View Full Version : Horrible knocking sound? Help!

04-19-2003, 07:25 PM
I was driving home today and I noticed a horrible knocking sound that quickly got louder.

It's really loud now, louder than the engine. Not a tap or a click, but a knock.

It happened very fast, I started my car about an hour ago... it was fine. I ran some errands... was driving it around for about 30 minutes. I didn't notice it until I was almost home... it definately wasnt making the same noise earlier than the last 5 minuets of the drive.

Temp was fine (never got above the R in norm) Oil level is fine. When I checked it... it was just above the "add" line, so I added another quart real quick, but the noise is still there.

What do you guys think this is?

EDIT: Some other pertinent information in case it helps.

I noticed nothing wrong with the performance of the car. It ran fine, but obviously after it started knocking I didn't stomp on it. No loud bangs or booms, no sudden losses in performance...

There's is nothing visually wrong with the engine bay. Everything looks as it should. No oil spewed everywhere, no disconnected hoses, nothing.

04-19-2003, 10:01 PM
How many miles are on your engine?

Have you fixed blown head gaskets recently?

is it a hollow knock in the bottom end or a higher pitched ticking sound.. One can be a rod bearing or broken piston skirt (usually loudest when the engine is cold) or a bad rocker arm if it is ticking.

The latest problem going through the board looks to be rod bearings. I hope not for your sake.

04-19-2003, 10:11 PM
Head gasket was replaced before I bought the car.

Right now there are 174k on the engine... I imagine about 20-30k on the Head gasket, but not sure.

I dont suspect the head gasket because through all the driving I did today, the temp stayed constant. Didn't even approach overheating.

The volume of the knock is LOUD... regardless of whether the engine is warm or cold. Immediately after I got home, I started it back up only to hear the knock... just now I did it again and it's the same volume (the engine has had a couple hours to cool down).

All guages read normal... it almost sounds as if there's junk somewhere thats banging around... it's not really a hollow sounding knock. The best thing I can compare it to would be someone knocking on a piece of wood with their knuckles. Doesn't sound metallic at all. It's a rhytmic knocking... but it sounds significantly different from when my car knocks in the morning when it is cold.

Ok, I've got it narrowed down. I popped the hood and watched it run for a bit...

The harmonic balancer (is that the name of the large wheel thing that runs the serpentine belt) is all shaky... it looks like it's not balanced anymore. It's still spinning and running everything, but it's very shaky (causing all the tensioners on the belt to shake).

04-19-2003, 10:28 PM
Do you have a piece of pipe you can use as a poor mans stethoscope? You need to isolate what area of the engine the noise is coming from.

With that many miles it could be a rocker arm that is giving up the ghost. No miss though?

Has Hoffman sold that good used engine out of his 89 SC?

Worst case that would be a good fix for you.

I hope it is something simple.

04-19-2003, 10:34 PM
So if the harmonic balancer appears messed up, you think it could be something in the internals?

It almost sounds to me like the noise is simply the HB bouncing around

04-19-2003, 10:38 PM
Dont run it anymore!!!!

I missed your edit.

Check to see if the bolt is intact for the harmonic balancer in the crank.

If it is you dodged the bullet that killed me...

Sounds like you have a broken harmonic balancer.

04-19-2003, 10:39 PM
its a good bet your balancer is gonna take a crap.
if you change it use caution, because if you snap the already crappy stock bolt of in the crank youll be bummin in a big way.
you can get a replacement from a (94?) mustang. I wouldnt drive it till you isolate/repair it. If its the balancer youre in luck..easy fix.
If it isnt the balancer it may be a broken piston and/or rod..if it breaks in the bore you wont lose oil pressure until the broken piece disintegrates or dislodges. if this is the case your hosed...find a new motor.
Hope this helps

04-19-2003, 10:40 PM
Well... the HB is still attached to the engine. How broken can the bolt be if it's still on there and spinning?

What would cause it to break like this? it LOOKS fine... but I dont understand why this happened.

04-19-2003, 10:46 PM
well first of all i said to be careful not to break it if you remove it...they are weak and prone to breakage..
Many guys have had them snap off just driving the cars..
The HB also can fail due to delamination of the rubber to metal area...itll actually just literally fall apart. Really look closely. I hope it isnt anything more serious than the HB.
Keep on rollin

04-19-2003, 11:00 PM
The Balancer can be cracked without breaking the bolt yet.

Thats the point. Fix it before it breaks off...

I have read where the bolts in the pulley have sheared off too.

Check them to make sure they are intact.

I sent you a pm you can call me if you want more details.

04-19-2003, 11:05 PM
I'm not sure how the balancer was making the kocking noise you reported. If the ring attached for the crank sensor was to come loose you wouldn't have any spark. The pully is attached to the aluminum center hub which is connected to your crank, so it shouldn't move around unless the aluminum hub has become loose on the crank. But you state that the bolt is still in place. The outer ring of the balancer is metal and attached to the aluminum center hub with a rubber bond, but even if the bond is no longer adhearing to the aluminum hub, the outer metal ring is still captured between the crank sensor ring and the pulley, so for it to make noise the rubber bond which connects the aluminum hub to the outer metal ring would have to be gone completely.
Mine is no longer bonded to the aluminum but it all turns true to the crank. In fact, I'll bet most SC's that still have the stock balancer are no longer bonded to the aluminum center hub. This throws off your timing mark and other than that is hard to tell without removing the belt and pulley to check it. I have checked three SC's and one super charged cougar and all of them had the rubber seperated from the aluminum center hub. I haven't seen one with the rubber gone completely though, but maybe that is the next step for mine?