I was helping a friend assemble his A55 engine that belongs in his 2012 Tomos ST that he bought new in 2013. We found that the four stud holes in the head gasket were too small for the size of the studs in the engine. A 2008 Tomas A55 has M6 studs, and his 2012 has larger studs, I think M8, maybe M7. There is a clue in the parts manual:
233716 CYLINDER STUD BOLT M6/M7X115
236639 NUT M6-8 DIN 986 A2F
I think maybe the nut designation may mean either M6 or M8? The stud size is hard to figure out as it might be that one end is M7, the other M6? There doesn't seem to be M8 in the stud designation in the parts manual.
In any event, the 2012 was bought new, and the studs were installed at the Tomas factory. My friend says the 2012 easily gets to 40 mph, while a 2008 with M6 studs will get to about 34 mph. The larger studs in his engine make me think the 2012 has more horsepower than the 2008, and perhaps heavier studs were necessary. The 2008 speedometer goes to 40 mph, his 2012 goes to 60 mph. My question is, was the change in engine studs and speedometer simply a model year change, and if so, in what year was the change made? Thanks in advance.