I thought I heard a bit of squeaking, which would point to main bearings, but like it was said, you will need to give it a quick rev to be sure, and I'm not sure if you can do this, but it would be great if you could just unbolt the fan for the video, to make it easier to hear the knocking.

 

Oh, that isnt good...

 

No its not. If you've got a rod knocking and its knocking all the time its probably best that you don't run the engine.

The 300 that was originally in my 82 F100 developed a quiet knock when it was cold. That quiet cold knock turned into a loud constant knock in no time at all, less then a 1000 miles at least. Before I knew it I had a rod stuck through the block and pieces of my number 3 piston laying on the bottom of the oil pan.

She's literally a ticking time bomb you've got right now, best that you get it fixed before it blows. Your still at the stage where you could have a good running engine again with a simple rebuild and minimal machine work. Normally when they blow there's zero chance of saving the block and crank and it turns into a much more expensive job.

I'm not trying to scare ya man, just trying to give you a heads up and hopefully save you a few bucks in the long run.

 

My uncle used to drive it...and it knocked then too. And that was like 6 years ago.

 

Here... YouTube - 1985 Ford F-150 Exhaust #3

In that vid at 0:18, you can hear the knock.

 

Now that I've listened to your video I'm not quite sure what to make of the noise.

Every engine I've ever encountered with a rod knock didn't sound like that. By that I mean the knocking of a rod is quite loud, kinda like someone smacking the side of the engine with a hammer. I'd think if it were a rod you'd be able to clearly hear it over the exhaust flow noise.

It might be long shot but if you have, or have access to, a screwdriver with a really long handle you could use that to listen to the engine. Just place the head of the screwdriver in random spots around around the engine block and put your ear to the top of the handle to listen around. That will at least let you know what region of the engine the noise is coming from. Of course any solid 'thud' type noises from the bottom end are never good. But at this point there's a number of different things that it could be, if you could track down what part of the engine the noise is coming from that would at least help single out some things.

The screwdriver stethoscope idea might sound crazy but it actually works quite well, and its no near as loud as you'd think. I've used the method to listen to the internals of engines at junkyards that were just sitting on the floor running with their exhausts dumping out of open manifolds.

 

Its hard to tell but i'm only hearing it at idle. Crawl underneath and see if it sounds like its coming from the flywheel area, maybe cracked or loose bolts. Rod bgs will rap harder on acceleration, it sounds like your noise is when the motor is unloaded. I had the plate between the eng/trans rub the flex plate and it sounded like a rod getting ready to fly out of the block. Only made the noise hot and at cruising speeds

 

Ive done that before. It seems to be louder at the passenger side of the engine, but im not sure if i twas bottom or top end.

If you watch some of the other vids i have, you can also hear the knock a little.

 

Hmmm, i will have to check that out.

 

yeh thats what i was starting to think is cracked or loose bolts in the flywheel area.

 

Ive heard loose torque conv bolts that when you shut off the engine, youd hear a quick few knocs as the converter bounces back and forth against the flex plate. Makes crazy noises when its running

 

If this is true, just build the other motor and drive this one into the grave.

The reason I asked what kind of trans you had was that a buddy of mine had a Chevy that knocked like a main bearing , but turned out to be a flexplate bolt that had backed off. He had had transmission work done in the not to distant past from that, so I hesitated to give out the info, lest it keep you from getting it to a mechanic.

Now you say this is a 6 year old issue? It is probably a collapsed skirt, and it will never stop it from running, but has probably taken that cylinder .010" past the others, ( or more) to be honest, IDK, but at worst will make the block unusable for a rebuild.

This is one of those issues that are hard to diagnose and help with over the net. Lack of full disclosure as to the exact details of the problem only exasperate the difficulty of diagnosis.

The more info you can supply in a "what is it?" situation the better. People are hesitant to give more than the bare essentials, which makes it take 3 times as much give and take that just reading (or posting) a more complete scenario in the first place.

A while back, someone found an undersized piston in a set, something like this could be the problem as well. One cylinder could have been oversized.

You REALLY, REALLY, REALLY ought to take the suggestion given twice now to use some stethoscope type of method and at LEAST isolate the location. We can guess all day long.

 

To try and isolate the noise, you can pull one plug wire off the distributor at a time and see if removing one quiets the noise. If a rod is knocking, that rod will quiet down if there isnt any combustion going on in that cylinder.

 

Here is a new video. It seems to be coming from the drivers side.

http://www.youtube.com/watch?v=Nte-hxy3lAI

 

Kinda hard to tell from the sound quality, almost sounds like a cracked exhaust manifold when it revs.