Thread: 300TDi knock noise

Bigger.
Pop it out, that'll tell everything

Originally Posted by Finnius

Someone please tell me that i'm wrong and this doesn't mean what i think it means...





Both above pics from number one cylinder. The other cylinders look fine.
I checked the bottom jet that sprays oil up into the base of piston/cylinder - expecting it to be blocked - but it wasn't...
Any idea why 1x piston would have heated up enough to grab the cylinder and then cause piston slap?
I know the engine hasn't overheated since i put the a new head gasket on a couple of thousand kms ago! Maybe the piston was on the way out before that?

I don't think you need further third party info! Sorry man....
Any chance you missed that before when you had the head off? Maybe cooling system wasn't bleed properly , but that's probably unlikely.
The piston will look worse than the bore as well.

Cheers
James

If you were lucky you might get away with a hone and replacement piston, depends how fussy you are.

Originally Posted by shack

If you were lucky you might get away with a hone and replacement piston, depends how fussy you are.

Yep. I'll hone it and drop a new piston in.
Just hope the machine shops stay open to do the little end bush...

so whats the worse it could mean? i know when i did my head i have a knocking noise (i assume since then). i remember having issues bleeding cooling system and but shut it off as soon as i noticed gauge moving. had some other issues like spigot on radiator had a leak from over tightening. my engine has been going for 3-4 years without issues and knocking still there, some times worse than others. could it be i cause some slap but not bad enough or would i know about it if i had caused any damage. in the case of finnius' car, would it have kept driving like this but with the noise or would it mean something terminal? is it just loss of compression?

could it be the reason why on startup it takes a few seconds to idle properly at correct speed? ie losing compression at start up until its warm enough to expand out?

mine seems to have good compression and not burning oil or smoking.

Originally Posted by Fausto79

so whats the worse it could mean? i know when i did my head i have a knocking noise (i assume since then). i remember having issues bleeding cooling system and but shut it off as soon as i noticed gauge moving. had some other issues like spigot on radiator had a leak from over tightening. my engine has been going for 3-4 years without issues and knocking still there, some times worse than others. could it be i cause some slap but not bad enough or would i know about it if i had caused any damage. in the case of finnius' car, would it have kept driving like this but with the noise or would it mean something terminal? is it just loss of compression?

could it be the reason why on startup it takes a few seconds to idle properly at correct speed? ie losing compression at start up until its warm enough to expand out?

mine seems to have good compression and not burning oil or smoking.

I tested and my compression was fine on that cylinder. I'm not an expert but i am presuming that the slap would get worse and worse as the clearance with the cylinder slowly increases?
Hopefully someone else will chime in.

Originally Posted by Finnius

Someone please tell me that i'm wrong and this doesn't mean what i think it means...





Both above pics from number one cylinder. The other cylinders look fine.
I checked the bottom jet that sprays oil up into the base of piston/cylinder - expecting it to be blocked - but it wasn't...
Any idea why 1x piston would have heated up enough to grab the cylinder and then cause piston slap?
I know the engine hasn't overheated since i put the a new head gasket on a couple of thousand kms ago! Maybe the piston was on the way out before that?

Whilst the scores in the bore are obviously not good, a read of this article might provde some insight into piston slap and allay some of the anxiety.

Blog - What Is Piston Slap And False Knock?

Tom.

I'm going to be blunt here, but I worked in recond engine shop for years.

When honing and maybe putting in new rings/pistons, did you in fact remove the "ridge' at top of cylinder. There are tools for doing this.
This is clearly shown in your pictures, it was not done, DANGER, failing to remove this ridge, caused by wear of rings and bore, or more correctly, limit of wear of rings.
This leaves a ridge at top of bore, ie. where no wear occurs. BEFORE honing, this ridge 'MUST' be removed. Fitting new rings or pistons with very slightly
different thickness, 'aftermarket' rings/pistons' can hit this ridge. Some ring sets can be thicker than standard, And yes, knock noise, causing new rings hitting ridge, followed by deformation of the new rings, usually around gaps, then scoring of the bores. same issue at bottom of bore, and a reason why complete new rebore is recommended in cases where wear exceeds a certain amount, over simply honing and installing DIFFERENT pistons and or rings. Diesels have very high compression, not so noticeable on petrol engines.
Piston slap is obvious, just measure bore and piston, is it within specs?

Sound familiar,