Can I reuse this piston? (pic/video)

[gaspaccio]

Hello,

As it's 50/50 around me, I'm asking you this question.
On my hdi 1.6 90, while trying to change the injector screws, a small piece of one of the torx heads broke off and fell on the piston through the well hole. I didn't know this, so I drove the vehicle...

As I drove along, there was a clatter, but no loss of power, no smoke, normal behavior.
I disassembled the engine and here are the marks left by the torx head below.



In my misfortune I was lucky because the head only made a few impacts before planting itself in the piston (I removed it). The cylinder has no impact or scratches, it's normal.

So my question is, can I continue to use this piston?
I've already put a lot of money in the engine disassembly, purchase of parts (belts, gaskets, screws, chain kit, thermostat...) and I can't afford to buy a new piston, rings, bearings, new tools....

I was told that aluminum hdi pistons are thick enough and that this won't be a problem.
But of course that's just theory. I know that ideally they should be replaced, but...

Do you have any experience on this to share with me please, should it be ok according to you?

Videos :



Thank you very much for reading.

[Gibbo2286]

It's a gamble but one I would take if it was my car.

[gaspaccio]

It's a gamble but one I would take if it was my car.

I like gambling minds
I'm thinking of reusing it, the only concern I have is the little crack between the 2 stars at the bottom right. It seems to be just a scratch on the surface though.
On the other hand replacing the piston is a potential source of problems (unbalancing the crankshaft, bad rings mounting, scratching the cylinder inside, etc... Plus the price.

[CitroJim]

Reusing it is a big gamble in my opinion. I'd not as I'd worry those little cracks could grow and especially those out toward the ring land could be potential stress-risers and may lead to the piston breaking up.

You should be able to replace the piston without worrying about balance or ring problems.

I would..

Is there any marks/damage on the cylinder head?

[gaspaccio]

Reusing it is a big gamble in my opinion. I'd not as I'd worry those little cracks could grow and especially those out toward the ring land could be potential stress-risers and may lead to the piston breaking up.

You should be able to replace the piston without worrying about balance or ring problems.

I would..

Is there any marks/damage on the cylinder head?

Thanks for your help Jim. Yes the points you raise are concerning me to be franck. That's why I posted, in order to know if some of you had a similar experience. For the moment I only get advices, but it's good too
The head had 3 marks, 2 not concerning, and one a bit more but not alarming though since the valve seal is intact and after a leak test everything is fine. Here is a pic. I won't replace the head.

[moizeau]

I'd be concerned about 2 things there. The indentation next to inlet valve, How is the valve seat? The other is how close the indentations are to the outside of the piston crown, is it still round or deformed? The crack or score wouldn't concern me. A lot of old Kwak heads have a crack between the spark plug hole and valve seat, no issues.

[gaspaccio]

I'd be concerned about 2 things there. The indentation next to inlet valve, How is the valve seat? The other is how close the indentations are to the outside of the piston crown, is it still round or deformed? The crack or score wouldn't concern me. A lot of old Kwak heads have a crack between the spark plug hole and valve seat, no issues.

Thanks for your help Moizeau. When you use the term "indentation" and I translate it in french (my native language) it is the same term and I can't see exactly what you mean here, for the inlet valve I think it's a bit of dirt on the pic, I poor some water on top of each valve and I didn't have any leakage. I hope it answers the question, if not please don(t hesitate to tell me more.
Same thing for the piston indentation I am not sure if I understood correctly but to me everything is round, and the cylinder has no scratch. I'm going to make a leak test (poor some oil on top of the piston and let it rest for the night) to see if everything's fine

[moizeau]

And a 3rd. The valve must have caused 2 of those marks so although it's OK on a Leak test I would take the valve out to confirm the condition of the stem. Also check the corresponding cam lobe.

[moizeau]

Salut, use diesel for a leak test, not water, the mark I was referring to is on the edge of the upper inlet valve but I can't zoom in on your photo. Hopefully it is dirt and not damage.
i

[gaspaccio]

And a 3rd. The valve must have caused 2 of those marks so although it's OK on a Leak test I would take the valve out to confirm the condition of the stem. Also check the corresponding cam lobe.

Visually the valve fits perfectly into its place, so I've deduced that the stem and everything inside is straight. It was a tiny screw head I dont think it would cause problem against the hard metal of the valve but you're right, ideally it should be checked. I don't have the tools to remove the valves...

[gaspaccio]

I was thinking about something, concerning the impacts.. calamine should plug these holes quite rapidly after a few hundreds km, no?
Before taking the pics I cleaned a bunch of calamine, the impacts were less visible with calamine on top of them. And it was just after an hour or 2 using the vehicle, so imagine after a few hundred kilometers the impacts should be totally covered with rock solid calamine, no?

[CitroJim]

I'd be very surprised of that valve was sealing....

[Steve Walsh]

There is no way I would use that piston, and wouldn't consider running it without removing the valves from that cylinder for a close inspection. You can't see microscopic damage that may have been caused and it might cause engine failure in the future, Do the job once and do it right.. Just my opinion with 47 years of engine work in my experience bank.

[moizeau]

If it was my engine I'd another leak test with diesel or central heating fioul or petrole (not petrol, but you know what I mean bieng French) whichever is easiest for you to get hold off. The reason to use the above is that they are excellent seeking agents and don't evaporate. While checking the damaged part, fill the other combustion chambers as well. The reason for this is strictly for a comparison between the 3 'good' ones and the damaged one. I would then remove the valve to check for damage to the outer circumference of the seat and make sure the valve moves freely in it's guide. By removing the valve collets you can also now check the head of the stem. Ideally the valve should be checked in 'V' blocks for straightness with a dti. If all of the above is good I'd relap that that valve in (may as well, belt and braces) and then replace it's valve guide seal as this may have been damaged to some extent when removing and replacing the valve, also it needs to be removed anyway to ensure the area is totally clean of lapping paste. That should have the head covered.
Now onto the piston.If possible (I don't know this engine) remove the piston by removing the sump. Check for any deformation around the outer circumference of the piston crown. Also check the piston rings, especially the top one for free movement. The impact on the crown could have closed up part of the piston ring groove. If any damage is found on the edge of the crown but the ring grooves are OK the damage can be cleaned up will a fine file and emery paper.
Finally check the cam lobe for visual damage.
The above sounds a lot but is cheap to do, the main expense is time. If you haven't got a valve spring compressor take the head to a local garage. It will take minutes to remove the valve so should only cost you a drink.

Bon courage

[CitroJim]

Very good advice Pete