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My 1995 Nissan Pulsar (N15 engine) made a nasty rattling sound when started and then stopped. I was worried about doing further damage by attempting to restart so first removed the spark plugs and turned to motor by hand.One plug had the contacts completely closed which made me think it was a timing fault and valve damage. However the engine has a timing chain and all seems ok. Have taken off sump and checked no apparent conrod or bearing play. There is a faint impact scar on the no2 piston crown so it must have contacted the plug. About to try compression test. What next please?

Hi there,
For impact with a sparkplug to occur, there has to be something inside the combustion chamber. Timing chains can stretch and cause the valve timing to be out and the piston could hit and break the valves. Or a valve has simply let go, by turning the engine over you will make things worse, you will need to carryout a cylinder leakage test. I recommending checking the valve clearances under the rocker cover first and seeing if that cylinder has let go.