I vote, getting lucky and rolling bearings in usually works with lowered oil pressure , almost never works with rod knocks.
Knock Developing
Thread Starter
Instructor
Joined: Apr 2011
Posts: 218
Likes: 16
From: Littleton CO
Knock Developing
The patient is an L98 with 105k miles on it. The knock only exists at an audible level at idle. If you shut the car off and let it sit for just a little bit and then start it back up it takes awhile to come back. I am not sure what it is but I can tell you what it is not. It is not a valvetrain or exhaust leak sound. My oil pressure is still very good, never gets below about 20psi at idle and hot, and starts off in the 60-70 range when cold. When at higher rpm and hot it still gets up to 50 to 60.
If I had to guess I would say it is a rod knock, but after seeing some other posts about the possibility of the pre-cat fooling you, I am wondering about that. Does anybody know if rod knock shows up on a datamaster log? I ran the thing for about 20 minutes and only picked up 14 knock counts, and none of those were at idle.
Thanks for any help you guys can provide.
If I had to guess I would say it is a rod knock, but after seeing some other posts about the possibility of the pre-cat fooling you, I am wondering about that. Does anybody know if rod knock shows up on a datamaster log? I ran the thing for about 20 minutes and only picked up 14 knock counts, and none of those were at idle.
Thanks for any help you guys can provide.
Le Mans Master
Joined: Aug 2010
Posts: 9,272
Likes: 17
if the cat rock has come loose, you can put a long screwdriver to one ear and the tip on the cat and it will magnify the noise and transmit it so you can tell if thats it, other option, mechanics stethescope from harbor frieght $5. if its a rod the same procedure will work.
Burning Brakes
Joined: Sep 2008
Posts: 810
Likes: 58
From: Alva Florida
If you think its a rod, unplug a cylinder at a time and let it run. If the knock goes away, it's likely that cylinder. This would of course be after eliminating other things.
Whatever you do.... Find the problem sooner than later. bearings are cheaper than engines, and if it is just a light bearing knock you might be able to fix it rather in-expensively.
Good luck
Whatever you do.... Find the problem sooner than later. bearings are cheaper than engines, and if it is just a light bearing knock you might be able to fix it rather in-expensively.
Good luck
Thread Starter
Instructor
Joined: Apr 2011
Posts: 218
Likes: 16
From: Littleton CO
OK. So after some more investigation I have found that the sound improves with the #6 or #5 spark plug wire removed. Probably not a good sign. I also have posted a recording of the knock sound on YouTube (address below). Let me know what you guys think. How hard is the oil pan to R&R? It looks like it might be worth doing since my oil pressure is still good and the knock doesn't come on until after the car has been run hard for about 10-15 mins.
--Calvin
http://www.youtube.com/watch?v=ZxRtMfNrf6s
--Calvin
http://www.youtube.com/watch?v=ZxRtMfNrf6s
Melting Slicks
Joined: Dec 2008
Posts: 2,772
Likes: 64
From: Mystic CT
OK. So after some more investigation I have found that the sound improves with the #6 or #5 spark plug wire removed. Probably not a good sign. I also have posted a recording of the knock sound on YouTube (address below). Let me know what you guys think. How hard is the oil pan to R&R? It looks like it might be worth doing since my oil pressure is still good and the knock doesn't come on until after the car has been run hard for about 10-15 mins.
--Calvin
http://www.youtube.com/watch?v=ZxRtMfNrf6s
--Calvin
http://www.youtube.com/watch?v=ZxRtMfNrf6s
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Burning Brakes
Joined: Sep 2008
Posts: 810
Likes: 58
From: Alva Florida
I was thinking of a faint, almost inaudiable noise. I agree, pull it out and get rod bearings and rods reconditioned. Possibly some crank work or a kit.
Here's the hard part though....while its apart......a little more cam, head work, intake... what starts as a repair could be a big $$$ project.
With 105,000 miles though, a solid clean rebuild should be in order. Probably wont need to bore it out, either.
Find a LOCAL reputable re-builder. I've had bad luck dealing with out of towners on engines and transmissions.
Here's the hard part though....while its apart......a little more cam, head work, intake... what starts as a repair could be a big $$$ project.
With 105,000 miles though, a solid clean rebuild should be in order. Probably wont need to bore it out, either.
Find a LOCAL reputable re-builder. I've had bad luck dealing with out of towners on engines and transmissions.
Thread Starter
Instructor
Joined: Apr 2011
Posts: 218
Likes: 16
From: Littleton CO
Thanks, guys. I am going to pull the pan to see if I get lucky before I go full tilt and pull the engine, but I am afraid everybody is probably right, it will need a complete rebuild. *sigh* oh well, that's the chances you take with 20 year old used cars 
Is it just me, or has anybody else noticed that the engine compartment is easy to work in except for the fricking right hand front part of the engine? They crammed everything they could possible think of into that corner!
Is it just me, or has anybody else noticed that the engine compartment is easy to work in except for the fricking right hand front part of the engine? They crammed everything they could possible think of into that corner!
