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areknocun

Yz450 burned 400ml of oil

9 posts in this topic

Hi guys.

Recently I've noticed that my yz450f year 2008 started smoking a little while getting hard on throttle.

It did have valved adjusted recently and new cam chain/ tensioner installed.

When i did oil change (after few rides) to my surprise there was only this much of oil that came out of the bike 1431161712725.jpg

Bike went through nearly 400 ml of oil.

Bike is on oem top/bottom end, and it's very low hours.

Is it time for piston and rings?

Any of other ideas where it might be going?

Regards

Arek

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There are really only two paths into the combustion chamber, and those are the valve guide seals and the rings.  Usually, smoking under a load is rings.  Figure on at least a piston to go with it, and carefully check the condition of the bore.

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Try a compression test, if it's burning that much oil (smoking) than ur rings are probably worn. Unless you have a oil leak. It's definitely eather coming out of the engine (leaking) or burning it (smoking). lol

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Hi. Yes it's definitely leaking as you can see small puffs of smoke when hard on gas. There's no leaks whatsoever, and it's not being pushed through breather hose (which is moded to go to air filter).

This model has auto decompression so I've heard it would need leak down test rather that compression test.

If it turns out to be rings can I just simply buy oem kit like this : http://m.ebay.ca/itm/121288287420?nav=SEARCH and swap it over? I will obviously check if there's any internal damage, scratches etc. Any other specific things that I should pay attention to when doing this job.

Thanks in advance

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Hi. Yes it's definitely leaking as you can see small puffs of smoke when hard on gas. There's no leaks whatsoever, and it's not being pushed through breather hose (which is moded to go to air filter).

This model has auto decompression so I've heard it would need leak down test rather that compression test.

If it turns out to be rings can I just simply buy oem kit like this : http://m.ebay.ca/itm/121288287420?nav=SEARCH and swap it over? I will obviously check if there's any internal damage, scratches etc. Any other specific things that I should pay attention to when doing this job.

Thanks in advance

Yeah as long as you have a stock cylinder that should work... If you bought the bike used and you have not rebuild it yet than I would suggest you take it apart and measure the cylinder first to make sure it's the stock size. Just hone/ deglaze the cylinder with a scotch bright pad if you don't have a hone available and that should be all you need to do...

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Conventional compression testing is completely meaningless on a YZ450 or any similar engine because it has auto decompression for one thing.  For another, if it did not have that, the engine in good condition could not be kicked through a full compression stroke in the first place.  Besides, compression tests are more useful for finding one cylinder out of a set that is distinctly lower than others in the engine, so not so much in a single.  Leak down tests are the only viable approach.

 

Compression isn't in question here anyway, oil control is.  If you have smoke under a load, you should plan on needing to replace the piston and either replate or replace the cylinder.  It's rare that the oil rings would be the only component out of spec under such conditions.  You won't know until you open it up, though.

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Conventional compression testing is completely meaningless on a YZ450 or any similar engine because it has auto decompression for one thing. For another, if it did not have that, the engine in good condition could not be kicked through a full compression stroke in the first place. Besides, compression tests are more useful for finding one cylinder out of a set that is distinctly lower than others in the engine, so not so much in a single. Leak down tests are the only viable approach.

Compression isn't in question here anyway, oil control is. If you have smoke under a load, you should plan on needing to replace the piston and either replate or replace the cylinder. It's rare that the oil rings would be the only component out of spec under such conditions. You won't know until you open it up, though.

Yes I ment leak down test I'm just used to saying compression test because I usually ride/work on smaller bikes.

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Ok time for some update. I went ahead and ordered oem piston kit and valve seals. Upon taking top end apart it looks like I might need new cylinder also, as there's quite a bit of marking on it . also top of piston has oily gunk on top of it. Any feedback appreciated.

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Bore condition is hard to tell from photos. General rule of thumb i use if u can't feel the marks with your fingernail it should be fine. When your new rings arrive place one in the bore and hold it up to a light and inspect for light showing around the outside of the ring and measure ring gap.

Without high quality specialist measuring equipment that's about as much as you can do.

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