PRO RACING DESIGN
7
Piston to Cylinder Clearance:
If piston to cylinder measurement exceeds maximum tolerance – replace piston.
WARNING:
If it is necessary to remove the piston from the conrod to carry out these procedures then care
must be taken to prevent the piston pin circlips or any other foreign object falling into the
crankcase of the engine.
Do not use excessive force to remove the piston pin.
Whilst disassembled inspect piston pin and bearing for wear or abnormality, replace if necessary.
As a precaution on reassembly, replace old circlips with new.
5.3 Cylinder head and cylinder should be inspected for any damage or abnormality.
5.3.1 Carbon deposits in the cylinder head can be removed with #600-800 wet & dry sandpaper.
Carbon deposits in the exhaust ports of the cylinder can be carefully removed with a round edge
scraper and wet & dry sandpaper.
5.3.2 The cylinder should be inspected for any damage to the liner and if damage is evident and
cannot be removed by wet & dry sandpaper the cylinder should be re-bored. The cylinder
should be measured for concentricity and if any out-of-roundness is detected, the cylinder
should be re-bored and a new piston and ring fitted. Measurement should be taken by either and
inside micrometer or a cylinder bore gauge.
IMPORTANT:
When refitting the cylinder assembly,
care must be taken that you compress the piston ring with one hand and gently lower the cylinder
onto the piston with the other hand.
Care must be taken that the ring is correctly located in the piston groove during this procedure.
5.4 Spark Plugs:
The heat range of a spark plug refers to the classification of a spark plug’s ability to transfer heat
from the firing tip of the insulator to the cylinder head.
The engine manufacturer through testing has determined the heat range appropriate to the
engine. However, variables such as atmospheric conditions, carburetor tuning and engine
modifications can have an influence on the recommended heat range.
WARNING:
When selecting a spark plug with a hotter or colder heat range then do so carefully and cautiously.
A spark plug with TOO HOT a heat range may lead to pre-ignition and possible engine damage.
A spark plug with TOO COLD a heat range may lead to fouling of the plug and failure to start or
erratic poor performance.
