Loud Engine Noise 1998 Disco

[ecaii]

The other day when I first started the truck I heard a very loud noise coming from under the hood. It had a grinding or scraping quality to it that made me think something was caught up in the serpentine belt or a bearing had gone bad on a pulley. It was bad enough that I turned the truck off right away and checked under the hood. I didn't see anything out of the ordinary, so I restarted it to see if I could pinpoint it and the sound was gone. I drove the car that day and the next few. Then, after driving the car for 15 minutes or so and stopping for 45 minutes, I went to restart the it and got the noise again. Now it won't go away and is there within a second of the truck starting. The motor turns over, catches, revs and then the noise kicks in. So, I've parked it until I can resolve it. Here's a video:

http://www.youtube.com/watch?v=P40xb9tBB0M

You can see in the video that it seems to either diminish or at least get smoother and masked with more RPMs. The noise is definitely louder under the car and seems louder toward the back of the engine. With a stethoscope I can hear it most clearly through the oil pan. On the top end, with the stethoscope, the rocker covers on each side sound fine. It's so loud, my initial thought was an exhaust leak, but I can't locate any cracks or feel any escaping exhaust underneath. I've checked all the fluid levels, pulled the spark plugs sequentially from each cylinder with no change in the noise, and ran the car with the serpentine belt off, also with no change in the noise. I also moved the differential from high, to neutral to low and locked and unlocked it, all with no changes. Lastly, moving the main gear selector through all the gears also doesn't produce a change.

I'm planning on pulling the oil pan today to see if I can locate anything else. No check engine lights or oil pressure light. Any thoughts?

 

[Bahnstorm]

It doesn't sound quite loose enough to be this, but it isn't waffle banging in one of the cats is it?

 

[ecaii]

It's possible, but when put the stethoscope to the cat, I don't really hear it. It's much more prevalent through the oil pan and, to a slightly lesser extent, the transmission. I would think that if a waffle were banging around in there and making that much external noise, then putting the stethoscope on the cat would almost blow my ears off. Hard to say if the harmonics are messing with my ability to zero in on it though.

 

[singingcamel]

Doesnt sound good whatever it is , I'd pull the belt and start it , that would eliminate and idler pulleys and water pump.Doubt it
Bang on the cat ,any difference? Sound to fast for a cat rattle tho.
sounds internal, slipped main bearing. Is your oil light on?

 

[riceybean]

Sounds like an massive exhaust leak or a choo-choo train.

 

[ecaii]

Yeah, one of the first things I tried was running it without the belt. I also spun all the pulleys to check for noise and play. No change in the noise and nothing noticeable on any of the pulleys. If it was a bearing wouldn't pulling the plug wires one at a time expose that? As soon as the cylinder that's a problem stops firing, the noise should go away or at least change right?

I agree, it sounds horrible. I cringe to even run it for diagnosis. My mind keeps going back to exhaust leak, but the fact that I can't find one and that it seems to be coming from the bottom end of the engine and not the exhaust is throwing me off. Anyone got a good method for tracking down an exhaust leak, a DYI smoke test of some sort?

 

[ecaii]

No oil light or other lights for that matter. I thought about checking the oil pressure, but it seems unlikely without the oil light on. I'd need to buy the tester anyway, so I wanted to eliminate other possibilities first. I haven't banged on the cat yet, to see if it does anything, just put the stethoscope to them and didn't hear anything out of the ordinary.

 

[Bahnstorm]

Oil light could fail, but that really doesn't sound like a low oil situation, maybe a spun bearing, but not quite clunky enough. Metal bits on your oil plug? you say it is louder towards the back, are all your plugs/holes around the bell housing covered so nothing could've gotten in and is wedged rubbing up on the flywheel? Transmission fluid ok? Listen, look around the flywheel torque converter area, cracked flywheel maybe? If it sounds louder there, you can get in there by the bell housing and sort of inspect the edge, check a little for play. It doesn't sound quite like that, its hard to tell over video if that is like a metal on metal sound or a vacuum air pressure sound.
I think I agree with riceybean it sounds like a steam train is about to come around the corner.

 

[ecaii]

I haven't had a chance to drain the oil and check the plug or pull the pan yet. I'm hoping to do that tomorrow or Saturday. Work has gotten in the way a bit, plus I wanted to run some BG 109 in the old oil first. Both trains fluid and oil levels are fine. I can pull the plate on the bell housing and take a look. I hadn't thought of a cracked flywheel, I've never seen that happen. I'll let you guys know the results of everything.

 

[ecaii]

Bit of an update, or lack of one. I pulled the bell housing inspection plate and the front plate (the one facing the oil pan). All the bolts feel tight. the flex plate has play and space when you get midway between each bolt point, but that's consistent and doesn't seem to be abnormal. I can't find any debris or signs of scraping.

However, when I rotate the engine from the crank pulley I can hear a ticking coming from the bell housing now that's opened up. I haven't been able to have a partner turn the crank while I look to see what might be causing it or if it's just normal. I also noticed, looking in from the front cover, to tabs on either side of the the central shaft that all the plates are spinning around. One tab is shorter than the other, with an irregular looking end. I'm not sure if it snapped off somehow and I can't find a diagram in the RAVE that would tell me if they're supposed to be that way or not.

I'll be draining the oil today and pulling the oil pan to see what else I can find. Does anyone know if there is an issue running the car to warm up the oil with the bell housing opened up? I can't see from a mechanical standpoint why I shouldn't be able to. It seems like the main purpose of the plates is keeping foreign objects out. Just sitting still in the garage, I can't see why it would matter. Any thoughts or input?

 

[olyller]

This sounds like the starter is/was not disengaging! What was the issue?

 

[discostew]

Sounds like the flex plate is broken. You might not see anything from the inspection cover. I would get the trans out and get a good look at it.

 

[discostew]

This sounds like the starter is/was not disengaging! What was the issue?

I didn't realize how old this thread was. People don't usually tell you what fixed the shit. It sounds like his drive plate was cracked. When that happens you hear knocking, snapping, chirping and all kind of strange noises.probably loud. If the starter stayed engaged it would have been loud but different.

I think I would have removed the 4 torque converter bolts and pushed the converter back away from the engine then ran it like that. If the noise was gone or noticeably different I would have pulled the trans.