Hearing Strange Noise From Engine Compartment

Well finally got a hundred miles on the rebuilt motor. Things have been going well until yesterday I heard a new noise when I got over 30 miles per hour. It's a rattle kind of sound. The wife said it sounds like the clatter when low on oil but a bit harsher. I've done some experimenting to narrow it down. It sound like coming from the engine and starts at around 2,000 rpm no matter what gear I'm in. When I first started hearing it, if I put in the clutch, it stops. So at stand still I rev the engine up 2,000 and no noise. Took it all the way to about 2,700 and no noise. No drips, no leaks, nothing I've check so far is low. If I get over that rpm and put the clutch in, it goes away. If I put in neutral and clutch out, it goes away. Where should I move to next.

 

Try coasting with the trans in neutral clutch out see if it is in trans or transfer case, just a thought, sounds like it is not in the motor or clutch to me. Good Luck.

 

Is exhaust close to anything rigid? Any other part of engine, bell housing, tranny close to rubbing?

 

So you know it's not in the engine. Put the transfer case in neutral and run the engine up in RPM and shift the transmission through the gears and see if you can duplicate the sound while sitting still.

 

Like Chilly says, based on your description I'd suspect a body part vibrating, fan shroud interference, a loose part hitting the frame, etc.

 

Good idea, I hadn't thought about that.

 

I'm hoping that's all it is. Headed out of town for few weeks then I'll get to crawling under and looking around.

 

Today I heard it just a little when I backed out and up a slight hill behind the house, then it was gone. But it's like you said, mostly when it warms up. So I did test today after warming up, staying in first gear as I went to check the mail. No noise up to 2500 rpm.

 

To me, this seems unlikely to be main or rod bearings, since there should be plenty of oil above that speed. Engine bearing noise also is notably variable depending on load/no-load transitions.

By the original description, it does not occur unless the clutch is engaged. Therefore, throw-out or transmission bearings may be suspect.

Or possibly (?) some excess end-play in the crank, eliminated when the clutch is putting pressure to it?

Still better to hope for a loose accessory...

 

I was thinking bad throwout bearing. Do pilot bushings eventually start wailing?

 

Throw-out should not be spinning unless pedal is depressed - but a bad adjustment will spin it all the time and wear it out. Then pushing the pedal will often kill the noise... at first.

 

Didn't see any obvious part rubbing anywhere. Fan and shroud still have clean paint, haven't found anything loose or dangling. So I tried the TC in neutral and ran thru all the gears up to 2800 and no noise. Just trying up and down my on drive as I'm at intentionally not going far from home for awhile. So during that approx 1/4 mile, today no noise thru second but third the drive is too short with twists to get it up to the over 2,000 speeds. More testing and checking when I get back from trip.

 

I know in my own experience, I have several times been very sensitive to "noises" in a new engine, but in the end it was just an over-abundance of caution.

 

Fingers crossed. I know I have some loss of hearing issues as I've aged, just ask the wife, but I've always been very sensitive to car noises in my known vehicles. Goes back to my days as a kid hot rodder. I hear car noises that are not normal way before others. I hope this is just not one of those times. These things have more noises than you can shake a stick at.

 

Loose wheel? Rocks in the hubcaps? Rattlesnake in the glovebox?

 

I think that's called "selective hearing", comes in handy sometimes....