I was performing a leak down test on a chevy vortec 4.3L V6.

In order to find TDC on the #3 cylinder, I stuck a screwdriver down the spark plug hole and slowly turned the crank pulley with a wrench. My assistant was supposed to alert me when the screwdriver reached the apex. However, they missed it and somehow the screwdriver got stuck/pinched. I noticed the extra resistance almost immediately and reversed the engine slightly and freed the screwdriver.

Is it possible I did any damage to the engine with the screwdriver?

  • 1
    Theoretically possible, but highly unlikely. The engine would have to be running when it happened, like when a valve destroys an engine. I once dropped a piston on hard concrete and it didn't affect the engine at all once re-assembled. The answer below by XC Source is very thorough, but I wouldn't lose any more sleep. – Carguy Dec 29 '20 at 11:35
  • Next time you try this, use a straightened coat hanger. If you support the coat hanger wire at a good angle, it won't accidentally bind. You can even do it as a one-man job if you check it after each small movement. Add a mark with a felt marker. – John Canon Dec 30 '20 at 3:23

Yes and no, with blind guess your piston is usually made from composite aluminium, and a screwdriver is usually hardened steel. You can guess which one is harder.

If the piston just gets a small scratch then it is ok (usually), and most likely your spark plug hole will dented.

But the chipped part of the piston (if) could damage your engine further.

The cheapest way to get the chipped part or just to make sure it doesn't have any strange part on it:

  • Open the spark plug, all of it.
  • Remove the injector (nozzle) all of it.
  • You can remove your exhaust (but it will make a mess)

Start the engine. The chipped or the trash should be out from the nozzle hole or exhaust.

If you are worried the chipped part is large and will damage your engine while starting it:

  • blow with compressor, or
  • remove the cylinder head (it's the only safe way to do it) and check it carefully.

If scratching the cylinder wall (piston cylinder / piston liner) the symptoms:

  • A lot of smoke usually white (burning oil)
  • Loss of compression (will make the loss of power and your fuel consumption increased)
  • Loss of power
  • Heat problem
  • Loss of oil because the burning oil

But all of that could be none because the piston ring maybe still make it tight enough to close the scratch (still on tolerance).

To check if there is a loss of compression:

  • Check your service manual or your car spec how much your engine compression (in bar or psi, not the compression ratio).
  • Remove all spark plug.
  • Install Cylinder Compression tester kit. Like this from AMAZON.
  • Check the compression from the suspected cylinder. (crank the engine and see the max pressure)
  • Compare with the other cylinder. Or compare with your specs.

So if your suspected cylinder has less pressure than the other, that likely needs service.

  • What if the screwdriver scratched the cylinder wall? – James Dec 29 '20 at 22:41
  • you will be scratch your head :D because you need to change the cylinder liner which is take everything out :) – Cubic273.15 Dec 30 '20 at 3:45
  • What symptoms would I experience if the cylinder wall was scratched? – James Dec 30 '20 at 6:28
  • the symptom could be burning oil (a lot of smoke), loss of compression, loss of power, heat problem. But sometimes you didn't see any difference because your compression ring (piston ring) still tight enough and only minor smoke that hard to notice the difference. – Cubic273.15 Dec 30 '20 at 7:28
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    @james check it again my answer in last section – Cubic273.15 Dec 30 '20 at 7:43

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