Absent airbox leaves spewing oil.

First, I need to blow some smoke. KZRider and its members are the reason I am riding my kz650, your forums and filebase adorn the walls of my garage and allow me to keep my bike running. Thanks for all the help you didnt know you gave me.

Now on to this issue I seem unable to resolve. :sick: My 77' KZ650B2A has had the factory airbox removed and some K&n style after market filters are attached directly to the carbs. I personally prefer this config because of the eas of access to everything and the speed with which I can have my carbs on the bench. The problem is that there is a breather hose, a 90 degree elbow, protruding from the top of the crankcase breather cover, this used to connect to the bottom of the airbox, since I dont have the airbox and this is how the bike was when I got it, I can only assume that if oil sprayed up into the airbox, that it would run back down the tube at some point and reenter the crank case. On my bike however, at high RPMs the breather spits oil in whatever direction the elbow is pointed, either a pantleg, the engine or onto the plastic fender at the front of the rear tire. Now I dont need to tell anyone how dangerous a James Bond style oil slick device would be acting on my own bike, but the real issue here is that its wasting my oil and is messy and of course dangerous. :dry: Other bike have similar configs so I guess my questions are:

1. is this oil venting behavior normal?
2. what can I do about it (besides return to factory airbox)

Thanks for any and all advice!

cheers!

You can make a catch can for the oil by running
a hose to a small plastic bottle under the seat.
Make sure the bottle has a small vent hole up top.
Or you can rout the hose down near the drive chain
and make a chain oiler,if the blowby is minimal.

Welcome Franco! Here is what I put on mine:

Crankcase Vent Filter

Not sure if there are other manufacturers, maybe some members have found others. So I guess you don't really have much use for a headlight up there, do you? :laugh:

Franco, The tube coming up from your crankcase breather is intended to convey engine vapors into the airbox where they will be sucked into the engine and burned... Guess that implies that there are supposed to be vapors and not an oil spray. To route the oil off your pant legs, remove and keep the tube as those things aren't available anymore. Take a piece of tubing and connect it to the breather and install a clamp to hold the tube in place and route the tube over your swingarm... as to the oil... well, it ain't supposed to be blowing oil out the crankcase breather. This is oil that is getting by your piston rings. This problem is called BLOW-BY. Blow-by can occur when:

1. crankcase overfilled - remove some oil
2. rings are shot - replace rings and hone
3. cylinder bores are shot - replace pistons, rings and rebore
4. pistons skirts are cracked - replace pistons, rings, rebore
5. cylinders are out of round - replace pistons, rings, rebore

There are not too many other ways you can blow enough oil out the crank breather to wet your britches. First thing would be to check your oil. If oil is at an acceptable level, next this is to buy a caliper, a set of bore gauges and measure your pistons and cylinder bores using a shop manual for the correct clearance spec and procedure.

I put a longer hose on, then attach a breather filter, got mine at a speed shop, think it was about 9.00, clamped it to the frame down below,
you might want to run a compression check on the bike also

Lol, only to run my battery down, the funny thing is, that Canadian law prohibits running with the light off so factory switch is not present but you can ride at 3am with no lights in the summer

Thanks folks for your quick replies, sounds like I need to sort out why Im getting the blowby, I suspect it is most likely related to the poor visibility in my oil window and perhaps a paranoia about oil and I have overfilled the crankcase oil. I did a dry compression test on all cylinders and got about 130 psi after 6 kicks of the starter. all 4 are about the same +/-5 psi. An oldtimer at work suggested a wet compression test (putting a few drops of oil in the cylinder and testing again) he recommended this to see if there is perhaps valve seating issuesthat are missed by a dry compression test, I have read on this forum that nominal PSI readings for a kz650 should be about 150 psi and I am quite under that so perhaps there is issies after all. regardless, I will temporarily create a blyby retaining bottle as suggested while I wat for a crankcase filter to arrive via slow dogsled.

thanks folks!
Franco Nogarin

As a precaution -- would check oil level, freshness and condition. Do the crankcase oil "smell test" to determine whether fuel has intruded into the crankcase and diluted the oil (could result from leakage past carb float needle whether parked or running if overflows not functioning properly). Fuel contamination of crankcase oil is a serious condition and can alone cause the problem as described (and engine ruination).

And welcome to the joys of posting!

The use of a filter is not a good choice I think. The filter will soon clog with oil and you will not vent the crank. Leave a hose open and route it over your swingarm and away from the rear tire. #130 psi isn't terrible as far as compression checks. Hopefully you held the throttle open when you did it because if not, the test wasn't particularly valid. Putting a spoon of oil down each plug hole is a way to tell if your rings are sealing but compression will be bumped dramatically if you use a spoon of oil and they are not. Not sure how you could tell if the valves were sealing by pouring oil in the combustion chamber as the oil won't make a difference to the valves. You sort of guess at valves using the oil compression test when the compression doesn't jump up dramatically and you have otherwise low compression. To check your valves, you need to use a leak down tester. Roll the crank so the cams shut both valves and put compressed air in the combustion chamber via the plug hole. If the air escapes through the exhaust valves or intake valves you can hear/feel it.

good advice, I will only use a filter if I solve the blowby issue, I suspect the oil is to full. I have had this bike a month so I am learning her little oddities, one is the poor oil lens, so I probably overfilled.