I have an 1990 yamaha xt600 with 7000 miles on it. It has started to smoke badely when you first start the bike after sitting over night for 2-3 minutes then it's fine and doesn't smoke at all. I'm quite confident that the valve seals are leaking and need replaced. My question is has anyone changed the valve seals without removal of the engine and head by pressurizing the cylinder with air and pulling the valve springs off the top side. What is the easiest method for valve seal replacement. I really don't want to do a full tear down as everything else seams perfectly fine unless I have to. Thanks..

Are you sure it's oil? Have you checked the oil level over a period of time to see how fast it's dropping?

I'd look further into it before getting elbows deep in a head rebuild, nothing should be that worn out on a 3TB with that few miles on it yet.

Hi, I had the exact same problem with my 1990 3aj, but it has 40,000kms on it. I replaced the camchain, 2 crankshaft bearings, 2 balance shaft bearings, cylinder honed and new rings and replaced the valve seals. Since doing all this work it has smoked badly every time i start it from cold!!! I have had this engine down several times but cannot find anything wrong. I am now convinced that the non return valve that stops oil returning into the crank cases from the oil tank is the culprit!! How to get at this valve, i don,t know. I have looked at the clymer manual but cant see any valve. If you do find out the problem please let me know how you cured it. cheers T

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big T

I had a weird episode a while back after an oil change.
I had been using Belray EXL 10w40.
At the first oil change I switched to Maxima Maxum4 Premium oil.Everytime I started the bike,it blew lots of smoke out for about 1-2 minutes.
I thought my seals were gone too...Till I changed back to the Belray oil and the smoke stopped. :confused1:
Had no more problems since in nearly a years worth of riding.

Hi,
My 2000 4PT does exactly the same. Now upto 52k km. No measurable drop in oil level between changes. What i would lay money on being the cause is...... the condensed oil that ends up in the airbox. (Have a look in yours). Which of course ends up being sucked into the carb the next day you start the engine.

I'm inclined to agree with XTorange's post. Especially if you have over filled your oil tank. The clue is in your assessment that it smokes for 2 -3 minutes. If it were valve stem seals you are more likely to find that it smokes really badly for about 20 seconds at most. Really just a big puff before clearing up. If you have overfilled on oil, crank case pressure will build and blow excessively back into the airbox. This is exacerbated by the common failing of the oil stop valve (ball and olive affair next to the oil filter) allowing excessive oil to pool in the crank case overnight rather than retaining it in the oil tank.
Check your oil tank level after parking up overnight before switching on the engine. If it shows to be low by comparison after running for a minute or two you will have an strong indication that this may well be the case.

well I think we are on to something here. Here is what I found this morning. First thing I did was pull the air box side cover off and yes I found oil resting on the edge of it. I then checked my oil level cold and it was 1/4 below the full line with the lid NOT screwed down but just resting on top of the threads. ( I was told this is how you check it and to not screw it down, is this correct?) Then I put the cover back on and fired it up. sure enough smokes like mad. I ran it for about 45 seconds or so as seen in the movie and about 60 seconds later I rececked the oil. It wasn't even hardly on the dip stick. So I started it up and let it run for a minute and now it's reading like it's way over filled. I tend to believe it may be as I just did and oil change for the first time and it took 3.75 quarts of oil with a filter change to read correctly or what I thought was correctly. So I'm thinking it''s overfilled but I don't know why it's sucking the oil tank down and taking so long to replennish it? How much oil should it take with the crank case drained and the oil tank emptied. I thought it was 3.3 liters which should be what 3.5-3.6 quarts? Any help is greatly appreciated as I just bought the bike and am learning about it. I know the air box is filthy so I'll clean that today but notice how it ran for a bit before it started smoking too.

picture of the oil
ImageShack - Hosting :: 1004412dl9.jpg

Video of start up.
http://www.youtube.com/v/JGtAQLGjsPM

I believe 3.3 litre is way too much.

The manual states approximate levels as such..

periodic oil change ... 2000cc / 2.1 US qt
with filter change ... 2100cc / 2.2 US qt
Engine rebuild ... 2400cc / 2.5 US qt

To check the oil level is a debacle in itself. Here is verbatim what the manual states:

1) If the engine is cold start it and let it reach normal operting temperature. Usually 10- 15 minutes of stop and go riding is sufficient
2)Allow the engine to idle for more than 10 seconds and switch off.
3)stop the engine and allow the oil to settle for 1 - 2 minutes
4)park the bike on level ground and hold upright.
5)Remove and clean the oil dipstick
6)reinsert it onto the threads in the hole, do not screw it in
7)check reading


if adding oil repeat above... etc etc


Hope this helps. DO DOUBLE CHECK OIL QUANTITY I HAVE STATED. From your video it looks like the 89 release model and not the 90 as you said. My figures are for the 89 model here....Yamaha XT 600