KZ900 Crankcase Vent

I have been reading forum topics for the last two days on crankcase venting with pods. I see many of you have just run a hose while others have created some fairly interesting setups to return the crankcase vent to the carbs. It does not appear that the standard crankcase vent has any kind of valve and is simply just a fairly elaborate looking vent. I was trying, without success, to find out if anyone uses a reed valve vent setup like the XS650 Yamaha uses. That would eliminate the worry of anything going back in the crankcase while still allowing proper venting to the outside. Mikes XS seems the valve for under thirty dollars. This is a common upgrade to Norton Commandos which had dubious venting at best. I have had it on my 1970 Commado for the last ten years are so without any problems, although I will say that that one connects into the external oil tank. I would love to return this bike to the stock airbox but I can't find one for any kind of reasonable price (thought of having someone make one out of gold as a cheaper alternative). Any thoughts or insight would be much appreciated. Thanks in advance.

I guess I don’t understand the setup. Am I correct in my understanding that you are considering using a one-way valve so that any crankcase pressure is vented to the atmosphere but that no outside air can then return to the crankcase? If that is true, wouldn’t a vacuum eventually develop inside the crankcase since air would go out but no air would come back in? Ed

All you need is a small breather that fits on the stem from the crankcase. If you just use a piece of hose it may kink causing excess crankcase pressure.

The stock setup is just a tube going to the airbox.

Edit: z1parts.net/z1-900-kz900-kz1000-crank-ca...ther-blow-by-filter/

Some of the Kawasaki Vulcan models have a little bottle connected to tubing from the air filter assy that catches the crankcase blow-by oil. I've never heard of anyone doing this on a KZ. just throwing it out there.

RECEIVER-OIL 13045-1057

My hope was that this would prevent any undesirable material or moisture from returning into the crankcase. Not sure about the vacuum issue, but I know it works on the Commando.

Thanks. I have seen that people have done that and I will probably go there in the end. As long as I have things apart I wanted to figure the best solution and get going on it, particularly if it involves routing hoses, etc.. I have to admit yours is a pretty simple fix.

I have never seen that on a KZ either but it is worth a look.

I use one on my bike

650ed wrote: If that is true, wouldn’t a vacuum eventually develop inside the crankcase since air would go out but no air would come back in? Ed

I was thinking this is how the PCV system on modern engines work, but I read a bit and it seems a second great air intake vent is required.

en.m.wikipedia.org/wiki/Crankcase_ventil...se_ventilation_(PCV)

Given that the kz engine only has the single vent, a check valve wouldn't really be the same as a real PCV system. But I'm guessing at speed there would be enough blow-by, and very little vacuum (vented to atmosphere) that I can't image any real negative pressure in the crankcase.

I suspect you could find an in-line PCV at the auto parts store that would work as a check valve to prevent back flow.

Agree with DOHC, and think WCO worries too much over nothing.

Initially, the crank was simply open to the atmosphere, until someone realized it was making pollution worse. The PCV was developed in WWII for military vehicles to function under water. So it was to prevent water getting through the crankcase ventilation.

In modern cars, initially the crank was ventilated to the intake manifold, but at idle, this extra air made it too lean, so the PCV valve also regulates WHEN and HOW MUCH goes to the intake manifold depending on engine speed.

Because in this simple old bikes the Crank ventilates to the air box, then a PCV or PCV control is not needed. ...and because of the pumping of the cylinders, ….yes...the cylinder pump up and down, .....the crank will always have a higher pressure.

So too me this is like having a gravity fuel system what is simple and works well enough, and someone trying to add a fuel pump to make it 'better'

......and agree than simply adding a filter pod to atmosphere, is bad, as it pollutes badly and is VERY, VERY NOISY....

Thanks to everyone for your thoughts. I probably was overthinking things and it seems that there are plenty of Z bikes out there that are running the simple fix with no adverse issues. I hope to be testing it out in a few weeks.