was out for a ride about today and after about 20 mins i noticed the "rainbow"oil effect on the top of my right boot. my first though was fuel leaking but i couldnt smell anything. upon further looking and poking i noticed that the left side (clutch side) had ATF all over it and it seemed to be coming out round the gearbox filler plug' i tried to tighten this but couldn't. when i got back to the workshop i took the chain off and front sprocket and saw that the seal round the output shaft was leaking slightly. it seems to me that it wouldnt be enough to cover the the left side including the carb! do i need to look any where else??

clutch cover o-ring?

It would be plenty enough to cover the left side of the bike if its the shaft seal. As of course it will be flung off the sprocket!

thats what i would have thought but the shaft and sprocket were dry and not soaked in ATF? is it simple to check the clutch O ring?

Hmm... Wouldn't 100% mean that it's not the shaft. Oil spreads like a bad rumour, what covers your bike may indeed only be about 50mls. It may be thrown off the shaft quicker than the oil is coming out of the engine. First place I would check is the shaft seal.

The o-ring. Simple job, whip off the small clutch cover, not the large side casing (should only be 4 or 5 allen bolts holding it on.) Stuck in the groove on here will be the o-ring, check it for damage. If it's alright, shove it back on.

The biggest part of solving problems and expanding your knowledge is not only repairing and understanding the problem, but diagnosing too. You have an oil leak, you understand that it's oil leaking from somewhere. If you had a very limited budget, and each part took a few days to change, you'd want to diagnose and eliminate what it's not, before wasting your time, and money.

So... Oil leak, final drive side of engine. This narrows it down too (depending on model/side of clutch cover) Sprocket Shaft Seal, Clutch cover, Clutch slave cylinder, Oil filler plug, crank-case breather.

Clean the engine up with wd40 so the side is spotless. Either get some chalk dust, or easier... Talkum powder. Sprinkle some over the side of your engine... Top up your oil and run the engine. Look out for your first damp/dark patch. Where is it?

If this dark patch is under or around the Sprocket shaft... it's that seal thats gone. Seal pick and

wow! thats some reply! would never have thought of the talc trick.... will try it tonight when i get home. the problem i have is there are no montesa dealers in ireland and any parts take 10 days to get here i also forgot the golden rule of asking a question on forums... make, model, year its a 315r, 1997my thanks vince

right then i did as advised and cleaned it to an inch of its life! then topped up the oil and changed the O ring on the filler plug, checked the clutch cover as well , all good. just back after an hour's fairly hard riding and nothing is leaking at all so maybe it was just the O ring on the filler. fingers crossed thats all that it was. many thanks for the help guys and thank god its a simple one!

right then i did as advised and cleaned it to an inch of its life! then topped up the oil and changed the O ring on the filler plug, checked the clutch cover as well , all good. just back after an hour's fairly hard riding and nothing is leaking at all so maybe it was just the O ring on the filler. fingers crossed thats all that it was. many thanks for the help guys and thank god its a simple one!

No bother... it's just little tricks like these we learn, living in the Scottish Highlands with the most unreliable postal service ever, you want to make sure its the correct part for sure before you order!