17’000 miles – drippy drippy!

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!


9 thoughts on “17’000 miles – drippy drippy!

  1. Got this to look forward too then! isn’t it good now the sadlers farm is finished am tempted into buying a bigger bike now the 50 limit has been lifted, but still love the fuel consumption, or lack of, on the cbf125!

    Ride Safe!

  2. I’ve just fitted an indicator buzzer as I was leaving them on to often, £3.50 from Maplin, 5 minutes to fit.

    • Can you please let me know the part number for this and also fitting instruction if possible… I need to fit one as well…thanks

  3. Hi, I’m not sure if I’ve just piggybacked this thread or posted a new one! apologies in advance!
    My issue is, I picked up my brand new CBF125 2 weeks ago and yesterday I noticed quiet a lot of oil on the right hand side engine casing, foot rest, and along the exhaust, it actually covers the whole right side engine casing! I’ve looked for the possible leak but being a total novice I am unable to make a true diagnosis! I checked the oil level before my first ride, which was fine so I know its not through overfilling. My bike is booked in with belle Vue for its 600 miles service on Monday, and they have stated they will have a look, being a new bike it is under warranty, I would just like to have half an idea before I get there! any help at all would be very much appreciated!
    PS, could this leak been caused at all by my riding of the bike? from the second day of having it, I have been doing 50 mile round journeys on the A127/A12 at 60mph

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