I recently put a new water pump and changed timing belt and pulleys. It ran for a while, then lost compression in #1 cylinder.Spark plug grounding electrode touched piston just enough to touch.


Asked by Nov 17, 2013 at 04:14 PM about the 2004 Jeep Wrangler SE

Question type: Maintenance & Repair

Is this a timing issue? Could the timing have been off just enough to cause piston to
hit grounding electrode on spark plug to bend it to touch positive electrode on plug?

7 Answers


As long as proper plug was installed I don't think so. But if its an interference engine and the timing is off. the piston could hit a valve and bend it into the end of the spark plug causing damage to the plug.

Best Answer

that does not sound like a good thing if your piston is hiting your spark plug that generaly means you have a bad piston rod or you have the wrong spark plugs. the piston should not be touching the spark plug at all as the piston rod only goes so far and its set so it does not go that far. if you heard a loud thunking noise before it did this thats the confirmation that you blew a rod or a valve possibly a piston ring. i can't be sure on this as i don't deal with jeeps so hoping its not any of what i said. do your self a favor open your oil pan and check for any metal debree if theere is then you threw a piston rod or a ring


what is an interference engine? This is the original engine, Jeep only has 55,000 miles. No loud thunking noise was noticed. It had been loosing power, was running a little hot so I parked , let it cool down and tryed to start it. It would try to run , but no more.


What size motor do you have? An interference engine means that the piston comes close enough to the valves(when the valves are open) to hit them if the timing is off.

1 out of 1 people think this is helpful.

Some jeeps do have them.

1 out of 1 people think this is helpful.

2.4 litre inline 4 cylinder


Ok here's what I have found and its getting confusing. Some trusted sites I use say that 2.4 dohc "vin 1"put in jeep wranglers in 2003-2004 were interference engines. Other sites say that the 2.4 that jeep got from Chrysler for these years was not an interference engine. So here's what I think. I think yours is an interference engine due to the damage to the plug right after a timing belt change. Now with an interference engine the piston can not hit the spark plug but it can hit a valve and bent it into the spark plug. Do a compression check. Hope this helps some.

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