Thanks to all who've taken the time to participate - I think we've reached a conclusion! Which is:-

As the XT600e ages, its oil pump "leaks", allowing too much oil in the crankcase, some of which is expelled via the breather, and too little oil in the reservoir, causing us to scratch our heads and top up too generously.

The gradual wear in the oil pump explains why some of us experience a greater problem than others eg, BlackdogZulu, my motor needs to run for 10 minutes rather than seconds to bring the reservoir level up. Also, my pump is still strong enough to dribble oil out the breather above the filter - which is why I thought it was OK.
I suppose I'm pleased at having spent the bucks on new piston and rings and a refurbished head but I now feel confident that money spent on the oil pump will cure the problem.
Thank you! Thank you!

Well, I checked the oil as per book this weekend, and I couldn't get it to show on the dipstick at all. I topped it up with all I had (which was the half-litre I drained out following the last post). That's with a full 4 litres in from empty. When I ride it a bit tomorrow, I'm sure I will check it again and find the level way too high.

Dontcha love bikes with "character"?

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1994 XT600E in weird green and lilac, 2002 Triumph Sprint ST 955i in fast red, Blog: http://goingfastgettingnowhere.blogspot.com/

Haha. Ran the bike last night for 20-30 seconds, left it 5 minutes, no oil on the dipstick. Ran it hard for 30 minutes this morning, left it 5 minutes, checked the oil, bang on the full mark.

The XT Oil Fairies must have filled it up overnight.

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1994 XT600E in weird green and lilac, 2002 Triumph Sprint ST 955i in fast red, Blog: http://goingfastgettingnowhere.blogspot.com/

BlackdogZulu, with the help of a couple of guys like Lawries, I think the solution is within our grasp.
The manual gives max clearances for the oil pump but "my mechanic" has worked on bikes for 30 years and says he has never yet had to "mike" the insides of an oil pump.
A new one, here, is R700 ($70), imported from Japan in 3 weeks, which sounds like the way to go.
Incidentally, I live in KwaZulu/Natal. "KwaZulu" means "home of the Zulu" so give me a shout if you want me to look up any of your relatives!

Hi Stu - sounds like you are right on this one. A new oil pump won't break the bank. And if it's a doddle to fit, well, so much the better.

Thank you for your kind comments about my relatives! I'll pass them on the real Zulu - my dog. He is a "black dog", and when we named him we were going through various silly options (the daft stuff you do when you're in a car with a tiny Lab puppy weeing in your lap) and we went through all the Star Trek names. We sort of settled on Mr Sulu, after rejecting all the others, but my wife (not a Trek fan) misheard, and he's been Zulu ever since.

I've been advised by friends in certain parts of the UK that this name would offend some people, but it was certainly not meant disrespectfully. In fact, in Wales, where I live now and where my wife is from, the Zulu nation are objects of great respect and admiration, after the battle at Rorke's Drift. Luckily, he also responds to being called "Zu", so when we are out and about that's what he's called.

I'll have to start calling our house KwaZulu :-)

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1994 XT600E in weird green and lilac, 2002 Triumph Sprint ST 955i in fast red, Blog: http://goingfastgettingnowhere.blogspot.com/

BlackDogZulu, I'm struggling to attach a picture of Isandhlwana where the Zulus wiped out the central column invading Zululand under Lord Chelmsford. The Zulus were then repulsed at Rorke's Drift, where eleven VCs were awarded to the defenders.
You should come for a ride here.

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Cool picture! Thanks - that's now my desktop background on my work PC (it's damp and cold here, and I like the warm feeling). As to a ride there - you bet. Never been to SA, and always wanted to. One day ...

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1994 XT600E in weird green and lilac, 2002 Triumph Sprint ST 955i in fast red, Blog: http://goingfastgettingnowhere.blogspot.com/

Hi,

Having owned and looked after a XT600Z Tenere and XT600E for about 10 years, I have found that the following is the only reliable method of checkinh the oil level:

To get a true oil level reading you must ride the bike for at least 10 minutes, let it tick over for 30 seconds or more while holding the bike verticle and check using the dip stick that is part of the oil filler cap as soon as you switch the engine off. You must hold the bike vertical and don't screw the cap on, just rest it on top to make the reading.

Yamahas recommended method just doesn't work, at least once there is a bit of ware in the oil pump.

The one way valve that has been mentioned is, I believe to stop oil draining from the top of the engine, not to stop oil leaking out of the oil tank, past the oil pump and into the engine.

It would appear that if you have a bad case of wet sumping that replacing the oil pump would be the obvious thing to do, but when I did this with my Tenere I still had to check the oil level as described or the oil level would be lower than the dip stick could reach.

I now check my oil level at the end of a ride, instead of at the start.

I'm not sure what the mechanic meant when he said he had never needed to mike an oil pump, but I'm guessing that my experience is fairly typical and that the scoring / pitting makes it obvious that it needs replacing without taking any measurements.

Hope this helps

Mark

"Yamahas recommended method just doesn't work, at least once there is a bit of ware in the oil pump."
That's a bit irritating, isn't it?
Thanks, Mark, I think we're getting to the bottom of this whole oil thing now.
I have a manual for the bike which gives some fairly accurate and fine measurements for checking if the oil pump needs replacing and asked my mechanic (who is "old school") if he would be able to take these measurements. That was when he said he'd never found it necessary to measure the moving parts of an oil pump before.
I think you've summarised the discussion nicely. As your oil pump wears, your "cold" oil level will drop. Don't top it up - until you have run the bike for ten minutes and checked again.

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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1994 XT600E in weird green and lilac, 2002 Triumph Sprint ST 955i in fast red, Blog: http://goingfastgettingnowhere.blogspot.com/