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Old 07-10-2011, 12:43 PM   #1 (permalink)
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4.0L engine noise

Have a 4.0L which I got in a cherokee out of a scrapyard, today I started it and is was working perfectly, after about 10 min on idle I revved it up to ~5000rpm and it started making this noise, even on idle you can hear it but as you rev up it it increases.

YouTube - ‪Weird jeep 4.0 "knock"‬‏

Dont know where to start looking for the problem so any help is very well welcome.

Thanks
James
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Old 07-10-2011, 06:05 PM   #2 (permalink)
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Id start with the valvetrain. have you pulled the valve cover off yet? It sounds like a valve to me, could be a broken rocker, bent pushrod, fucked up lifter, or you screwed up a valve.
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Old 07-11-2011, 08:51 AM   #3 (permalink)
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It could also be a collapsed lifter.
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Old 07-11-2011, 11:30 AM   #4 (permalink)
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it sounds like a wrist pin or a lower bearing knock to me...... drain the oil and see if there is any silver or gold flakes in the oil
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Old 07-11-2011, 01:31 PM   #5 (permalink)
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5k rpm under no load? Not really good for a very long crank and flat tappet motor.

I'd also go valvetrain, lifter or rocker.
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Old 07-11-2011, 03:19 PM   #6 (permalink)
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Like others have said. Pull the valve cover and drain the oil.
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Old 07-11-2011, 05:36 PM   #7 (permalink)
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Quote:
Originally Posted by SCRAPPY#1 View Post
it sounds like a wrist pin or a lower bearing knock to me...... drain the oil and see if there is any silver or gold flakes in the oil
Could be. But when my 401 decided to freeze up a wristpin, the sound was much deeper...sounded like a main or rod bearing. This sounds more at the top end to me

Do a compression test, wet and dry. Check for burning oil in your exhaust, pull plugs and look for fresh oil.......just pull the damn valve cover and start there
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Old 07-11-2011, 09:49 PM   #8 (permalink)
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will do so after work, thanks for your help guys. Ill post up if I find something.
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