I have a broken Spark plug in a 2SZFE engine. Oil level is not changing. Does it means the piston is safe?

There’s a spark plug part in the first cylinder because previous owner chose a low cost model not adapted to higher temperature of lpg. There’s a sealing problem on exhaust but not on admission.

The cylinder head might be damaged, but since there’s no specific sound (the engine can run on 3 cylinder) and the oil colour doesn’t change and the oil level doesn’t change, is it safe to assume the cylinder or piston ring don’t need to be replaced ?

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    Why don't you just fix the problem now, before it gets worse over time?
    – kokobill
    Commented Dec 5, 2018 at 12:38
  • @kokobill the repair shop want to make me an additional 150€ for inspection of the piston while a more expansive repair shop don’t think it’s required. Commented Dec 5, 2018 at 12:49
  • The problem is that a piston with a scratch in the crown from the bits of broken plug bouncing around will work just fine - until the day when it breaks into two pieces, one of which comes out of the side of the engine block. It's your call whether you want to pay 150€ "insurance" against that.
    – alephzero
    Commented Dec 5, 2018 at 12:57
  • @alephzero I am wondering if it is possible the broken spark part could just get aspirated in the exhaust poppet valve by just breaking at the right moment. I have an insurrance on mechanical damages. But it only pays repairs if the engine can’t run anymore (since the engine can work on 3 cylinder this isn’t the case here). Commented Dec 5, 2018 at 13:00
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    You can definitely get a bore scope down the spark plug hole. Commented Dec 5, 2018 at 13:22

1 Answer 1


You can't really assume anything regarding the state of the internals until you get it open and inspected.

If the engine has been run for any length of time without spark there could be significant damage to the piston and ring from being repeatedly covered in unburnt fuel. And of course any impacts with bits of the broken plug (even relatively small flakes) could have done significant damage also.

  • I forgot to say that the engine run on gas. So I don’t think unburnt fuel is a problem. I also wonder if it’s possible the broken spark part could just get aspirated in the exhaust poppet valve by just breaking at the right moment. Commented Dec 5, 2018 at 12:57
  • @user2284570 Firstly it doesn't run exclusively on lpg - there will have been a good amount of fuel sloshed through there each time the engine was started. Secondly if the bit of the spark plug was small enough to pass through the exhaust valve and if it broke off at just the right moment I guess that's possible but I have to say it's not very likely. If any remained (or if it broke off bits of the exhaust valve on it's way past for example) then you'll have had bits of material grinding around inside the cylinder for all the time the engine has been running since. Commented Dec 5, 2018 at 13:09
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    @SteveMatthews Yeah could well be damage to the bore etc. I imagine the first thing a garage will do would be to take a peek with a borescope, if shows a complete mess in there you can at least save the time and money of opening it up and go straight to either a replacement engine or replacement car. Commented Dec 5, 2018 at 13:22
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    @SteveMatthews agreed... if nothing else unburned LPG will be doing the same to the cat as unburned petrol. Even a closed-loop system won't be able to account for the loss of the spark on the cylinder. I expect that catalytic converter has been having a very hard time! Commented Dec 5, 2018 at 13:33
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    @user2284570 You drove 3000Km after part of the plug broke off? The state of the lambda probe will be the least of your worries. Unless you are an exceptionally lucky person the next stop for that engine is going to be the scrapheap. Commented Dec 5, 2018 at 13:35

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