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Super Tigre G4500 Wrist Pin Circlip Failures

Old 01-04-2024, 10:16 AM
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Default Super Tigre G4500 Wrist Pin Circlip Failures

Many have commented about ST G4500 circlip failures, damaging the piston and cylinder. They have decided that breaking off the 90 degree tab on the clip is the solution. This should not be necessary. The primary cause of the failure appears to be among engines whereby the factory installed the clip with the tab horizontal, perpendicular to the piston travel, which is WRONG! It should be installed with the tab vertical, inline with the piston travel.

Apparently not all G4500 clips have been installed this way and why all engines do not experience this problem. The tab should be in the vertical position, either up or down, inline with the piston travel, as stated above.

I have found on my own NIB ST G4500, the clip was installed with the tab horizontal. The reason for the failures is primarily due to the flexing of the tab as the piston stops and reverses direction at TDC and BDC. The piston has significant insertia and each time it stops and changes direction, the circlip tab will flex. At the maximum recommended 8,000 rpm, that equals 16,000 times the tab will flex "per minute". It doesn't take long for the steel wire clip to fatigue and the tab breaking off, damaging your engine.

With the tab facing up or down in the "vertical" position, the flex is minimized, if not completely eliminated.

Remove your piston and check how the clip was inserted and if wrong, correct it. This just might save your engine!


Last edited by Red Baron Mike; 01-04-2024 at 10:41 AM.

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