Valve Clatter and Piston Slap

I mentioned valve train clatter at 3 and 4K RPMs in a previous post. I was told that valve clatter and piston slap to some degree was normal for the 4 Oh.

With a desire to educate myself on this more, I am wanting to know what causes valve clatter?

What IS piston slap, and what causes it?

What is it ABOUT the 4 Oh that makes this a trait of the engine?

Thanks much for any input,
Andrew

I've always been told that the 4 liter is a "loose tolerance motor"......

Piston slap in mine (Renix) is mostly only noticeable at idle. Is your valve clatter, octane clatter? Does it happen when you are accelerating or at low vacuum? I've found a good oil, tends to help, if it`s just a slight valve rattle.
The wifes 96 HO, has never had any octane (or noticeable valve) clatter, but if it every did, I´d probably change to super. Or possibly go to a colder plug. Possibly go to the next thicker oil.
I've read a bit about piston slap, it seems to be a combination of piston to cylinder wall clearance and the natural harmonic of the motor. Or in other words, it's in many motors and you just don't hear it as loud.
I had a 4.2 YJ with a few hundred thousand miles on it and the pistons slapped like crazy. I was always dreading taking it apart and seeing scratches down the cylinder walls, but there weren't any.
Loud valve clatter in an old motor is usually worn parts, but to some degree seems to show up with low oil pressure also. Maybe the low oil pressure isn't related to the valve train noise, but just another sign of wear.
I just put a load of Castrol in my motor (it was on sale) and noticed everything got a lot louder. I was running mobil 1 10-50 (which was also on sale) and the motor was much quieter. The Castrol is just temporary until I get finished changing gaskets and stuff on the motor, then I´m going back to Mobil 1, but maybe 10-40 for the winter.
How many miles do you have on the motor?

MyJeepXJ said:

I mentioned valve train clatter at 3 and 4K RPMs in a previous post. I was told that valve clatter and piston slap to some degree was normal for the 4 Oh.

With a desire to educate myself on this more, I am wanting to know what causes valve clatter?

What IS piston slap, and what causes it?

What is it ABOUT the 4 Oh that makes this a trait of the engine?

Thanks much for any input,
Andrew

Click to expand...

The 4.0 has cast aluminium pistons that tend to rock in the bores at TDC and BDC especially when the engine's cold due to a higher piston to bore clearance, causing the characteristic ticking sound (piston slap) on cold start up. As the engine warms up, the pistons expand and the noise diminishes or even disappears. It doesn't cause any long term reliability issue and many 4.0 engines reach 200k miles with oil consumption still being negligible.
Valvetrain noise (usually from the rockers, sometimes noisy lifters) is another characteristic of the 4.0 and usually increases with mileage. Many engines will sound like a diesel and still run like a champ for a very long time.

Follow up: Its got 134K on it. It runs strong, just when you rev to 3K in 1st and 2ed gear, and around 4K in 3rd, the valve train clatters. Its not an octane clatter that I can tell, no pings, sounds like valve train to me. I dont think Im having piston slap, or any that I can "hear".

Im thinking its probly just time for a full head job (err... not THAT kind of head job guys). Until theres other problems that go with it, Ill leave it alone though...

Thanx for your info!
Andrew

It might be one or the other, but while you're searching, you might do well to get in there and look at other components, such as water pump and pulleys. The sound of a water pump going out happens to sound almost exactly the same as the existing piston slap, which can lead to late diagnosis on an engine that has both.

If you can't find anything visibly wrong, and the engine runs well, I would not touch it. My 95 has slapped, clattered and rattled its way happily to 247 thousand miles and shows no sign of being ready to quit.

Solved:
http://www.naxja.org/forum/showthread.php?t=66999