RCP Phx
NAXJA Forum User
- Location
- Phoenix,Az
The 87-90 is the same so it sounds like you definitely have the wrong one.
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Can I have some opinions on this knock?
- Thread starter GravyDavey
- Start date
The 87-90 is the same so it sounds like you definitely have the wrong one.
- Location
- San Diego, CA
I don't see any cracking in the flex plate. It looks like the flexplate to torque converter bolts were bolted in off center, but that's it. Since I've gone this far, I'm going to get another good flexplate and bolt that in.
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Unclewolverine
NAXJA Forum User
- Location
- Kansas
Sorry to hear that the flexplate looks good, but from your description it sure sounds like rod knock to me. Might as well pull the pan at this point, it's easier with the transmission and flex plate out. Do the rmc as well.
- Location
- San Diego, CA
Wouldn't you be able to hear a rod knock with throttle? This knock goes away at 1200-1300 rpm.
8Mud
NAXJA Forum User
- Location
- Central Germany
I've used plastic tubing and localized the knock to around six inches. Most common is loose connecting rod bearings, often the top bearing half. Another is a chipped piston, the piston knocks on the cylinder wall. but there is any number of parts that can go wrong. As the oil pressure rises with RPM's, heat expansion, or plain old harmonics the knock can become less with RPM. Been my experience mild rod knock is more noticeable at idle or lower RPM. Serious rod knock can change pitch and be loud under any RPM.
8Mud
NAXJA Forum User
- Location
- Central Germany
Compression IMO It's more important that the cylinders are all the same or similar over a 20 PSI (or less) difference and you are going to notice the shaking/balance getting bad. I've seen them run OK with 105 PSI, of course, 150+ is going to give you more HP. The 4.0 is basically a 4.2 truck motor and pretty forgiving, they are built to last.
Unclewolverine
NAXJA Forum User
- Location
- Kansas
My 1st junkyard engine only had a knock at idle, particularly cold idle until one day it gradually got louder and grenaded. Up until that day I thought it was the lifters. My current junkyard engine sounds pretty similar, I plan on putting a rod bearing set in it when I get a chance. Others have had great luck doing that.
- Location
- San Diego, CA
Thanks everyone. With the compression numbers that I have, I think I'll just shoot for a rebuild at some point.
- Location
- San Diego, CA
Just a follow up. Finally got the flexplate swapped and the tranny back in. Knock is still there, no change, so definitely not a flex plate. Now I know and the brightside is I have plenty of spare flexplates. Lol
Side note the torque converter really sits back quite far when it finally goes in. Looked like about 1" from the TC bolt holes to bell housing mating surface.
Side note the torque converter really sits back quite far when it finally goes in. Looked like about 1" from the TC bolt holes to bell housing mating surface.
Unclewolverine
NAXJA Forum User
- Location
- Kansas
That's normal.
- Location
- San Diego, CA
Changed oil yesterday to Rotella 15w40 conventional looking to see if that changed my knock. Hard to tell tho. Top end is so loud now, really can't tell what I'm hearing. I let it idle for about ten minutes, but then had to go back inside. It never got fully up to temp. Wonder if I should get it nice and hot or just dump it? Kinda leaning towards dumping it and going to a lighter oil.
Unclewolverine
NAXJA Forum User
- Location
- Kansas
Lighter oil won't change it, just tried that on mine. Only thing that happened was I lost 10 pounds of oil pressure at hot idle. You should of put rod bearings in while you had the tranny out.
- Location
- San Diego, CA
I thought I'd provide some closure to this discussion for anyone that reads it in the future.
I finally managed the time to pull the pan a couple of weeks and take a look at the bearings. Rod bearings are shot. I did not come across any broken pieces in the pan, and the wrist pins looked okay from what I could tell, so I'd say the knock I had was rod knock.
Since my exhaust manifold is cracked in 2 places, and the manifold gasket decided to start working it's way out after my last off roading trip, I decided to pull the motor for a rebuild.
I finally managed the time to pull the pan a couple of weeks and take a look at the bearings. Rod bearings are shot. I did not come across any broken pieces in the pan, and the wrist pins looked okay from what I could tell, so I'd say the knock I had was rod knock.
Since my exhaust manifold is cracked in 2 places, and the manifold gasket decided to start working it's way out after my last off roading trip, I decided to pull the motor for a rebuild.
old_man
NAXJA Forum User
- Location
- Loveland, Colorado
For a cheap fix, just replace the rod bearings and mains while you are apart, as long as the journals aren't scored too badly.
