Stage 2 PK-80 Top End Kit 80cc:
This Stage 2 Engine Kit provides turnkey performance for your PK-80, GT-5A, or GT-5SR engines that use a 40mm stroke crankshaft. This is not for the GT-5 Skyhawk, which currently uses fine thread cylinder studs. The cylinder body features additional widening of intake and exhaust ports. Transfer ports are smoothed to reduce turbulence. The newly redesigned intake plenum features a lengthened intake spigot which greatly enhances low engine speed performance. This kit also features a PHBG racing carburetor which is connected to the intake manifold with a rubber hose coupler. Maximum power is achieved when the engine is connected to a good expansion chamber style exhaust system. If your engine will be connected to a moderately advanced exhaust system, choose the 19.5mm carburetor. If your engine will be connected to a highly advanced exhaust system, choose the 21mm carburetor. The ample cooling capacity of CR Machine’s cylinder head will not only allow greatly increased output, but will also extend overall engine life by reducing the chances of detonation.
- Your choice of cylinder head, with coarse thread extra tall nuts. *see note below
- 1 Stage 2 hand ported cylinder body
- 1 Billet special intake plenum with spigot mount
- 1 Rubber hose coupling with hose clamps
- 1 High quality Dellorto clone PHBG racing carburetor prefitted with correct slide, needle and jets
- 2 extra main jets
- 1 High quality air filter
- 1 Modified PK-80 (Type-A) piston with rings
- 1 Wrist pin set
- 1 Aluminum head gasket
- 1 High quality base gasket
- 1 High quality exhaust port gasket
- 1 NGK spark plug
*For engines using medium advanced exhaust, like the SBP expansion chamber with 1 inch header and plan to run race fuel, then the 5.0 cc head will be fine. For highly advanced motors using race fuel and equipped with Arrow's snake pipe or other large expansion chamber exhaust systems, the 5.5 cc new competition head would be a safer choice. For engines with an advanced exhaust system and using normal pump fuel, use the 7.0 cc head.This is only a rough guide; optimal results are usually gained through your own experimentation. Other factors, like efficiency of exhaust system, rider weight, and road course layout will also affect which combustion chamber size is optimal. For example: Short courses that envolve short periods of full throttle can tolerate smaller combustion chamber volumes, whereas courses that envolve long periods of full throttle will require larger combustion chamber volumes in order to prevent detonation from occuring. There are other heads that can be substituted. Contact Fred and explain your engine configuration. The price will be higher for slant head or twin ignition head types.
Coarse thread cylinder head nut torque spec: 60 inch pounds
Fine thread cylinder head nut torque spec: 48 inch pounds
Squish clearance should be between .010 - .030"
- Before fitting the spark plug, gently rotate the engine to verify that the piston does not hit the cylinder head.