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Old 03-17-17, 08:50 AM   #1
mayday1775
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Default What is this?

Changing my plugs and doing a compression test to check out a misfire we looked in the cylinder to check for piston damage and seen this. What am I seeing here? Also my plugs were gapped out to .045.
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Old 03-17-17, 09:04 AM   #2
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Default Re: What is this?

All I'm seeing is the valve relief cutout in the top of the piston (fingernail looking), which is normal. Is this what you're talkin about?

Other than that, MAYBE some carbon build-up, and depending on your mileage is also normal.
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Old 03-17-17, 09:07 AM   #3
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Default Re: What is this?

Quote:
Originally Posted by BootsJunkie View Post
All I'm seeing is the valve relief cutout in the top of the piston (fingernail looking), which is normal. Is this what you're talkin about?



Other than that, MAYBE some carbon build-up, and depending on your mileage is also normal.


I am looking at the small depression just to the left of that. 60k on the engine, plugs look nasty and gapped wide.
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Old 03-17-17, 04:40 PM   #4
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Default Re: What is this?

plugs are gapped way to far probably the source of the misfire, should be .028-.032

the piston top image shows a piston top with combustion marks/flame propagation

what were the compression results?

Last edited by blacknblue06STI; 03-17-17 at 04:44 PM.
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Old 03-18-17, 04:22 AM   #5
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Default Re: What is this?

Quote:
Originally Posted by blacknblue06STI View Post
plugs are gapped way to far probably the source of the misfire, should be .028-.032



the piston top image shows a piston top with combustion marks/flame propagation



what were the compression results?


I put new plugs back in at .030, there was so much more pep in the step of it now. The compression checked out at 107/112/110/110.

I couldn't believe how bad those plugs where when I pulled them, heck I can't believe it was running decent with that gap and carbon buildup.
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