Minor Engine Noise

[Joe Flanagan]

Continued work on the under-dash wiring today but as I was working, I decided to run the engine. I ran it at various times throughout the day and then toward the late afternoon, I started it up and got a tapping sound coming from around the number 6 cylinder somewhere. It wasn't as heavy as the noise that caused me to tear the whole thing down last summer, but was very pronounced. I had the noise at all RPMs: idle, accelerated, etc. It's more like a click than anything else.

This happened a week ago as well. I hadn't run the engine for about two weeks and when I finally started it up I got this noise. After some running, it went away and I didn't think about it anymore. But now, after consecutive days of running it, the noise returns. Eventually, it was no longer there during idle but only at the very beginning and very end of an acceleration. My guess is a valve. Just sounds like it and seems to be about the right frequency.

Anyway, after a while, it went away. I have enough oil in the crankcase so it's not low oil.

I did notice that my oil pressure dropped below 40 at idle for the first time ever. It was idling around 50 when I first started it and for weeks after. Today, it nearly dropped to 20 at one point (idling). I think this is an OK pressure for idling but I wonder why it dropped. I'd been running it for longer than normal and it's almost 100 degrees here, so I assume the oil got hot and thinned out, hence the drop in pressure. Any thoughts on this?

[Don Coatney]

Check your timing and set it at 2 degrees advance.

[Joe Flanagan]

Don, I checked it and that's about where I am. I don't have the individual degree marks on my pulley anymore, so it's an estimate. But I'd say it's very close to 2 degrees before TDC.

[Joe Flanagan]

Just went out there and ran it again. It sounded fine. No noise at all. Maybe it's something that doesn't develop until the engine gets hot. I'll research more tomorrow.

[Joe Flanagan]

I've now determined that the sound appears once the engine gets hot. This morning I started it up and let it idle for ten minutes. Then I ran it at about 1500 RPMs for five minutes. That was enough to get the noise started. Once it starts, it is present at all RPMs. Now going out to find a mechanic's stethoscope to see if I can narrow it down. It sounds like it's high in the engine and definitely back toward the firewall around number six. This is when I really wish there were more forum members close by.

[Joe Flanagan]

It seems it is not a valve noise. I just ran the engine until the sound started and then inserted a feeler gauge at all tappets. The noise never changed. Pulling the spark plug wire at numbers 4, 5, and 6 does not cause any change in the noise, either. You have to run the engine at high RPMs in order to get the noise to kick in. It's loudest under the car, like near the bell housing/clutch cover. I haven't gone out to get the stethoscope yet, but that is next. If you let the engine idle for a while, the noise will disappear. But it's very noticeable now at high RPMs and also for the first few minutes of idle after deceleration. It sounds to me like something is hitting something else. But I can't feel any impact with my hand while the engine is running. More updates later.

[Plymouthy Adams]

Joe..quick question..do you have the return spring on the throw out bearing arm to ensure full retraction..put your hand on this and see if you can detect a bumping assocaited with the tapping..

[Joe Flanagan]

Will do, Tim. Thanks.

[Joe Flanagan]

I checked the clutch fork and spring. No vibration or impact noticeable there. I crawled under the car with a mechanic's stethoscope and started following the sound. I've never used one of these things, and though I was very skeptical, I have to say I was amazed at how many different sounds you can pick up with it. In no time, I was led directly to this:

Now, I don't want to say this is what's causing the noise, but when I put the probe on the dent, it sounded like I was right on top of it. I didn't get the rapping sound anywhere except when I put it right on this dent. My guess is the flywheel teeth are nicking the sheet metal. In fact, if you look at the second picture, it almost looks like the teeth are getting ready to wear through the clutch cover.

