This new awesome cylinder head is designed to be used with stock ignition and comes with a nice compression release mechanism.

The head is designed to be fitted to the 66/70/"80"cc motorized bicycle engines with 8 MM studs.

This stage 2 head has a 6.0 cc combustion chamber volume.

If this head is to be used on a highly advanced engine, racing fuel should be used.

Or this head will work excellent on a stock to mildly advanced engine running normal pump fuel. 

The compression release valve hex size is 21mm. A spark plug socket can work to install the valve, but it's a tight fit.

When setting up the valve, make sure it doesn't open too far, as the piston could hit the valve poppet

The spark plug shown in the image is for reference only. Spark plug is not included.

Do not use a hot plug, as it will overheat if driving hard. I recommend using a cold plug like NGK B8HS spark plug if operating in hot weather. In cold weather, you can run a hotter plug, like a NGK B7HS or B6HS.

 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. 

A close "squish" clearance has better combustion efficiency.

*The GT-5 engine has a different crankshaft assembly and piston than most other engines. It has a shorter stroke (38 MM), and has low compression.

Check out the complete top end kits for the GT-5 engine.

The increased cooling capacity of this head will  not only extend the life of your piston and cylinder, but it will also allow increased output.

This head comes with four nice, extra tall 8MM X 1.25 high nuts and four flat washers

Use a 9/16" socket for the special head nuts.

There is one more thing I need to mention:

You cannot use this compression release on a bike equipped with a shift kit or other type of spring loaded tensioning device!

The stock, rigid system should be able to work, but those are a little flimsy, so be careful!

The best is to fabricate and weld or braze a robust tensioner mounting plate onto the frame.

Take a look at the image of how I took care of that situation.

I may start to offer these kind of parts as well.

Your feedback about that would help me make those decisions.