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post #1 of (permalink) Old 02-28-2002, 08:50 AM Thread Starter
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258 Engine Noise

I need your help to nail down a strange noise in my engine. My 258 runs great both at idle and during acceleration. The only problem is I've started hearing a screeching metallic type noise when a load is put on the engine or at the top of 2nd-4th gears. At idle or cruising, no noise. The noise sounds like a bunch of tiny bolts rattling around in a coffee can.

I've fiddled with the timing to try to fix it. It's timed at 9 degrees before TDC and when I retarded the timing a few degrees, the noise actually got worse. When I advance the timing a few degrees, I run into spark knock/detonation.

Since the noise only shows up under load, I'm pretty convinced it's internal. Does anyone have an idea of what this might be?

TEXAS1AL

84 CJ-7; 258 I6; Restored-to-Stock Condition, TR Ignition Upgrade
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post #2 of (permalink) Old 02-28-2002, 08:55 AM
 
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Re: 258 Engine Noise

Are you sure it's the engine? Mine was making a noise like that under load and it was the t/c shifter handle. I replaced the little rubber thing at the bottom of the shifter and no more noise.

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post #3 of (permalink) Old 02-28-2002, 09:16 AM
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Re: 258 Engine Noise

A screeching usually comes from the accessory drive belt slipping, but it will be related to engine speed, not load. If it's still there at the top of 2nd when you back off the throttle, it's the drive belt. You should also hear it when stopped by revving the $hit out of the engine. Check the tension and look for a glazed shiny cracked appearance on the drive surface.

Another possibility is broken damper springs in the clutch plate. That can produce a high-pitched rattling under certain loads. Try driving it with the transmission cover off to see if you can identify where it's coming from. That problem might be made worse by retarded timing causing a little more power-pulse vibration in the crankshaft.

One more hard-to-find underhood rattle is the heat riser valve on the exhaust manifold. If the bi-metal spring is weak and the shaft and bore worn, you can get some strange rattles.


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post #4 of (permalink) Old 02-28-2002, 09:55 AM Thread Starter
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Re: 258 Engine Noise

Thanks Guys, I'm pretty sure it's not the belts as I replaced them 2 months ago and I don't have an accessory belt, only a power steering and alternator belt. Although, the noise slightly reseambles a worn fan belt, at high RPM while sitting still, there is no noise present.

The transmission is a suspect, but as far as I can tell, the noise is from the engine. Where is the exhaust manifold valve that was mentioned, near the hot air furnace?

TEXAS1AL

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post #5 of (permalink) Old 02-28-2002, 10:09 AM
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Re: 258 Engine Noise

Don't rule out belts because they were recently replaced; you might not have gotten them tight enough. When I said accessory belt, I meant water pump-steering pump-alternator-fan belt (real Jeeps don't have an AC compressor).

The heat riser is under the carb at the junction of the exhaust pipe and exhaust manifold. The spring is in front, the weight in back. Wiggle the weight with your finger. It should move freely, but not enough to rattle around.

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post #6 of (permalink) Old 02-28-2002, 10:32 AM
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Re: 258 Engine Noise

Check the bearings in your alternator. Mine is making a similar noise to what you described. I know it needs a rebuild but it still works!

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post #7 of (permalink) Old 02-28-2002, 10:55 AM
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Re: 258 Engine Noise

My altenator berrings squeeled too, but that was when I started the motor and when I took off - not when I got it up to speed.

If your motor has been rebuilt it could be all the extra nuts and bolts in the oil pan that were left there by the whoever rebuilt it! That's where I put them so when I finally find out where they go I know where I last put them!

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post #8 of (permalink) Old 02-28-2002, 11:08 AM
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Re: 258 Engine Noise

Excuse me Jim, but real jeeps DO have AC Compressors...but we use them to air up our tires and run our lockers...(no flame, just ragging on ya bro).

I have had rotten luck with fan belt. Every new one I bought makes noise. You can elimanate it by using a bar of soap and letting it rub against the belt while running for a couple of seconds. If the sound goes away, its the belt. If not, then keep looking.

I fixed one noise on mine that was caused by the trasfer case shifter. There is a rubber grommet on the shifter that keeps is from rattling like hell. You can tell if that is it by putting your hand on it when your getting the noise.

How many miles on the engine?

John...
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post #9 of (permalink) Old 02-28-2002, 12:15 PM
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Re: 258 Engine Noise

Sorry to expose your error, DDawg, but real Jeeps DON'T have AC compressors. The things we air our tires with are AIR compressors, converted from AC compressors At least we can agree REAL Jeeps don't have AC, can't we?

The original post has me a little confused. The sound is first described as a screeching, then as a bunch of little nuts in a coffee can. I can't think of anything that could make both sounds. If the description of the sounds is right, I'd bet that the source is going to be something off the wall.

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post #10 of (permalink) Old 02-28-2002, 12:50 PM
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Re: 258 Engine Noise

Ok...maybe we can agree on this...the only AC on 'real' jeeps is the AC coming out of the altinator before it hits the regulator....however, my York AC compressor is still an AC compressor, the only difference is that it's pumping air instead of Freon....and enough of this....we are starting to sound like TR...and speeking of TR, it must be going good with his new jeep chick....we havn't heard much from him lately.....women will do it to you every time...(it's when they stop doing 'it'.......and...maybe I shouldn't go there....)

Anyway...back to the original problem....I have to agree that it may be one of those 'off the wall' kinds....can't wait to find out what it is..."enquiring minds want to know"

John...
84CJ7, 3"lift, 32"BFG, 4.10's, R/ARB, F/Detroit, Onboard Air....89 Cherokee - New Project

They say we learn by our mistakes.....I guess thats why we are all so smart.
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