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every nut, bolt, washer, screw and rivet in any application has a torque specification based upon the diameter of the fastener. it is not a function of engine size.
the 6mm nuts used by the Chinese will strip out @ 12 ft lbs of torque. so limit them to 10 ft lbs or under.
8mm will safely take 15 ft lbs and not strip
remember when applying the torque, do it in a cross pattern and in steps - also use a good quality torque wrench with known good accuracy
here is an example of how to torque a 50cc gy6 engine up.
1.. torque all fasteners to 5 ft lbs
2.. wait a couple minutes, recheck the torque
3.. torque to 10 ft lbs, wait again, then recheck
4.. torque the nuts ONLY to 15 ft lbs, wait, recheck
as to gasket dressing; that is a function of the gasket type and whether it was reused or new
Copper Coat spray is best used on base and head gaskets, but it must be allowed to "cure in" and be almost dry
if the paper gasket between the engine halves has a silicone strip, install dry. if it does not have the silicone strip use gasket shellac, but allow it to dry. if you try to install a gasket while it is wet it will get pushed out like your photo shows.
when installing engine half gaskets, remember to check the surfaces for porosity as the aluminum cases sometimes do have porous areas in them which does not seal and causes a loss of clamping force. if you have those they can be fixed with a little two part epoxy like jb weld-- just allow it to cure and shave it flat with a razor before assembly
also sparingly apply a little grey bolt prep on the bolt threads-- near but not at the bottom of the thread-- this seals against weepage through the threads - you can also use (low acetic acid content) rtv silicone if in a jam
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