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Old 09-21-2013, 07:14 PM
Nashville Kat's Avatar
Nashville Kat Nashville Kat is offline
Motorized Bicycle Elite Member
Join Date: Apr 2009
Location: Jacksonville, Florida
Posts: 1,403
Default Re: Building an engine

The one major difference to know is- I believe- whether the engine block (jug) studs are 6 mm or 8mm.

I believe- and there may be exceptions I'm not aware of- almost all top ends will fit the 6 mm stud bottom, except those specifically 8mm

6mm is an older standard, and while 66 motors and top ends still come in 6mm,
there's a gradual change to 8mm in 66 cc motors.

That's part of this game- some suppliers and their stocks may be YEARS behind trends otherwise. 8 mm studs in 66 motors began a few years back and has become more common I'm sure, but if you have a concern or preference you really have to ask a vendor.

It's getting harder these days to come by either 6mm stud bottoms and 50 cc parts, though they are as of now still generally available, their share of the market decreases

Too bad I think- after almost 5 years, I sorta prefer a smaller motor- and mostly for the carburetion aspect- they decrease in revs quicker and idle better, even if they aren't as powerful.

for instance- boygofast was largely selling bottom end with 6 mm studs until very recently- now advertising only 8mm -

Last edited by Nashville Kat; 09-21-2013 at 07:19 PM.
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