SYM Crank Case Casting Errors

If you’ve worked on enough engines, you’d know that manufacturing anomalies do on occasion cause issues. Anything mass produced in a factory is prone to the occasional error, even with the most stringent quality control.

On a recent SYM Jet job we worked on, we discovered one such anomaly – an error in the crank case casting.

Upon further inspection, it seems that this is less of an anomaly and more of a common casting error on the SYM horizontal 2 stroke engine (Honda based engine).

This casting tolerances haven’t allowed enough room for the cylinder skirt to clear the bottom edge of the left intake port edge.

The issue was first reported to us by a customer who installed a cylinder kit on his bike, and experienced a loud noise at start up – and upon pulling the cylinder back down noticed the marks on the crank casing. Fortunately the noise was unrelated to this casting error, it was instead a cylinder installation error.

Aftermarket manufacturers are often on the look out for such errors when designing their own parts, and this particular issue is a great example. The 9 port cylinder kit for this scooter features a chamfered edge on this particular side of the cylinder skirt, to clear the crank case where the factory does not.

Because performance part manufacturers do smaller runs of parts compared to the original manufacturers, its often far easier for them to make adjustments to casting.

One of the many benefits to installing upgraded parts!