I know this issue has been raised before but I can't find the thread.
My 2002 XT600e leaks oil like a sixties British twin. It is coming out the engine breather via the air filter.
Put in new piston and rings, honed the bore and refurbished the head with new seals etc. But it still squirts out enough oil onto the rear tyre to give me the odd scary corner!
I see from other threads that overfilling can be a problem but I've checked this carefully and, in any case, the problem has only manifested itself after about 45000 km.
Any advice will be appreciated.

My first thought on this is that your oil scavenge is not working like it should, leading to a high volume of oil in the crankcase, therefore high crankcase pressure and oil breathing into the air filter compartment.
Take the bike for a short (10-15 mins) run then remove the crankcase oil drain plug and see how much oil comes out, it shouldn't be very much .. half a jam jar or so. (sorry for the imprecise measurement)
If you have more than this, suspect the oil pump.
Hope this helps

Thanks, Lawries - that is a precise and understandable solution. I'll give it a go.

Hey mate,
Did you find the problem and cure? I'm interested as I have oil regularly in the airbox. The oil level is good, I've even let it go low to see if it does the same, Checked the oil crankcase breather and some, a bit, comes out each time.
I'm in Timbuktu and buggered if I want the engine to go bang way out here but then again I might take up the offer of 3 camels and a Tuareg wife for the bike just to shut them up!

Cheers!

__________________
Geoffshing

'Security is a product of one's own imagination, it does not exist in nature as a rule, life is either a daring adventure or nothing.'

Have just tried Lawries's test. 500ml came gushing out the crankcase before I blocked off the drain. In short, it might be what we used to call "wet sumping" on old British dry sump bikes. The difference is, when those old bikes' crankcases filled with oil, you struggled to start them, and when you did, oil came pissing out everywhere, including great clouds of blue smoke from the exhaust. The XT doesn't show any symptoms like this - just the leak from the breather.
The old Triumphs, BSAs and Nortons had a valve to prevent oil draining from the tank back to the crankcase, which used to pack up. The XT manual makes no mention of such a valve.
The mechanic who services my bike spoke to old Yamaha hands in SA and they told him to be careful not to overfill the oil. This is the same advice I have seen a few times on this site. I am advised by these guys to only check the oil after running the bike for 10 minutes. So, this morning, I check the dipstick and it is absolutely dry - not a drop of oil on it. I ride the bike for 10 minutes, expecting it to seize at any time, check the level again and it is way over the max mark on the dipstick! I drain the 500ml out of the crankcase as mentioned above and the level is still over "max".
The XT manual says nothing about checking the oil only after running the bike and, in fact, for years (with the same mechanic) I've checked the oil "cold" and the bike has run very nicely without leaking.
So, when the bike is cold, the oil reservoir is empty. When the engine is warm, both the crankcase and reservoir have more oil than they should. And yet, the bike goes very nicely! Is this what they call an Act of God?
Lawries, if your diagnosis is correct, what do I do to fix it?
Geoffshing, beware the Tuareg wife, she is probably also a thumper with a few leaks!

Hey Stu,

I am also familiar with the old twin "wet sumping" problem having cut my teeth on Triumph twins of a certain age, and I know how to fix the problem but ...

I'm not so sure how to fix the problem on an XT. I believe I have seen questions about a non-return valve for the oil tank on the forum before and think the consensus is that one exists even tho it's not mentioned in the manual. If memory serves me right it's positioned at the bottom of the front fork tube where the oil way connects. But, I'm vague on this.

If you don't get any clarification on this forum, I suggest you contact David Lambeth and ask him as he seems to be the font of all knowlege for XT's

DAVID LAMBETH RALLY & OVERLAND

Good luck!

From my owner's manual:

To check the engine oil level:

1. Place the motorcycle on a level surface and hold it in an upright position.

2. Remove the oil filler cap cover by removing the screw.

3. Start the engine, warm it up for at least 10 seconds, and then turn it off.

4. Wait a few minutes until the oil settles, remove the oil filler cap, wipe the dipstick clean, insert it back into the oil filler hole (without screwing it in), and then remove it again to check the oil level.

NOTE: The engine oil should be between the maximum and minimum level marks.

Hope this helps.

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2006 XT660R daily ride, 1994 XT600E about to be reborn, Blog: http://goingfastgettingnowhere.blogspot.com/

Hello, the non return valve is in the crankcase mating flange. Remove the clutch cover and look around this face. It is a rubber ring about the size of a ten pence piece with a steel ball in the centre. poke it with something to make sure it's seating properly. If it's screwed you can get a new one from Kedo.de. they cost a couple of quid at most.

Thanks to all for the helpful posts.

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2006 XT660R daily ride, 1994 XT600E about to be reborn, Blog: http://goingfastgettingnowhere.blogspot.com/