31 -- Piston slap or rattling from cylinder
Cylinder bore/piston clearance excessive. Resulting from wear or partial seizure. This condition can often be heard as a high, rapid tapping noise when the engine is under little or no load, particularly when power is just beginning to be applied. Either fit new pistons or renew the cylinder block.
Connecting rod bent. This can be caused by over-revving, trying to start a very badly flooded engine (resulting in a hydraulic leek in the cylinder) or by earlier mechanical failure such as a dropped valve. Attempts at straightening a bent connecting rod from a high performance engine are not recommended. Careful inspection of the crankshaft should be made before renewing the damaged connecting rod.
Gudgeon pin, piston boss bore or small-end bearing wear or seizure. Excess clearance or partial seizure between normal moving parts of these items can cause continuous or intermittent tapping noises. Rapid wear or seizure is caused by lubrication starvation resulting from an insufficient engine oil level or oilway blockage.
Piston rings worn, broken or sticking. Renew the rings after careful inspection of the piston and bore.
© April 2014