Engine Knock: the search has begun

[Columbo]

Last summer my 1975 2002 developed a knock.  The knock seemed to get louder when revving the engine and at a certain rpm range.  I unplugged the plug wires one at a time and it would be less pronounced when the #2 wire was pulled.

 

Fast forward to today in my cold, unheated garage.  I removed the front subframe because I want to rebuild the steering box, replace some bushings and also needed to replace my leaking oil pan gasket.  It was also a good time to take a look see at my bottom end rod bearings.

 

First, there is NO metal in the oil pan, none.  Second, the rod bearing have no vertical play that I can tell, just a tinyIMG_1049.MOV bit of play in the forward/aft direction.  However, the timing chain, when pushing the portion in between the two gears, has about a half inch movement.

 

Any thoughts and/or any additional checks would be much appreciated while I have the oil pan removed.

 

 

[ingramlee]

I'm experiencing the same symptoms. Almost exact! The difference in my case is there is no change in sound when pulling the plug wires one at a time. I shimmed the oil pump several months ago, which also had no effect on the knock. I too have no metal in oil pan. So much for my plans to try and make the Vintage this year.

[E39guy]

Sounds a lot like my symptoms. My rod bearings were cashed out. 

[Hans]

With the pan off, it's not much more work to Plastiguage the bearings and re-torque the bearing caps. At minimum I would do #2. The noise is coming from someplace.

[Columbo]

E39Guy, did you have metal in your oil?  Is it possible to have a shot bearing without seeing metal in the oil?  

 

 

 

[Hans]

The metal could be in your oil filter.

[E39guy]

The oil didn't really flag any obvious issues. It was really a mystery until I tore it apart. 

 

It really didn't make the noise unless I held it at just the right RPM. I was convinced it was the top end, I adjusted the valves 3 times before I tore it down. Mind you I don't know the history of this engine very well. 

 

 

[TobyB]

Quote

At minimum I would do #2.

And #3.  It's the most- likely to starve...

 

The chain can loosen from working on the engine.  The tensioner can fail, too, and chain slap is pretty noisy- but if you're listening around, it's super- easy to isolate.

 

t

 

[Columbo]

I removed the #2 lower rod bearing and it has a grove wore roughly down the center (see picture).  The crank is shiny and smooth.

 

What do you think?  Could this tiny groove be the source of the knock?  Remember that when I would unplug the #2 plug wire the knock would lessen quite a bit.  

 

The bearing has "STD" stamped on it so I guess that's a good thing, not having an over sized one put in in the past.

 

 

[Columbo]

Or is that groove supposed to be there in order for oil to pass?  

[TobyB]

That bearing shell looks pretty done to me.  

The babbit is either gone or pretty deformed and discolored, and whatever cut that groove wasn't small.

And it had a friend- look at the other groove low on the surface in your picture...

Feel the entire circumference of the crank- and take a look at the top shell, too.  Most crank wear happens on the inside 

(part that seems deepest- set between the counterweights) where the piston's shoving on it hardest.

 

Then you get to measure- the 'real' way is with tools. but you could get a new set of bearings, put them in,

and plasti-gauge it.  It's not going to be perfect, but new bearings may get it running again.

 

t

 

[JerryC]

I'm no engine expert, but I've seen a few bearing inserts. That one looks pretty ugly, in my opinion. Just saying...

[kbmb02]

22 minutes ago, TobyB said:

That bearing shell looks pretty done to me.  

The babbit is either gone or pretty deformed and discolored, and whatever cut that groove wasn't small.

And it had a friend- look at the other groove low on the surface in your picture...

Feel the entire circumference of the crank- and take a look at the top shell, too.  Most crank wear happens on the inside 

(part that seems deepest- set between the counterweights) where the piston's shoving on it hardest.

 

Then you get to measure- the 'real' way is with tools. but you could get a new set of bearings, put them in,

and plasti-gauge it.  It's not going to be perfect, but new bearings may get it running again.

 

t

 

 

I've heard the 510 guys we race with sometimes cut grooves like that (lots of them) in their bearings to reduce friction in an effort to go faster.

(or, they trim the shells so only a percentage is actually touching the journal). 

 

More on topic, I'd agree that bearing is toast. But, highly doubt that groove is the source of the knock. -KB

[Columbo]

I just got the upper half out and it is even worse looking.

[Columbo]

So I'm looking in my handy dandy Haynes manual and it states the "big end bearing running clearance" as .00090 to 00272 in.

 

Where am I to take this measurement?  I have a digital micrometer.

 

Also, is it standard practice to change all of the bearings while I'm at it or just the bad one?

 

Thank you for all of the replies.