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Yamaha Tech Originally the Yamaha XT600 Tech Forum, due to demand it now includes all Yamaha's technical / mechanical / repair / preparation questions.
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Old 12 Dec 2002
Oz Oz is offline
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oil leaking from timing mark covers

my friend has a 1986 xt600z. he recently tried to check the tappets. when removing the circular crankcase cover to turn the engine round, oil poured out of it. this does not happen on my dommie. is this normal, i think not. if not would it likely to be a blown oil seal. are these hard to replace, ie can you take off the crankcase cover and replace it or do you have to split the engine crankcase. any ideas would be much appreciated.
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Old 12 Dec 2002
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This could be normal. The behaviour of the XT600's oil system is governed by some wizardry.
1-In short, what happens at cold start is that the oil is pumped by one of the oil pumps into the engine from the oil tank. for some reason unknown (yet) to me it takes a while before the other oil pump starts pumping it back into the oil tank. Consequently, the oil level in the sump rises and might lead to the phenomenon you describe. Although I think it is pretty extreme what you have here.
2-What also could happen is that the primary oil pump (the one first referenced to in this text) is worn in combination with a leaking check valve at primary pump outlet. At standstill, and higher ambient temperatures, the oil seeps slowly from oil tank to sump.
3-Far to much oil in the oil system.

To check 1 and 3: Drive the bike around for about 30 minutes, normal start-stop etc. Check oil level after 10 seconds of idling, then stop. Level in oil tank should be OK, level in sump should at least be below the stop. If level in tank is OK and level in sump is OK, no worries. If level in tank is OK and level in sump above stop, see case 3: drain oil.
Check 2: Check oil level as described in check 1 and 3. Let bike stand for extended period. If level in tank has fallen significantly and level in sump has risen, it's case 3. Replacement of check valve and / or oil pump through removal of r/h cover and clutch (pump only).

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Old 13 Dec 2002
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I have a 1986 XT600z too and I can say that what your mate has experienced is dead normal and not a problem. I've had two of these bikes and the same thing happens. There may be a little too much oil in the engine but I would just lean the bike iover on the opposite side - against all wall or something and try again. The problme is that the side stand leans the bike over on to the timing cover mark side and tip sthe oil there too.

The oil all drains from the tank in to the crankcases unless the engine is running. But if you check the oil levels as decribed above you'll prbably still get oil coming out of the timing cover whole even if the levels are correct.

Anyway, thats what I reckon !

good luck,

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Old 15 Dec 2002
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Oh dear, the old oil level debate.
Run engine with the bike completely upright (not on the side stand, because the oil pickup is on the RHS of the crankcase)
The scavenge half of the oil pump is now pumping all of the oil out of the sump into the oil tank (scavenge has a much greater flow rate than the inlet half of the pump so sump is allways kept empty)
The oil level will rise while the scavenge fills the oil tank.
With a torch, look inside the tank and watch the level rise - if you have the right amount of oil in the tank the level will settle just below the top of the tank.
You could now open the timing plugs on the gen cover and no oil would come out, UNLESS of course your tank was overfilled, as any excess oil is simply fed back to the engine via an overflow tube.
Also,when an XT has not been running for a while the oil in the tank can slowly seep past the non return valve (bottom of clutch casing) and fill the engine to above the timing plug levels.
David Lambeth.
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