failed barrel/crankcase gasket

[Bill Newman]

My '76 Z900 A4 suddenly leaked copious amounts of engine oil all over my right boot on saturday night,15 miles into a 25 mile run. It has been no trouble for the last two years.On investigation it appears to be past the gasket between the base of the barrels and the crankcase,on the right hand side-just over the top of the intermediate casing that holds the contact breaker back plate.

Over 4000 revs it really gushes out-over the side casing, footrest, top pipe and my boot!

Anything I should look out for-so I can pick it up when I separate the barrels and cases. I can't think why the gasket should fail so catestrophically and so suddenly.

Thank for any thoughts on this.

[chrisNI]

Very odd - you should check the torque settings of the head nuts on that side before you take it all apart to see if they've been loose - there shouldn't really be that much pressure on the base gasket as opposed to the head gasket which you would expect to have given first in that case - but it's hard to see why it would have let go if everything's tight.

[Rich]

better check your breather system as well

[Bill Newman]

What should I look for in the breather system?

[Rich]

Make sure it breathes to somewhere and is not blocked.

[Bill Newman]

To give some closure- got the head and barrels off and it was the base gasket(between the barrel and crankcase that had failed. there were no problems with the torque settings on the head, nor any blockages in the breather system. I will have to write it off to experience.

Of concern was thecontion of one of the bores- which looks like a piston had picked up in a previous ownership. So its new pistons, rings, gudgeon pins and gaskets all round.The up side is the head is in brilliant condition.

Thanks to all who commented

[chrisNI]

Still, an unusual failure I would have thought.... Good luck with it.

[Bill Newman]

Done it. Several new parts and its worth it. Really good outcome to rebuild - done 300 miles ish now and no problems.