Pete the .4 mm appears to almost be "foil" & I was super cautious while slipping it over the studs. Side by side the new gasket appeared to be 1/4th the thickness of the original, not half. I'll be watching for any elevated temps while riding, but don't think I'll notice much if any change, the reason being that the piston at TDC isn't. This reduces compression and thus heat. I'd guess this engine now sets at about the same power as a well setup and carefully manufactured stock motor...getting one of those happens, luck of the draw, even from the best manfacturer & dealer/distributor. I like the California compliant kit motors that require light assembly as it saves time tearing down a motor for inspection and really is required for cleanup of transfer ports on both cylinder and case. I've also flushed out metal debris from machining operations as well. There is commonly some casting " flash" & constriction, rough edges and poor matching at the transfers as well as at intake & exhaust ports. Cylinder base gaskets are often too thick to build good compression, my engine base gasket falls into this category and will be replaced with a thinner one. Stock heads typically need some attention, I had 4 unused stock heads on the shelf and 3 of them were not flat requiring a surfacing cut for truing (shaved head which also increses compression). Of the four 3 also had a large casting lump at the edge of the spark plug, creating a hot spot, at the least, in the chamber which is a rough finish at best and all cc'd significantly different volume. Pete it's easy to find ways to build power in these little motors unfortunately. Attention to detail brings them to life. I've used quality CNC heads on my last 7 China girl motors for these reasons plus additional engine cooling and cool look as well. Using a stock head on the Schwinn X-celsior has reminded me of what I learned years ago when stock was what you got, deal with it. Jury is still out; I may switch to an aftermarket head on the Schwinn at some point & have a spare on order.
Even when building an engine with a perfect head, flat and well finished with a consistent combustion chamber volume the cylinder to head fit needs to be near perfect & both top and head gaskets selected that allow a good "squish" that brings the piston to TDC while completely filling the cylinder without coming in contact with head or plug.
Note that port timing will be altered by either increasing or decreasing the cylinder base gasket thickness. I've experienced no port timing problems going with thinner gaskets only improvement. When building a highly modified China girl I prefer to begin with the thinner base gasket, if piston position at TDC is too low in the cylinder after all truing cuts are completed on jug and head. Shaving the head for a compression increase is my least favorite power builder & my last resort.
Though reed valve case induction is now quite common on the China girl & getting more inexpensive to accomplish with a kit the piston reed port setup is still an excellent choice for most builders. Hard core racers will probably gravitate to case reed induction for max power, but most builders seem to go piston port with the reed for the next power stage level in an easy to tune and live with street engine that has really good performance.
The piston port reed valve (I use the RSE valve with a Dellorto clone carb) used with a piston "window" is necessary to see a nice performance increase with a reed valve. Just bolting on a reed valve will not help a non modified, for reed valve,motor. I tried that on a highly modifed engine (non reed valve mods) & lost speed, with no noticeable improvement at any point in the power range. A piston window is necessary to feel a performance improvement. The piston window also helps cool the motor with the direct straight shot of cool fuel to the interior of the piston and wrist pin. More lubrication at the wrist is a very good thing as is any cooling. Aids in engine life and catastrophic seizure or bearing failure.
Cutting a third transfer port in the cylinder on the intake side really maximizes the use of the reed valve for top to bottom performance improvement and added in combination with previous modifications to head and cylinder, plus the piston window turns the CG engine into a very sporting power plant for light weight bikes. I like performance available on demand, but without drama. I don't want to spend my time tuning. I prefer riding and fabricating in that order, so if it's not dependable or if it's labor intensive I have no use for it. I have built one engine for max power and it was powerful but was all of the above as well & has set on the shelf for several years for a reason. I was a real P.I.T.A. much more trouble than it's worth. Some of the race builders won't sell outside the racing fraternity I'm told because they know it will come back to haunt them. I'm not a vendor nor do I sell what I build, for that reason coupled with the liability issues. I did sell a motor recently to a motorcycle service tech who can flat build tune and ride 'cause I wanted to do him a solid for aiding this old guy from time to time. He refused to accept it for free...great young man.
Just info and observations specific to the Chinese type kit bike variety 2 strokes. Just having fun. Rick C.
