How Much Crankcase Pressure Is Too Much?

[stuck amals]

I fired up my newly refreshed big twin engine. Oil pressure was in the upper 50s which was a good sign. After a few moments there was oil dripping from the bell housing.

Removing the the dipstick was like removing a spark plug. High pressure pulses with lots of oil mist.

Certainly this is not correct, right?

I installed a new Guzzi check valve and checked the flapper operation of the breather box during assembly.

The block is an 850 Eldorado modified (by someone experienced in doing this modification) to incorporate an oil filter.

I must confess, I reused the rings. Compression on both cylinders is around 170 psi.

[Antietam Classic Cycle]

I fired up my newly refreshed big twin engine. Oil pressure was in the upper 50s which was a good sign. After a few moments there was oil dripping from the bell housing.

Removing the the dipstick was like removing a spark plug. High pressure pulses with lots of oil mist.

Certainly this is not correct, right?

I installed a new Guzzi check valve and checked the flapper operation of the breather box during assembly.

The block is an 850 Eldorado modified (by someone experienced in doing this modification) to incorporate an oil filter.

I must confess, I reused the rings. Compression on both cylinders is around 170 psi.

Removed the dipstick while the engine was running? If so, then yes, oil would definitely be expelled.
 
You should only have a ball-type check valve or the flapper in the breather box, not both.

[Muzz]

Removed the dipstick while the engine was running? If so, then yes, oil would definitely be expelled.
 

Too true, trust me. My LH boot is still completely waterproof.

To me it sounds as though your rear main seal is not doing what it is supposed to be doing.

[stuck amals]

The oil mist was no surprise. It was the pressure of the air pulses that concerns me.

When I removed the dipstick from a BMW airhead I found the air pulse to be much lower. I would think the Guzzi  would similar.

It appears the oil is coming from the rear seal. Is it leaking or is the oil being pushed out?

[Muzz]

It was the pressure of the air pulses that concerns me.

I know the 750 pulses are quite pronounced. Be more pronounced with a big block. Not sure whether the Beemer pistons follow each other or not; if they did the air displacement would be less pronounced.  BM owners could answer that.

It appears the oil is coming from the rear seal. Is it leaking or is the oil being pushed out?

Don't know, could be either. Suspect a leak as the motor is actually vented. Make sure the vents are clear.

[Old Jock]

I've got a similar problem right now with a Sport 1100 and posted about it though it's kinda specific so nobody replied

I've got leaks in the base gaskets, the Sporti doesn't run the check valve because of the return lines to the sump at the back of the frame (a check valve would not work on that system)

Check valve is there as crankcase pressure can be negative for short periods (providing it's within reason that's a good thing) so it helps reduce overall mean crankcase pressure

I suppose the easiest way to check is to remove the check valve and the hose, place a bit of gauze or the like over the pipe to stop rocks getting into the engine and take it out for short ride. If the leak reduces then the chances are you have a problem with the system causing a pressure drop thereby pressurizing the case

I don't think it needs much to cause this 10s of inches of H20 is enough perhaps less.

With the Sporti though I am getting weeping in all sorts of places, my seals are holding but a lot of the gaskets are not.

You should fix it if it is the problem as it's not good for the rings either I've read (but don't know for sure if that is true)

I'm going to test ride mine with the overboard hose disconnected, I'm prepared for some oil mist and the bike needing cleaned up a little afterwards, but that should tell me if pressure is the cause of my leaks

Good luck with yours

John

[Old Jock]

I am also assuming that the rings were fitted staggered.

Compression sounds good, have you tried a leak down test just to make sure some compressed combustion gas isn't making it's way past the rings

That said I have yet to do one on the 1100 so I can talk

[pete roper]

Did you replace the rear main seal? If so did you install it flush with the flange or pushed right in until it wouldn't go any further?

[stuck amals]

Yes the rings were staggered. I will do a leak down test.

Yes, I installed a new rear main seal. I even bought the tool so It should be installed properly. I soaked it in oil also.