Crankcase breather modification

[Pat Conlon]

It's from Oil pressure...not crankcase gas pressure, eg. Blow by, etc.

It is impressive.

[ribbert]

I beg to differ on the principle involved here.

Ventilating the crankcase is not just providing a means of escape for the pressure but to actually draw off the air.
The reason the pipe goes between the air cleaner and the carby is so that it sucks air (creating negative pressure) and the stuff it carries is put back through the combustion chamber and burnt, nothing to do with returning filtered air to the engine.
Crankcases have a mist of a number of things floating around in them from the blow by (all engines have blow by) all of which will contaminate and degrade the oil, that is what you want to draw off.
Flame arresters and PCV valves on cars will all eventually block with the oil and contaminants carried in the air from the motor.
I have repaired two in the last year with blocked flame arresters (in the breather pipe) that blew out the welsh plugs at the back of the camshaft and dumped the contents of the crankcase  on the road.
PCV valves actually prevent air returning to the crankcase.
The seal on you dipstick is not so much to stop oil escaping but to stop air entering.
A pipe into the airbox can't return air to the engine, think how hard those carbs suck.
Some of you will remember on older cars, for decades, say up to the early 60's, there was an external pipe from the rocker cover down to the bottom of the motor. It was called a draft pipe. The reason it reached to the bottom of the motor and ran vertically was that the airflow under the car would cause a vacuum in the pipe and suck air from the rocker cover or side cover with compensating air drawn in through the filler cap. Remember those caps with steel mesh in them.
Even back then they realised the need to siphon off the gases.
All modern 4 stroke engines have some form of assisted crankcase breathing, not just a pipe to the atmosphere.
Noel
BTW, I run unipods because I like the induction noise (it is after all a toy) and the ease of access to the carbs and the room they leave for other things. I have an inline baffle to separate the oil from the air and the filter to stop the odd stone dropping in. I also change my oil more often and I'm not too fussed whether it's got 100,000 or 110,000 km's left in it.
I also have a motor sitting on the floor that was blowing oil out everywhere but that's another story.

[The General]

I have an inline baffle to separate the oil from the air and the filter to stop the odd stone dropping in.

Mate, ..Inline Baffle?. Please explain for this mere mortal. Cheers, Doug

[FJSpringy]

I have an inline baffle to separate the oil from the air and the filter to stop the odd stone dropping in.

Mate, ..Inline Baffle?. Please explain for this mere mortal. Cheers, Doug

I think it's a fosters tin wiff lots a liitle holes  

btw can't wait for Noels real answer

[Tiger]

...I think it's a fosters tin wiff lots a liitle holes  

Ahhhhh, thats what you do wiv fosters cans...but does the contents help wiv the vetilation/back pressure/oil saturation etc...or do ya just chuck it out for the pretty Blue can??  ...

John

[andyb]

The bottom of the motor (pistons) displace as much air as the combustion side.  As such, they must breathe.

No, not really. 

Sure, the pistons move up and down, but the volume of the crankcases never change.  As #1 goes down in an attempt to pressurize the crankcases, #2 is going up, matching the displacement.  Air is shuffled around a lot, but the absolute volume doesn't change.  The combustion gas getting past the rings is what's going to give you pressurization in the cases... as such, it shouldn't be all that much on a healthy engine.  On an unhealthy engine, the breather is sorta the least of your worries.

What I've seen done in cases where there was lots of blowby on a fairly healthy engine (think turbocharged or nitrous users) is to make a longer hose than the stock, and run it well up into the tailsection, with the last foot or so packed with steel wool, exiting down into a small catch can.

Ideally, you'd use a one way valve on it, and vent the cases into the exhaust, using the vacuum of the exhaust to put a negative pressure against the crankcase.  Often worth a couple ponies, particularly on very large engines (i.e., car guys do this regularly), and helps prevent the pressurization which leads to various gaskets failing and leaking.


On the pushrod thing, I agree that "copious" is the correct word to describe the oil coming out.  I've heard of other bike owners/racers grinding a flat along most of the length of the clutch pushrod, leaving it unmolested where it passes through the seal on the left.  The theory is that this allows more oil to reach the clutch.  Haven't heard of an FJ owner doing this, and dunno what kind of effects it could have on our engines.

[fj1289]

...
I've heard of other bike owners/racers grinding a flat along most of the length of the clutch pushrod, leaving it unmolested where it passes through the seal on the left.  The theory is that this allows more oil to reach the clutch.  Haven't heard of an FJ owner doing this, and dunno what kind of effects it could have on our engines.

I had issues with not enough oil gettng to the clutch on the dragbike (different design than stock!).  The most direct solution was to remove the o-ring from the pusher - no more cooked steels   

disclaimer - I would not do this on a stock FJ clutch!

[Zwartie]

Not to re-open the debate, I thought I would just post a couple photos of the old breather bottle vs. the new one. And yes, I've had the old one in place for over 20,000 km with nary a hiccup, or if it did hiccup it was into the bottle. No signs of oil or water at all in the bottle from home to Alaska and back...

Old vs. new


New bottle installed


Charlie, thanks for the bottle! Bet you didn't think I would use it like that!

Zwartie