too much venting = blowby?

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This may seem a dumb query, so please excuse me in that case.
After a series of dramas with starters, solenoids and oil filter bases I have bodged enough bits to run my Mk3 for the third time since its major re-build.
During the downtime it had wet-sumped. I drained 1.6l from the c/case and replaced it in the oil tank - which then read as overfull!
After starting and running it for five minutes, checking scavenged oil rate into tank I stopped engine and checked level - half way between marks! Must leave quite a bit in the cases and circulation.
My most concerning thing was the volume of air coming from the breather in the neck of the tank. If you place your hand near the neck there is a very noticeable strong airflow out. Is this normal? All the threads I can find refer to c/case pressure. I ended up running the tank vent straight into the back of the pancake air filter. All this air would be flowing in there when the cap is on the oil tank. I am not sure what to make of this.
 
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If compression is Ok and the bike goes well enough, and isn't burning oil, I wouldn't worry. What you describe sounds normal to me.

Don't forget, you have two pistons going up and down moving 828cc of air about, and the breather vents this as you know. If you want to stop it, that is the physical blowing of the air through the breather into the neck of the tank, put a non-return valve in the breather pipe. I have done this on mine, and now have apparently still air in the neck of the oil tank, although there will be very slight venting due to blow by, past the pistons, but this is not noticeable. But it isn't necessary to do this.

Are you running the breather pipe directly into the pancake filter? If you are you may find that the oil mist is soaking the filter, and may impede the filters efficiency.
 
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If your Mk3 850 is wet sumping badly the anti sumping valve may well be stuck open or even missing. Other causes can be the oil pump gasket leaking or the oil pump rubber seal faulty. If you are confident all's well in there it's more than likely the valve is stuck and it'll may well right its self.
Put your finger over the breather as it blows into the tank and you should feel it suck as well as blow, it does make a lot of noise so don't worry. My Mk3 behaves as yours the only time it returns all the oil is when its on the road. I stopped bothering about it years ago.

Cash
 

L.A.B.

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cash said:
If your Mk3 850 is wet sumping badly

But we don't know either the time-scale involved, or the viscosity of the engine oil?
Even a Mk3 with the timing case valve will drain its oil to the sump after a number of weeks of non-use, especially if the oil is a multigrade type.
 
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That's what I ment by "if" Should have been more clear.
I don't have that problem on my own Mk3 and I use fully synthetic 20/50. I suppose it's down to how good a seal the valve makes.

Cash
 

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cash said:
I don't have that problem on my own Mk3 and I use fully synthetic 20/50. I suppose it's down to how good a seal the valve makes.


But the Mk3 timing case anti-drain valve won't stop the oil from finding its way out between the oil pump drive spindle and the pump body, so I consider that it's only a partial answer to the problem, although there is the O-ring modification that can be done to the spindle which may help to stop that happening.
 

Ron L

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I have found the Mk3 anti-drainback piston stuck in the timing cover on several occasions on several different engines when reomoving said cover. Boring the hole for a brass sleeve might help this, but in stock condition this valve is pretty much useless.
 
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I have found the Mk3 anti-drainback piston stuck in the timing cover on several occasions on several different engines when reomoving said cover. Boring the hole for a brass sleeve might help this, but in stock condition this valve is pretty much useless.

AGREE
 
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LAB,
Forgot about that, it's even worse when the owner taps the spindle through the oil pump gear and pump head at the same time. The key cuts a nice new groove in the pump head bore. I've made a couple of pump heads in bronze over the years.

Cash
 
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Hello , about the crank venting and the blow-by which was part of this question, had anyone get experiences about bunn breather kit or any thing else to help crank venting, lot of people are talking about BMW serie 5 breather valve but somebody say they are for 1/2 inch tubing, any ideas??????
the Frog
 

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marinatlas said:
lot of people are talking about BMW serie 5 breather valve but somebody say they are for 1/2 inch tubing, any ideas??????

Do you mean a Series 5 BMW Car? Or Series 5 (/5) BMW motorcycle?

I know there has been some discussion elsewhere previously, about using the /7-on type BMW twin cylinder motorcycle breather, but as this type and the earlier BMW /5 & /6 motorcycle breather valves are not a pipe fitting type, some kind of housing would need to be made up to contain it and adapt it for pipe fitting, however if the breather you are referring to is some type of BMW car unit then I have not heard about that?
 
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tlas

Happy new year !!!!!!!!!!!!!!!
I was not talking about serie 5 Bmw cars but I have heard somewhere that a serie 5 boxer breather could be usefull as a vent kit for our twins , so I was wondering ....., but elsewhere as you say I had heard too about those brunn kit , and I am concerned about venting my race ( or say pseudo race ) 750 commando engine , I was looking for more info...
 

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Use of the BMW boxer breather has been discussed elsewhere, and I do have one of these items that I intended to fit to my own modified Mk3 breather system.
The later BMW item being the obvious choice, as it is a small reliable reed valve unit, the earlier /5 &/6 unit is a spring loaded disc valve that can be replaced with the later type, which is recommended if replacement is required, the earlier /5 /6 and (early /7) breather being discontinued.

The actual valve unit is a small circular plate that is pressed into a recess on the BMW boxer crankcase with a small cast bolt on cover.

It isn't a self contained unit that can just be connected to a pipe. Some kind of housing would need to be made to house the breather disc.


See old unit (2) and reed type (3)
http://maxbmwmotorcycles.com/fiche/Diag ... 000093.png


I have heard of the Bunn breather kit, as it has been around for a few years now, but I have no personal experience of how it performs.
 
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L.A.B. said:
cash said:
If your Mk3 850 is wet sumping badly

But we don't know either the time-scale involved, or the viscosity of the engine oil?
Even a Mk3 with the timing case valve will drain its oil to the sump after a number of weeks of non-use, especially if the oil is a multigrade type.

Was over about two weeks with Valvoline 20/50. I have since kept it at TDC by putting it in gear and turning rear wheel(still waiting for kick start parts from ANIL) with much better results.

Thanks for reassurance Reggie. I was a bit surprised at the volume but I do see the logic/physics of it.
 
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