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Is it piston rings or valve stem seals? ;/

Is it piston rings or valve stem seals? ;/

(OP)
Heeyo, i`m not quite sure what that would be. I have yzf r125 with 15k miles on.

So - it starts to smoke at certain rpm. Like 7-8k and above. As ive done the video i held the revs at 3k, nothing. 6k - nothing. Above 8k - smoked like bob marley.
As far as i know this could be valve seals? If it would definately be piston rings, it would smoke all the time? Even just a bit?

To be honest, it ate 1L of oil in 100miles. But i was riding it agressively. When i`ve noticed the smoke and lack of oil, i have topped it up, and done about 20miles since then, and the oil is still in ( i was riding it on low rpms all the time.)

Any help will be appreciated.

Heres a video that explains everything :

https://www.youtube.com/watch?v=wHkKm26Qmzo&fe...

RE: Is it piston rings or valve stem seals? ;/

How long have you had the bike?

Any chance there is an issue with the oil dipstick/oil level indicator?
Engines with wet sumps when over filled sometimes are very rpm sensitive, becoming very smokey when some magic rpm is reached.

RE: Is it piston rings or valve stem seals? ;/

Make sure the crankcase vent isn't blocked. If it is, there's your problem. Exit this diagnosis procedure.

Make sure the correct procedure was followed when checking the engine oil level. It's supposed to be done with the bike held vertically (read the owner's book - it should explain this). Checking it with the bike on the side stand will overfill it very substantially and then see above post for what happens. If the engine is overfilled, there's your problem. Drain the excess and then exit this diagnosis procedure. You might need a new air filter and a new spark plug to clear up the oil contamination.

Open the air filter housing and check for oil built up in there, especially around the area where the crankcase vent connects to it. If you have gotten to this point in this diagnosis procedure, this is not because of excess oil in the crankcase and it means there is excessive crankcase blowby. That means it needs piston rings.

Regardless of whether it's rings or valve seals, the engine has to come apart at this point. Fortunately, it's a simple engine. One cylinder, 4 valves. The condition of the engine when inspected during disassembly could very well reveal the actual problem.

RE: Is it piston rings or valve stem seals? ;/

(OP)
I do not trust myself to strip the engine.. I am doing motor vehicle maintenance and repair, and i do know how to do it, but last time ive replaced rings on my old bike, the engine just seized. ( it was bad cam bearing anyway) But this particular engine is quite an expensive one to fix. I will check the crankcase breather, forgot about it! Thank you!

P.S. replying to a first reply :
I have had the bike for 2weeks, bought it second hand. It has 15k miles on clock. And i dont think there is any issue with the dipstick at all. I can see and smell oil burining just going by the blue smoke. As i said - it does not overheat and does not smoke at rpm up to 8k. After 8k it starts to smoke badly. Ive heard that this particular isssue might be associated with valve stem seals?

RE: Is it piston rings or valve stem seals? ;/

Is the oil level correct (not overfilled) when holding the bike vertically (NOT sitting on the side stand), yes or no.

RE: Is it piston rings or valve stem seals? ;/

Valve seals would typically smoke at idle, or to consume oil at that rate, across the entire RPM band, not just at high RPMs.

RE: Is it piston rings or valve stem seals? ;/

I'd recommend performing a leak down test to check the condition of the rings. Beyond that, have you filled it with fresh fuel? I see many small engines locally smoking like crazy upon their first seasonal startup due to owners overenthusiastic use of fuel preservatives in the off-season.

RE: Is it piston rings or valve stem seals? ;/

Maybe this could help in diagnosing: leakage along valve stem seals is most likely to occur at higher revs in contamination with high vacuum in the cylinder. thus, to test for this you need to ride the bike under enough load and then just shut down the throttle. if it smokes not under load but starts to smoke under high rev idle conditions the valve stem seals might be the cause.

If on the other hand the bike smokes when under high load and higher revs, the piston rings more likely are at fault. At high revs and high load piston rings may get into a vibrating mode which will lead to more oil entering the combustion chamber. the piston rings may also have worn considerably, especially when the bike has been driven in a dusty environment and maintenance of the airfilter system has been somewhat neglected.

RE: Is it piston rings or valve stem seals? ;/

Had a bike in the shop last year, smoking and burning oil. Another dealer had fitted a completely new top end, but it was still the same. I was given another top end, and told to keep my eyes open. It was pretty obvious when I saw the diagonal wear pattern on the piston - a bent rod. A new rod and it was all good.

RE: Is it piston rings or valve stem seals? ;/

I think it's smoking all the time, just not enough volume of gases to make it easily visible. Do you have a borescope? Pull the plugs and take a look at the pistons with it. Clean around the edges = bad rings.

RE: Is it piston rings or valve stem seals? ;/

Oil control rings. Are you using 0W-0 oil? Yeah being funny.

RE: Is it piston rings or valve stem seals? ;/

just some information the valve stem seals usually create smoke on the first startup when the oil has had the chance to seep past the seals unless there is excessive valve stem clearance that causes a rocking moment to occur at the speeds you have it could be ring flutter but I remember you had a problem with a ticking from the valve area so check with a dial gauge what the side play is in the valves use an old spark plug to make a compressed air fitting to hold the valves up while you take the springs off the movement will show up if you have glazed bores you can try an old mechanic's trick and rev it up and pour some neat powdered jif floor cleaner only a little and that will score the bores so the rings re-bed in if they are glazed only try some of that before a strip down

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