Piston /Head Damage

[debaron]

Just noticed some marks in the crown of one my Rover V8 4.6 pistons - looks like someone has taken the corner of a chisel blade and knocked 5 or so sharp depressions (0.5 mm deep) into the metal. Looking at the cylinder head, it has corresponding marks and protrusions!!! Don't have any pics but will put some up later

What has caused this? One of this liners was known to have leaked a bit but not sure if it was this one. Rest of the pistons are all ok.

Have looked at water damaged piston pics but this doesn't look the same - looks as if something small and metallic has got into the cylinder during the engine cycle!

Ryan

[itiejim]

Sounds like some marks from pre-ignition.

[Boosted LS1]

There was a similar thread recently and the conclusion was that it was caused by a spark plug electrode which had fallen from the plug. May also be detonation related but a pic would be needed for a diagnosis.

[debaron]

Boosted LS1 said:

There was a similar thread recently and the conclusion was that it was caused by a spark plug electrode which had fallen from the plug. May also be detonation related but a pic would be needed for a diagnosis.

Thanks guys- Yeah that sounds about right - ill put a pic up as soon as I get back to the garage. What's the prognosis? Replace piston?

R

[ian_uk1975]

Sounds like det. Saying this with the caveat that I haven't seen a pic, but you could probably get away with smoothing the edges off the dings in the piston crown (same for the combustion chamber) to prevent hot spots.

[debaron]

OK guys - pics as follows!

Having a good look at the spark plug reveals it has completely lost it's electrode as Boosted said.

Thing is - it seems to have got into some of the other pistons? Is that possible?

Bearing this in mind shall I keep the pistons and just smooth them off or replace?

[Boosted LS1]

You could smooth off and deburr. As for the electrode, things travel up the inlet tract and do a tour of the cylinders before finally being spat out of an exhaust port. It's quite common.

[Pumaracing]

If the top rings are still free in their grooves then the pistons will be fine. It's very minor damage. However check that the valve seats are still ok and that no valves are slightly bent.

[debaron]

Pumaracing said:

If the top rings are still free in their grooves then the pistons will be fine. It's very minor damage. However check that the valve seats are still ok and that no valves are slightly bent.

Cheers guys thanks for taking a look - I'm not using the old heads - got new stage 3's on the way The pistons, rods, block and crank were reused and new top hat liners with new rings and bearings all round.
I'm sure it will be all fine but fingers crossed anyway!

Ryan