Trying to Diagnose Knocking Sound

[Joe Flanagan]

This morning I started my Plymouth and it sounded fine. Once it warmed up, I put it in reverse and when I backed up, there was a really strange grinding or scraping noise. I can't really describe it because it was very sudden and lasted only a second or two. Whatever it was, it sounded bad. Anyway, I drove it around the block to see what was up and there is a moderate knock coming from somewhere. It is definitely not drive train-related. It picks up rhythm when I accelerate and does this with the car in neutral standing still. It's most pronounced at idle. If you let the car sit awhile and then start it up, it sounds OK. But the more you drive it, the worse the sound gets. I took it for a 25 mile highway run to see what effect that would have and at the end of that trip, the sound was much worse. I took each spark plug wire off and ran the engine and the sound does not change when any of them are disconnected. It sounded to me like the noise was coming from the front of the engine. I took a stethoscope and you can definitely hear it where the crank pulley passes through the timing chain cover. I had the stethoscope on the timing chain cover at that point, right on the sleeve where the crank pulley goes through. That's really the only place you can hear it with the stethoscope. I checked everywhere along the head and along the sides of the block, and I don't hear it. I also checked everywhere on the oil pan, on the valve covers, the water pump, and the generator. Whatever it is, it seems like it's in the vicinity of the timing chain cover/pulley.

Here's what I know for sure:

The more you drive, the louder it gets. 

It's most pronounced at idle (road noise might prevent you from hearing it at speed)

Oil pressure is normal.

The car operates normally in all other respects.

If you shut the car off and let it sit, then start it up again, it sounds normal. But if you drive it for a while, the noise comes back.

It does not seem to be cylinder-specific.

 

A couple of things that are probably not related but which I will mention anyway:

My crank pulley is crooked. It has been from the start. I figured it wouldn't be a problem as long as the belt stayed on it. It does seem to me it's worse now, if that's possible. There is an awful lot of wobbling going on. Any connection there?

 

Finally, two days ago I changed the oil and went from a 10w40 to a 20w50 because it was on sale. Is that oil too heavy? 

 

This engine has about 950 miles on it. It had a stuck exhaust valve which some forum members told me would clear up with use and that is exactly what happened. It also had a serious issue with hard shifting which cleared up with use as well. Any chance this is something that will magically go away? 

Edited October 5, 2014 by Joe Flanagan

[Plymouthy Adams]

concentrate around the fuel pump with your stethoscope..do look into the wobble at the crank.....and ensure the crank bolt is not backed off..

Edited October 5, 2014 by Plymouthy Adams

[Joe Flanagan]

Thanks, Tim. What are the possibilities around the fuel pump? 

[Don Coatney]

The wobble may be an indication the rubber has separated in the vibration damper. You might start looking for a replacement.

 

Fuel pump could be the pivot pin backing out.

[Joe Flanagan]

Would either of those cause the noise I'm hearing?

[Don Coatney]

possibly

[Jeff Balazs]

Joe;

You might try listening with a length of hose as well. Some times it takes using both methods to pinpoint the problem. Often times using a just a stethoscope can give you false impressions about the exact position of the offending noise.

 

One other thought.....do you know if the timing chain was replaced when the engine was rebuilt? I would definitely check the crank nut too.

 

Jeff

[Joe Flanagan]

Thanks, Jeff. Yes, I replaced the timing chain when I rebuilt the engine. I'm really stumped at this point as to the origin of the noise. I'll follow some of these suggestions tomorrow and report back. 

[Jeff Balazs]

Joe;

One other thing you might try. You say it is most pronounced at idle. Try holding the clutch in at idle and see if it goes away.

 

Jeff

[zHxIxPxPxIxEz]

I had a simaller experience, try tighting and lossening the v belt. I did this and diagnosed the sound. In my case it was a bad water pump (mine also wobbled) good luck

Edited October 6, 2014 by zHxIxPxPxIxEz

[Joe Flanagan]

The sound does not go away when the clutch is depressed with the engine idling. I bought the water pump new from NAPA a few years ago. I suppose it could still be bad but I put the stethoscope directly on the water pump at several points and I do not hear the knock there. 

[Lloyd]

Couple thoughts. I would start with the wobble. The wobbling could have damaged the key for the vibration dampener or even warbled out the dampener itself. Or the shaking belt could have damaged the water pump bearings.

Either way, if it keeps wobbling something is going to happen. I put a vibration dampener on a small chevette and damaged the keyway in the process, I filed it some then put it back on anyway. It ran fine for quite a few miles then started banging and flew right off.

 

Something else that crossed my mind is the oil tube inside the timing chain cover for the timing chain. Perhaps its clogged up.

