cactusjack
August 23rd, 2010, 01:54 PM
While going through the bike (’06 ZX-6R) to diagnose a (probably) unrelated problem, I noticed that the intake valves closest to the center of the engine (so one valve on #1 cylinder, both valves on #2 and #3, and one valve on #4 cylinder) looked pretty fouled (I was peeking in through the throttle assembly). The valves on the outside of the engine looked to have a very light coating of oil on them, but the closer to centerline, the more this oil looked darker and burnt.
I checked the plugs, and they shared a similar pattern. The closer to the center, the more wet but also burnt oil deposit; the further from the center, just a light coating of oil.
My first thought was along the lines of valve seals or piston rings, but then I noticed that the throttle butterflies also had a light misting of oil on them. And, sure enough, the airbox was all slick and sticky with oil. It suddenly all made sense – the crankcase vent hose is located approximately in the centerline of the airbox and thus the cylinders, so if there was excessive oil mist being sucked into the airbox from the vent hose, the cylinders closest to the center would get the bulk of the misting.
The degree to which the oil was burned was probably caused by my other problem this weekend, secondary throttles stuck in the open position, causing everything to be generally lean at partial throttle openings and causing some nasty lean misfires when rolling on the throttle aggressively at corner exits . . . based on prior experience with an older Kawi, the problem is likely the ECU and not the throttle assembly, but I have both coming in just to make sure.
But the amount of oil that got sucked up is somewhat troubling. What caused it? Could it be that the crankcase vent system was designed with street speeds in mind on average, but when the bike is ridden on the track at consistently high speeds, the ram air system creates more vacuum than intended (acting kind of like a carburetor, intake air rushing past and sucking in oil from the crankcase vent tube)?
Assuming this is a known problem and not something wrong with my bike, what’s the best way to fix it? An obvious choice is to run a bit less oil . . . I’m in the middle of my sight window, and some Kawi riders have noted that it’s best to run at the very bottom of the window. But this would only improve the situation by a small degree; ideally, I want the oil entirely out of my intake.
I know that some people run the KLEEN/PAIR mod, which reroutes the crankcase vent into the exhaust manifold through the reed valves that were intended to draw intake air into the exhaust to help the catalytic converter do its thing. But at wide-open throttle, wouldn’t the exhaust pressure overcome the crankcase pressure, thus closing the reed valves and limiting the venting to when the throttle is closed or only partially open? Would this be a problem?
Another alternative would be to put a catch can inline between the crankcase vent and the airbox. Ideally this would prevent much/most of the misting problem, and the crankcase would be vented at all throttle positions (by manifold vacuum when throttle is closed/partial, by venturi effect on the crankcase vent tube itself when the throttle is open).
Any thoughts?
I checked the plugs, and they shared a similar pattern. The closer to the center, the more wet but also burnt oil deposit; the further from the center, just a light coating of oil.
My first thought was along the lines of valve seals or piston rings, but then I noticed that the throttle butterflies also had a light misting of oil on them. And, sure enough, the airbox was all slick and sticky with oil. It suddenly all made sense – the crankcase vent hose is located approximately in the centerline of the airbox and thus the cylinders, so if there was excessive oil mist being sucked into the airbox from the vent hose, the cylinders closest to the center would get the bulk of the misting.
The degree to which the oil was burned was probably caused by my other problem this weekend, secondary throttles stuck in the open position, causing everything to be generally lean at partial throttle openings and causing some nasty lean misfires when rolling on the throttle aggressively at corner exits . . . based on prior experience with an older Kawi, the problem is likely the ECU and not the throttle assembly, but I have both coming in just to make sure.
But the amount of oil that got sucked up is somewhat troubling. What caused it? Could it be that the crankcase vent system was designed with street speeds in mind on average, but when the bike is ridden on the track at consistently high speeds, the ram air system creates more vacuum than intended (acting kind of like a carburetor, intake air rushing past and sucking in oil from the crankcase vent tube)?
Assuming this is a known problem and not something wrong with my bike, what’s the best way to fix it? An obvious choice is to run a bit less oil . . . I’m in the middle of my sight window, and some Kawi riders have noted that it’s best to run at the very bottom of the window. But this would only improve the situation by a small degree; ideally, I want the oil entirely out of my intake.
I know that some people run the KLEEN/PAIR mod, which reroutes the crankcase vent into the exhaust manifold through the reed valves that were intended to draw intake air into the exhaust to help the catalytic converter do its thing. But at wide-open throttle, wouldn’t the exhaust pressure overcome the crankcase pressure, thus closing the reed valves and limiting the venting to when the throttle is closed or only partially open? Would this be a problem?
Another alternative would be to put a catch can inline between the crankcase vent and the airbox. Ideally this would prevent much/most of the misting problem, and the crankcase would be vented at all throttle positions (by manifold vacuum when throttle is closed/partial, by venturi effect on the crankcase vent tube itself when the throttle is open).
Any thoughts?