just been reeding the postings here and something caught my eye.
Its been stated that the valve was tough to remove from the head.

Be aware that when doing this you should gently remove the burrs caused by the collets. if you dont forcing the valve through the guide will damage the guide and then you have a whole lot more money to spend getting the head fixed with new guides.

not sure if this was done in this case but most manualls i have seen have recommended this to avoid damaging the guides.
similarly when removing shafts from oil seals(final drive, gear change) tape up the ends where splines or grooves are to avoid damage to seals as they are pulled through.

is the engine breather pipe causing oil to collect in the air box during your ride and then when its been stood and you start it again this flushes into the engine causing the smoke??
if the choke is making it very rich to ease starting maybe its washing some oil from the bore on startup. from what you say i presume it doesnt use loads of oil??

Gday Smokinrider.
Yes one of the inlet valves was tough to get out of the valve guide, but we planned to replace the valve and valve guide anyway, so we just pulled it through. Even after we ran a file and then some wet and dry paper around the end of the valve stem to remove any burrs, the old valve still wouldn't fit in any of the valve guides. Still not sure what was happening there?
There is absolutely nothing going into the airbox via the crankcase breather. The airbox has always been clean and I've currently got the breather disconnected from the airbox which has made absolutely no difference.
I have tried turning the choke off instantly after the bike starts, but I will try that little trick again tomorrow.
I have even run the carbs dry by turning off the fuel tap and letting the engine run until it stops, to check that fuel isn't leaking down through the carb and washing down the bore. This made no difference either.
Thanks for the suggestions. Keep them coming!
Cheers, Dan.

Potentially sounds like a sticking valve to me. Pehaps bent or worn.

Does the bike only smoke when its been left overnight etc. Does it smoke all the time ??

You say it drinks "a bit". How much is a bit ??

If an engine smokes for a few seconds on start up its usually always a leaky valve guide seal. If its smoking all the time then its potentially worn piston rings too.

Have you reassembled and retried yet mate ??

Gday Ted.
I'm assuming that your questions are for me and not the other fellas in this thread that are having the same problems.....
My bike seems to blow smoke any time after it has been left long enough to cool down.
I've started it about 90 minutes after riding it to work and it blew smoke, but then i've started it about 4 hours after riding it to work on another day and it started without blowing a thing... It's pretty unpredictable.
It doesn't really appear to be using any oil, but when this problem first arose and i took the bike to yamaha for a service, they thought that the oil was very dis-coloured (it had been in the bike for around 1500kms and not even 6 months).
All the valve stem seals have been replaced with new, genuine yamaha ones and everything in the head seems to be in good order now. No valves are sticking and/or bent.
Even though the symptoms point towards the valve stem seal / valve guide region, i'm thinking that i will have to strip it down and replace the piston / rings, just to rule them out as the problem.
Dan.

Dan,
10 out of 10 for perseverance.
I am not too surprised the original valve guide was not bored central, it is machined after the guide is fitted in the head and the bore should line up with the valve seat.
It would appear to me that oil is some how getting into the chamber, it may be getting in while it is running but in such small amounts you don't see it.
Could it be a porous head casting some where on the inlet side.

Don’t let it beat you

Steve

Whats the mileage on the bike ?? have you done a compression check ?

these faults all sound a bit of a pain. i would say from my experiences of this sort of problem that if its only smoking for a few seconds on start up and the oil level doesnt drop then it isnt really worth pulling the engine apart several times to fix. it may be the oil control ring as suggested previously and if this is the only ring worn it wont make a blind bit of difference to the compression. make sure when you reassemble the pistion the rings all join at different places on the piston. eg top ring at 1 oclock 2nd at 7oclock top oil ring at 11oclock and botton oil at 4 oclock.

my dr uses about 250mm per 150mile ride. no leaks and no smoke?? i put it down to too thick oil staying on the bore and being burnt so efficiently it doesnt produse smoke.

Unless its a 2-smoke, there shouldnt be any oil on the bore when the piston stops. Maybe a film but not enough for visible smoking. If your getting oil slipping past the rings then it "should" show up on a compression test but i dont think i would bother pulling it apart for that unless compression is down and you want to keep the bike.

Dans smoking but not ALL the time theres a clue in there somewhere..mines a good thick cloud of white smoke till it warms up then its fine..certainly its not a usual oil burning issue..somethings not right..i will have another poke about..ty

i think yours in prob a bad valve seal or head gasket !!

The bike is a 2002 model (I bought it brand new myself) and it's now done just over 15000kms. Not much!
Yamaha did a compression test for me (at my request) when i last took it there for a service. It came back at 140psi, so according to the manual, its still within tolerance.

As Smokinrider has said, it could possibly be a dodgy oil control ring (but this wouldn't necessarily cause the oil in the inlet port).

As SteveAttwood has said, the head casting may be a pouruos somewhere around the inlet port? Probably not, as it never blew smoke from new, but a crack is always possible.... We had a look for any cracks when we removed the head, but we couldn't see anything that we were suspicious of. Next time the head comes off, i'm going to send it off to be inspected anyway, just to make sure.

Thanks again guys, Dan.

There aint many places you can get oil leaking in really... valve seals, rings or maybe a bad head gasket.

Maybe a cylinder leakage test is next !!

Good luck either way.

XT600E Smokes on cold start
 

To add my experience on the cold start smoking issue... My 02, 22500km XT600E smokes probably 5 out of 10 times on startup - almost certainly due to overfilling with oil and it getting back into the air filter/breather circuit. The bike is used 70% off road and due to it's hard life gets oil changes about every 1700km / 3 months. I'm scrupulous about putting in the amount Yamaha recommend (about 2.8 litres), but the breather pipe is always oozing a little oil and the airbox is pretty oily - it doesn't use any oil in between changes. It's never blown any seals etc, so I'd rather err on the side of caution and have it oily - it's better than too little!
A be a bit of an idiosyncracy with this particular engine perhaps?

hey dan.. Jumped back from the second thread on this.

Im still very jubious about your valve seals, maybe the shop didnt do a good job and maybe their "custom" valve guide isnt upto the job.

you compression seems fine if its in the 140's. You say it only leaks when its been sitting !!

I think oils working its way past the valve guide ever so slowly and smoking on start up.

i think its unpredictable as you valves are always in random positions when you stop the engine..

I think the shops maybe made a bad job of your valve.

A cylinder leakage test is required here...

also..... You can remove the head, lay it on a non-absorbant surface, clean it and drop WD40 down the ports and leave it 8 hours. See if any works its way through the valve guides and seals.