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Yamaha YZF-R125 blow-by?

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Riejufixing
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PostPosted: 23:38 - 24 Mar 2019    Post subject: Yamaha YZF-R125 blow-by? Reply with quote

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.
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uberkron
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PostPosted: 00:59 - 25 Mar 2019    Post subject: Reply with quote

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?
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Riejufixing
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PostPosted: 01:06 - 25 Mar 2019    Post subject: Reply with quote

uberkron wrote:
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?

Thank you for your reply. It has not been on the road. I do not understand "Is the breather filling the airbox with oil?". I cannot see smoke from the exhaust.
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ThatDippyTwat
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PostPosted: 07:47 - 25 Mar 2019    Post subject: Reply with quote

Riejufixing wrote:
uberkron wrote:
Is the breather filling the airbox with oil?

Thank you for your reply. It has not been on the road. I do not understand "Is the breather filling the airbox with oil?".

It's basic - Is there oil in the airbox? Open it and look. If there is, how much? A film around the airbox and filter? A small pool? A Large pool? Tidal wave gushing out when you opened the airbox?

In addition, what's the mileage? These motor's are notorious for going pop around the 30K mark.
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Robby
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PostPosted: 10:23 - 25 Mar 2019    Post subject: Reply with quote

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.
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Pete.
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PostPosted: 10:45 - 25 Mar 2019    Post subject: Reply with quote

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.
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Riejufixing
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PostPosted: 14:11 - 25 Mar 2019    Post subject: Reply with quote

Robby wrote:
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.


OK thanks (people), I'll assume that's what it is. I know what blow-by is. I have not seen such a small engine as this pumping "air" all "out" before.

This engine has a gauze strainer and a "paper" oil filter.

The inside of the airbox is not oily.

I don't know why people stint on oil and filters. A change for 125s, plus an oil filter, is only about a tenner. Ignorance & inability I guess.

Edit: A bit too "modern emissions", this crankcase breather discharging into the airbox malarky. I'm more used to the breather venting to outside, where the slight oil mist is useful to stop things going rusty.
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stevo as b4
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PostPosted: 20:24 - 25 Mar 2019    Post subject: Reply with quote

I'd generally determine blow by as brown/black stains and deposits past the ring pack on the piston skirt.
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Pete.
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PostPosted: 07:56 - 27 Mar 2019    Post subject: Reply with quote

Robby wrote:
Riejufixing wrote:

Edit: A bit too "modern emissions", this crankcase breather discharging into the airbox malarky. I'm more used to the breather venting to outside, where the slight oil mist is useful to stop things going rusty.


My 1980 CB250RS vents the crankcases into the airbox. It was common practice long before that. Either you're over 65, or talking out of your arse.


Quite. An old trick for 'heavy breathers' is to re-direct the breather FROM the airbox to the front sprocket, so that the oily mist lubricates the chain.
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