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trailboss14

yz450 burns oil ONLY at startup?

13 posts in this topic

I recently traded off my 2 stroke for a 2005 yz450f. It runs fine and hasn't really given me any big issues. But occasionally when I will start it it blows smoke and smells like its burning oil. This always stops once the engine has warmed up for a few minutes. It shouldn't need to be rebuilt, could this problem be due to a valve adjustment issue?? Or something else? Thanks.

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It's possible you valve guides and valve stem seals are worn. Allows oil to seep down into the cylinder during storage.

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I recently traded off my 2 stroke for a 2005 yz450f. It runs fine and hasn't really given me any big issues. But occasionally when I will start it it blows smoke and smells like its burning oil. This always stops once the engine has warmed up for a few minutes. It shouldn't need to be rebuilt, could this problem be due to a valve adjustment issue?? Or something else? Thanks.

why shouldn't it need to be rebuilt. you do not say.

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Do a leak-down test to check the rings. If they are OK, it's time to rebuild the head.

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Smoke on startup only is a classic symptom of leaking valve guide seals. Rings generally blow oil under a load.

A leak down test is worth doing as well, but I'd plan on pulling the cylinder as well to do a visual on the rings, piston, and bore while you're in there.

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why shouldn't it need to be rebuilt. you do not say.

It shouldn't need a full rebuild because it doesn't smoke while I am riding. Only sometimes when I first start the engine, the smoke then goes away once it is warmed up.

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Smoke on startup only is a classic symptom of leaking valve guide seals. Rings generally blow oil under a load.

A leak down test is worth doing as well, but I'd plan on pulling the cylinder as well to do a visual on the rings, piston, and bore while you're in there.

Yeah it's not smoking during the ride, so the cylinder, rings, etc... is all good. I was reading on a yfz forum and they said smoke could also be due to the mixture being too rich? It does backfire pretty bad when cold which makes me think the carb needs a slight adjustment. IF by chance the valve guide seals need replaced I would probably have a shop do it. Do you have any idea on what that may run?? And this problem can't ruin or hurt the engine if left unchecked for a really long time can it? Thanks.

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I didn't get a manual or anything with the bike, so I'm having to find everything online. But I did trade a 1995 CR125 for it so I'd say it was a pretty good deal overall lol.

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Yeah it's not smoking during the ride, so the cylinder, rings, etc... is all good. I was reading on a yfz forum and they said smoke could also be due to the mixture being too rich? It does backfire pretty bad when cold which makes me think the carb needs a slight adjustment. IF by chance the valve guide seals need replaced I would probably have a shop do it. Do you have any idea on what that may run?? And this problem can't ruin or hurt the engine if left unchecked for a really long time can it? Thanks.

yes as a tech I would be interested to see what the average expectation of this service is to gague the public. like a "buddy in his garage" price and a motorcycle shop with a business license price. I get approached with guys asking about work all the time and it seems like I give an undercut price and still most folks are shocked that what they're asking about costs more than 5 bucks and I get this so much I don't have any idea of what are realistic, competitive rates for popular jobs are anymore.

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As a tech, you should be familiar with flat rate manuals.  I'll guess 4-5 hours for valve seals. 

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Yeah it's not smoking during the ride, so the cylinder, rings, etc... is all good.

 

 

Just an FYI, just because it doesn't smoke does not mean the piston and rings aren't worn. Modern four-strokes run "slipper" pistons with extremely short skirts, it doesn't take much wear at all for the piston to begin rocking in the bore. And worn rings can still seal the cylinder as long as they still have enough metal and enough tension, and move freely enough in the ring grooves, to be forced against the cylinder wall by combustion pressures.

 

There's a reason why compression tests and etc. aren't really a very good indicator of engine wear other than to tell you that an engine is completely worn out.

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