feetupfun

If the motor has been sitting for years without the big end covered in oil then it would be a good idea to replace the conrod while it is apart. It's fairly common for a big end that has been sitting for a long time to show no movement or play but fail quite soon after going back into service, due to corrosion of the rollers or the surface of the pin. You can always have a look through the oil slot in the big end for any tell-tale marks (lines of discolouration running across the pin where the rollers run) on the big end pin. The bloke who rebuilds my cranks prefers to push them apart to have a better look but you might not have that luxury. The usual failure mode for two-stroke trials bike big ends is running the engine after a long static storage rather than due to hours of use. If you know it has been run regularly over the years then there probably isn't corrosion in the big end. I've got a few 1970s trials bikes that still have good big ends and have done lots of trials and trail riding work, because the oil in them has never had the chance to dry out.

Same as moleman except I machine the drum surface with a lathe. My "jig" is a piece of steel rod that is a neat fit in the backing plate hole and with a male thread cut on one end so I can pull the backing plate against the chuck jaws with a nut.

I have an early M49 (4900100) rider and from memory, the primary chain tensioner that it came with is different to later M49 and M80 engines. Maybe just the spring is different. I can't remember if the shape of the arm or the mounting arrangement was different, but it did have a brass rubbing block rather than a rubber wheel. After working out that the strange damage marks I found inside the primary casing were from a tensioner coming apart, I run it without a primary chain tensioner. Another thing to watch out for is that if it is an early M49 it might have a clutch that is different to the later single row chain clutches. One of my M49 engines has original fibre plates and the steel plates have no holes. I've not checked if later type (all-steel) plates are interchangeable with that clutch

I can't be sure of the question. Maybe "trials" and "trial" have been used instead of "trail"

http://amalcarb.co.uk/mk-ii-concentric-series/2600-series/needles.html sounds like the markings for an AMAL needle This link should take you to parts listings for MK2 AMAL concentrics so you can look to see what needle your carby would normally have

Sounds too loose, but they are usually able to rock a bit in AMALs. What markings are on the needle? If it's a foam filter, it should be oiled. If it's a dry paper element, it should be dry. They normally have a foam filter element The needle is normally held in a hole in the throttle slide. I figure that's what you mean by throttle seat.

I would love to see some video of you using that clutch in sections

Sounds like something stopping the flow of fuel to the float bowl when there is no motor vibration. When you stop a hot motor, fuel evaporates from the float bowl. This fuel is usually replaced through the float valve, but sometimes a float valve requires vibration from the motor running to keep it working properly. This can deplete the fuel level in the bowl, causing a lean stall after you start it. By giving it a good rev when you start it you are causing lots of vibration. Another possible cause is that you might have a vapour (or air) lock in the fuel line or fuel tap, which can cause similar symptoms. As for the idle RPM increasing as it warms up, that may be perfectly normal or may indicate an air leak, or may be the fuel level going low - need more information. The standard AMAL faults of worn needle jet and worn jet needle have no effect on idle, they just detract from the pleasure of riding what would otherwise be lovely smooth engine performance by making the motor run lumpy and causing premature sparkplug fouling.

Powder coating will look sub-standard or odd from the beginning. If you polish or hydrablast at least it will look great for a while. Where I live it doesn't rain much and I spray them with WD40 after a wash, so my polished Spanish trials bike engine covers look great for years without any repolishing. I imagine if someone rode where was acidic mud, or didn't wash their bike properly then they would lose shine pretty fast. Many "truck wash" detergents are quite alkaline which takes the shine off aluminium pretty fast, but you can use neutral pH cleaners instead.

I'm wondering if you have the original header pipe or a replica pipe because some replicas are not exactly the right shape. Whether it is a replica or the original, the under-tank clearance can be adjusted by rotating the front pipe in its cylinder end connection.

