U.M.R. Engines

PISTON - SEIZED

Seized pistons in an engine that has had no serious overheating problems is usually caused by a breakdown of lubrication.

This can be the final result of rings fitted with insufficient ring back clearance or ring end gap.

If the engine is driven long enough after symptoms start to develop (lack of power, pinging, etc) the result will eventually be piston seizure.

As the friction increases the lubrication breaks down and a complete piston seizure will result in a very short time. If the engine has had a serious overheat the abnormal expansion of pistons and rings in the bore will cause excessive friction and again a breakdown of lubrication will eventually result in an exchange of molten material from the pistons to the bore and visa versa.

As this happens the piston will be permanently seized in the bore.

Items to eliminate as the cause include: ring back clearance, ring end clearance, lubrication, cooling system, piston to bore minimum clearance, severe loading conditions and severe tuning problems. ( retarded, overadvanced, lean mixture.)