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Old 08-26-2014, 11:30 PM   #1
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4.2 knock help!

So I recently built my 4.2 and the motor went together very well. I had the best rebuilder in town do the block and spec and get the parts. The motor is tight and felt great in the process of putting it together. Me and my dad who have put lots of motors together put it all together right. All bearings in right place and pistons (motor builder assembled) are in the right hole and the machinist/engine builder did the heads. I have 2500 miles on it and it's done great until the other day I noticed a knock and it's louder cold then quiets down as it runs. I am thinking it could be a scored piston from the piston heating and expanding before the block does or a really bad pre denting (firing before piston is all the way up) I know it's not a spun rod Bering because that would get louder as it warms up. What's your opinion on this?

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Old 08-27-2014, 02:20 AM   #2
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What oil viscosity are you running?

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Old 08-27-2014, 11:14 PM   #3
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20w-50 ... Only one with zinc for the flat tappet cam not to collapse. Told to run it by my machinist who builds motors as his job
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Old 08-27-2014, 11:27 PM   #4
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What lifters did you use?
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Old 08-28-2014, 01:10 AM   #5
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Quote:
Originally Posted by Milo22-243 View Post
20w-50 ... Only one with zinc for the flat tappet cam not to collapse. Told to run it by my machinist who builds motors as his job
What's he say about the knocking?
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Old 08-28-2014, 01:14 AM   #6
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What oil is he having you run. Rotella T?

If so, maybe try the 10w30. 20 w50 is a little stout for a new tight engine
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Old 08-28-2014, 10:48 AM   #7
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It's all stock lifters only after market is the .40 over pistons. Rest is stock parts. It's mid block knock with the mechanics stethoscope. Any other ideas what it could be?
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Old 08-28-2014, 08:56 PM   #8
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Fuel Pump arm?
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Old 08-31-2014, 11:45 AM   #9
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Replaced fuel pump after knock started. I thought it could have been that but wasn't
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Old 08-31-2014, 11:46 AM   #10
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Machinist said I probably scored a piston

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