S2000 Under The Hood S2000 Technical and Mechanical discussions.

Compression and broken spark plug

Old Apr 24, 2019 | 09:07 AM
  #1  
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Default Compression and broken spark plug

Hello,

my AP1 lost nod and prong of the spark plug in cylinder one. I have checked the oil and filter and no metal flakes are present. The plugs are less than 2 years old and 15,000 miles. The compression is as follows:

cylinder 1 200
cylinder 2 210
cylinder 3 210
cylinder 4 220

I am going to rent a bore scope tonight. What is other’s experience with a rebuild?

Here is a picture of the piston head

Ouch

Last edited by Toothlessjoe; Apr 24, 2019 at 03:33 PM. Reason: Update
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Old Apr 24, 2019 | 09:21 AM
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Compression looks ok. Id Inspect the bore for any gouges for some peace of mind. May have got lucky and piece blew out the exhaust before it had any chance to harm anything.
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Old Apr 24, 2019 | 12:09 PM
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And be sure to torque new plugs down properly. Original spec was something like 13 lb/ft, which proved inadequate. New spec is higher, and I believe Billman says use 24 lb/ft.

Loose plug causes detonation and tip breaking off. Don't tempt fate twice.
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Old Apr 24, 2019 | 03:45 PM
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Default Update

Originally Posted by Car Analogy
And be sure to torque new plugs down properly. Original spec was something like 13 lb/ft, which proved inadequate. New spec is higher, and I believe Billman says use 24 lb/ft.

Loose plug causes detonation and tip breaking off. Don't tempt fate twice.
I followed the service bulletin from NKG. So, if they were loose other’s shouldn’t follow it.
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Old Apr 24, 2019 | 04:53 PM
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What is NGK's recommendation number?

Thanks!
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Old Apr 24, 2019 | 05:03 PM
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Well that's not good I dont know what id do in this case. My inclination is to dump the oil and just run it and cross your fingers you can get some good remaining mileage out of it. You will get some indication of engine health based on your future oil usage and other signs. but damage is already done. Inst going to offer anything to rebuild now vs down the road unless you discover the motor is drinking a quart of oil ever 200 miles and cant stand it. Compression is down a little off the others but not drastically - No more then some motors without this pitting damage. So im thinking just run it.

Last edited by s2000Junky; Apr 24, 2019 at 05:39 PM.
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Old Apr 25, 2019 | 03:43 AM
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Could maybe remove cat and see if anything is in there.
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Old Apr 25, 2019 | 04:25 AM
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I've got to think that the cylinder walls were spared, or at least not damaged enough to affect compression. In a perfect world you don't want sharp edges on the pistons to avoid hot spots and detonation, so you could remove the head and polish the piston smooth. But over time the piston may be covered over by new deposits so the small dents might be covered, and the S2000 motor isn't prone to detonation issues. I'd say the tip has gone out the exhaust valves at this point in time as you have not found it.. I'd probably keep driving it barring any negative symptoms if it drives and sounds normal.
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