Oil Breather Check Valve

[fredheiler@aol.com]

I rebuilt my entire R75/5 engine, and it runs well; however, I can't find the oil breather check valve (#3 below). Am I gonna end up with an oil-soaked air cleaner running without one? Other possible ramifications?

Since the factory check valve is $50+, I'm considering buying a $5-10 generic one and splicing it into the oil breather hose. Would that be a problem?

1725 - ENGINE HOUSING​

 

[20774]

Can't find it?? Not sure what you mean. EuroMotoElectrics has it...this list a price of $33. MaxBMW has it for the mentioned $50+

I can't imagine trying to find something that will do the same thing. I think the BMW part is designed to work with the understood pressures from the engine crankcase. Can a generic unit do the exact same thing? If not, you invite over or under pressure in the case...could affect engine seals.

 

[fredheiler@aol.com]

Can't find it?? Not sure what you mean. EuroMotoElectrics has it...this list a price of $33. MaxBMW has it for the mentioned $50+

I can't imagine trying to find something that will do the same thing. I think the BMW part is designed to work with the understood pressures from the engine crankcase. Can a generic unit do the exact same thing? If not, you invite over or under pressure in the case...could affect engine seals.

Hi Kurt:

Thanks for the prompt reply! Yeah, I'm puzzled about where the valve went; I had all the engine parts organized in a bunch of boxes, and perhaps the valve slid under a flap in the bottom of a box. Anyway, I threw out the boxes (after looking through them carefully) when the project was done, and it's gone.

Just wondering how important (or not) the check valve is; guess I should try to find its opening pressure. I recall most engines didn't use them until well into the 1970s, and I was under the impression venting oil fumes back into the intake was purely a measure to reduce HC emissions.

 

[omega man]

You went to all that work. I wouldn’t skimp now. The pressure needs to go somewhere.
OM

 

[20774]

It's more than just venting or trying to removed carbon emissions. With the pistons coming from top dead center to the bottom of the stroke, there's build up of pressure in the case. If the pressure isn't vented properly, it will reduce engine efficiency. Plus with that excess pressure, it will try and find a way out and often that is through the engine seals...leading to new problems.

 

[stevenrankin]

LOL, I first thought you couldn't find the unit on the engine block, forgive me for thinking that. Yeah things can disappear during restorations, the longer the restoration the better chance something will end up lost or misplaced.

I would go to either EME or BMW and spend the money for the part. Frankly these days I know Max BMW deals with EME on occasion so I question the BMW source of parts.
It very well could be the EME part is the exact same as the BMW part, or maybe not. Either way, both will most likely work fine. St.

 

[robsryder]

Snowbum has a discussion about the breather system (it is down the page a bit - look for the heading "Breather System"). It might be worthwhile to see what he says.

BMW Airhead motorcycle Oiling and Breather Systems

BMW motorcycle, Airhead, snowbum, snobum, oiling system, breather disc and reed breather, breather system, oil temperature thermostat

bmwmotorcycletech.info

Somewhere (don't recall where) I read of someone having difficulty with the extraction and replacement of the breather valve. If I recall correctly there was cold (e.g. freezer) used on the new breather valve and heat on the engine case (or at least area about breather valve) to help these tight fitting parts come together more easily. [Anyone else recall the details or source of the troubled install / extraction??] Snowbum does mention the heat / cold for installation as well as a suggested orientation. I find Snowbum's stuff requires careful reading.

 

[20774]

Somewhere (don't recall where) I read of someone having difficulty with the extraction and replacement of the breather valve. If I recall correctly there was cold (e.g. freezer) used on the new breather valve and heat on the engine case (or at least area about breather valve) to help these tight fitting parts come together more easily. [Anyone else recall the details or source??]

It's right there near the bottom of Snowbum's page.

