What kind of knock is this?

[cp2295]

So slowly I have developed a little knock. Not a tick, a knock, at first I could only hear it on deceleration (in neutral) down around 1300, and then at idle it would be there intermittently. Now I hear it more often. It seems like if it was a rod knock or main bearing knock it would be consistent and there all the time. I can't hear it when the engine is cold. It's weird...

 

[cp2295]

I only have 10k on this rebuild btw

 

[RonD]

Cold engine has thicker oil so will have less bearing noise if that is the source of the noise.

Connecting rod knock is usually heard on the power stroke.
Piston is pushed to the top of the cylinder then crank starts to go down, if there is a worn bearing a gap forms between top of connecting rod journal and crank journal.
When cylinder fires piston goes down fast and the two parts SLAP together making the knock noise.

On the other 3 strokes the crank is just pushing/pulling the connecting rod so knock noise is not noticeable above engine noise.

If you can hear the knock at idle then disable one spark plug at a time, if knock goes away or becomes very quiet then that cylinder probably has a bad bearing on the connecting rod.

A knock can also be an exhaust leak, they can sound very similar if the leak is on the exhaust manifold to head gasket.

 

[enjr44]

A knock can also be an exhaust leak, they can sound very similar if the leak is on the exhaust manifold to head gasket.

Can you expand on this??

I also have a very light knock on my 4L OHV. It does not start immediately upon cold start-up. It takes about 15 to 30 seconds to start. And then it goes away when the temp gauge starts to move off its at-rest position. At first it seemed like it was coming from the trans (auto), then the exhaust system and finally, someplace in the engine; but, the more I looked, the less sure I have become...... It starts and drives like it should.

I have used a dowel on everything that moves or has moving parts in it and can’t hear it. By then, of course, the engine is warm and it goes away. While it is warming up, randomly the knock will go away for a second or two and come back until it goes away completely. If drive it from a cold start the noise goes away within a mile or mile and a half. Removing the drive belt does not change anything.

This noise (knock??) has been there since I got the truck six months and a thousand miles ago. It has not got better or worse. It does not come back until the truck is completely cold.

There is another member here that has the exact same knock and symptoms in a BII 4L and he can't locate it either. Since he noticed it, he has put about 5000 miles on his without change. He did say that it was louder on start-up when it was really cold outside.

Ed

 

[cp2295]

Okay if it happens to be a rod bearing can I have a machinist clean up the journal and just replace that rod bearing (or all of them I don't care) and not pull the pistons and all that? It would be a lot cheaper that way, and I just rebuilt the damn thing!! Doesn't burn oil or anything, worked out pretty good for my first rebuild, but this is saddening...

Or should I just put a 4.0 or 5.0 in it and call it good?

 

[cp2295]

Can you expand on this??

I also have a very light knock on my 4L OHV. It does not start immediately upon cold start-up. It takes about 15 to 30 seconds to start. And then it goes away when the temp gauge starts to move off its at-rest position. At first it seemed like it was coming from the trans (auto), then the exhaust system and finally, someplace in the engine; but, the more I looked, the less sure I have become...... It starts and drives like it should.

I have used a dowel on everything that moves or has moving parts in it and can’t hear it. By then, of course, the engine is warm and it goes away. While it is warming up, randomly the knock will go away for a second or two and come back until it goes away completely. If drive it from a cold start the noise goes away within a mile or mile and a half. Removing the drive belt does not change anything.

This noise (knock??) has been there since I got the truck six months and a thousand miles ago. It has not got better or worse. It does not come back until the truck is completely cold.

There is another member here that has the exact same knock and symptoms in a BII 4L and he can't locate it either. Since he noticed it, he has put about 5000 miles on his without change. He did say that it was louder on start-up when it was really cold outside.

Ed

And it's not a tick? I know if it's louder when it's colder and goes away as it warms up that's usually lifters/valve train. Mine starts becoming noticeable when the engine is hot. So it's the opposite.

And RonD that also doesn't make sense for me about the exhaust leak, why would it become noticeable when it's hot and not cold? Seems like the metal would expand and close up the hole?

Also it changes with engine speed if that's indicative of a rod knock.

 

[cp2295]

Also ed, get a stethoscope, they are like $3 at harbor freight, and poke around on the lower intake manifold and valve covers..

 

[Rearanger]

Okay if it happens to be a rod bearing can I have a machinist clean up the journal and just replace that rod bearing (or all of them I don't care) and not pull the pistons and all that? It would be a lot cheaper that way, and I just rebuilt the damn thing!! Doesn't burn oil or anything, worked out pretty good for my first rebuild, but this is saddening...

Or should I just put a 4.0 or 5.0 in it and call it good?

I have decided that I am going to let my engine die as I hear knocking in it and I'm tired of always screwing with this dumb motor.

Some confusion?

 

[cp2295]

Yes.. I don't know I'm wondering which to do.. 5.0 is an awesome motor but so is a 4.0 and it's easier to swap. I have found out today that it is the #4 cylinder with the rod knock. Can I have a machinist redo that crank journal and replace only the bearings or do I have to do pistons and everything? The rings are just fine no oil ever burnt and good compression..

 

[Rearanger]

How much money do you have?

 

[cp2295]

I have $1000 but I don't wanna spend all of it.. Will if need be thiugh

 

[cp2295]

Also just a side question how popular are 4.0 5 spd manual trannies? I definitely wanna keep it a stick.

 

[RonD]

And it's not a tick? I know if it's louder when it's colder and goes away as it warms up that's usually lifters/valve train. Mine starts becoming noticeable when the engine is hot. So it's the opposite.

And RonD that also doesn't make sense for me about the exhaust leak, why would it become noticeable when it's hot and not cold? Seems like the metal would expand and close up the hole?

Also it changes with engine speed if that's indicative of a rod knock.

yes, metal expands as it warms up and can change shapes, this is why you shouldn't over torque bolts, also a crack may only be noticed warm.

As far as the rod, do the spark test first to see if it is a rod bearing.
Then yes, you can just do that 1 rod bearing.
Pay close attention to the torque on that bearing cap, maybe it was loose.
Visually inspect the journals as much as possible and use plasigauge on a few places to see if rod is out of round, if it is you have to pull the head.

 

[cp2295]

Alright so I found a 99-01 5 speed manual for a 4.0, my question is will a computer from an automatic 4.0 accept the manual transmission? What kind of issues may I run into and what will I need from the 4.0 truck? Will the fuel pump workout and all?

 

[cp2295]

I think I'm just doing away with the 3.0 Ron, it gets the same mileage as a 4.0 and it had way less power, my 3.0 can never find it's idle, it's just terrible I think..