Piston Slap: Just Give The Motor A Rev Up, Mate!

Paul writes:

I have either a piston slap or a gudgeon pin noise in my 1970 Ford Escort with the Kent 1.3-liter engine. I use 20/50 multigrade engine oil. I appreciate any advice you may have.

Sajeev answers:

In my 15 years as a judge in the 24 Hours of Lemons, I've been lucky enough to hear a lot of dying motors in my life. I think the answer is simple: If the noise fades away as you 1) rev the engine and 2) listen as the motor settles back down to idle, it's piston slap.

If (unlike what happens in the video above) the noise does not go away, it's something related to the rod bearings or the gudgeon/wrist pin. The video above explains this issue with a boxer engine, but the same applies to a more conventional layout. So let's hear an example of a problem with the rods in a motor:

This YouTuber nailed it, as the "pup-pup-pup" sound he used to emulate the engine upon revving is definitely not piston slap. With any luck the Kent mill in your Escort does not make this noise.

While unfortunate, piston slap is a condition you can live with. You can still drive the vehicle for months, years and maybe even decades with this noise. A rod knock is, well, a bold indicator that a new (or rebuilt) engine is in your future.

I will keep my fingers crossed that a bit of revs when parked will lead to a happy ending. Well, happier at least…