O.S. Engine OS29203400 Piston Ring for 108FSR and 105HZ Engines  [OS29203400]

Precision piston ring and fit notes

This replacement piston ring is supplied for use with engines identified as 108FSR and 105HZ and carries the O.S. Engine OS29203400 part number. The text highlights correct fitment checks, installation best practice, and the component's role in engine service without claiming unverified construction details.

In operation, the piston ring seals the gap between piston and cylinder to restore compression and minimise blow-by. When fitting, ensure the ring profile aligns with the piston groove and verify the end gap is within the engine maker's specified clearance, as an incorrect gap will alter compression and idle characteristics.

Installation guidance: prepare a clean bench area, lightly coat the ring and piston with appropriate glow-engine oil during assembly, and turn the crank by hand to confirm smooth rotation before final assembly. Check the cylinder and ring for scoring or wear to determine whether a ring replacement alone will suffice.

Impact on tuning: replacing a worn ring can stabilise compression and improve throttle response, making engine behavior more predictable during setup and trimming sessions.