Holes in pistons?

[chrisdc]

Hi everyone,
What would cause pistons to be holed on a Diesel engine? (2 out of 4) It's a Renault K9K1.5dci 70. Owner says he had a new turbo fitted about 1000km before this catastrophic failure. He also had new injectors fitted. I'm not sure when, possibly before the turbo. Apparently the engine is rebuildable but I'd be very reluctant to do this without knowing what caused the problem. It has been suggested that the injectors were incorrectly calibrated or that the boost from the new turbo was just too much for the old engine. It had done about 200,000km when it blew. What say you guys?
Thanks, Chris

[Mr2Mike]

Overfueling is usually the root cause of holed pistons in a diesel. Most often a faulty injector on common rail systems.

[chrisdc]

Mr2Mike said:

Overfueling is usually the root cause of holed pistons in a diesel. Most often a faulty injector on common rail systems.

Thank you Mr2Mike,

So it's possible one of the new injectors was faulty? Owner says original Renault parts were used. If one were to rebuild this motor, and the injectors were sent for specialist testing and passed; it would be ok to reuse them? Is there anything else to look out for?

As a matter of interest, when pistons are holed, does debris sometimes damage injectors and turbo's?

[Sardonicus]

Mr2Mike said:

Overfueling is usually the root cause of holed pistons in a diesel. Most often a faulty injector on common rail systems.

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[chrisdc]

Thanks, that does seem to be the general consensus. So I'll tell him to throw away the new set of injectors he had fitted last month and to fit another new set of injectors? And we can rule out faulty ECU, diesel pump, valve gear, calibration, maintenance, driving style, etc?

[Mr2Mike]

ECU and bad calibration can not be ruled out, though faulty ECU's are pretty rare and the injector calibration would have to be a long way out to cause this fault.

It would probably be worth getting the injectors tested by a specialist before condemning them, as I doubt they are cheap! A quick google shows http://www.testingcommonrailinjectors.co.uk/ can do this, and there may well be someone closer to you.

Debris from a melted piston could conceivably cause damage to the turbo so it's well worth visibly checking the turbine wheel, and the extreme temperatures that caused the hole won't be kind to the injector either. Obviously an oil change should be added to the budget as well.

Edited by Mr2Mike on Monday 26th August 20:39

[bearman68]

But what causes the injectors to go? Assuming the previous owner was truthful, it's likely the fuel pump is in trouble. When I removed the tank on mine (massively recommended) the bottom of the tank was almost completely covered in small metallic particles, shining nicely in the virgin torchlight.
For this reason it's well worth checking the tank.

[chrisdc]

Mr2Mike said:

Debris from a melted piston could conceivably cause damage to the turbo so it's well worth visibly checking the turbine wheel, and the extreme temperatures that caused the hole won't be kind to the injector either.

Edited by Mr2Mike on Monday 26th August 20:39

That's a very interesting point about the extreme temps. I've been looking at photos of melted pistons and it's not a pretty sight. I'll be careful to check the turbo too. Who knows how long the motor ran? - before it shut down.

[chrisdc]

bearman68 said:

But what causes the injectors to go? Assuming the previous owner was truthful, it's likely the fuel pump is in trouble. When I removed the tank on mine (massively recommended) the bottom of the tank was almost completely covered in small metallic particles, shining nicely in the virgin torchlight.
For this reason it's well worth checking the tank.

Thanks for the suggestion, I've been doing some reading on the subject of burnt pistons in Diesel engines, on the net and apparently petrol in the diesel could also cause this - so draining the tank will be a good idea on those grounds alone. It would seem EGR related problems and exhaust problems can also contribute to this type of failure. Remember the turbo had just been replaced. Perhaps the old one leaked oil (and maybe some debris) into places it shouldn't go.

[bearman68]

Or maybe pump failed, causing injector failure, causing the oil to go bad (diesel in the oil), causing the turbo to fail, and causing holes in the pistons.
TBF the injectors are the easiest thing to test - crank it over and look at the decline in fuel pressure with an oscilloscope - Should be about 10 seconds, and I'd be willing to bet it's nearer 1s on your engine. (ie system is incapable of retaining pressure).

Mind you I'm only guessing and not trying to be argumentative.

[chrisdc]

bearman68 said:

Or maybe pump failed, causing injector failure, causing the oil to go bad (diesel in the oil), causing the turbo to fail, and causing holes in the pistons.
TBF the injectors are the easiest thing to test - crank it over and look at the decline in fuel pressure with an oscilloscope - Should be about 10 seconds, and I'd be willing to bet it's nearer 1s on your engine. (ie system is incapable of retaining pressure).

Mind you I'm only guessing and not trying to be argumentative.

Every suggestion is worth checking out. The cost of repairing this engine will be considerable to say the least. I do have an oscilloscope by the way.
My Volvo is thinning it's oil due to a problem with the DPF regen control system it uses. Fortunately these Kangoo's don't have a DPF but apparently some diesel pumps can fail in a way that allows diesel to get into the sump.
I'm guessing this guys problem was as you suspect, the end result of a series of failures.