fastducs

Instead of silicone or grease I recommend Hylomar Gasket Dressing. One little tube will last you many years. I think it is some kind of polymer paste, much thicker and tackier than grease, and it never dries, doesn't wash out, and doesn't run when the engine gets hot. Like the name says, it is specifically designed for use on gaskets. I use it on brand new gaskets, and years later they come off the cases with no effort whatsoever, and I can reuse a gasket many times if I'm careful not to over-torque the cover bolts in the first place.

In New England we have a pretty good youth trials scene. We keep our youngest trials competitors away from the adult loop, even though they pay an entry fee. AFAIK, everyone on an Oset rides in the Youth class for which we set up a separate loop and sections. When kids get big enough and skilled enough, they transition to a 50cc gas bike and move up to Rookie class which uses the same loop and sections as the adult Novice loop, but with dedicated easy splits in the sections. AFAIK, we don't allow any spectators on bikes, so if you swing your leg over a bike during the event you are either a competitor, a minder, or a worker. Here are some pics of our Youth class: http://newenglandtrials.org/Coppermine/thu...ls.php?album=20

I believe the crankshaft oil seals are on the outside of crankcases. Look on page 4-22 of the service manual. This is fairly typical of modern 2-strokes. So if you are careful, you might be able to pry the oil seals from the outside, and drive in new ones without having to split the cases. DO NOT pry against crankshaft, or else you'll scratch it and your new seals won't last long. You may need to drill the face of the oil seal so you can get a pry pick into it. Or try driving a sharp pick into the seal at the seam where it meets the crankcase.

There should be no twitch. Either flywheel isn't on tight, or the crank main bearings have gone bad. Remove flywheel, grab end of crankshaft and try pulling up/down. Also try pulling crank in/out of the crankcase. Any noticeable up/down play in crank bearing means that the bearing and/or crank requires replacement. In/out play also indicates a worn bearing and/or crankshaft, but is a bit more tolerable than up/down play.

I agree with B40RT, namely that it sounds fuel-related. Good tip on tapping bowl in case of sticky float valve. Also try this: turn on fuel petcock and lean the bike on the left side at about 45 degrees. This should force more fuel into the bowl. Then stand her upright and give 'er a kick, try with and without choke. BTW, you should measure compression before considering piston ring replacement. Just for reference, if memory serves me right (I don't have my service log nearby) mine was over 200 psi cold.

If memory serves me right, the sub-cleaner feeds air to the Main Air Jet, which is necessary to emulsify the fuel as it travels up the needle jet. On most carburetors the MAJ is fed by a small opening drilled in the carb bellmouth lip, but this particular Dell'Orto is different. Drilled-bellmouth-lip type is subject to pressure pulses in the airbox, so apparently for trials bikes it is advantageous to eliminate the pressure pulse effect by feeding MAJ externally.

Montesa doesn't expect you to rebuild the shock, but the shock can be rebuilt. It is a gas-emulsion Showa shock. My rebound adjuster seized and broke, so I had the shock rebuilt by Peter Kates of GMD Computrack Boston. He even machined a small batch of replacement rebound adjusters, in case you need one. You can send him your shock for service, or if you insist on doing it yourself maybe he will sell you the seals, etc. Contact info: http://computra.startlogic.com/Contact%20Info.htm

Here is a parts diagram. Hopefully this helps: http://www.apexmotosports.com/montesa%20parts%20book/f-6.htm I took some photos when I disassembled my forks. Click here for photo of fork internals I also have some closeup photos, as well as photos of homemade damper rod holder and cartridge holder which I made. Unfortunately I am out of space, so if you need those pics, let me know your email addr and I'll email them to you.

