U.M.R. Engines

PISTON - BROKEN

Smashed or broken pistons are usually the result of another failed engine part. The result of a broken big-end bolt or Conrod generally results in severe piston skirt breakage due to the broken rod contacting the piston at high revs.

If the damage is confined to the breakage of the piston pin bosses the cause can be identified by pin seizure in the piston pin boss. Dry assembly and dry starts can cause this failure, even when the pin is freely fitted.

If the damage is concentrated on the crown of the piston it is usually foreign material entering the combustion chamber or a failure of a cylinder head component such as valve or valve seat. Ample evidence can usually be gathered by close examination of the head, carburetor and intake system. Often the failed part may belong to another cylinder but finds its way via the intake manifold. Care must be taken to completely clean all remaining failed components from the intake manifold as they will re-enter the engine on start up and cause the repaired engine to fail. Reconditioned long engines have been destroyed in this manner.

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