Crankcase ventilation, what to do?

[greginisn]

I’ve recently read an article about how poorly the early Honda Metro 4t 49cc crankcase ventilation system worked. In fact, according to the writer, so much evil stuff built up in there that the main bearings would rot - corrode away before the engine logged 6,000 miles.

If that is true would us 139QMB people be better off with the PCV system recycling the vapors through the engine again and possibly pulling a slight vacuum on the crankcase clearing the vapors rather than just letting the crankcase breathe out to the atmosphere?

Any thoughts or theories on this?

Thanks, Greg

[90GTVert]

Vacuum should be good for the crankcase, but I don't know if the intake connection supplies sufficient vacuum to accomplish much. It is commonly said that vacuum there can improve piston ring sealing, but I'm not sure if there is much change. I know that in cars many racers use vacuum pumps and claim gains, but I would imagine they are on a whole different level than a little hose to the intake. My gut feeling is that you wouldn't notice the difference in power on these scoots if you connect to the intake or let it vent to atmosphere. I would think a decent setup (without any pumps) would connect to engine vacuum, but have a means of catching oil so you aren't recirculating that through the engine. I don't know that the stock setup is too bad for that, since they often can catch oil in a section of the airbox and allow it to be drained. Once the airbox is ditched, you'd need a catch can.

www.dragracingscene.com/tech-content/aerospace-components-vacuum-pump/

[greginisn]

I'm kind of a "keep it simple" kind of person and was only thinking of re-connecting the crankcase breather hose to the intake tube to the carb area where it was attached originally. Just a little extra suction to help purge the fumes from the crankcase and burn them during the combustion cycle. And if any oil vapors happened along they could burn, a la 2T, and I won't be troubled by a can full of nasty oil. Ish, it makes me think of the nasty oil & grease crud your gas grill will collect for you to dispose of. 

My only goal here is to try to prevent the early crank & main bearing failures that the Honda expert was attributing to poor crankcase venting of the original 4t Honda Metros.

Greg

[AtariGuy]

its a thought - depends on the nipple size/hose size - i hadn't considered putting it on the vacuum port of the intake, i just made the mini-catch can filter vented to outside air for mine. isn't it possible though that the vacuum could create a really bad negative pressure in the head and suck the oil up and out of the engine and into combustion?

[jeff84]

I just vent the breather ose from the head to atmosphere. its never dripped a drop of oil even though its routed downward from the head and ziptied to the brake cable.

[greginisn]

Oct 21, 2017 16:18:01 GMT -5 jeff84 said:

I just vent the breather ose from the head to atmosphere. its never dripped a drop of oil even though its routed downward from the head and ziptied to the brake cable.

That's how I'm currently configured it's just that those old comments on the first Honda 4T Metros got me to wondering & worrying about engine bearing life. I probably shouldn't concern myself about it, I don't recall anyone complaining about bearing life due to contaminated oil. Maybe because of a too big BBK but not oil.

Ah hell, never mind. Greg

[jeff84]

mine is a 2012 model so it has the pcv. but as long as to are venting the crankcase pressure and changing your oil regularly with quality oil I think it will be fine.

I know the manual says every 3k miles but I would look into a 1k mile oil change

[jackrides]

Unless your scoot has a real oil filter and a cooler, change at 1000 miles.

[cagiva4ever]

Naraku makes Crankcase breather assy, which is piss easy to diy, and from Naraku is a daylight robbery by price.

personally im going to Modify my aluminium Thermometer oil dipstick to have a 5~7mm hole in it for breathing purpose. so its win win, 4 funtion part then...