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Could a slightly leaky valve seal be beneficial?

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I was told my bike has a leaky valve seal which is the cause of my bike blowing some smoke on the first throttle blip after starting it. I've been told a bad valves seal will also cause smoke on deccel.

I also read somewhere that some people mix oil into their gas to reduce maintenance intervals on modern high performance 4ts. (Like some one dual sporting a WR450 and not wanting to change the piston ever 150hrs)

So what I'm thinking is that my leaky valve seal leaks a bit of oil into my cylinder while the bike sits, and once I blip the throttle it burns it out. BUT I don't start my bike and immediately blip the throttle, I wait a couple minutes. So in those couple minutes while I wait for the engine and rads to be warm to the touch, that oil is still in the cylinder and it's lubricating the cylinder during the time when the most wear is happening to the engine. (Warm up)

Isn't this kind of a good thing?

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I thought the point of the valve seal was to prevent oil leakage? If it was good they all would leak. The cylinder is already lubricated with your engine oil. I'm not sure what the harm, if any, could be? But if you wanted to mix oil in fuel...then get a reliable 2 stroke. lol

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I knew some guys in the 70's and 80's that ran XR600's in Baja, they claimed it kept the topend cooler.

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I know it's not a good thing performance wise and I should have included that in the OP. BUT I'm am riding this bike at nowhere near it's full potential, so if I'm losing a bit of performance I'm not worried.

My point is, on start up there is less oil in the cylinder (and the rest of the engine) because after sitting most of it settles to the bottom of the case. With a leaky valve seal, a bit of oil is leaking into your cylinder providing you with possibly some extra lubrication right when you need it.

NOW what my argument against this would be:

How do you know where this leaked oil is resting. It could just be resting on the top of a valve or something. Or somewhere else where it is not lubricating anything. Then the crank of the throttle pulls it off of wherever it's sitting.

If it is a leaky exhaust valve it could just be sitting on/above the exhaust valve..some of it getting pulled through the exhaust port. The blip of the throttle increases speed and temp of the gases pulling the oil into the air and burning it.

This also has me thinking that a leaky exhaust valve seal wouldn't affect performance because of the valves being closed on intake. Gasses could go into the valve area though.

There is also always the argument KXkawirider made that the amount of oil might be so minute that it makes no difference.

I don't know very much about engines so this is all under educated speculation on my part so I hope one of the TT Gods may correct any false assumptions I've made.

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A leak down test will tell you the source of the oil.

If it is a valve stem seal, and the valve is closed and it oozed down on top of the valve, as soon as the engine is rotated, it would get sucked in. However, that is rarely what it is. Most of the time, oil smoke on start up is rings. As soon as some heat gets in the engine, clearences tighten enough to stop the leak. But it is only going to get worse and power is down significantly. A worn engine is only going to get worse, and get worse quicker as the loose parts hammer into each other. Fix a small problem now or a big one later.

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It doesn't smoke on start up. I can start it and it start/idle with no smoke at all. When you say smoke on start up I picture it smoking steady until the engine gets warm. I let it idle until the rads and cylinder/head are warm to the touch. Then I blip the throttle and it will blow a puff of smoke. If I blip the throttle again immmediatly after the first blip, I get no smoke.

The only other time I noticed smoke was when a friend took the bike for a ride and missed neutral and revved the bike really high, saw some smoke there.

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Oil consumption/burring of oil starts out slowly and gets worse over time. It occurs so slow most of the time, it is barely perceptible until one day you finally notice the 'puffs'. Eventually, those puffs will be constant and the engine rattles will be loud and at some point, it will cease working.

Your bike is telling you it is sick. Your bike, your money.

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It's amazing the contrast in opinions you can get. I did a lot of reading on here about the oil consumption and what I've said was the general consensus. BUT I did buy a new piston kit anyway. So at least I have the piston kit here and ready to put in, riding season is over here in Canada, so sometime before next season I will bring up the courage to pull that engine apart and get a new piston in there.

Thanks for the advice.

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well smoke on startup is a telltail sign of valve seals, the oil will sit on the seals and leak down the stem when the bike is shut off

all signs point to rings, check your compression

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What color smoke is it? Blue? Could be excess gas from start-up. Is the the choke on when idling?

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Don't fear a piston change on a thumper. There are tons of tutorials here and on youtube and it's an easy job.

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What i got from reading his posts: He said it blows some smoke when he blips the throttle after starting and letting idle to warm up. If you let a bike idle with the choke and then blip it, it'll blow some blue smoke (excess gas).

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Hey guys, thanks for all the posts :smashpc:

Ok it is blue smoke, and smells of oil. I think if it were gas it would blow black smoke, right?

I don't know wether I should be saying it smokes on start up or not, I could start the bike from dead cold and run it without any smoke so long as I don't blip the throttle. I can slowly open the throttle and bring RPM up and no smoke will come out. It is only on that first blip of the throttle that it will puff smoke. After that I can blip the throttle repeatedly and no smoke comes out.

I've watched and read many tutorials and I am fairly confident but I can never help but worry when I start taking those bolts out for the first time.

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yes, blue smoke is oil, black is gas, white is coolant. I have to do rings on my XR this winter and i'm a little apprehensive. I've only had two strokes the last 15 years and pulling the jug to do rings on those is not a big deal at all. I don't like messing with timing chains and such, i'm always afraid i'm going to screw it up putting it back together. I'm going to try to get a factory service manual before doing it, if i can stop spending all my money on school books and gas for my car.

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I'd never do it without the manual...How would you know your torq specs, etc?

As for the cam chain, use a marker and mark a spot on the chain and a spot on the cam gear...Thats what I plan to do. (Straight from the 250X valve adjustment tutorial)

Worked a charm when I adjusted my ol' X's valves.

What I'm worried about are those little things that tend to happen that don't end up getting covered by the tutorials. In my experience, something unexpected usually happens...wether you are chainging a piston for the first time, or trying to get your damn ring out of the sink.

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