feetupfun

I just measured the original Telesco shocks from my 1976 Cota 348. They are 360mm eye to eye. Axle travel to the point where the shock body just touches the bump rubber is 114mm. Axle travel to compressing the bump rubber 10mm is 129mm. You asked what the shockie length "should be". All I know is what works for me. I have 1980's vintage Marzocchi shocks on my 348. They are 352mm eye to eye and still work great. If I needed new shocks for the 348, I would buy Falcon Classic Trials shocks without hesitation.

The two stroke decompressor as on that Cota 247 works by opening only a small hole between the combustion chamber and the outside air. The small hole allows air to flow in and out in a controlled manner dissipating energy just like fork oil moving through the orifices in the damper rods also creates a drag which dissipates energy. A big hole in the head (as in taking the spark plug out) doesn't restrict the flow as much so doesn't provide as much braking effect. On a 4 stroke, the decompressor is there to allow the motor to turn over easier for starting so it works by opening a large hole between the combustion chamber and the exhaust header. In the case of a 4 stroke, an exhaust valve is held open continuously to provide the big hole. Please be aware that in dusty conditions, with the type of decompressor shown on that Cota 247 it is possible for dust to enter the combustion chamber via the decompressor hole (unless it has a filter), increasing ring, bore and piston wear rates.

BillyT You are spot on about the benefits of the pulsing effect on traction in marginal conditions. Modern (2-stroke) trials bike manufacturers design their engines to provide a strong pulsing effect at low RPM to maximise traction in slippery conditions. Being a regular rider of 1970s trials bikes since they were new, one of the things that is very obvious to me when riding a modern trials 2 stroke is the strong pulsing effect at low RPM compared with almost electric motor smoothness of the 1970s 2 stroke trials bikes. The physics is quite simple of why the pulsing helps. A tyre slipping on a muddy rock has less grip than a tyre that has the tread stationary relative to the rock ie static friction is greater than sliding friction. When drive is on the verge of being lost due to low traction, the part of the engine cycle when no drive is occurring (between when the exhaust port opens and when the next power stroke starts) allows the tyre to regain the benefits of static friction in time for the next power pulse. A four stroke engine simply has a stronger version of this effect because it has a longer period between power strokes for the same RPM. The effect is only a benefit when the tyre is on the verge of slipping. Once a tyre is spinning on a slippery rock, there is no benefit from the pulsing effect. The same effect is being used in MotoGP bike engine development. These bikes also operate at the margins of traction during acceleration and are being developed to maximise static tyre friction by optimising the pulsing effect. Another example is ABS braking systems on cars. They are are designed to pulse the braking to maximise tyre friction during emergency braking.

You will find lots of useful info on Jared Bates' site below and a good RHS photo of a 1972 Cota 247 in his photo gallery. http://www.southwestmontesa.com/ There are also many other sites with Cota photos. Have you seen www.todotrial.com It has good info and a good set of links to sites with plenty of photos of perfectly restored Spanish trials bikes. I'm glad you got a pre '76 Cota 247. They certainly are a fantastic looking bike.

It may indeed be the CDI box. If you have another Rev 3 there to use a test parts why don't you swap the CDI box first if you don't have a flywheel puller yet? London to a brick it's the stator coil though. Yes if the timing is right at idle it's not a sheared flywheel locating key.

Good to hear. I totally agree. I love riding my Cota 348 and OSSA MAR because in my eyes they are the coolest looking bikes I have ever seen. I suspect that the bike that someone likes the look of most has something to do with their association with that bike when they were at a certain age. I've found that unless a bike was made between 1972 and 1976, it really doesn't rate in the looks dept for me. That means that I was 13 to 17 years old when the strong impressions were made. How old were you guys when the bikes you love were made?

Well done checking with a strobe. Yes whet you are probably seeing is what MarkyG has suggested. To prove to yourself that it is the stator before you shell out for a new one, can you swap just the rotor with another Rev3 to see if the problem goes away? About half the early Rev3s in my club have suffered this failure so we are geting pretty good at diagnosing it now.

Dear Vintage Cota I can't beat your Cota 123 story because I don't have a bike that old but this story must come close. I discovered after taking the head off my 1976 Cota 348 for it's first ever decoke a few months ago that it still has the crosshatch pattern bore finish put there by the factory. The fork tube surfaces also have the original crosshatch pattern. Those Montesa fork gaiters do a good job protecting the forks. My 1974 Yamaha TY250A has never had the head off and still runs perfectly and is quiet mechanically. I guess one day it will also need a decoke? The speedo read 3000km and was still working when I took it off the bike nine years ago. David Lahey Gladstone Australia

I have only got Ross' message machine so far so don't know for sure but I wouldn't hold out much hope for original 123 handlebars. Time zones are easy. If you are in the USA or the UK just phone Australia in the middle of your night and you'll be pretty close. He probably has an email address but I don't know it yet.

