Crankcase ventilation - how much is too much? - SV650.org

14-04-10, 02:11 AM

Hi all,

I had my airbox off the other day while doing some carburetor tuning, and I noticed that there was a surprising amount of air flow coming from the two crankcase ventilation hoses ('01 curvy)... Is this a sign my rings might be getting a little old (26,000 mi / ~41,600 km) or is it fairly normal in an SV's engine?

The compression tester I have for car work doesn't quite work on my bike...

Just curious!

-Troy

Sid Squid · 14-04-10, 07:26 AM

Lots. Being a common crankpin 90 degree V-twin when one cylinder is at top dead the other is at midstroke, following from this you will see that 180 degrees of crank rotation later, one is at bottom dead when one is at midstroke. Thus the crankcase volume changes by one cylinder's worth, (~320ish cc) each revolution - that's quite a sizeable pump, hence the similarly sizeable breathers and lots of crankcase pumping. Which is what you've just noticed.
Contrast this with a typical four cylinder inline engine, (and some other configurations too), as each piston moves another piston moves in the opposite direction, thus there is no overall change is crankcase volume, which is why fours have rather smaller breathers.

14-04-10, 03:31 PM

That's one of those things that makes so much sense that I just gave my brain a high-five for missing the obvious. Thanks Sid!

-Troy

punyXpress · 14-04-10, 06:40 PM

Rod/s through the side is too much! IMO

14-04-10, 02:11 AM	#1
Troy Guest Posts: n/a	Crankcase ventilation - how much is too much? Hi all, I had my airbox off the other day while doing some carburetor tuning, and I noticed that there was a surprising amount of air flow coming from the two crankcase ventilation hoses ('01 curvy)... Is this a sign my rings might be getting a little old (26,000 mi / ~41,600 km) or is it fairly normal in an SV's engine? The compression tester I have for car work doesn't quite work on my bike... Just curious! -Troy

14-04-10, 07:26 AM	#2
Sid Squid No, I don't lend tools. Mega Poster Join Date: Jul 2003 Location: Skunk Works, Nth London Posts: 8,680	Re: Crankcase ventilation - how much is too much? Lots. Being a common crankpin 90 degree V-twin when one cylinder is at top dead the other is at midstroke, following from this you will see that 180 degrees of crank rotation later, one is at bottom dead when one is at midstroke. Thus the crankcase volume changes by one cylinder's worth, (~320ish cc) each revolution - that's quite a sizeable pump, hence the similarly sizeable breathers and lots of crankcase pumping. Which is what you've just noticed. Contrast this with a typical four cylinder inline engine, (and some other configurations too), as each piston moves another piston moves in the opposite direction, thus there is no overall change is crankcase volume, which is why fours have rather smaller breathers. __________________ If an SV650 has a flat tyre in the forest and no-one is there to blow it up, how long will it be 'til someone posts that the reg/rec is duff and the world will end unless a CBR unit is fitted? A little bit of knowledge = a dangerous thing. "a deathless anthem of nuclear-strength romantic angst" Last edited by Sid Squid; 14-04-10 at 07:29 AM.

14-04-10, 03:31 PM	#3
Troy Guest Posts: n/a	Re: Crankcase ventilation - how much is too much? That's one of those things that makes so much sense that I just gave my brain a high-five for missing the obvious. Thanks Sid! -Troy

14-04-10, 06:40 PM	#4
punyXpress Member Mega Poster Join Date: Feb 2008 Location: Riding, North Posts: 2,664	Re: Crankcase ventilation - how much is too much? Rod/s through the side is too much! IMO __________________ Was: K2 naked in rapid yellow - gone to a better? place Now: Street Triple R

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