feetupfun

When you change the fork seals, put in at least 175ml of oil per leg. My previous post mentioning 125 millimetres is a distance measurement, not millilitres (volume). Sorry for the confusion. I see the pits in the tube chrome and will post again here when I've checked if your pits are high enough not to worry about. It looks like your fuel tank has previously been quite rusty inside and someone has treated it chemically to remove the rust. It is possible that your leak is a tiny rust hole somewhere in the tunnel above the seam weld and may be very hard to see. This would explain why it only leaks when the tank is near full. Another thing that may help is maybe you aren't loosening the top tube clamps when you remove the fork caps. These clamps need to be loosened whenever you take the caps off or put them on. The clamping action causes the fork tube to reduce slightly in diameter which can cause the cap threads to jam.

First work out exactly where the leak is. If you are lucky it will be underneath the rear end where many of the A model tanks develop a crack. That way it can be welded without damaging the paint job. No don't line a steel tank with kreem. If it is a fatigue crack then a repair with anything rigid like JB weld is unlikely to work for long. If you have some repair compound that can do a flexible repair on the outside then you might get away with it. Before you buy new springs, change the fork seals and set the oil level to 125mm from the top of the tubes, forks fully compressed with springs out. Use 5 or 10wt fork oil. Using the air space in the forks as a spring by running the oil level at that height will provide better bottoming resistance. When you have the springs out, measure their lengths and post it up here for advice on if you should add anything to the length of the preload spacers to set the sag to a good number.

If it's the one that uses U bolts to grip the handlebars, it will probably be the same as early M49 in which case there are plenty around

I saw a full set for sale on eBay yesterday (top and bottom triples and the stem) http://www.ebay.com.au/itm/Montesa-yokes-trials-pre-65-twinshock/222632902124?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2055119.m1438.l2649

No, the M27 pipe runs higher where it goes over the head. M49 Sherpa T head is the same except it has cut-away fins to allow the pipe to run lower. If you are not worried about it looking like a M49, you could fit an M49 head. They are way more common than M27 heads because the head from the M49 is used on M80 Sherpa T and Alpina M85 and all three of these models sold very well while the M27 only sold something like 1200. Using a head with cutaway fins would also allow you to use that M49 tank, which would be too low underneath for a M27 pipe to fit under. Another option would be to cut the fins away to provide clearance for a M49 header. Please don't do that though. I would be happy to do a head swap with you because I would like an M27 head and have spare M49 heads.

My money is on the blue and red stickers being road rego stickers from 1987

Have a look first, you will have a good chance knowing it is in an odd place

oldaz please post photos as you bring it back to life. They are a nice bike

There are no windows or test holes or dipsticks for the gearbox or the primary drive compartments. While you are changing the oils, I challenge you to find the gearbox breather without the help of a manual or help from someone.

I have no idea who Steve is. The extra neutrals may not necessarily be due to a shimming issue, and may not require splitting the cases to fix. Whether you want to investigate what is happening yourself depends on how confident you are with this sort of work. We have OSSA specialists here in OZ that could fix whatever is wrong, but I suspect you might be in the UK.

http://www.southwestmontesa.com/manuals.html Many photos of what they should look like on the internet too There are plenty of people on here who are intimately familiar with your bike so if there is something you aren't sure of just post up photos here of what you are wondering about

Use a M212/213 Alpina tank

I've got some early Bultaco front hubs and brake plates that might be what you are looking for, but I need photos to identify exactly what it is you want

Q1 yes you can buy 428 chain sprockets for Ty250 Q2 Chain size/type has nothing to do with gearing. It is the ratio of the sprocket sizes that determines gearing 14/53 ratio = 3.79 = too fast for trials 12/44 ratio = 3.67 = even faster! 12/53 ratio = 4.42 = good for trials - good choice for 428 chain 10/44 ratio = 4.4 = good for trials - good choice for 520 chain

This shows the thin flat sticker I bought in 1975 when I repainted this M99 Alpina

My memory is that the thin flat stickers were all you could buy at Frasers as replacements in the early and mid 1970s

Yes with a 14 it will be crap for trials competition. The BCDE models had 13 as standard. I would need to look up a book to see what A model had. No Idea about the number of links. I usually just buy a 120 link and shorten it to whatever is needed. Going from 12 to 14 on the front makes very little difference to the chain length. If the axle is near the rear end of the slots with a 12, it should allow a 14 with no extra links. You will need bigger than 14 to ride at highway speed.

