Here is the totally new CR Machine cylinder head for the 66cc Grubee motorized bicycle engine!
This cylinder head increases horse power for your 66cc 2 stroke bicycle engine* and greatly improves cooling of the engine.
It is very easy to over heat these bicycle engines if you drive fast or live in hot climate.
Poor engine life will result of running a hot engine, as the oil film cannot hold up to overly high operating temperatures.
This cylinder head incorporates a squish band which has been proven to allow increased compression while reducing the risk of detonation.
Please be aware that in order gain the maximum benefit from this cylinder head, you will need to bring the outer edge of the piston to (or close to) the top of the cylinder.
*The GT-5 engine has a different crankshaft assembly and piston than most other engines, and has low compression.
Adjusting the compression by decking the cylinder jug is necessary for the GT-5 engine in order to gain proper compression ratio.
There is more that one way to set an engine up: For example, the CR Machine test bike is using two bottom gaskets to allow better opening of the transfer ports. This modification required us to take off .100" off the top face of the cylinder body on our GT-5 engine. When the engine is set up so that the outer edge of the piston comes flush with the top face of the cylinder, the thickness of the head gasket will determine the squish clearance. A close "squish clearance" will maximize combustion efficiency.
If you have any performance enhancing equipment on your motorized bicycle, like an expansion chamber, there is a risk of overheating your engine. Piston, cylinder, and overall engine life will be greatly enhanced by running a cooler engine!
This cylinder head is proven to keep your engine cooler, while allowing increased output!
This head now comes with four nice, extra tall 8MM X 1.25 high nuts and four "plain jane" washers.
Use a 9/16" socket for the special head nuts.
This is one nice head! Your engine will be happy with it!