I have a mysterious "rattle" noise coming from my 302. The noise is only heard at idle (750RPM) and goes away if the engine is revved up. It sounds like it is coming from around the crankshaft pulley area. It's not loose and doesn't appear to be damaged. The engine and transmission were both rebuilt about 3000 miles ago. The cam, lifters, and timing chain were replaced at that time with a Comp Cams 31-255-5 with matching components.

I spent 4 hours checking over my whole engine. It doesn't sound like the top end. I have eliminated the following:

- belts and pulleys are fine
- water pump is good
- power steering pump is good
- alternator is good
- fan is good
- motor mounts are good
- torque converter bolts are all tight (I discovered my dust shield was missing)
- flex plate is good
- starter bolts are tight
- crank bolt is tight
- I tried turning the crank pulley, but it was too tight to turn by hand

With the engine running, I got under my truck and got a good listen, and the noise seems to be concentrated in the oil pan or where the transmission bolts to the engine. The odd thing is, when the engine has cooled off a bit and I start it again, the noise is greatly reduced. As the engine warms up, the noise gets louder and more irritating. Again, the noise is heard at idle and goes away when I give it gas. I dropped the transmission a few days ago, and the flex plate is in almost perfect condition.

It sounds like a hollow rattle, almost like a loose bolt or baffle. What in the world could that be? I've checked every nut and bolt in the area, but could not find anything loose.

 

Oil pump? (Just a WAG)

 

Perhaps the lost dust cover is in the oil pan? j/k

Since you already looked in the bell housing plenty, the next logical place to peek is the oil pan. I've never had mine off while the engine was in the truck. Maybe you can drop it the 1 inch and then use mirrors and lights to peek in there.

The interesting part is that it only sounds during idle. Is there another explanation for that? Does the engine shimmy more at idle? A couple things I can think of that are different at adle, if it helps:
- More oil in pan generally
- engine less torqued off it's resting position. maybe the engine or trans comes in contact with body in the resting position.

 

i am willing to bet you are hearing either the heat shield on the catalitic converter or the cat itself internally is failing and causing the rattle. smack the cat with a rubber hammer.

 

My truck doesn't have a catalytic converter.

 

I just had a good friend check it out, who owns his own transmission shop. He did find the starter was binding up some, and he rebuilt it for me. He inspected everything else, including the flex plate and replaced the torque converter.

The rattle is still there!

Using a screwdriver as a stethoscope, he told me that the noise is coming from the front of the engine, but he is stumped too. He doesn't think it is a rod or bearing noise.

 

wow, that must be some long screw driver to have the motor running and your ear on the end to listen for the noise. Ive always used a broom stick.

if you remove your belt and start the motor for a brief time to see if its still there.

what year? efi or carb?

 

OK, I found a certified mechanic to put it up on a lift for me and he checked everything out with a stethoscope. He narrowed it down to the area around the fuel pump. Even though the old fuel pump looked fine, I replaced the fuel pump, and the noise went away.

When the truck is warmed up, the rattle comes back. If I let the engine cool, the noise is gone until it warms back up, and then the noise returns.

What does that mean?

 

I got a suggestion..

Let the engine warm up till you hear it. Pull the plug wires from #1, listen, and then from #5, listen. Does the rattle appear to change? Could be a wrist pin... Only other thought is to check all the bolts on the lower intake, check that the spark plugs are tightened down, perhaps check header/exhaust manifold bolts for right amount of torque.

Also did you try what Kemical suggested with removing the belt and listening? I mentioned wrist pin, since mine is doing the same thing but isolated it to #8. Also have you checked the the motor mounts are tight? Maybe Radiator shroud flopping around hitting the radiator?

 

I'm affraid that I'm a little late to your thread. But, I have the same exact issue and you described it perfectly. We're you able to figure it out? I'll be crawling around under my 2004 Expedition tomorrow.

 

I have a 302 everything gone through. Bored .030 over, .010-.010 crank, reconditioned rods, rotating assembly balanced, new oil pump, fuel pump, water pump, cam , timing chain & gear, heads, flex plate and rebuilt AOD. I have run the engine about a hour in the chassis. When temp gets to 150+ you can start hearing the noise in the pan. I have gone all over the engine and tranny with stethoscope and oil pan is where the sound is. Removed fuel pump, blocked off opening and ran engine while hand pumping fuel pump, no change. Let cool a little and no noise. I have pulled the pan and inspected rod bearings, pan for signs of rubbing, inspected flex plate again. Trying to resolve issue before assembling truck. Looking for a miracle before completely tear down the engine for inspection. Pulled plug wires one at a time while running and no change to sound. This is not a steady constant sound. I will describe it as knock sound for no better word. I will go knock, knock, knock then maybe three fast close together knocks and then repeat.

 

There used to be such a thing as "fuel pump" knock in 302's. It was described in the old "Motor Repair Manual" of the 1960's. I don't recall the fix. I'll dig up my copy tomorrow and look it up and get back to you. Only other thing would be a cracked flexplate, look at the hub of it around the bolts.

 

I had same symptoms. It was catalytic converter breaking internally