Yamaha YZF-R125 blow-by?

[Riejufixing]

There seems to be a fair bit of blow-by, shown when removing the dipstick, when there's noticable blowing. First start after about 6 months. Oil seeps out from the oil check bolt as the book says it should, so oil circulation seems OK. Normal, or something the matter, what? Edit: 14K miles.

[uberkron]

If you are removing dip stick with a running engine, I don't think it is blowby.

Is the breather filling the airbox with oil?

Is oil being consumed?
____________________
i ride a zip 50 2smoke. It overtakes a hundred times a day.

[Riejufixing]

[ThatDippyTwat]

[Robby]

Are you assuming blow-by because air is gusting out of the dipstick hole when you remove the dipstick with a running engine?

That is not blow-by. That is just the consequence of having things spinning around and moving up and down in a small area with not much air. When the piston comes down, all of the air under it has to be pushed out of the way. Usually this is pushed out of the crankcase breather into the airbox, but if you remove the dipstick it will push out of that hole instead. Less resistance.

Blow-by is when your piston rings are failing and exhaust gases are pressurising the crankcases. This means a lot more gas getting pushed into the airbox, and picking up some oil along the way. Lots of oil in the airbox is a symptom, along with fouled plug and smoke (from burning said oil).

Whilst a lot of the 125 4-stroke engines have acquired a reputation for going pop before 30k, this isn't down to piston ring failure. It's usually bottom end failure due to a lack of mainenance. Running out of oil, missed oil changes (often leading to burning knackered oil and running out of it), or people failing to clean the unusual oil-filtering methods - centrifugal oil filters that people ignore, and little gauze screens that require removing a crankcase cover to clean periodically. Blocked screens leads to no oil pressure and a knackered crank.

[Pete.]

As above that's just pumping.

Q: Does it start easy and idle well?
A: No - might be a problem
Yes - forget about it and ride.
____________________
a.k.a 'Geri'

132.9mph off and walked away. Gear is good, gear is good, gear is very very good

[Riejufixing]

[stevo as b4]

I'd generally determine blow by as brown/black stains and deposits past the ring pack on the piston skirt.

[Robby]

[Pete.]