what does it sound like and when does it occure.
will a engine do it just idle or reving with no load on it.

 

My 200SX has a horrable case of it.. sounds just like a bad rod and knocks loud when reving it up while it is cold. It will do it bad when backing up in reverse on a cold engine. Pistion slap goes away as soon as the engine warms up. My old 200ES big red has a cam knock that rumbles while flooring it in middle to high rev's. what are you hearing? tick, knock, muffled knock?

 

My ATVs are fine but I have a Buick 2L 4 cyl with bad piston slap!

I disagree that it goes away when the engine warms up. It may on some engines but it certainly doesn't on the Buick! I would guess it to be different on different engines.

This thing has 380,000 kms on it and has been slapping for the last 150,000 kms. My understanding is, no harm done, just annoying. People look at you as if you forgot to add oil after the oil change or something.

The slap is a very load knocking sound. On a car you can isolate and remove the knock by removing spark to that cylinder (short it out or pull the wire off while running). The change in pressure on the top of the piston temporarily removes the knock.

In the Buick it is the worst at idle and appears inaudible at running speeds.

Like I said, no harm done, but damn annoying!

DJ

 

My Blaster had a light pinging/ringing sound which I now know was piston slap. It usually did it on a no load rev, or if I had an ear for it, when I was WFO in 2nd or 3rd on a hill climb. I found out when the skirt dropped off the piston and the motor pretty much stopped dead right there.
If your motor is making funny noises your least expensive recourse is to check it out, or get it checked.

 

I have a 1984 200es and I found out that it is not even related to the motor. I found this out because I put in a high gear and boged it and no noise was hear but when it started moving it was. I found out it was a slightly warn clutch that was shaking under load. No big deal