Thread: Knock Knock?

Originally Posted by RickRover

From the symptoms you describe, my money is on piston slap. Noise only there on light idle, no oil light so pressure good(!) noise disappears when revved or under load.

Correct me if i'm wrong. But if he had piston slap that would indicate worn rings and cylinders?

I had worn rings and cylinders (13 thou) on no. 1 & 5 in my TD5. No slapping sound. But I did have bad blow by.

If 1976_michelle does have sldp, would it be reasonable to remove the oil filler cap and check for blow by to help confirm this may be the issue?

Also, could it be the turbo? When boost pressure picks up the noise disappears? Just a thought.

Originally Posted by Jazzman

Also, could it be the turbo? When boost pressure picks up the noise disappears? Just a thought.

I very much doubt the noise will be from a turbo...

I can't remember if yours has ACE or not, but the ACE pump low on oil will clunk like a bearing.

Can't be turbo, V8.

Originally Posted by Jazzman

Correct me if i'm wrong. But if he had piston slap that would indicate worn rings and cylinders?.

No not necessarily, a worn piston skirt is all thats required. Would not even show on a pressure test. May not even show up on cylinder walls either.

IMO it is best to investigate all possible root causes and conclude with a satisfactory repair.

Originally Posted by RickRover

No not necessarily, a worn piston skirt is all thats required. Would not even show on a pressure test. May not even show up on cylinder walls either.

IMO it is best to investigate all possible root causes and conclude with a satisfactory repair.

Fair enough. I remember having cracked pistons in a VK I6 and it had that exact example.

Piston slap is repeatable.
time after time.

If the sound has changed----

Could be the harmonic balancer?

They make a nice knocking noise when they are stuffed.

Mechanic had a listen today, and is quite content it is the Idler pully /tensioner ?assembly. But also, my Serp belt is shot. Again (only replaced 5000k ago.. so I will be looking up who I purchased it from and making sure not to purchase from them again, looks liek I ended up with heat affected or old stock though the cracks were not visible upon arrival).
Unfortunately.. I didn't quite hear the explanation but a simple bearing is no the fix this time (I thought I heard him say he'd be getting the metal one so that next time it will just be a matter of pushing in a new bearing).. so lord knows what is on it now but anyway...
Unfortunately he'll be getting the parts from LR (god help me but I haven't the time to wait for mail order sellers nor do I want perished parts again).