When I took the plugs out and turned the engine a mixture of water and oil came out of one of the cylinders.After further research and talking with other people who know more about engines than I do I am coming to the conclusion that the cylinder head gasket has gone.I hope that this is the case as otherwise something more internal in the engine has failed which would probably mean the engine is caput in which case my lovely bis has come to its final resting place!!I could not afford an engine rebuild so would have to sell to the best bidder.Have had the bis since 2001,only done local miles and generally in the summer months,have regularly serviced it and replaced many original parts-all catalogued.It is also in perfect structural and cosmetic condition.Let's hope it is just the head gasket!!