I cut down a pair of Domino trials grips that I removed from my Montesa, along with bar-end protectors, and installed them on my son's Oset. It works very well for him - much better than the awful stock fat-ass grips. BTW, I consider bar-ends necessary to protect the fragile throttle, which I've already had to replace once after the housing cracked from a crash in the middle of my son's first race. My son was devastated that he couldn't finish the event. Tip: the bar-ends which I had were too skinny for the Oset's handlebars, but it was the day before a trial, so I just wrapped some electrical tape around the expanding portion until it matched the handlebar I.D. and then I hammered bar-ends into the handlebars. It was supposed to be a temporary solution, but it has worked so well that I've just left it as is.

Ignition is unlikely to be your problem. If you had a weak ignition, it would not improve even after the bike warms up. But you say the bike starts fine after it's warm, so I would not put ignition at the top of the suspect list. However, there is a modification that people sometimes do to the 315 crankshaft position sensor to change ignition advance, so it might be worthwhile checking if previous owner got it completely out of whack. Again, not top priority IMHO. The most likely suspect is the starter circuit in your carb (aka choke). Did you take it apart and clean it? Did you get all air passages clean too? And both halves of the pilot jet? What jets do you have in there, and what is your air screw set at? My 315 starts on the 2-nd kick with choke when cold, so your problem is not typical.

I've tried 50/50 mix of 93-octane pump gas and VP C12. I've tried 50/50 mix of 93-octane pump gas and CAM2 110 octane. I wasn't very happy with any leaded race fuel options. After doing some research I currently run pure Sunoco 260 GT-100. It is 100-octane Unleaded street-legal race fuel (RON 105, MON 95). I run it straight, and I mix it 80:1 with Motul 710 or Motul 800 full synthetic oil (whichever is available). My 315r really likes this Sunoco fuel, and I really like NOT breathing leaded exhaust. I pay $8 USD / gallon, so running this fuel straight costs me about as much as 50/50 mix of pump93 with VP C12. I keep it in a sealed metal container and it seems to stay good for several months. Another nice thing about it being unleaded is that at the end of the season I can pour leftovers into my car without worrying about damaging catalytic converter. Here are the fuel specs: http://www.sunocoinc.com/Site/Consumer/Rac...Sunoco260GT.htm You can find retailers here: http://www.sunocoinc.com/site/Consumer/Rac...GT100Locations/ Sunoco also makes 260 GTX, which is not street-legal (harder to find and more expensive) but has no ethanol whatsoever, and presumably very long shelf life. I haven't tried it yet.

Hi Sam. I see you are in my neck of the woods. "for artie" gave you the key to interpreting part numbers. Parts without NNx are standard Honda parts, and can be purchased either online from e.g. ronayers.com or from your local honda dealer. Montesa-specific parts can not be purchased through Honda dealers here in US. Most of them don't even know how to spell "Montesa". One potential local (Fall River, MA) source is Rising Sun Cycles, since they import HRC race bikes (roadracing mostly). Remember that the engine is not a run of the mill Honda - rather it is HRC. And of course you can get parts from Lewisport. Vitaly NETA #145

I got one of these for my 315, but it is supposed to fit 4RT as well: http://www.lewisportusa.com/Images/vmar/vm...rakepedal_1.jpg It is about halfway down this page, along with some other aftermarket brake pedals: http://www.lewisportusa.com/parts_montesa.htm The Vmar was quite expensive, but works very well. So far I really like the feel of it, and it tucks in nicely out of harm's way.

Big screw (the one in the middle) is the throttle stop, i.e. idle speed adjustment. The small screw on the right is the pilot circuit air screw. If memory serves me right, both screws should have rubber o-rings to help seal the threads. Normally you first fit a spring onto the screw, then a small metal washer, and finally the rubber o-ring (so the o-ring ends up deepest in the carburetor). The seepage stains look like they come from the throttle stop screw, or maybe even all the way from the top of your carburetor. BTW, the vent tube doesn't look stock. It's the black tube at the top of carb angled towards front of bike. Normally it is a thin black tube that connects both vents, and has a slit opening at its lowest point. Yours has some sort of thick rubber hose going over the stock vent tube. Not that there is anything wrong with that, as long as it doesn't cover the slit. The two crankcase breather hoses are both supposed to go into the frame. There are 2 holes drilled on the inside of the frame next to the carburetor.

