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To continue with timing chain thread earlier this month...I replace a very old and worn out timing chain that had a ton of slop. The reason that I started this project was a loud tapping noise while idling and driving. The noise hasn't changed. I checked the rods while I had the oil pan off, didnt see any issues...checked the rocker arms for any slop and didnt see any issues there. It appeared that there wasn't any flat lobes on the cam as all the rocker arms moved the same distance. The one question I did have was maybe the timing chain might have jumped a tooth or so before I removed the old one and the cam might be out of timing with the TDC of the crank. I am not sure exactly how to align the cam to the crank. Does anyone have the Chiltons book for a 96 4.0 motor and maybe can give me some insight? Also, soes anyone have any other suggestions that might be causing a noise like this? Would an oil pump thats worn out do this? I can say this, before tearing into this, the oil pressure gauge at idle would run at about 40 lbs, and during driving it would jump erractically between 40 and 80. Any suggestions?
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Some say that if you listen to the little voices, you are open minded, if you answer them, you belong in a white padded room. I say, have a conversation!! -
I'd have to hear it, a hydraulic lifter that is gummed up or otherwise isn't sufficiently pumping up enough will cause a tapping noise, and it's very common. Another thing that can cause a sort of tapping noise is a loose or cracked exhaust manifold or burned out exhaust manifold gasket.
As far as measuring the movement of the rocker arms goes, valve lash is measured with a feeler gauge to be within a few .001" of a given tolerance. The hydraulic lifters in a your 4.0 are supposed to automatically adjust, so there is no means of adjustment on the rocker arms themselves. It's years since I've adjusted valve lash (back in the day it was a ritual for me), but .015" sounds about right for solid lifters--depends on the motor.holes = cowbell -
I had a tapping sound on my YJ 4.0 for a long time. I tried heavier oil and Restore for a long time to try to get it quiet. It sounded just like a loose tappet on a Chevy. I found that my exhaust manifold was split completely off where the front three ports come into the collector. All of the individual runners were cracked around the welds. When I replaced the manifold with this one http://www.ineedparts.com/auto-parts...-manifold.html Sound gone. The other characteristic of the 4.0 is that the exhaust manifold likes to back off from the block. Just reach in with a 9/16 wrench and snug it all up. The other thing it could be, if you can't find anything else is a bad bearing in your water pump. I've herd tapping, rumbling and even sounding like a coffee can full of marbles falling down stairs.God forgives, rocks don't
-sons of thunderComment
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I tried looking at the exhaust manifold from underneath the car to look for cracks, couldnt see any...but that doesnt mean that its not..as it is difficult to see the whole thing with it installed. When I get back on it tomorrow, I will try giving a turn on the manifold bolts. It sounds like the tapping is coming internally...but Im crossing fingers its a nanifold. Still to figure out is the mysterious oil pressure going from 40 to 80+ lbs while driving. Anyone think a bearing going bad internally might cause such a thing? The bearings that I havent checked are the main bearings.Some say that if you listen to the little voices, you are open minded, if you answer them, you belong in a white padded room. I say, have a conversation!!Comment
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Another thing I noticed while working on this the other day is with the distributor cap off and the #1 cylinder in TDC, the rotor was pointing well past the location of the #1 location on the cap. When I backed the cranked up maunally to align the rotor to the #1 location on the cap, it put the timing mark on the harmonic balancer back at about 40 degrees BTDC. That to me just doesnt seem right. I would think that the degrees where it fires at would be in the neighborhood of about 10 to 15 degrees BTDC. Does anyone know where it should be firing at in relation to the TDC?Some say that if you listen to the little voices, you are open minded, if you answer them, you belong in a white padded room. I say, have a conversation!!Comment
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The fun part about the 4.0 is that the distributor position actually controls the moment that your injectors fire. I still haven't figured out the tower/rotor relationship. 40 degrees does sound like a lot. I'll check my manual.God forgives, rocks don't
-sons of thunderComment
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Well after trying a few things, I tried retarding the crank position back to TDC with the rotor position at the #1 firing tower, actually the crank @ 18 degrees BTDC...not good. That definitely wasnt the noise source nor did the engine run worth a darn. So...I put it back to where it was originally, cleaned off the tools and put them away, grabbed a cold coke and hit the computer for a used 4.0 to drop instead.
Im thinking that I will rebuild the old one and drop it in my 69' Nissan Patrol. I need to get that vehicle up and running soon as well.:gun:Some say that if you listen to the little voices, you are open minded, if you answer them, you belong in a white padded room. I say, have a conversation!!Comment
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