blowby, how much is too much?

[pishta]

Sort of off topic but i got a 4cyl carb motor (just think of it as a low po 6 with 2 less cylinders for this question) and i have some serious blowby coming out of the valce cover filler hole. Its enought to float a ping pong ball on! Im wonderi g how much is about average? Have not done a cylindwr test as i got a weak spark plug thread hole i dont want to mes with, but it doeant burn oil and aems to run prwtty good. Rings or guides? I get a little smoke on ckoked cold start for about 30 seconds but i think the po replaced the seals, but i still get a little blip on my vacuum. Gauge, drops 2 inches every cycle. Maybe a sticking or bent intake valve? Thanks

 

[inkjunkie]

Can you still run it? If so maybe you could post a video of the ping pong ball, just for entertainment purposes?

 

[RustyRatRod]

I wouldn't sweat it. All of them have some degree of blowby. As long as compression is good, it's runnin good and not burning oil it's probably fine. Remember a 4 cylinder might have 4 less cylinders, but they also have a MUCH smaller crankcase area and sometimes they can have more blowby than a V8 because of that.

 

[pishta]

Ya know, Im fresh out of ping pong balls, and the cap is right over the timing chain so it flings alot of oil out the top but when I find one Ill try it. All this blowby goes right into the air cleaner through a 1/2 inch hose and the PCV hose. But then again, alot of the air inside the air cleaner gets sucked into the exhaust manifold from the pulse injection this truck has. Sort of a header evac system to get air into the exhaust in the absence of a parasitic air pump.

 

[sireland67]

If it is running good and not throwing milky oil up it will run a few more miles.

 

[TrailBeast]

Are you sure it's blowby?
A lot of (wind) comes of a spinning timing chain.

 

[wjajr]

Sort of off topic but i got a 4cyl carb motor (just think of it as a low po 6 with 2 less cylinders for this question) and i have some serious blowby coming out of the valce cover filler hole. Its enought to float a ping pong ball on! Im wonderi g how much is about average

?

By any chance do you have a 2.6 Mitsubishi Jet engine with complicated reed exhaust recirculation? If so it has a pressurized crankcase, and pulsating air mixed with droplets of oil blowing out of oil fill opening in valve cover when running is normal. I have owned one from new in my 82 LeBaron.

I get a little smoke on ckoked cold start for about 30 seconds

Is it making bluish white smoke, or black? If it is black and a carbureted 2.6, check for a stuck “Sub ERG Valve” located in base of carb activated by throttle opening. My ‘82 LeBaron suffered long chugging rich starts for years (600 summer miles/yr for the last ten or more) and I thought it was a choke problem, but a timing chain replacement project this winter reviled stuck sub EGR.

 

[cudavert]

I agree with wjajr and trailbeast......it can fool you with a pulsing of the crankcase fumes. Excessive blow-by can start to pump oil up into your air cleaner. Also, might wanna check if your PCV valve is clogged up or stuck.

 

[pishta]

Thanks for the suggestions. It is a mazda MA 2.0 that does not have an air pump or reed valve, only a check valve from the anti-backfire valve to the exhaust manifold. Im thinking a valve guide might be the ticking but cant imagine that much blowby from an intake valve guide. Rings and head gasket together are under 50 so it may be a weekend project. That way i can look at the valves too. Pcv is good.

 

[Swinger803]

This may be a stupid question, but what is blow by? How do you diagnose this? What causes this?

 

[pishta]

Blowby is combustion pressure getting into crtankcase by bad compression rings or bad exhaust vale guides. There is a certain unavoidble amount but lots is a sign of something worn out. Usually PCV takes carte of it either through a breatjer or a check. Valve tied into your intake. Some old carts would get so much pressure in the case that they would ooze oil from about every gaslet or even buckle the valley pan.

 

[TrailBeast]

Thanks for the suggestions. It is a mazda MA 2.0 that does not have an air pump or reed valve, only a check valve from the anti-backfire valve to the exhaust manifold. Im thinking a valve guide might be the ticking but cant imagine that much blowby from an intake valve guide. Rings and head gasket together are under 50 so it may be a weekend project. That way i can look at the valves too. Pcv is good.

An intake valve guide would have a vacuum on it, not release pressure into the case.
An exhaust valve guide could pressure the case but I'd hate to imagine how bad it would be to do that.
I'd bet ya it's just piston related turbulence coupled with wind off the timing chain, but the only way to actually test that theory would be to close off all the case vents and see what kind of pressure it builds.
This isn't really reasonable to do, so we go to the compression test for the next best clue.