Sorry, misread, thought you asked about the piston bolts and didn't see you asked about the pistons themselves - yes, as said, they are aluminium. Round O-ring on first (smaller as well) and then flat seal after. Make sure that the O-ring is not twisted when fitting.
moranor@axis said:
follow the guide and look carefully at the pics... RTV is only used on 4 small sections in the front of the head it is not super critical to making it seal well... make sure it is O2 sensor safe
Their guide is really well laid out and detailed - I simply followed it to the T. There are lots of different RTV sealants, but as said, just be sure that it is sensor safe (it will say oxygen sensor safe or just sensor safe), and as said above, literally just a small amount to be applied to the half moon edges (front and rear of the head) and where the Vanos and head meet, basically as they show on their guide.
a1exander said:
Do not use sealer on vanos unit face where it mates the head.
Do you mean where the metal gasket goes (obviously not there) or on top where the Vanos and head meet? How come, they indicate this as being one of the spots that needs some RTV.