Because the monty uses cross pins through holes, options are limited Replace the springs with lower rate springs, or shorter springs, or a combination (you would need to work out your existing spring rate and preload and free length, and have access to the dimensions of other clutch springs to choose from) Machine the pressure plate friction surface back a bit at a time. If the pressure plate is borderline stiffness already this would not be a good choice Take out a driven and drive plate pair (this is very cheap and easy will probably be too much reduction in pressure plate force and also reduces the effective plate area so will probably slip) If you have 6 springs you can usually take two out and try it. With 3, 4 or 5 spring clutches, this idea won't work well because the pressure plate will not stay straight when the clutch is disengaged. If you take 2 (opposing) springs out of a 6 spring pressure plate, there is a risk of the pressure plate flexing which means that the clamping force may not be evenly distributed which may cause uneven wear of the plates and pressure plate, and poor disengagement. I can't remember how stiff a montesa pressure plate is to make a recommendation on this, but I have done this mod to some of my TY250 motor trials bikes and it works great. Shorten your springs a bit at a time by grinding and retesting. This requires care to maintain the end flat and perpendicular, and to keep all the springs the same length My 348 has a completely standard clutch carefully set up, good cable routing, high quality cable, lever ratio (AMAL levers), lubricated cable, lubricated camshaft and cam and has a nice smooth action. I don't use it in sections though because I don't like the way it engages slowly, and the motor characteristics better suit riding with a dead throttle and not touching the clutch lever.

Maybe your mudguard is a bit wider than mine. This shows the arrangement on my 348

Polishing using power tools is probably not as hard as you think. I use a combination of bench grinder buff and buffs that go in hand held tools. There are stages before the polishing starts that make the polishing bit quite fast. Google is your friend Alternatively a suitable and longer-lasting finish for those items is hydrablasting. It's not as shiny, but is very attractive and much more long lasting before a repeat is needed.

Make sure you have high leverage ratio hand levers. The standard AMAL levers they came with provide such a ratio. Many other common levers do not. You can reduce the lift of the clutch release cam. You can reduce the clutch pressure plate force. A good way to judge when it has just enough force to not slip in top gear, without having to keep putting the cover back on again and test-riding, is the knowledge that if you can kick it over compression without the clutch slipping, there is enough force on the pressure plate that it wont slip in top gear when riding.

Yes it looks wrong. I'm thinking the cable holder should be on the inside of the mudguard mount and then when you straighten the brake arm, the cable will have a straight pull. I have done as I just described with my Cota 348 which appears to have the same brake hub, arm and mudguard mounting arrangement, and it works very well

OSSA MAR motor is fabulous with a dead throttle ("idle" set so the motor eventually stops if you leave the throttle alone with clutch in)

Yes the cylinder nuts are concealed by the head. I think as well as looking amazing, they handle wonderfully Some other character-building aspects are: 7mm threads on casing screws 7mm AF internal hex drive on cylinder nuts Square drives on both brake arms Unique tiny diameter brake shoe springs Plastic (anti) bottoming cones in forks that spread and swell and jam Triple clamps machined from alloy plate that eventually falls apart Bizarre gearbox vent system

The reason you could disengage the clutch in 6th gear but not the low gears is because 6th gear puts the highest torque on the clutch

There are different length pushers so you can adjust the position of the arm to suit your particular motor. If the arm is too far inwards when it starts to disengage the clutch, use a longer pusher.

349s have all steel clutch plates so are sensitive to the quality of the oil film between the plates as they come together. Lack of oil, oil of too low a viscosity, oil with water in it or the plates being too hot can all cause it to judder/shriek as it engages under load.

I sometimes pack out the shoes at the pivot ends when the linings wear down a bit. On some bikes, it is easier to do that than packing out the camshaft ends.

If the kickstart won't rotate the crankshaft when you pull the clutch in, then the clutch is disengaging. There will always be some clutch drag when it is disengaged and this drag will be most noticable with the motor stopped. Minimising clutch drag is a worthy goal, but don't expect a 349 clutch to be drag-free. A better test than putting the bike on a box is to put it on its wheels on a high friction surface like rough concrete, select 6th gear, sit on the seat, pull the clutch in and move the bike backwards.

Yes having a square drive for the arm is a bit of a weakness at times like that

One photo shows how the ends were machined down to 7/8". The other is the stamping that was between the mounting clamps, looking like an advertisement for Akront

My 1976 348 came with Akront 1" bars and they were great bars. They lasted until about 2014 before breaking which is quite a bit longer life than 1970s (unbraced) 7/8" Renthals