I took delivery of a new Oset 16 with the 36-Volt motor 2 days ago. The bike looks great, and the custom-welded frame is very solid - no complaints there. The power of a 36-Volt motor is impressive! This little bike can really go! But the first thing I noticed was that steering was notchy, which is usually an indication of an over-tightened steering stem. This is a typical problem of cheap Chinese-made bicycles (except Osets aren't cheap!) - EVERYTHING is over-tightened and under-lubricated. So the bike goes on the workbench and I took it all apart last night. Sure enough, there is barely any grease in the steering stem bearings. Added some high quality waterproof grease, set bearing preload correctly, and now the steering is nice and smooth. I move on to the front wheel, and it's the same problems. It had a bit more grease than the steering stem, but not enough IMHO. BTW, be careful with the wheel bearings - they are simple steel balls without a cage, so once you remove the axle, the balls will easily fall out. I loosened the axle, greased and re-set preload on wheel bearings, and now the front wheel spins pretty well. But now I notice the wheel is wobbly - oh well, I will true it later (assuming it's not the hub itself). Move on to the swingarm. OMG! The swingarm pivot is a metal stem in a plastic bushing! My son rode the bike for 2 hours, and the metal stem was already galled. For a bike this expensive I expected needle bearings, or at least bronze bushings with reasonably close tolerances. Come on! It is the swingarm pivot - the most stressed pivot on any motorcycle! It was also badly over-tightened, which resulted in extremely stiff swingarm movement. There is also a hole drilled in the swingarm pivot boss. I don't know why it is there, but it is an invitation for water and dirt to get into the pivot and destroy it. I plugged the hole with silicone. Rear shock had the exact same problems - over-tightened at both mounts and no lubrication anywhere. My son weighs less than 50 lbs, so I set fairly little preload on the spring, and I noticed that the shock spring preload collar got loose while my son was riding the bike. It really needs to have 2 counter-locking collars. After greasing all swingarm and shock pivoting surfaces and reassembling it without over-tightening I see a big improvement: the bike's rear suspension actually moves nicely. There is no damping of course (rear shock is just a simple spring) but all that stiction from over-tightening isn't a substitute for damping. The front fork is stiff and wobbly - I suspect the clearance between telescoping tubes is just huge. I think I won't waste any time on it and replace the fork with a RST20 mountain bike unit mentioned elsewhere in this thread. Chain was too tight and made quite a bit of noise when running on the stand. I loosened it a bit and sprayed chain lube on it - now it is better but not perfect. Drive sprocket looks a bit off center, which causes loose-and-tight spots in the chain. Maybe it's the motor axle itself - I didn't get into the motor, so I can't say at this point. Brakes were easy enough to adjust, but be careful! The owners manual says that you can adjust back pad stop by turning it with an allen wrench from the back side of the caliper. The manual fails to mention that there is a hidden set screw which you must loosen first. If you don't, you will strip the pad stop. My biggest complaint is the throttle. When speed limiter potentiometer is in its "maximum speed" position the throttle has a nice progressive response, except for a bit of a dead zone at the beginning. But as you reduce maximum speed with the pot, the dead zone becomes bigger and bigger. If your kid is a beginner then it makes sense to reduce max speed a lot, especially on this 36-Volt rocketship, but unfortunately it makes the throttle act almost like an on/off switch. I called Oset tech support about this issue. It is wonderful that in this day and age of off-shore tech support centers staffed by people who might as well be robots there are still companies like Oset that are staffed by real knowledgeable people that answer the phone! Talking to Mike at Oset made my day: he is knowledgeable, honest, and straight-forward. He explained that this throttle behaviour is a side-effect of the motor controller design. It is an off-the-shelf unit, so that's just the way it is. So the bad news is that apparently there is no way to remedy this problem without having a custom-designed motor controller.

