So after thousands of miles of uneventful riding, the engine decided to start ‘marking its territory’. Little drips of oil appeared below the engine whenever I parked up and left the bike for a while. Maybe it had seen a Harley and was envious, or maybe it was just a sign of something being faulty. After all, this is the sort of thing you start to get happening after the miles start to clock up.
Tracking down an oil leak, especially one so small, can often be quite a challenge. If the leak isn’t obvious, then my advice would be to give the engine a really good clean and degrease – paraffin is extremely cheap and does this well. Make sure everything is dry and run the engine for a while, perhaps riding the bike for a few miles or so. This will get the oil nice and warm, thinning it out a bit, making the leak more obvious. Once you get back home, put some newspaper under the bike and play the waiting game. You’ll see drips on the paper, or bigger puddles if things are more serious… You’ll also be able to look around your clean engine to find the origin of said drippage. Once you locate the source, then you can work out what needs to be done.
In my case, the neutral switch, located behind the front sprocket cover, was the culprit (the black plastic block in the centre of this photo):
And here’s the leak:
This little device is a round ‘switch’ that has only a small portion as the conductor. On the other side, in the engine is a peg that shorts the conductor when the transmission is in neutral, completing the circuit and giving you that nice green light on your instrument cluster, as well as disabling the starter safety interlock (can’t start the bike when it’s in gear and the clutch is out, can we?).
The rear of the switch is held in the engine by interference fit and with the help of an o-ring who’s job it is to keep oil inside the crankcase. In my case, this o-ring had failed and needed replacing. A new o-ring from Honda was 94p (but postage was nearly £5!). Still, a fairly cheap DIY fix, done properly.
Here’s what the rear side of the switch looks like, with the o-ring installed. The metallic ‘spot’ is the conductive part of the switch and you can just make out the ‘peg’ in the engine casing (top of photo) that rotates along with the transmission, only lining up with the spot when it’s in neutral:
Keep in mind that you need to align the spot properly when re-installing the switch.
Here’s the old o-ring – note the deformation it’s suffered, especially the bulging around one part of its circumference. It was also quite brittle and stiff – that’s what happens to rubber over time, especially when it’s subjected to extremes of temperature:
Here’s the new o-ring:
So, after smearing it with fresh engine oil, sticking it on the switch and reinstalling the assembly (torque the two bolts up to 10Nm), it’s job done!