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Old 05-09-2013, 10:03 AM   #1
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Knocking sound when turning over

Newbie here with a problem. Yesterday while starting my 1990 YJ I had a few loud knocks while turning over and went away once the vehicle started. The noise never came back until I stopped and restarted the Jeep. I continue to have a few knocks when I start it and it seems to be louder/worse the longer the time period is between starts? Any ideas what this could be, thanks in advance for responses...

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Old 05-09-2013, 10:20 AM   #2
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Hate to be the bearer of bad news but a loud knocking sound from the engine is usually a blown cylinder. As to why it goes away after starting that seems strange a blown piston would be a loud knocking constantly and louder as you accelerate because the rod is just spinning and causing damage.

If the loud knocking sound is coming from the starter it could be your lucky day and that you only need to replace the starter get someone to assist you and listen closely to wear the noise is coming from have them rev the engine if noise truly goes away after start up and not being muffled by loud radio or bad hearing on your part then you may only have a starter issue. If the loud knocking goes away and is replaced by a muffled ticking that goes up and down as you rev the engine then you have an engine problem and it is loud at first because all the oil is in the drain pan and not circulating through the engine.

How many miles on the engine?

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Old 05-09-2013, 10:31 AM   #3
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Thanks SaharaGreen...I don't believe its a blown cylinder as it completely goes away after its started. I am going to have a buddy listen to where the noise is coming from later this afternoon. I inspect the starter this morning and looks like the bottom starter bolt is missing! Ant idea on what size that may be and could this be the potential problem? My 1990 YJ has 96,000 Miles on it. Thanks for your help!
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Old 05-09-2013, 01:26 PM   #4
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I was going to say loose starter...

If it only knocks when cranking, has to be in the starter. If it knocks while idleing then its internal.

Pull out the top starter bolt and take it to a parts store, tell 'em you need another just like it and use threadlocker. (Locktite) Go with blue locktite if you ever want to get the starter out again in the future.
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Old 05-09-2013, 01:59 PM   #5
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Thanks Chris, will do!!
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