Crankcase pressure measured

I've followed most all of the crankcase breather threads for the last few years, and always agreed with all of the benefits that come with them, but I had never done anything with my '72 750 untill today. I ordered an XS650 on Monday morning and received it Thursday afternoon. It cost $18 plus $12 shipping.

One thing that I had never seen in any of the threads was actual pressure/vacuum data. Since I happened to have an old gauge laying around, I thought that it might be interesting to conduct some tests and see if I could measure the difference before and after the installation. (I never doubted that it would be an improvement,I was just curious) I fabricated a T fitting so I could plumb the gauge in to the breather system right where it exits the crankcase. I believe that a measurement taken inside the crankcase would be more accurate, but this was easy.

Here is a picture of my test equipment. My final installation is the same minus the T fitting, and I I used new hose.



I placed the gauge between the tach and speedo so I could see it as I was riding.



I wanted to take the readings as close to the crankcase as possible.



Findings;

At tickover, the needle jumped all over the dial, both with or without the breather valve in place. However, when I disconnected the gauge and put my finger on the end of the hose a noticeable difference could be detected. Without the breather valve, I could feel pulses alternating from weak suction to weak pressure. With the breather valve installed, the vacuum pulses felt much stronger.

Above idle, without the XS 650 installed, the gauge basically read neutral. It didn't seem to change much at all as I ran it through varying rpm on the road. Here is where I think that if the reading was actually taken from inside the crankcase, I would have detected a positive pressure. I would suspect some pressure drop as the vapors pass through the crankcase housing and factory breather and then there is very little resistance through the hoses, oil tank, and to the air cleaner?

Above idle with the valve installed is quite a different story! Just roll on a little throttle and the needle quickly goes to about 3 1/2 inches of vacuum. This changes only slightly as rpm increases but it did get very close to 4 inches @ 5000 rpm. I didn't go any higher than that as my gauge wasn't fastened good enough, and I didn't want to take a hand off of the bars at 80 mph.

So, my test isn't 100% controlled and scientific, but it certainly is proof that these valves will create negative crankcase pressure.

Mike Wolf

Cool. Seems to work.

Dave
69S

Wonderful to see some objective measures. Might be further education to place the PCV close to oil tank for importance of its placement to piston pumping. Tape the gauge on and see if it sucks down even lower.

hobot said:

Wonderful to see some objective measures. Might be further education to place the PCV close to oil tank for importance of its placement to piston pumping. Tape the gauge on and see if it sucks down even lower.

Click to expand...

Closer to the crankcase will be better.

Want to bet? I don't know for sure but do know a bit of vapor pressure waves and volumes. I bet it don't make a whitworth of difference beyond maybe a few revolutions then reads and functions the same, maybe better w/o oil mist in flappers or diaphragms. I think 'long' tube column of air may even help concentrate the case volume pulses to work a valve a bit more as density-pressure lowers. Even if far away from case PCV ain't the optimal location I know its more than Combat adequate. Academic banter to me but would love to see a gauge test to settle it.

Hobot............ Your assessment of the valve and plumbing makes sense, especially the part about oil mist. However, your beginning to repeat yourself.
(hobot's duplicate post deleted - L.A.B.) :wink:

thanks for the hard work there mike, i bought one of those pcv a week ago and not put it on yet. roll on next weekend and maybe a few less oil weeps

Ugh, 'puter or forum hung up on send page, said it sent but never showed the text, so sent it again for a double tap eh.

Everyone is claiming close mounting to the case volume matters for PCV and at first glance makes sense but deeper thinking and some my own experience says it don't matter much if at all. On my factory Combat KranK vavle is close as can get to tank. On Peel her exhaust eductor will eliminate need for PCV - I think. May have to restrict the suction if oil smoke shows up but didn't get even slightest white glove mist in Peel's breather tube after 1000's miles and over rev event. Another mystery is if one type of valve gives lower pressure than another or if they all give similar evacuation.

mw21837 said:

Findings;

At tickover, the needle jumped all over the dial, both with or without the breather valve in place. However, when I disconnected the gauge and put my finger on the end of the hose a noticeable difference could be detected. Without the breather valve, I could feel pulses alternating from weak suction to weak pressure. With the breather valve installed, the vacuum pulses felt much stronger.

