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Old 18-10-2015, 06:35   #1
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Volvo MD2020 Breather Hole

Removed valve cover to check valve clearances recently and was looking at the breather hole in the valve cover. Never thought about this before, but it has a plug in it, always has...so no breathing going on here. Been like this for 15 years so obviously not a big problem.

For those of you with MD series engines, is the breather plugged or open?
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Old 18-10-2015, 06:56   #2
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Re: Volvo MD2020 Breather Hole

Plugged on the MD2030.

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Old 18-10-2015, 11:53   #3
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Re: Volvo MD2020 Breather Hole

Same on my MD2020 circa 1995.
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Old 18-10-2015, 12:04   #4
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Re: Volvo MD2020 Breather Hole

Hmmm, I assume in some uses it must be vented, but apparently not in marine installs. Has a little serviceable metal filter (under that square hump on top).

Anybody know the whys & wherefores of crank case venting?
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Old 19-10-2015, 09:43   #5
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Re: Volvo MD2020 Breather Hole

A crankcase ventilation system is a one way passage for gases to escape in a controlled manner from the crankcase of an internal combustion engine.

This is necessary because internal combustion inevitably involves a small but continual amount of blow-by, which occurs when some of the gases from the combustion leak past the piston rings (that is, blow by them) to end up inside the crankcase, causing pressure to build up in the crank case. For control of the pressure inside it, a PCV (Positive crankshaft ventilation) is used to vent the crank case.
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Old 19-10-2015, 10:03   #6
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Re: Volvo MD2020 Breather Hole

You have to vent the crankcase, there is one somewhere, if you don't it will blow out the seals in a short time, usually a crankshaft seal will go. Happens rarely in airplanes if the vent tube ices over and no "whistle slot" is in the tube.
Old style is just a tube like my Yanmar is, plumbed into the airfilter to give the oily air somewhere to go. PCV is a spark ignition engine thing, it's plumbed into the intake manifold that has a vacuum, so a slight negative pressure is maintained in the crankcase, Diesels have no vacuum, so no PCV.
Only say that as you don't have to worry about a PCV valve in a Diesel as there isn't one.
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Old 19-10-2015, 10:04   #7
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Re: Volvo MD2020 Breather Hole

Mramoo is correct. Without that PCV, oil can be pushed by the crank seals and other areas due to crankcase positive pressure from blowby of the rings. A simple fitting and hose going to the air intake will suffice to ingest and burn any oil and water vapor coming out of the crankcase.
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Old 19-10-2015, 15:20   #8
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Re: Volvo MD2020 Breather Hole

Both of my MD2020s are plugged, that port is probably an outlet to allow the engine to pass emission regulations when the engine is used in alternative applications. My valve cover/intake manifold is a little different than the one shown in Belizesailors' picture, but the pertinent detail is the same. At 180 degrees to the plugged off port is what looks like a vent that goes directly into the intake side. If so, that would take care of crankcase ventilation. I'm not taking mine off to verify this though....
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Old 19-10-2015, 17:05   #9
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Re: Volvo MD2020 Breather Hole

Quote:
Originally Posted by jimbunyard View Post
Both of my MD2020s are plugged, that port is probably an outlet to allow the engine to pass emission regulations when the engine is used in alternative applications. My valve cover/intake manifold is a little different than the one shown in Belizesailors' picture, but the pertinent detail is the same. At 180 degrees to the plugged off port is what looks like a vent that goes directly into the intake side. If so, that would take care of crankcase ventilation. I'm not taking mine off to verify this though....

The open round port visible in the picture is where the airfilter tube attaches. Any pressure that made it to there should just escape out the air filter (unless air intake managed to over come it).

Valve cover covers the valves and ports in the head for air intake. No openings I can see that would vent the crank case...unless somehow incorporated into the air intake ports.

No blown seals on my MD2020, or others posted here, so there is nothing wrong with this set-up, just looking to understand it. Nothing I've ever noticed anywhere on the block itself that looks like a vent.
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Old 19-10-2015, 17:20   #10
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Re: Volvo MD2020 Breather Hole

There is a crankcase vent somewhere, often times in one clogs the first indication is when the dip stick is blown out and you get oil out of the tube, the pressure has to go somewhere, it will find the weakest link.


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Old 19-10-2015, 17:32   #11
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Re: Volvo MD2020 Breather Hole

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Originally Posted by a64pilot View Post
There is a crankcase vent somewhere, often times in one clogs the first indication is when the dip stick is blown out and you get oil out of the tube, the pressure has to go somewhere, it will find the weakest link.


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Been there done that...fortunately wasnt my engine.
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Old 19-10-2015, 20:01   #12
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Re: Volvo MD2020 Breather Hole

2010, 2020, etc. have an internal passage in the valve cover which runs from the valve/rocker arm side of the valve cover into the inlet tract side of the valve cover. The vapor passes thru a wire mesh/filter which acts as a rudimentary oil separator before entering the inlet air flow.

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Old 19-10-2015, 21:35   #13
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Re: Volvo MD2020 Breather Hole

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Originally Posted by DougR View Post
2010, 2020, etc. have an internal passage in the valve cover which runs from the valve/rocker arm side of the valve cover into the inlet tract side of the valve cover. The vapor passes thru a wire mesh/filter which acts as a rudimentary oil separator before entering the inlet air flow.

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Aha! Thanks for the info. Unfortunately, Ive already put the valve cover back on so cant look at this in detail...but I still have to check valves on the other engine!
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Old 20-10-2015, 01:54   #14
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Re: Volvo MD2020 Breather Hole

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Originally Posted by belizesailor View Post
The open round port visible in the picture is where the airfilter tube attaches. Any pressure that made it to there should just escape out the air filter (unless air intake managed to over come it).

Valve cover covers the valves and ports in the head for air intake. No openings I can see that would vent the crank case...unless somehow incorporated into the air intake ports.

No blown seals on my MD2020, or others posted here, so there is nothing wrong with this set-up, just looking to understand it. Nothing I've ever noticed anywhere on the block itself that looks like a vent.
Guess what, I'm aware of where your air filter attaches. The crankcase ventilation is performed by the passage illustrated in your own picture, shown below. Again, and certainly not so gently, I'm not taking my engine apart to verify something so obvious...
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Old 20-10-2015, 07:06   #15
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Re: Volvo MD2020 Breather Hole

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Originally Posted by jimbunyard View Post
Guess what, I'm aware of where your air filter attaches. The crankcase ventilation is performed by the passage illustrated in your own picture, shown below. Again, and certainly not so gently, I'm not taking my engine apart to verify something so obvious...
No need to get all huffy. No one is asking you to take your engine apart.
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