Mosler CB40 engine

[Mark Kramer]

I am looking to find anyone who is using or has used a Mosler CB40 engine. I do not have one of the original pcv valves and have had no success with catch cans, oil separator tanks etc, still pumps oil out at wot. I spoke with a gentleman who worked at Mosler back in the 90s and  remembers that venting the crankcase was in fact a problem. All he could offer me was to have a large venting orifice to slow air down which would make it easier to remove the oil from the air. He also did not feel that trying to feed oil back into the sump would work either. Below the oil level in the sump of course. The breather hole is up front over the timing gears. Ever put an outboard motor in a barrel of water and crank up the throttle? I wonder if I had the appropriate little pcv valve on top of that hole, would it handle that hurricane of oil underneath it? Didn’t think to ask him that. I’m reading everything I can find about crankcase pressure and how to deal with it. The use of an appropriate pcv valve, I’m told, should promote a slight negative pressure which would help keep oil in the engine. But won’t the oil just come thru the pcv valve when it is venting pressure out? I also thought about venting out thru both valve covers, either exclusively or in conjunction with the hole on the top front. Worried that any air flow up the push rod tubes would hinder oil flow back to the crankcase. Just don’t know what to do. A VW breather will not fit on the flat spot on top of the engine. Besides, is it wrong to try and vent from over top of the oil hurricane anyway? Have not done a leak down test, but when you move the prop against the compression and hold it there it still pushes the prop backwards after quite a bit of time. Also has 141 and 145 pounds compression. Believe me it’s a two handed flip. Starts and runs great. Anyone have any ideas about how to vent this engine?

[Dan_]

You can imagine the oil hurricane in a large Harley engine, what with that long stroke rod and a crankcase barely big enough to hold the crank.  Read this:  https://thunderpress.net/editorial/columnists/463/2012/04/12.htm

[Mark Kramer]

Thanks, some very good reading Dan. I read a discussion about non valved  open Venting, but the crankcase opening had to be  so large as to allow all of the air in and out every stroke, or pressure will quickly build causing oil leaks and horsepower loss. Not to mention the filtering that would be needed . I’m convinced that the negative pressure system is the way to go. The problem with a two cylinder with a very small case is that you need a very large check valve to evacuate all of the down stroke pressure. Then on the up stroke you can create some negative pressure, controlling oil leaks and reducing hp loss. There is a lot of different opinions on the subject. I just wish someone could tell me how to put a large enough pcv valve (and what type) over the timing gear hole and have it not see gushers of oil on it’s underside. Seems to me that oil would simply come thru the check valve with all the crankcase pressure. Then you must separate out the oil and return it to the crankcase somehow.

[Dan_]

The Harley drawing in that article shows a small flapper valve in each rocker cover.  Seems you could plumb hoses to each valve cover and mount the stock Casler/Hummel timed negative pressure giant (by comparison) flapper valve on the firewall or any where on the engine.

Put a plate over that hole above the timing gears and stick a dip stick in it.

[Mark Kramer]

Believe me, I’ve thought long and hard about that Harley drawing. I’ve found and read a lot of information on this subject. Mostly other kinds of engines, not boxer twins. Worried that escaping gases from crankcase pressure, headed for the valve cover valves, would hinder oil trying to return to the sump. Not a lot of air space left in those tubes with the push rods. Thus causing a glut of oil in the valve covers and somewhat of a loss in the sump. Maybe I worry too much. One guy stated that the up stroke vacuum is cancelled out by the downstroke, and that the only thing needing to be vented is a little bit of blow by and some air sucking in thru the seals and such. Maybe I don’t need such a large breather as I think?

[okdonn]

What do the BMW boxer twins use? I've owned two, and they were great trouble free engines, but for the life of me I can't remember how the case was vented.

