feetupfun

the offset can be measured from anywhere you like - whatever will be easiest for you to measure when you are respoking. To get the rim in the right place, I usually fit the wheel to the bike and measure from the rim edge to the forks/swingarm. From memory, MAR wheels have no offset, ie the centre line of the rim is in the centre of the spoke flanges on both hubs

For info, this is also a M49 brake pedal, but from an earlier M49 than the ones with the pivot located inside the frame

It is important to protect the gearbox bearing and the chain from overload by making sure that when the sprocket centre, swingarm pivot centre and the axle centre are all aligned, that there is still a bit of free play in the chain. The other end of the scale (too loose) on your bike would be if the tensioner is going high enough to touch the swingarm when the suspension is fully extended. If you set yours between these two extremes, you will have a happy chain The ideal measurement you are asking about (the distance between the tensioner and the swingarm) will vary with different size sprockets and where in the stroke of the suspension you are taking the measurement, so there is no single correct dimension for a given bike unless you specify those variables.

as far as modern trials bikes go, I have not known of any two stroke piston needing to be replaced due to normal wear (a few due to seizing though), and of the bikes that get owned by the one person for long enough to be able to measure such a thing, the rings seem to last 6 - 8 seasons. If modern trials bikes were used on the road (they are not used on the road here) piston life may become important, as it was in the 1970s when it was common to ride a trials bike on the road. My original TY175 was road ridden for many years and after about 20 years had finally had enough rebores that it needed a new sleeve (at the time the biggest OS piston was +1.0mm). Another of my old trials bikes (a 1973 TY250) is still going on it's original piston and rings and runs like a dream. I bought it in 1994 and the speedo showed 3000km, and it has had lots of trail and trials riding since 1994, but has never had the cylinder head off.

front wheel, forks and triple clamps look standard. The front guard looks odd because they are usually mounted to the fork sliders, and it is a guard off something else. It would probably feel better to ride with higher bars and trials shocks. The shocks look like TS185ER The end muffler is off something else It will weigh about 95kg The year model makes no difference

They can be set up to turn tightly. 360mm rear shocks and setting the forks up properly does wonders. The motor is a beaut to use and does not stall easily. No mechanical weaknesses at all - they are very sturdy and well made. The only design criticism I can think of is that they are a bit heavier all over than their competitors. As far as ease of trials riding goes they are almost as easy to ride as a TY250, and better to ride than a standard TL250 and standard Suzuki RL250. Late model twinshocks like Fantics and Honda TLRs are noticeably easier to ride while spanish bikes of the same design era as the KT (early to mid 1970s) are a bit easier to ride than the KT. While they are fabulously reliable, you could look for rust inside the fuel tank and all the other things to look at on an air cooled drum braked bike ie worn drums, pitted fork tubes, rusty exhaust, noisy motor, parts missing, clutch action, gear shifting action They were made in 1975 and 1976 No idea what KTs are worth in NZ or what a Cota 311 is worth

the effect you describe can be caused by poor piston ring sealing

There are people who have modified 1970s MX bikes for trials, and it is a lot of work, but the designs of MX and trials bikes diverged after that era to the point that by the 1990s, MX bike design became so far removed from trials bike design that it would be extremely difficult and expensive to make some sort of trials bike from a 1990s MX bike that worked well.

the TY175 JC/JE muffler also works well on the TY250, but needs the inlet tube shortened to fit the TY250

The standard end muffler/spark arrestor on the competition model TY175s (prefix 525) is noisy no matter how well it is repacked. The WES end muffler is much quieter and lighter. A super quiet alternative is the end muffler from the Yamaha JC and JE models of the TY175, which combined with a rubber snorkel in the top of the airbox, made it an amazingly quiet bike, and meet the strict road registration noise level requirements of the time. The Ty175JC model (prefix 1N4) was sold in Australia and a similar model the TY175JE was sold in some European countries, and their mufflers are sometimes advertised for sale. The WES muffler is not quite as quiet as the JC/JE muffler. The JC/JE muffler is bigger and heavier than the muffler from the prefix 525 bikes.

It's possible that one or both of the tubes have a bend, or one of the yokes has a bend, and you might need to experiment a bit to fit the tubes back into the yokes exactly the way they came out. To work out what is wrong, fit only one tube to the bike at a time and see what you need to do to get it to move fully into the tapered hole.

Cota 348

there is a UK seller on ebay

Very good to be able to have a look inside an OW10 motor. Thankyou Interesting about the splined crankshaft for the primary gear. The early Yamaha single cylinder dirt bike motors (like the DT-1) also have spline drive to the primary gear. The bigger diameter main bearings are also interesting. What is the stroke? That gearbox oil filler location would have been hard to access.

The Yamaha gasket is composite with the outer layer being a thin layer of aluminium. It would fall apart if it was reduced in OD to fit a 54mm hole

I just checked this and found that a genuine TY250 gasket was a bit too big in OD (56mm) to fit in the OSSA exhaust port (54mm)

New nuts are available. Yes never-seize is a good idea. Tie wire is the best way to stop it unscrewing. The nut comes loose because the header pipe moves relative to the barrel a tiny bit in use and takes the nut with it, so a springy o-ring will probably not help to stop it undoing. Yes a high temp silicone o-ring should seal off better than the copper gasket. Compressible composite exhaust gaskets as used on Japanese bike exhaust joints would also be an improvement compared with a flat copper gasket if you can get one the right size.

If the cause of the tightness is gummed exhaust residue in the thread, then heating it up will allow it to move Yes its a RH thread You will do a lot better with steady pressure rather than using a punch. A "C" spanner can be made from some flat steel, or bought from a tool supplier Not uncommon for the those threads to be crossed either. You should be able to see if the tube nut is crooked

very similar to Suzuki RM80X clutch lever

here is what mine looks like

as to why it shift hard, what do you mean by shift hard? more detail needed

The clutch arm shaft can stay in the cover when it comes off Can't tell what went wrong with the rear guard from your photo

348 parts also from the UK http://www.inmotiontrials.com/product-category/montesa/ and if you look around on the web you will also find parts suppliers in Spain

With any axial flow fan you can tell which way it is intended to run, by the curve of the blades. The concave side of the blade should always be on the downstream side. There have been trials bikes made with the radiator cooling air direction intentionally being towards the front of the bike. I don't remember which bike it was yet.

earlier (pre 2002 approx) tubeless with the rubber ring were 36 hole and are now hard to get new but of course are available S/H from wreckers. The flanged ones are available in 36 hole but I can't remember where from