My '99 XT600E has developed a disturbing trait, which I'm wondering if anyone else has experienced. The plastic bung in the top of the gearbox, under the starter motor, which plugs the hole where the clutch shaft used to be, has started to pop out at inopportune moments. The first time was at speed and the engine pumped out a large quantity of very hot oil onto my left foot (and rear tyre!). Just recently it has happened again while I was off the bike closing a gate, with only a little oil loss.
The hole itself is on the low pressure side of the oil system (I think), so I'm not sure why it is popping out. However with the bung out, the engine will quite happily pump oil out of the hole. I'm not sure if this is relevant, but my bike has a CoolBlok oil cooler and thermostat fitted, from Wunderlich in Germany.
I've tried to replace the bung using various adhesives, but the high temperature and plastic-metal interface aren't ideal for this. From an engineering point of view the optimal solution would be to tap the hole and get a threaded cap made up to screw into it. But this would involve me removing the engine, and finding a precision engineering workshop, which would probably cost a lot of money as well.
So, has anyone else experienced this as well? Is there a simple solution to this problem?
I have experienced an identical problem with the oil seal on the drive shaft when the flimsy steel bracket holding it in place was bent.
It could be that the thermostat set-up has increased oil pressure in the scavenging system, especially when the control valve is somewhere in the middle (part of flow through cooler, part directly to tank). The type of pump used means that at less flow pressure increases enormously, but I think that in general this setup is OK if the oil is pumped back correctly into the tank. The pump will deliver sufficient flow regardless of the backpressure.
The solution you propose would be ideal but does involve a lot of work. The bushmechanic would fabricate a kind of wedge to push between starter and plug. Wood would be the most practical material.
Then, when the engine has to be removed for other reasons you can have the threaded plug which would not be that costly as it is a simple operation.
I would replace the plug for a new one anyway as it has been tinkered with and the oil system is too important to take risks.
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