[Mark Kramer]

Not sure what BMW did, will have to do a little research maybe. Been looking at a lot of old motorcycle stuff trying to get some ideas. A lot of them were dry sumped with oil pumps to tanks. They still had to have crankcase ventilation though. I spoke again to a guy who worked at Mosler yesterday. He said his boss shut down the two cylinder engine production before he could work out a good working oil separation/vent system. If I could come up with something that worked, he would like to know. We talked about venting out thru both valve covers. The question is whether to use valves or not. I feel that, on a free air system, the amount of air the pistons would have to move in and out would require huge Vent plumbing. Otherwise air being restricted would rob horsepower. A one way valve system in theory lets air out but not in, creating a slight negative pressure. This helps keep the oil in, and I think less resistance on the under sides of the pistons. The big question is where to let the air out, with the least amount of oil saturation. I’m concerned that if using the valve covers, would the air rushing up the tubes hinder oil trying to return to the sump. One other thought. If when the pistons are traveling up towards TDC and no air can come in, creating a vacuum, then on the downward stroke the vacuum helps pull the pistons back down regaining the slight amount of lost power, and because they started up in a vacuum, there would be no air to push up the tubes and out the pcv valves? So does that mean that the only air coming up the tubes would be a small amount of piston ring blow by and some air sucked in thru the seals? So if all this is true, there would not be a lot of air rushing up the push rod tubes hindering oil flow back to the sump. I would love to hear some opinions on this subject before I make holes in my rocker covers and buy expensive reed valves. Any thoughts?

[Dan_]

If I were in your shoes...

I would make an adapter to bolt over the hole already there in the case. 

It would incorporate a shield preferably extending into the case if possible, far enough to divert the oil splash completely out of the picture while still allowing plenty of air movement.

Thence I would proceed to bolt the proven Hummel flapper valve on top of said adapter. 

Nothing to research nothing to understand.

The Hummel design has 2 reed valve flappers and a hole between them. 

One flapper opens when the pistons go in --the other closes and the hole "times" relief of the pressure pulse. 

The reverse is true when the pistons go out.

This magic leaves the crank case with slight negative relative pressure.

I'm sure I don't understand everything going on and have over simplified it, but I believe I have given a plausible description of how it works.

Talking to the Mosler folks is a dead end.  Talk to Scott Cassler..?

[Mark Kramer]

Success! Just like the Harley drawing Dan posted. Bought two reed style pcv valves from Mikes XS. I altered them so I could bolt them directly on the rocker covers. Ran cheap hoses to water bottles just to test everything. Also temporarily installed a pressure/vacuum gauge in one of the covers. Got the four minute, full throttle run that Leonard suggests with no oil puking out. The gauge showed a slight negative pressure, which is exactly what I was looking for. This should insure no oil leaks while flying. I was worried about disturbing the return oil flow in the push rod tubes, but after feeling very minimal air coming out of the hoses, I think this is not an issue. I put a removable rubber stopper in the original hole in the crankcase, which will be used to put oil in.

[Kamcoman77]

Looks like a very nice setup. When you said Mike's XS, is https://www.mikesxs.net/yamaha-xs650-reed-type-engine-breather-valve-pcv.html the valve you are using? Looks like a great solution for 1/2VW's or Moslers. What is the inside diameter of the plastic hoses you are using?

[Mark Kramer]

Yep, that’s the one. I did alter it considerably. I’ll send some pics. Removed the smaller tube (weaseled it out with curved jaw pliers). Finished opening that hole up to 1/2 in. Now, the rectangular plate that covers the reed valve, which has the barbed tube, ( accepts a 1/2 id hose), I cut down to a small oval shape. This now bolts onto the end where we removed the straight tube, using the two existing bolt holes. The flat surface where the rectangular cover was, now just mates-up to my flat scat head rocker cover. The reed valve itself has rubber around it’s perimeter, so it seals against the rocker cover. I also put a temporary vacuum gauge on and confirmed a slight vacuum in the case. I put one on each side, and have no oil coming out of either of the 1/2 hoses.

[Kamcoman77]

Great pictures of the valve. This may well be a lower cost alternative to some of the commercially available breathers. One thing 1/2 VW's with the full case should consider... mount the reed valve on the rear cylinder blocking plates & close the factory breather hole. Almost no oil being slung on blocking plates.

[Dan_]

Straight up slick as hell..!

[Mark Kramer]

After all of my trials, with all sorts of variations using the top front hole, I now firmly believe that a quality reed style, (or two of them) is the only way to go! And on my Mosler, the top front hole cannot be used. Way too much oil flying around in there. Of the several different automotive types I tried, none of them could keep up with the hertz or cycling of the engine. It is much quieter, so to speak, under the rocker covers. I think these little units from Mikes would be a good addition to any of these two cylinder engines we are using.