Question for some of you mechanics out there..

[rbull51]

I have a mystery rattle on my engine. Its been there since i have bought the car & which at the time only had 11000 miles on it. I did take it back to the garage where i had it from and they changed all the tappets. It wasnt them. So i took it back again and they fitted a brand new head and gasket. It did stop it for a while but after a 1000 miles or so it came back. I then decided to take it to my local garage and there i was told it is whats known as 'piston slap' which can be repaired but at the cost of around £1000! Has anyone else heard or got this problem?

[Maxxed_Ross]

yeah it's normally a problem with older engines

It is basically a sideways movement of the piston against the side of a cylinder bore. All piston driven internal combustion engines and compressors have a certain amount of piston slap. Excessive piston slap happens when the clearance between the piston and the cylinder bore becomes too great through wear, mismatched pistons and cylinder bores at manufacturing or, a combination of both. The noise associated with excessive piston slap is due to the impact of the piston against the wall of the cylinder bore, typically loudest when the engine is first started up. The pistons then expand with heat reducing the piston to cylinder bore clearance - reducing the impact of the piston against the cylinder wall and its resulting noise.

One way to check for piston slap is to remove all but one of the spark plugs, crank the engine over until you feel the resistance of the piston coming up on compression. Crank against compression until the piston is about half way up the cylinder. Now using the fan, rock the crankshaft back and forth and listen for a metallic clunking sound. Unfortunately with the V6 this might take a while, but will save you some hefty garage bills and potentially being told the wrong information again (most garages won't even touch suspected internal problems if they can help it)

If you hear a clunk, you have piston slap and the only way out is to rebuild the engine. Depending on how serious the slap is you might just need a new piston head, or it might mean a re-bore and sleeve if it is serious

[lukiep160]

Piston slap is very common on the later cars post 97, Rover did introduce modifyed pistons and liners around 2001 but it never really cured them.
My advice is if it starts to get worse then have the pistons and liners replaced. it proberbly won't get any worse

[rbull51]

thanks for the info, the noise isnt really that bad but because it is mine & you get used to what things make certain noises i notice it. when i change gear at 3000rpm you can hear it for a second, its like a a tappety noise but really fast. unless you was told about it it wouldnt be that noticable. also when its under load below 3000rpm it sounds a bit different to what it should.

[stamford]

I have my doubts in that, seems to easy a diagnosis for said garage, were they busy?

I would get a second opinion, one that is well known or trusted.

Why not give these guys a call www.lates600.com they are based in Coventry, you should get a more honest and accurate diagnosis.

If you were suffering piston slap since 11000 miles and gone away and come back, I would bet it isn't, it would get worse, not better. If at 11000 miles it was though to be piston slap, then the engine was not build to specification. Piston slap occurs in older engines where the bore is wearing and the piston's undersize, only the rings keeping it in compression.

When overboring an engine it is done in generally 20 thou steps, 0.020", 0.040" and 0.060", replacement pistons are also matched at the same increments. When boring an engine the new pistons are measured and these are what the jig borer uses to gauge the correct bore and tolerances. Not all sets of replacement pistons are machined to the engines build tolerances, they all vary a small amount.

A good case of piston slap is where someone has rebuilt a tired engine and fitted new rings and not measured the bores using telescopic bore gauges. It could be undersize thus requirung a rebore and a new set of pistons.

A sign of worn bores and a rebore required is when removing the pistons and seeing signs of scuffing on the skirts of the pistons, coupled with a step in the top of the bore jusdt below flush. But the proper way of doing this is to measure everything and seeing if the dimensions are within the tolerances of the engines blueprint.

[lukiep160]

Originally Posted by rbull51

thanks for the info, the noise isnt really that bad but because it is mine & you get used to what things make certain noises i notice it. when i change gear at 3000rpm you can hear it for a second, its like a a tappety noise but really fast. unless you was told about it it wouldnt be that noticable. also when its under load below 3000rpm it sounds a bit different to what it should.

it is very unlikely to get worse, i have yet to see one fail because of it.

Stamford, it is very easy to diagnose piston slap on the k series as it make a very distinctive noise a trained ear would only need to start it

[stamford]

I read your post after posting mine, seems the K-series is not your average engine build from your knowledge of them. I have based mine on older engines and experiences.........................I'll get me coat

[tcb 180]

Pistons are usually graded from new as well. Oversized varieties being available to account for any machining imperfections when cylinders were bored. But I agree. If piston slap was diagnosed it wouldn't have gone away at all. This does seem a rather antequated diagnosis for a modern engine. Defo get a second opinion.