Beware about front ends on 348s and 349s. Yes the forks legs are interchangable but the triple clamps put the fork tubes at different centres. The 349 had the tubes closer together. If you are using the 349 triple clamps in a 348 consider the front wheel width and fuel tank clearance.

There was a bit of chat about someone looking for Cota 123 parts a few days ago. On my last visit to a bike wrecker at Tiaro, Queensland, Australia, the owner had most of a Cota 123 for sale. If anyone is interested in it, please contact the owner (Ross) on +61 (0) 7 4129 2771. Please consider the time zone before you phone Ross.

I'm just about to do a pre-purchase inspection and test ride on a 2001 REV3 200. Is there anything special to look out for with this bike? I am familiar with 2001 REV3 270 and the well known Beta problems with ignition stators and carby connector failures. What I'm after is any problems particular to the 200. I'm told that the bike has recently had new rings fitted and that the reed land needed trimming to remove a bump. Thanks

The long wheelbase Montesa you were warned about is the red tanked model Cota 349. It was from around 1980 and has a longer swingarm than the later white tanked 349. If you don't ride in competition (need to turn tight) the longer swingarm of the red tank 349 makes for better steep terrain riding. The 348 series (76 to 79) handle and turn well, have good power and are all red. However the only light weight red Montesas of the 1970s are the ones with the small motors ie 123 and 172. The 247s are the same weight as the 348s. Depending on how tall you are, you may find the 123 and 172 a bit small.

Don't have a cow, Luke. Have a look at your first post again. It doesn't say you are getting a 250, just a Scorpa so it was pretty hard to work out what you were on about. They do make 125 4 stroke Scorpas too which are the bikes people usually want more power from.

Luke Are you getting a two stroke Scorpa SY250 or a four stroke? I suspect there is a bit of confusion about what Scorpa you are talking about.

Doesn't the photo of new Scorpas lined up outside the Scorpa factory posted by Ben R in this string show the latest SY175 including the rear mudguard?

We do get IRC tyres in Oz, I run one on the GG300ec of mine in the summer. The importer is located in Victoria, Bruce Collins used to import them. Thanks Splint. I haven't seen an IRC trials tyre yet but will now be on the lookout. From the sounds of what our friends from overseas are saying though the IRC probably isn't ideal for the dry riding seasons where I live.

Dunlops are better than Mitas and Pirelli but not quite as good as Michelin. We don't get IRC here in OZ so I don't know about them. It's pretty simple as someone else said: You get what you pay for. If you want rim protectors buy a cheap tyre. If you want to win in competition, buy the best. When the others start making tyres as good as Michelin, their price will go up to suit.

"Pinky" TY250 Yamahas don't have pink frames. The pink bit is the seat/rear mudguard. The fork legs are blue. They also were the only air cooled monoshock TY250 model to have a front disk brake. They were the last air cooled TY250 model made and were sold here in OZ from 1991 to 1993. The watercooled TY250Z came here in 1994. The only parts shared in common between the Pinky and the TY250Z are the front wheel.

If you have a set of bathroom scales you can weigh it one wheel at a time and add the two weights together to get the total weight. My guess would be that the steel tank air-cooled monoshock TY250 in competition trim ready to ride would weigh between 88kg and 92kg. With indicators and lights, speedo and mirrors it would be a few kg more.

The 220kg on the Japanese frame plate is probably the maximum legal all-up weight of the bike including rider/s. The usual abbreviation is GVM (gross vehicle mass).

29er suggested greasing the mating parts when you reinstall the flywheel. I hope that doesn't mean the taper? Mechanical drive tapers should be assembled dry and clean ie no water-dispersant, oil or grease. You are increasing the chance of another sheared key if you put grease on the taper. The suggestion to use lapping paste on a damaged taper can be helpful once any high spots caused by the key failure are carefully removed. If the damage has cut up the surfaces too much and key failures recur even when the flywheel is re-installed properly, loctite can be used as charliechitlins suggested but the flywheel may need heating to release the loctite next time it needs to come off.

