Can someone identify this noise? - JeepForum.com
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post #1 of 7 Old 08-18-2017, 04:20 PM Thread Starter
wranglerbangler
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Can someone identify this noise?

https://youtu.be/qfmtLquw6QI

this started happening after i made adjustments to my carb a few days ago. the sound is always there and never really goes away. It sounds like something isn't spinning smoothly (a bearing for the belt?) but someone told me it sounds like a cylinder not firing?

4.2l with weber carb.

42k on engine
187k on body and trans

recently replaced plugs wires rotors cap oil..

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post #2 of 7 Old 08-18-2017, 08:40 PM
RIPSAW
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Man, that is bad. Before you run it anymore, make sure the fan clutch bearing is smooth and snug. Get you a two ear Harbour Freight stethoscope and carefully probe front and back of the alternator and the rest of the spinning belt driven items. You should easily be able to isolate the sound. Stay away from the fan. Eye ball it while not running by turning it to make sure you do not get too close.

Drop the belt off if that does not isolate it and turn each pulley.

Start at number one cylinder on the wires and go from there to make sure you have them on correctly. Know you can switch a 4 and it will still run and sound terrible.

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Last edited by RIPSAW; 08-20-2017 at 04:27 PM.
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post #3 of 7 Old 08-20-2017, 12:41 PM
Drednot
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Yeah, the first thing I would look at is that top idler pulley. They can sound catastrophic when they go bad. Id also say take the belt off and check

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post #4 of 7 Old 08-20-2017, 02:34 PM
Chrisnvegas
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Check the harmonic balancer pulley. The rubber isolator deteriorates and the pulley section slides back and makes contact with the timing cover.

The carb adjustment could be a coincidence.

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post #5 of 7 Old 08-20-2017, 02:50 PM
Luuca
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All great responses, but there is an order with which you should tackle this to save you time and money.

1. Get a two-eared mechanics stethoscope as was stated. Point it at (or touch it to the mounts for the AC condenser, the Idler Pulley, the Power steering pump, the water pump and get under there and hold it close to the harmonic balancer to see if you can determine which unit is giving you the sound. Be VERY CAREFUL while using the scope near moving parts for gawds sake. go slow and carefully.

2. Once you figure out which part(s) it is, if it sound slike the water pump - replace the water pump. If its the Idler or the power steering pump, get a spray bottle with water and stream spray that part with water where the bearings are (do not try on the ac compressor nor the harmonic balancer as they won't quiet down with water if they are making the noise, replace them.) if they quiet down when wet, you confirmed the bearings need replaced or the unit does.

If you cannot determine which, if any of the serpentine system is making the noise, remove the belt and run the engine from a cold start (remember no water pump with no belt) and see if the noise is gone with no belt. If no belt = no noise, manually turn each item (except harmonic balancer) to see if you can feel or hear a crunchy/squeaky sound. If you do - replace that unit, if you do not, check the timing cover along the edge of the harmonic balancer for any wear marks. sometimes the harmonic balancer will become loose and rub on the timing cover making a gawd awful metalic noise like yours. If everything checks out, replace the belt and go to step 1.
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post #6 of 7 Old 08-20-2017, 04:38 PM
RIPSAW
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It's interesting how some of these YJ Jeeps are depending on year and options. Not sure if my motor is original and with no AC, just has the alternator mount and the open space on top with empty bolt holes for the AC compressor. Hard to believe it came that way. (Maybe it's just me use to Japan tidying up things?) What is interesting about mine is what tensions the one serpentine belt. What looks like a tensioner and actually spins only barely touches the belt. Not even sure why it's there. Not sure if it's the alternator or the power steering pump that is actually the tensioner.
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post #7 of 7 Old 08-20-2017, 05:38 PM
Drednot
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Quote:
Originally Posted by RIPSAW View Post
Not sure if my motor is original and with no AC, just has the alternator mount and the open space on top with empty bolt holes for the AC compressor. Hard to believe it came that way. (Maybe it's just me use to Japan tidying up things?) What is interesting about mine is what tensions the one serpentine belt. What looks like a tensioner and actually spins only barely touches the belt. Not even sure why it's there. Not sure if it's the alternator or the power steering pump that is actually the tensioner.
Yeah, a lot of them came stock with the A/C bracket empty. The systems were commonly dealer installed.

The idler pulleys are used to either eliminate long runs of unsupported belts, and/or increase contact between the belt and pulley. There needs to be more than 90 degrees of contact. 180-270 degrees is preferred. It would also direct the belt under the upper radiator hose and then up and around the A/C compressor if installed

The power steering pump should be the tensioner

91 YJ Sahara, 4.0L, AX-15/NP231, D30/D35@3.07
12 Cherokee 4x4,3.7L,42RLE/MP1522, D30M/8.25@3.73
Emission test=YES
"Non Vi Sed, Arte"
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