I'm out of time today, but I'll be taking it off tomorrow to see what's what. What I don't understand is why there is no noise until the engine gets hot. Maybe something expands just enough to start hitting? You can't reproduce the sound on first startup or any time within the first five minutes of running. You have to elevate the RPMs and keep them there for a while. Then you get the noise. Let it down to idle, and the noise stays for about five minutes or so and then fades away. Doesn't seem to jibe with the flywheel-hitting-the-dent theory, but there it is.

[Plymouthy Adams]

heat expansion Joe..heat expansion..pull that cover and bang it out..

[Jim Yergin]

Joe,

Given what you have gone throught with that engine, I am very glad to hear that the "minor engine noise" appears to be truly "minor".

Jim Yergin

[Young Ed]

Possible you have very slight movement of the crank under RPM?

[Joe Flanagan]

Don't know that that's the cause yet. I just put everything away and took a shower. It's about a hundred degrees outside but I'm hearing the call. I'll probably be under the car again and sweaty and filthy before the sun goes down. I really hope this is it.

[Joe Flanagan]

Possible you have very slight movement of the crank under RPM?

I sure hope not. All the clearances are correct and triple-checked. Plus it will make the sound at idle, too, once it's hot enough.

[JoelOkie]

Don't know that that's the cause yet. I just put everything away and took a shower. It's about a hundred degrees outside but I'm hearing the call. I'll probably be under the car again and sweaty and filthy before the sun goes down. I really hope this is it.

Hope you catch a break on it this time Joe. I CAN see the edge of that ring showing through in your pic.

I know how humid it can get there in Va., as I spent a few years doing maintainence on that big wooden roller coaster they call the Rebel Yell there at King's Dominion, near Ashland, and although the temp was only about 92 or 93 some days, not having a dry thread on me, and a few days at 100 one summer working there at Fredericksburg was brutal. I guess we are lucky here in that it's been dry so long the humidity is not now much of a factor, but when it gets this hot, there is not much comfort even in that. Good luck, Joel

[Joe Flanagan]

Thank you, Joel. Fredericksburg is not that far from me. Hot and humid, that is for sure.

I went out and took off the clutch cover. Here is what the inside looks llike:

It looks like this isn't the first time this happened. As you can see, there is a groove cut into the highest part of the dent. It has rust in it, so it's old, but on the lower half where the screwdriver is pointing, is fresh sheet metal and that's where I think my flywheel was making contact. It doesn't look like much and it doesn't look like it would be enough to make the noise I was hearing, but it's definitely a contact mark. It wasn't there when I had the cover off for cleaning a few weeks ago.

So I ran the engine at high RPMs for eight minutes continuously. There was no noise. Let it down to idle. Still no noise. I'm going to perform this test a few more times until I'm ready to say I've found the culprit.

Edited August 1, 2011 by Joe Flanagan

[oldodge41]

Nice find! I hope that was it.Sounds like it may be.

[Plymouthy Adams]

for those who don't own an automotive stethoscope..it's a must ..you can get a rather effective inexpensive one through Harbor Freight..

[Joe Flanagan]

I got a ten-dollar version at Auto Zone. Just for kicks, I listened to the generator. The thing was buzzing like a beehive. Lots of scuffing and scraping going on everywhere around the engine. At least that's what it sounds like. You take the stethoscope out of your ears and you don't hear a thing.

[oldodge41]

I have a stethoscope but have diagnosed many a problem with a broomstick. Still do when it isn't in a spot I want to get close enough to use the stethoscope.

[james curl]

I have a very long wooden handle screw driver that I use as oldpdge41 uses his broom stick.

[busycoupe]

I too have used a long wooden handled screwdriver many times. However I now have a Harbor Freight store near me and I now think that I will take Tim's advice and get an honest to goodness automotive stethoscope.

[gillettealvin]

Good on ya, Joe! So happy for you that it is just a minor fix, especially after all you've been through with that motor!! GA

[Joe Flanagan]

Thank you. I'll post again after I've run my tests.

[P-12 Tommy]

I think you got lucky, Joe!

Tom