Yamaha XS400 1978 - no batter loading and sudden leak


XS400 Member
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Poznań, POLAND

Yesterday my 1978 XS400 (2A2) suddenly started to leak oil from the bottom left side of engine, couple of kilometers after motorcycle stopped, looks like there is no electricity comming from the alternator, any way motorcycle was running only on battery.

1. is there a chance that oil filled alternator chamber and that coused no chargeing
2. how many kilometers can a XS400 do only on battery ( with headlight on )

Any ideas of what might have happend?
The capacity of the battery is 12AH, so assuming you were at full charge and are using at most 5A and traveling 100km/hr you should have a range of 240km (12 / 5 * 100). That's a lot of assumptions, but I think you should have been able to travel more than a few km on battery.

Edit: The resistivity of motor oil is apparently pretty huge (more than a million Ω*cm), so I don't see how it could short anything out.
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Under the alternator cover is open to the oil sump and should be. Even if overfilled, I don't see oil being the problem.
more than likely the wires from the alternator routing behind the sprocket cover.

I rewired mine last week!
Found the problem!!!

Couple off weeks ago, I've tried to take out electric starter, while putting it back i've pushed the starter gear into the alternator chamber, after 200 kilometers the free starter chain ripped out the alternator wireing, and cutted the seal.

New wires, seal and motor olis should do the trick...