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Old 09-03-2010, 11:46 AM
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Piston hitting spark plug...

If you have obvious signs of piston to spark plug contact (not detonation) what would be the main culprits and fixes associated with them in general?? No specific engine, just in general.

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Old 09-03-2010, 12:09 PM
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Piston to spark plug contact generally would give you an indication of to close of tolerance, BUT, too long of a reach on the plug would also.

Just a light touch on the plug can be overcome just by a simple head gasket change to a thicker gasket.
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Old 09-03-2010, 12:24 PM
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Wrong plug.

Mandatory indexing overlooked.

Some engine require surface gap plugs.
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Old 09-03-2010, 06:35 PM
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You would need to use a shorter reach plug.
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Old 09-03-2010, 11:31 PM
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could it be a more serious condition? Would valves be bent?
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Old 09-04-2010, 12:00 PM
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Using improper match of cylinder head to piston. Such as certain Edelbrock BBC style heads and GM or aftermkt dome piston. Or some of the Twisted Wedge style heads with wrong pistons.

Back in the day we had to "index" spark plugs in big compression Chevy's all the time..

Valve interference will show up as bent or worse valves.
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Old 09-04-2010, 02:52 PM
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Quote:
Originally Posted by Dajerseyrat
could it be a more serious condition? Would valves be bent?
No, valves would be bent from impact with the piston. If it's a new build with a big high lift cam and/or popup pistons it would indicate that the builder didn't check for valve to piston interference at assembly. If it's and old engine that used to run fine and suddenly developed bent valves then it was either;

- Over revved to where the piston got to where the valve was before the valve got closed, this would be the result of what's called valve float.

- Or the timing chain has stretched to the point where the valves are so far out of time they're still open when the piston gets to the top end of its travel and a collision occurred.

Bogie
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