Above idle, without the XS 650 installed, the gauge basically read neutral. It didn't seem to change much at all as I ran it through varying rpm on the road. Here is where I think that if the reading was actually taken from inside the crankcase, I would have detected a positive pressure. I would suspect some pressure drop as the vapors pass through the crankcase housing and factory breather and then there is very little resistance through the hoses, oil tank, and to the air cleaner?

Above idle with the valve installed is quite a different story! Just roll on a little throttle and the needle quickly goes to about 3 1/2 inches of vacuum. This changes only slightly as rpm increases but it did get very close to 4 inches @ 5000 rpm. I didn't go any higher than that as my gauge wasn't fastened good enough, and I didn't want to take a hand off of the bars at 80 mph.

So, my test isn't 100% controlled and scientific, but it certainly is proof that these valves will create negative crankcase pressure.

Mike Wolf

Click to expand...

Was there any need to ride the bike, surly the same reading would be measured stationary?

Stationary? But what kind of fun is that?

Good job and thanks for reporting.

Russ

Was there any need to ride the bike, surly the same reading would be measured stationary?john robert bould

Click to expand...

John, I was concerned that there could possibly be more blowby "under load "that might affect the readings.I wanted to see the results under actual road conditions. The bike does scoot rearward rather quickly on my concrete floor when I rev it up above 2500rpm, I didn't want to fight with that. I was also anxious to see if I could "feel" any difference, I didn't. Actually, any readings that I saw while stationary, were not noticably different from those rolling.

Originally, I was "determined" to mount the valve between the transmission and the engine where I truely believe it should work the best. If I couldn't accomplish that, my second plan was to connect the valve to the engine using hard copper plumbing parts. My thought was that the pulses could flex the hose and possibly absorb some of the vacuum. After seeing the results, I decided that the location, and the rubber hose connections were good enough for my "mature" driving habits. In my opinion, unless you are racing or involved in some other continuous high RPM application, that we are all getting way to hung up and nit picky about the mounting location, and getting the absolute most out of these valves. Just put one in !

Mike

mw21837 said:

In my opinion, unless you are racing or involved in some other continuous high RPM application, that we are all getting way to hung up and nit picky about the mounting location, and getting the absolute most out of these valves. Just put one in ...

Click to expand...

YAHTZEE!

mw21837 said:

Was there any need to ride the bike, surly the same reading would be measured stationary?john robert bould

Click to expand...

John, I was concerned that there could possibly be more blowby "under load "that might affect the readings.I wanted to see the results under actual road conditions. The bike does scoot rearward rather quickly on my concrete floor when I rev it up above 2500rpm, I didn't want to fight with that. I was also anxious to see if I could "feel" any difference, I didn't. Actually, any readings that I saw while stationary, were not noticably different from those rolling.

Originally, I was "determined" to mount the valve between the transmission and the engine where I truely believe it should work the best. If I couldn't accomplish that, my second plan was to connect the valve to the engine using hard copper plumbing parts. My thought was that the pulses could flex the hose and possibly absorb some of the vacuum. After seeing the results, I decided that the location, and the rubber hose connections were good enough for my "mature" driving habits. In my opinion, unless you are racing or involved in some other continuous high RPM application, that we are all getting way to hung up and nit picky about the mounting location, and getting the absolute most out of these valves. Just put one in !

Mike

Click to expand...

Mike, Yes the reverse on it's stand is a problem :!: and the extra cylinder pressure under load, I think the valve is better closer to the Hot parts,It will help in reducing the white frothy stuff, ...well so i am told.that is.

Les Emery tells my these valves are worth a extra BHP, Not sure about that, He say's the vacuum "sucks" the pistons back down ..But surely the pistons need to produce the vacuum in the first place? Math's do not add up on that ...For each action ,there is a equal and opposite re-action? well according to Newton anyway :shock: But what did he know about Nortons :lol:

There does seem to be a bit too much thinking on this matter but the question still remains, Does it work?
I am here to tell you in fact it does.
I bought the exact same reed valve. I had been plagued with oil leaks ever since I had owned this bike which is about 36 years and always out of the head.
I installed the valve in my battery box so it's mid point between the engine and the tank.
Not a single drop of oil at all. Absolutely amazing. I swear I have never not had a oil leak and now I am leak free.
I read about this valve on here and bought it.
I am going to start putting them on my race VW engines as they are plagued with too much pressure despite having 3 crank case vents and see if they stop leaking as well.