Thread Starter
Instructor
Joined: Apr 2011
Posts: 218
Likes: 16
From: Littleton CO
Yes, it is a 6 speed.
I have now pulled the oil pan off and pulled the #5 and #6 bearing caps and they look a bit discolored on the part of the bearing that is at the "bottom of the cap" in the shape of a butterfly.
Link to photos of bearings:
http://s1084.photobucket.com/albums/j413/calvinlc/
--Calvin
I have now pulled the oil pan off and pulled the #5 and #6 bearing caps and they look a bit discolored on the part of the bearing that is at the "bottom of the cap" in the shape of a butterfly.
Link to photos of bearings:
http://s1084.photobucket.com/albums/j413/calvinlc/
--Calvin
Thread Starter
Instructor
Joined: Apr 2011
Posts: 218
Likes: 16
From: Littleton CO
I will go with a 383 if I have to rebuild, but I was really hoping to get at least 4 to 5 road course HPDE events out of the car so I could tell how I liked it compared to the 2001 S4 I have been driving at the track. After I put the miniram on last week I finally got it up to the same straight line performance as the S4 so I was going to take it to the track to do a comparison.
BTW, I plastigauged the #6 bearing and it looks perfect at 0.0015. I am really scratching my head on this one.
Does anybody have any opinions on the photos of the bearings?
--Calvin
BTW, I plastigauged the #6 bearing and it looks perfect at 0.0015. I am really scratching my head on this one.
Does anybody have any opinions on the photos of the bearings?
--Calvin
Burning Brakes
Joined: Sep 2008
Posts: 810
Likes: 58
From: Alva Florida
And it starts...While it's apart.....
Since you already have a mini-ram on it, you can go mild to wild.
Heads, cam, stroke, all about $$$ now.
Problem is that once it starts knocking, the rod is likely not perfectly round now. The rod needs to be re-conditioned at the least.
You would be quite satisfied with the 383 upgrade though.
Get quality parts though. Scat I've read is better than eagle, and for my 421, I went to Ohio Crankshaft, after the engine builder recommended it. Ebay parts are tempting, but the aggravation might not be worth the savings.
Just trying to be helpful. I've wasted a lot of money trying to save money.
Since you already have a mini-ram on it, you can go mild to wild.
Heads, cam, stroke, all about $$$ now.
Problem is that once it starts knocking, the rod is likely not perfectly round now. The rod needs to be re-conditioned at the least.
You would be quite satisfied with the 383 upgrade though.
Get quality parts though. Scat I've read is better than eagle, and for my 421, I went to Ohio Crankshaft, after the engine builder recommended it. Ebay parts are tempting, but the aggravation might not be worth the savings.
Just trying to be helpful. I've wasted a lot of money trying to save money.
Burning Brakes
Joined: May 2011
Posts: 838
Likes: 2
From: Louisville Ky
I will go with a 383 if I have to rebuild, but I was really hoping to get at least 4 to 5 road course HPDE events out of the car so I could tell how I liked it compared to the 2001 S4 I have been driving at the track. After I put the miniram on last week I finally got it up to the same straight line performance as the S4 so I was going to take it to the track to do a comparison.
BTW, I plastigauged the #6 bearing and it looks perfect at 0.0015. I am really scratching my head on this one.
Does anybody have any opinions on the photos of the bearings?
--Calvin
BTW, I plastigauged the #6 bearing and it looks perfect at 0.0015. I am really scratching my head on this one.
Does anybody have any opinions on the photos of the bearings?
--Calvin
it has happened before, springs get loose, can't be heard except at idle, the ONE time I heard it.
your bearing looks "burnished" not worn, exactly. you can see burnish because of light reflection, or refraction, but sometimes cannot be measured except in millionths of inches, like the lapping process for parts that are lapped for finish.
I am not an expert, but was a refrigerator compressor engineer for years. just a thought.
Burning Brakes
Joined: Sep 2008
Posts: 810
Likes: 58
From: Alva Florida
Yes, I'd show those bearings to a professional rebuilder. They didn't look horrific, but i'm no expert either.
I've heard about the flywheel noise being mis-interpreted too.
Do your homework. It will save you time and $$$. How would you feel if you rebuilt the engine and found out it was something else?
I've heard about the flywheel noise being mis-interpreted too.
Do your homework. It will save you time and $$$. How would you feel if you rebuilt the engine and found out it was something else?
Thread Starter
Instructor
Joined: Apr 2011
Posts: 218
Likes: 16
From: Littleton CO
I will definitely take the bearings down to somebody who knows more than I do. I am also going to finish pulling the bearings today to check the others. If they all check out and the engine builder says they look OK then I will probably re-bearing while I am in there and then see what happens when I bolt it back together. The dual mass would be my next to look at if the noise is still there. The dual mass flywheel is an interesting one. Anyway to tell that while I am underneath the car without taking the damn tranny out?
--Calvin
--Calvin
