Left side crankcase cover removal to replace gasket

[Chris Williams]

Can anyone please remind me of the gear shift sequence for MZ251ETZ as I am trying to loosen the centre knurled (tachometer driving) nut which holds in the clutch mechanism as I am wanting to remove the crankcase due to a leaking gasket. I am aware that putting it into top gear and locking rear brake hard should loosen it when applying spanner clockwise on the nut. However I’m not sure I’m in top gear – or should it be bottom gear? So far unable to loosen even with assistant holding down rear brake. Any other suggestions welcomed.

[‘AAA Dummy]

Just put some rope down the spark plug hole?

[Chris Williams]

Haynes manual (I know folk don’t have much faith in this!) dictates that the left hand crankcase cannot be withdrawn without the removal of the speedometer knurled nut and washer from the clutch centre. However the maker’s manual does not say this! I only want to renew the gasket which seals the left crankcase cover to the central crankcase.
Anyone know if I can just lever off the left crankcase cover without loosening/removing the said nut?

[John Gray]

Definitely not! You might break the crankcase cover if you try. You must get the nut off. Keep trying.

[Chris Williams]

Thanks John ???? I’ll keep trying to undo it. Can you confirm it should unscrew in clockwise direction and how much torque is needed to loosen it off. It’s very stubborn but I won’t try to take off the crankcase cover until I’ve achieved this.
I’ve got it into top gear and stood hard on the rear brake but may need to take the bike off the centre stand and have assistance to keep the brake fully on.

[John Gray]

I’m fairly sure it’s a standard thread and unscrews anti-clockwise.

[Chris Williams]

Thanks John, You were right and I have now managed to remove crankcase! Once I had taken off the centre nut I had to take the footrest from the frame to allow easy extraction. Fortunately I have a side stand to lean it upright otherwise the bolts securing the footrest would not come off with bike on centre stand.

[John Gray]

Yep, whatever you want to remove there’s always something else that needs removing first.
Another couple of things:
1) When you refit the cover be sure to grease the splines on the gear change shaft to avoid damaging the o-ring. Grease that as well.
2) Don’t refit the cover with the oil pump still in. If it doesn’t align with the slot in the gear shaft it can break when you tighten the cover bolts.

[Chris Williams]

Great advice John! By the way the 1984 factory manual for ETZ 250 describes a silencer tube that goes into the oblong hollow of the frame under the fuel tank and connects somehow with the air box. It might not be an essential element and no reference is given to it in the Haynes manual. Do you know if this an actual pipe/tube that runs through the frame or just a way of describing the route of air into the air box before it is drawn into the carburettor? Hopefully this makes sense, and once again I appreciate everyone’s advices.

[John Gray]

Sorry Chris I know nothing about that.

[Chris Williams]

Hi John,

Sorted. The said tube is oblong and inset into the frame and would only need changing if a blockage or serious damage to it were to occur. The appearance of what looks like a hollow round tube in the repair manual is actually a representation of the passage of airflow into the frame opening. A blow through the frame opening with compressed air should ensure it isn’t clogged or fouled on its way to the air inlet connection.

[John Gray]

Hi Chris, thanks for bringing this to my attention, I was not even aware of the item labelled (1) in figure 188, however it is clear from section 7.1.2 that item (S) is a “broomstick or wooden rod” used to insert it in the frame.
I must soon check out my own ETZ and make sure it’s not blocked.

[Author]

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