I don't recall have much trouble when I replaced mine on the /7. Other than getting the old one out. I ended up fashioning a slide-hammer to pull it out. Guess I didn't read anything about heading the case around the valve. Going in wasn't much of an issue...it was interference fit but I think it was easy enough to tap it home.

 

[clmedlin]

There’s a video on Boxer2valve’s r90/6 barn find that depicts how to remove it easily with a cotter puller. I followed his technique and was easily able to pull the old style breather assembly out and replace it.

 

[fredheiler@aol.com]

It's more than just venting or trying to removed carbon emissions. With the pistons coming from top dead center to the bottom of the stroke, there's build up of pressure in the case. If the pressure isn't vented properly, it will reduce engine efficiency. Plus with that excess pressure, it will try and find a way out and often that is through the engine seals...leading to new problems.

Hi Kurt:

Right now, there's NO check valve, so all crankcase pressure is vented to atmosphere, like most old engines. Am I right that the only likely problem might be excessive oil consumption? We have started and run the rebuilt engine in my shop, but not yet on the road under load.

Thanks, Fred

 

[fredheiler@aol.com]

You went to all that work. I wouldn’t skimp now. The pressure needs to go somewhere.
OM

Right now, there's NO check valve, so all crankcase pressure is vented to atmosphere, like most old engines. Am I right that the only likely problem might be excessive oil consumption? We have started and run the rebuilt engine in my shop, but not yet on the road under load.

 

[20774]

So, air rushes out when the pistons go down and air rushes in when the pistons go up. They don't design engines like that, but I can't figure out what are the downsides other than venting to the outside. Scratching my head, but somehow air rushing into the engine case that way doesn't seem like a good idea.

 

[kbasa]

So, air rushes out when the pistons go down and air rushes in when the pistons go up. They don't design engines like that, but I can't figure out what are the downsides other than venting to the outside. Scratching my head, but somehow air rushing into the engine case that way doesn't seem like a good idea.

Nothing promotes longevity like breathing unfiltered air into the crankcase.

 

[omega man]

Right now, there's NO check valve, so all crankcase pressure is vented to atmosphere, like most old engines. Am I right that the only likely problem might be excessive oil consumption? We have started and run the rebuilt engine in my shop, but not yet on the road under load.

I have a number of (older) Diesel engines with just a “breather” tube that “vents” the engine. They are normally quite long and just point at the ground.
Nowadays the pressure relief is usually vented to the air intake (cleaner) circuit to cut down on emissions. And oil consumption is more a factor of engine conditions such as rings or valve seals- where applicable.
The venting should not be an oil consumption factor……although, if the venting, no matter how it’s done, can be a bit of a diagnostic feature for excess oil consumption if the exit port is getting real oily.
HTH.
OM

 

[melville]

The check valve, if efficiently designed, will actually help pull a bit of vacuum in the crankcase. This will improve ring seal.

As well, sucking air into and out of the crankcase comes at some cost in power. Just like sucking air in through the intake valve, but twice as often and without a power stroke.

 

[Lendog]

If you have not replaced the factory assembly yet use the /7 breather because the early breather chirps a bit, not a bother to me but it was a popular issue years ago

 

[Lendog]

I have a number of (older) Diesel engines with just a “breather” tube that “vents” the engine. They are normally quite long and just point at the ground.
Nowadays the pressure relief is usually vented to the air intake (cleaner) circuit to cut down on emissions. And oil consumption is more a factor of engine conditions such as rings or valve seals- where applicable.
The venting should not be an oil consumption factor……although, if the venting, no matter how it’s done, can be a bit of a diagnostic feature for excess oil consumption if the exit port is getting real oily.
HTH.
OM

on some occasions oil will migrate up a hose if there is not a valve to interrupt the movement and allow the oil to fall back to crankcase, a fire hazard at least

 

[kbasa]

If you have not replaced the factory assembly yet use the /7 breather because the early breather chirps a bit, not a bother to me but it was a popular issue years ago

We called it the "turkey gobble".