I think the 302 in my 1978 f100 threw a rod the other day, but I would like another opinion...here is what happened: I was headed to the local dirt race track, doing about 65(legal speed limit*LOL*). I let off the gas to make my turn, and when I let off, the engine started making this terrible knocking, rattling noise. No oil light came on or anything. I pulled into a parking place, and checked the oil, which should have been full because I just added half a quart the day before...the oil level was full. The noise is constant now. there is also a slight vibration in the motor under light throttle. I am not sure if the vibration is part of the problem or not, because it was there for about a week before the big noise started. The only test I know to do, and I did, was pull the plug wires one at a time to see if the noise stopped, and this should tell me which rod is bent....well, the noise never stopped on any of them. Is there any thing else I can do to try to tell where the noise is coming from? I crawled under the truck while it was running, and the noise seems to be coming from the bottom end. I also looked at the flex plate for cracks, and made sure the torque converter bolts were tight, everything seemed to be ok. I guess the question here is: Is there any other way to tell where the noise is coming from before I scrap the engine for another one, or sell the truck for parts? Thanks for the help...Ben

 

Buy a engine stethiscope or use a large screw driver (grasp the handle with your hand and hold your ear to the opposite end of your hand) and listen to different areas of the engine. I once had a water pump on a GM engine start making all kinds of noise and I thought it was something major.

 

Ben,
Try looking at the Harmonic-balancer on the front. I had somthing similar happen in my '84 F-150 with a 351W. I thought I was gonna have to replace the engine too, but it turned out to just be the balancer and it was cheep to replace. The rubber in bettween the outer ring and the hub of it broke, and the hub just spun around like a hoola-hoop making the engine vibrate very baddly. If it ain't the balancer, have a mechanic check it out.

-Matt

 

Derek, I don't want to start an argument, but I used one on an engine of mine with a bad wrist pin and the clacking is the same where ever you place it. They just aren't very reliable for an internal engine noise.

IMHO of course

John

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66F100s Rule
In the cool still quiet of night you can hear chevies rusting away.

 

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You could do a compression check. A gage is real cheep and if you have a broken rod you will not have any pressure on that cylinder. You may also pull your valve covers and make sure you haven't slipped a push rod. That can happen under high rpm with hydraulic lifters. If the push rod isn't bent (roll it across a flat table) just put it back in. I also knew someone that had an oil port plug up and ran a bearing dry. It wore so badly it sounded like a broken rod. I have known carbon build up on the pistons to break off and rattle around. It also sounded like a broken rod.

 

If it looks like the pan can come off easy, take a look inside. Pan gaskets are cheap. Look in the bottom of the pan for any metal or pieces of piston skirt. I had broken skirts from two pistons, and four other pistons had cracks in the skirts before I pulled the pan on my Bronco's 302 to see what all the noise was about. (Technically called piston slap)

It seemed to make the most noise under light acceleration and idleing. It was quieter when decelerating or accelerating hard.

The engine had about 185,000 miles on it which is quite a bit coinsidering 4:10 gearing and no overdrive.