so the nuts might not be in the same place as mine

Here's mine

Generally the longer the header the more evenly a two stroke motor will fire at low RPM. On 325 Bultacos this is quite important and a longer header makes them smoother, but then again so does packing the muffler properly or fitting a reed valve. On a TY175 the low RPM running is ridiculously smooth and even already. Having said that I recently fitted a long header to my 210cc TY175 in conjunction with the tyoffroad one-piece exhaust and it feels even stronger at low and mid RPM than with the standard type exhaust and it revs out better too. All I really wanted was the weight savings with the new exhaust so the way it runs is a bonus, but it may not be just due to the long header because the new exhaust is quite different in internal design to the Yamaha exhaust

Wiggle the clutch arm while you are trying to turn the clutch arm adjusting screw anti-clockwise. There may be a burr on the peg on the adjusting screw that is catching. If you are in doubt about what I'm saying, have a look at a parts diagram and you should be able to see how it works

Sounds very odd. That key shouldn't see any force if the taper is holding properly

You unscrew the clutch arm adjusting screw which is located in front of the sprocket

If there is not enough air space when you put the cap on, the pressure relief device will let out some coolant as the coolant heats up and expands. As it cools, the vacuum relief device will let some air in. If you leave it at that, you shouldn't lose any more coolant

Yes it's OK, it should have clearance the whole way along. It stops flowing fuel when the venturi effect stops which is when the slide gets to the bottom

beside the hinge for the oil tank

I still use my local auto trimmer/upholsterer

Yes the late TY250 is different to the TY175 and both are different to the early TY250 seat

Flywheel effect is definitely a personal taste thing. I suggest you try riding it however it is now before making changes. It can be a pain trying to refit the steel band to a TY250 flywheel. TY250 twinshocks have become fairly popular around here over the past 10 years so I've kept a flywheel with no band that I lend to people so they can try it on their bike before they do something to theirs that's hard to reverse. I machine about 1/3 of the steel band away on my late model TY250 flywheels and have left my A model flywheel with the small band standard.

The wikipedia story reminded me of yet another variation from an early Cat Stevens song that includes "pumpin' petrol gas"

I have always wondered where the "gas" name for US car fuel came from, but there is nothing strange about how they identify gas. Gases are identified by name, same as everywhere else.

The pressure relief valve may be blocked and that could be the weakest hose connection

I'm pretty sure those studs are cast in place

Photos would be much more useful for identification

Sorry I don't know what you are trying to remove but I'm sure you can also make use of gravity to help prevent particles entering the intake or exhaust port. On one of my bikes (an OSSA) I always string the bike up upside down when I take the cylinder off so that no rust or dirt falls into the crankcase.

Do you have the important dimensions JC? George is a master at sourcing pistons for oddball motors

There are plenty of coatings available to protect stored metal. They are usually waxy and work by not allowing water or oxygen to penetrate and can be removed with common solvents. Available at bearing, tool and machinery shops