The modern ones are much more crash resistant, but use a decent adhesive. Some modern ones come with a pressure-sensitive adhesive that does not work well when confronted with petrol, heat and vibration

Sad to hear, Guy

Thermal cycling is another possibility. This is how fuel tanks and magneto casings can collect water too. If the bike is stored somewhere there is day-to-night temperature variation, every enclosed (and vented) space will breathe in and out with each thermal cycle. In spaces like fuel tanks and crankcases and magneto casings and gearboxes, the air cools inside the space at night. Because it cools, the air contracts, which draws in some external (evening) air. If the metal gets cool enough overnight to go below the dewpoint temperature of the air inside, liquid water will form on the surfaces and collect at the bottom. The next day when the air warms up, the metal and the air inside will warm up and the space will expel some air. By then though the amount of water vapour in the air in the space will be less than it was when it entered (because the rest turned to liquid and ran to the bottom). Because of this, the air expelled will take out less water vapour than it brought in. Each thermal cycle that sees the temperature going below the dewpoint with the bike stored will add to the amount of water in the bottom of those vented spaces. While you can block the fuel tank vent and the gearbox vent and the magneto vent during storage, it is pretty hard to effectively seal up the exhaust and inlet of a two-stroke. It's a good thing to run each of your bikes at least every month to clear out the water from the motor and re-coat the insides with oil. I use semi-synthetic premix oil in my fuel because it gives added protection from corrosion damage between rides, compared with full synthetic premix oil. Another thing to consider is that if you run petrol (pump gas) that contains alcohol, there will be more water condense inside the crankcases each time after you run the motor and let it cool, compared with running petrol that does not contain alcohol. That's why racing engines that run on methanol are then run on petrol at the end of each competition.

Adjust the points so they start opening at the correct piston travel before top dead centre with the flywheel turning in the running direction. It is the opening of the points that causes the spark. The gap you end up with (when they are fully open) is not critical but once the points are set to provide the correct timing, is usually between 0.3 mm and 0.4 mm. The position of the piston/flywheel when the points reach fully open is irrelevant. TY backing plates are not adjustable.

The seal can be replaced by removing the clutch camshaft. The clutch camshaft is retained by its adjusting screw on the left side of the gearbox near the gearbox sprocket. To see this screw you will need to remove the magneto cover. The screw has a locknut which will need to be loosened to get the screw out. If the clutch camshaft won't come out with the adjusting screw removed, you will also need to remove the clutch pressure plate (inside the primary drive cover) to let the clutch pushrod move clear of the upper end of the clutch camshaft. There are service/repair manuals available for the B model which has the same arrangement for the clutch camshaft.

As for your fork seals, if you can, just buy seals of a width that takes up the space between the seat and the circlip. That spacer in the parts diagram is not a guide for the fork tube, it is just a spacer. Two narrow seals per side or one wide double-lipped seal per side will do the job of sealing the forks. The fork tubes are held centrally in the seals by the precision-machined bores of the sliders. If you are really determined to make plastic spacers for the fork seals, just make them the right width so that the circlip just touches the top of the seal. Bear in mind that a couple of my old Spanish trials bikes have no circlips on top of the fork seals and I have sealed up the vents in the fork caps and I run enough oil to firm up the last bit of fork travel using internal air pressure, and those fork seals have never moved out of position. From memory I think the seals are double-lipped and 10.5mm wide.

If you use the type of decompressor that resets itself, you set it to the open position using a knob on the end of it, move the piston to the right spot, kickstart the bike and it then closes itself. There is also a type of decompressor that has a handlebar lever so you can open it while easing over TDC, kicking it, and for braking effect while riding. Are you sure your head doesn't already have a hole for a decompressor? It was fairly common back then to have a decompressor hole. Cota 349s do take a lot of effort to kickstart. I have a 348 which is only 310cc and kickstarting it is usually the most tiring part of riding a trial and 349s are even harder to kick over. It would be good to just leave it running all day but it is fairly hot here and they overheat if you leave them idling for too long.

M99 was 325, marketed as 350. Here is my M99. Photo taken in 1976 in my parents' front yard