Z1OwnersClub GB

So, some clarification regarding head gaskets for a 1975 Z1B please. The gaskets which were fitted when I dismantled were the two piece type with a centre o-ring, as per the parts list.
The gasket set (Hendstler I believe) I picked up before dismantling the engine, and supposedly suitable for a Z1B has a one piece gasket AND a shaped o-ring for the barrel centre groove. Is this because you can use a one piece gasket with an o-ring for the barrel groove or? Maybe I have the wrong gasket set, but if so why would they supply the centre o-ring in a set intended for an earlier one piece gasket engine?
I noticed also that on eBay there are sellers selling both types of gasket set as being suitable for the Z1B, ie, with one piece gaskets, and with two piece gaskets sets with the o-ring.
If the one piece is incorrect, maybe it could be carefully converted into a two piece.....
Your thoughts appreciated, thanks all.
Chris

You can use either a one piece or two piece.
The two piece uses the cam tunnel 'O' and a one piece usually does not and instead the groove is filled proud with RTV which is left to cure overnight and then the excess sliced flush with the barrel top with a sharp razor blade etc.
I have not personally seen a Hendstler gasket set and never had an 'O' ring included with a one piece gasket.
Maybe the supplied 'O' ring is a lower profile one ( which would be by approx 1mm ) specifically to fit under the one piece gasket although this is the first time in many years of building these engines that i have heard of this if this is the case..
I favour the Cometic one piece and fill the groove with RTV.

Thanks for the reply, very helpful.
I had a look at the new and old gaskets today - the new o-ring measures 3.8mm thick which is approx. 0.2mm thinner than the original compressed one which was fitted with the two piece gasket. The barrel groove is 2.25mm thick, hence the new o-ring would need to be compressed by 1.55mm if fitted with the one piece gasket, which is to my way of thinking way too much. As I have a one piece gasket, I will go the suggested route of filling the barrel groove with high temperature silicon and leave out the o-ring. As to why there is an o-ring with the one piece head gasket is another matter!

Cheers - Chris