 

Sorry to hear your having problems Joe, good luck.

[Joe Flanagan]

I believe I just have the pulley. No vibration dampener. But the wobble is pretty dramatic and needs to be addressed. 

[Joe Flanagan]

This morning I jacked the car up, got good lighting underneath it, and went around with both a piece of hose and my stethoscope. I didn't have any luck tracing the noise. It does still seem to be most pronounced at the big hole in the timing chain cover but today it seems not by much. Yesterday, it was much clearer at that spot. I put my ear to the opening in the draft tube and you can really hear it clearly. So maybe I've got a bad bearing or wrist pin. I'm going to address the wobble in the crank pulley just to eliminate that, though. I've got to remove the radiator and all that, so more fun in store for me. I'm trying to figure out what the worst case is. I guess that I'd have to drop the pan and find whatever is damaged. I sure would hate to have to pull the entire engine. 

[Joe Flanagan]

Also, I just wanted to add that I checked the vacuum on the engine just to see if anything was going on there, and it's good and steady. The needle behaves normally on acceleration. The oil looks normal, too. No antifreeze or foaming. I do think it's strange that this happened shortly after I switched to a heavier weight oil. I noticed that when I started the engine this morning when it was cold, the oil pressure gauge sat at zero for a few seconds before it started to climb. It's never done that before. I wonder if that's just a cool weather thing or something else.

[Don Coatney]

Any way you could post a sound bite?

[soth122003]

Hey Joe,

 

I just looked at my Plymouth manual and the highest rated oil it recommends is a good 30 weight. The higher the number the thicker the weight, especially in colder weather. I use a straight 30 weight in mine and the only thing I notice is when the engine gets really warmed up the pressure is around 20 at idle, but goes back to 40 when I start moving.

 

As far as the knocking sound, if you crank pulley is wobbling you might check for a scrape or wear mark around the timing chain cover. As suggested before pull the pulley and check the key. While this will suck, I think your wobble problem will only get worse and damage something that will require pulling the engine.

 

Joe

[Joe Flanagan]

Don, yes I will post a sound bite. I've already pulled the radiator and am getting ready to remove the pulley. I'm trying to do it without removing the grille. I hope that's possible.

[Joe Flanagan]

OK, I removed the pulley. First thing I noticed was that it wasn't on anywhere nearly as tight as it should have been. The manual says 108 foot pounds. There's no way I had it secured to those specs. I only had to rock the car a few times and the nut came free. There is no wear or damage on either the pulley or the fan. The water pump turns freely and makes no noise. The crank hub that the pulley slips over has some scarring on it. I'm guessing that's from installing the hub, at least that's the way it looks to me. The key is in place and intact. No sign of wear or damage around the timing chain cover. 

By the way, I do not have a dampener. It's just a solid metal pulley. 

I won't be able to run the car until I get everything back together. At that time I'll see if I can record the sound and post it. I did pay close attention to the fuel pump as suggested, checking with the stethoscope the pump itself and the block around it. I didn't pick up any sign of the sound in that vicinity. 

Two rounds of testing by pulling each spark plug wire produced no change in the sound, so it would seem it is not cylinder specific. Does this make sense? If there were a problem with a main bearing, wouldn't you get those results?

And finally, I keep going back to the weird noise I heard and that started this knocking yesterday morning. It was the first time moving the vehicle for the day. I let up on the clutch, went in reverse, and it sounded like something grinding or scraping. It was a really weird sound. Ever since then, the engine has knocked. It kind of sounded like I was backing over a lawn chair or something. Did the sudden torque on the engine cause something to let go?  

I'm going to replace the radiator and the pulley, start the engine, and see what happens. If the noise is still there, which I feel certain it will be, I have to come up with what my next step is going to be.  

[Jeff Balazs]

Joe;

You might want to check that pulley to see if it is running true. When I initially got mine it was not running true. They can usually be trued up with either a dead blow hammer or a press. I checked mine on a lathe and made small adjustments until it spun true.

 

Jeff

[Joe Flanagan]

I'll see if I can find someplace that will do that. I really couldn't tell that it was installed lopsided, so it might in fact be out of round or something.

[Reg Evans]

Run the engine for 20 seconds with the pulley off.  If the noise is gone you've found the problem.

[Don Coatney]

Run the engine for 20 seconds with the pulley off.  If the noise is gone you've found the problem.

Good advice.

[Joe Flanagan]

Sometimes it takes 20 seconds for the noise to start. 

[deathbound]

So run it for 40 seconds or 60 seconds or 80 seconds, see if the noise returns without the pulley installed.