Engine Piston Hits # 6 Spark Plug

8:06 am Mistubishi, noises, ProVision, Reader Questions


©DenLorsTools.com  Summary: Question from reader about a spark plug being hit by the piston. It may be that the piston is not what’s hitting the sparkplug. There are a lot of images on-line showing broken valves which can cause the spark plug to be hit, which is much more likely. 

Readers Question; I have a 2003 Mitsubishi Montero that we are having trouble with. The piston keeps hitting the #6 spark plug. Why would this keep happening??? This started the same time it started making a loud ticking noise. We were told it was the lifters, had them replaced, didn’t fix. Need help!!!   Desire

My Answer; Desiree, Mitsubishi’s do have a common problem with faulty lifters, so it’s not surprising that you were told that was the cause. If there is a weak lifter, most of the time the ticking will subside when the idle or RPM’s (Revolutions Per Minute) are raised. The problem that you have sounds much more serious due to the fact that the spark plug is being struck. Assuming the correct spark plug is installed, the cause could only be something LOOSE in the cylinder.

Possible “loose pieces” could be a broken valve, valve seat or guide. Although mechanical parts can break at anytime; Typically what can happen is the lifter can fail first, then if continued to be driven the valve spring can break and then the valve, seat and guide are likely next to go next. The cylinder walls can be scored and ultimately damage piston rings, all of this can cause loss of compression, smoking out the tail pipe etc. One way to inspect inside the cylinder without removing the head is with an inspection borescope. This can help to determine if the engine is worth tearing down and repairing or if it’s time to consider options for a new, re-manufactured, or used engine. Click the image below to see details on one of our fiberoptic bore-scopes used for inspection of cylinders – accessed through the spark plug hole.

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