I think you have a little bit of some things backwards. There is a 155z but the V2 you are using is the name of the TB head not anything to do with the name of the engine. See look V2 head for China engines.. Honda Trail Bikes See the name of the head is called a V2 never heard of a Zongshen 155 V2 engine??? The V2 head will fit on a YX160 a KLX110 and a Pitster 155z... They do make a V2 head a piston kit as well so you get a V2 head with a piston to match.. Honda Trail Bikes.. All those kits come with a S20 grind cam but TB also has a S35 grind as well.. Honda Trail Bikes..
Oh, here in Sweden they say "Zongshen 155 V2" I have order a TB race head V2 with s25 cam. Do you think it will fit without any modification with the piston?
Hard to say personaly I would clay it.. But if the V2 head has a deeper area you are going to loose compression.. I would clay the valve pockets and see or wait for a Zongshen expert to reply. I know the piston they make just for the V2 head has a nice dome over my stock YX160 piston so if I would have just bolted on a V2 head to my YX I would have lost some compression. The V2 piston also has DEEP valve reliefs in it so unless someone else has done it I would at least clay the valve reliefs and make sure at minimum you have .040 clearance.. I like .060 to be safe... For the extra coin I would run the TB piston made for the V2 head and not take a chance..