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258 Engine Noise

1K views 14 replies 6 participants last post by  sas87yj 
#1 ·
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
 
#2 ·
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.

MY OTHER CAR HAS ROUND EYES TOO
 
#3 ·
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.


I might have been born at night, but it wasn't LAST night.
 
#4 ·
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

84 CJ-7; 258 I6; Restored-to-Stock Condition, TR Ignition Upgrade
 
#5 ·
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.

I might have been born at night, but it wasn't LAST night.
 
#7 ·
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!

My girlfriend said if I spent one more dime on my Jeep she would leave. Man I'm going to miss her!
 
G
#8 ·
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...
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.
 
#9 ·
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.

I might have been born at night, but it wasn't LAST night.
 
G
#10 ·
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.
 
#11 ·
Whenever I have trouble determining the source of a weird sound or vibration, I try to vary the conditions. When the noise begins, lightly accelerate, decelerate, depress the clutch, put the transmission in neutral and rev the engine with the clutch in and out. Note anything that increases or decreases the noise or vibration. Grab the tranny and t-case shifters and feel for vibration. Note if it is worse when cold or hot, both ambient temp and engine/tranny temp.


I've replaced so many parts that my old Jeep has become my new Jeep.
 
G
#12 ·
By chance what tranny do you have? I had a very similar noise coming from my '84 with a T4 transmission. Exactly as you had described with a load on the drive train in 2nd and 4th gear - it turned out to be the bearings in the tranny. The front bearing had leaked out all the oil and the tranny went dry - needless to say the rest of it burned up without the oil and now I'm in process of changing it.
There was no vibration in the shifter lever just a pitch whine and small 'coffee can full of bolts rattle' like you describe. I'd check your transmission oil first. I hope you find the noise before anything breaks.
Good Luck

Sully

84 CJ7 Laredo 258/HEI/Weber waiting on my T-19 conversion

 
#13 ·
Thanks for the help guys. I'll look into it further and get back to the board if I find the source anytime soon.

Just to answer a few of the follow-up questions. The sound is more like the "coffee can" rattling than a screeching, but since it only shows up under load at higher RPM, it's hard to hear it perfectly. I have a T-5, but it was rebuilt about 10K miles ago and I changed the fluid last month.

TEXAS1AL

84 CJ-7; 258 I6; Restored-to-Stock Condition, TR Ignition Upgrade
 
#14 ·
Um dumb question: is it like pinging/knocking from bad gas? Have you changed anything with the timing since the problem started? Perhaps you are hearing some sort of detonation?

An easy way to check this would be to check your timing. If that looks to be correct, try retarding it a bit and see if the problem goes away. If not, return to optimum timing.

'83 CJ-7 nothing original but the tub and axle tubes
 
G
#15 ·
now you're talking bluseman- i think we are talking about detonation rattling also. either we have carbon build-up on the pistons or the timing is too far advanced, or a little of both. as said, retard(turn dist clockwise) a bit and see if that helps. i wouldn't worry about the 9* BTDC. just remember, if you retard too much you will notice a decrease in power. just experiment till you get it right.

 
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