97 explorer engine knock cold starts

[camm]

I have a 1997 Ford Explorer with a 4 litre OHV, not the SOHC engine. After approx. 12,000 kms, the engine has developed a noticeable knocking sound on cold starts or when the engine has been shut off anytime over 5-6 hours. This noise lasts for approx 7 seconds, then disappears. Once the engine has been started, if the engine is then shut down and started again within a 5-6 hour period, the noise is gone.
Has anyone else experienced this problem?

 

[Jason_25]

Yeah it's piston slap. It's harmless. Happens on all the newer OHV's that I have heard.

 

[TwoToneX]

That happened on my Dad's '96...is it known to happen on the 5.0's too?

 

[Jason_25]

Nah it only happens on the 4.0's from 96 on I beleive. The reason I know is my truck has a 96 model engine. Something must have changed between 95 and 96...different head design maybe?