You could try flushing out the bottom end with brake parts cleaner.

Do you have photos? A picture is worth a thousand words. If a piece of piston skirt went past the rings and into the head, then there is likely damage to the cylinder wall. Do you see any damage / scoring? Again, without good photos it's hard to give any advice.

Felix, a photo would be very helpful. I am almost certain my midbox needs repacking, so I would be grateful if you can illustrate how this can be done without welding.

Did the piston fall apart as you were removing it? Or was the piston skirt already broken with bits of it flying around the bottom end? If all you see is loose pieces of piston skirt with no damage to the crankshaft, connecting rod, or the engine cases, then count your blessings. On a 2-stroke engine the transmission is sealed from the crankshaft, so it is safe from piston skirt debris. I would remove engine from frame, turn it upside-down and flush the crankshaft area really well, and inspect crankshaft main bearings and connecting rod big-end bearing. If all looks well, then put in a new piston, new little end bearing, new wrist pin, and new clips.

I assume your Dell'Orto model is PHBH26BS, right? When you say "fuel pouring out the back of the carb", which specific orifice is it coming from? Your carb has 4 orifices. One is a fuel feed line. The 2 on opposite sides are vents, and they are connected together by a single vent hose with a gash in the middle of it (the gash is how the air is supposed to get in there). Remove that hose and blow through it to make sure it isn't gummed up. The 4-th orifice is connected to a sub-air cleaner, which is basically a tiny foam air filter. Its purpose is to feed air to the air jet inside the carb. If you sealed off this circuit, then your bike doesn't have a prayer of running. BTW, there is no overflow tube on these carbs. The fuel can overflow through the vents, but only if you lay the bike on its side, or if the float valve is stuck open.

Frank, thanks very much! I will take you up on your offer and give you a call today. When is the best time to call? LOL! I promise to suppress my Boston accent Regards, Vitaly

Hello group. I hope you don't mind a visit from a Montesa owner :-) Can anyone enlighten me about the clutch pack composition of a SY250F? I am working on improving clutch action in my enduro bike (Yamaha wr250F) which is based on the same engine as the SY250F. Comparing the parts diagrams I see the clutch boss, clutch basket, and pressure plate are identical. The difference is actuator arm, and clutch plates. Actuator arm is longer, I presume? I would appreciate an actual measurement. But the real mystery to me is the clutch pack. The parts diagram shows 5 friction plates, 5 steel plates, and 1 mystery plate. The mystery part is #13 on the diagram, it is part # S108-11000-00-00 listed as "Clutch Fix". Can anybody tell me what it is, and how thick it is? Also, are there aftermarket clutch packs available for SY250F, e.g. Sureflex? How does it compare to stock?

I presume you are asking about the rear wheel bearings? Because the front ones come out no problem. But the rear spacer tube (the one inside the hub) is a little tricky. I thas a step machined on both ends, so it actually protrudes into the bearings' inner race. This fit is similar to how the spacers fit into the bearings. So ideally what you want is a drift with a step machined into it. Step diameter should be same as the axle diameter, and "fat" diameter should be same as bearing race I.D. I think somebody does sell them, but I can't find a link at the moment. But you can make do with a socket that matches as closely as possible the bearing race I.D. I suggest heating the hub to about 200 degrees F, which should greatly reduce the rquired hammering force.

The fact that your problem is so intermittent makes the electrics a prime suspect. Check the kill button/circuit. Possibly a problem in the button itself, which could be intermittently shorting out. When you kill the ignition by pressing the button, you may temporarily relieve the cause of short circuit (corrosion?)

I don't know about the 349, so take this info with a grain of salt. Every one of the few different engine types I've seen doesn't require splitting the cases to replace any part of kick starter mechanism. Usually there is a clutch cover that must be removed. Kick starter gear typically engages clutch basket gear.