Dear Charlie These are two of my favourite bikes and I often have trouble deciding which to ride. First the differences in geometry and weight: The TY175 has a 48.5 inch wheelbase. The TY250 is 50.5 inches. The TY175 has a more raked steering head angle (less steep) but with the same triple clamp offset so it has slower steering than the TY250. Both wheels, brakes and the front ends are interchangable (except for the dished sprocket on the TY250). The TY175 forks have skinnier tubes and have lighter springs than the TY250. The TY175 (83kg) is 10 kg (22.4 pounds) lighter than the TY250 (93kg). About 8kg of this difference in weight is in the engine. Riding them: Chalk and cheese. In sections, the TY175 feels much lighter than the TY250 and because of this can be ridden much longer without taxing the rider's endurance. However the TY175 has a unique feel to the front end that I've never come across on other trials bikes of the same era. The front end never feels totally confidence inspiring on obstacles. There are a few possible reasons for this: The forks flex noticably in rocks with an adult size rider. The steering rake is more like an MX bike of the era. The handlebars always seem too far back even when they are rotated well forward in the clamps. I am only 1740mm (5 foot 10 inches) tall. On my competition TY175, I've moved the pegs down and back to give more room and have fitted the front end from a TY250. This improves things a lot but the front end is still not as good as say a Cota or OSSA or the TY250 of the same era. The TY250 front end is more refined than the TY175 but one is always conscious of the TY250's weight when in sections. Both bikes are capable of turning as tightly or even more tightly than most of the other bikes probably due to their relatively short wheelbases. If there was a forte for both of them, I'd say it was in tight turns. The first TY250 had a motor that was not as forgiving at low revs as later model 250 motors but they are all are very competent and run very evenly and smoothly with standard settings. The first model TY250 flywheel was lighter than the later models and the porting was different too. The B and later TY250 motors all lug and rev out with magnificent gusto. The TY175 motor has noticably less grunt than the TY250 as you would expect but has the widest usable rev range I have ever witnessed on an old trials bike. It runs strongly right down to the point wher you could count the strokes yet will rev out far higher than other similar era bikes. This proves to be very important in competiton because you can run gearing that provides great clutch-out control at low ground speed yet the bike can also get to a usefully high speed in the same gear. The TY175 would usually be the bike to choose if you wanted to score the least points at a trial but because of the front end and cramped riding position does not feel as satisfying to ride for me as the TY250. In case you are a bit of a hoon, both are fantastic for pulling extended wheelies on. The TY175 makes the better trailbike ie the handling is quite good at higher speeds and when sitting down. I don't know why but suspect it is because of the slower steering. David Lahey Self confessed twinshock trials nut Gladstone Australia

Da Make is referring to what in English is called a "floating" rear brake. They have been used on bikes for many years. The theory is that the rotational forces generated about the swingarm pivot by applying the rear brake are transmitted directly to the main section of the bike frame to prevent these forces causing the rear suspension to compress or extend. Amongst other things, they require the brake backing plate to be able to rotate freely about the rear axle. The added weight of the additional axle bearings and longer torque arm required for this meant that it is a feature not usually seen on lightweight trials bikes and certainly not on any trials bikes ever made by Yamaha. It was popular on MX and road oriented (trail) bikes of the drum brake era. Note that a rear disc brake does not avoid the problem fully because a disc brake still generates a torque about the swingarm pivot which tends to compress the rear suspension (lift the wheel). The difference between disc and rod operated drum brakes that Da Make mentioned is that the force exerted by the drum brake actuating rod is avoided with hydraulic braking. The effect is also avoided on drum braked bikes that use sheathed cable actuation (OSSA MAR and Suzuki RL250). A similar concept for the front suspension was in vogue in about 1978. It was sold as a kit for popular MX bikes I think by Preston Petty. It used a floating front brake backing plate and a rod which transmitted the braking force up to the triple clamps. It worked exactly as intended but people soon discovered that having the forks stay extended as you brake into a corner actually made it worse for cornering so they dropped from favour. Some modern cars have anti-dive geometry built into the front suspension.

Here in OZ the Mitas competition trials tyres are also far cheaper than Michelin, Dunlop and Pirelli but due mainly to their low profile shape (shorter contact patch) they perform quite poorly in trials competition compared with the others. However one thing that Mitas trials tyres are good for is if you want road registration for your trials bike they have US DOT approval so can be used on the road here in Australia and are far better than any other trials type tyre that has DOT approval. Mitas trials tyres also sell like hot cakes for flat track (sliders) racing on decomposed granite tracks where previously the rear Michelin XII trials tyre was the favourite (because they are far cheaper but perform on that surface just as well). By the way the standard retail price for a rear Michelin tubeless XII here is AU$180 which is virtually the same as 60 UK quid. David Lahey Queensland Australia