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  #16  
Old August 30th, 2021, 20:00
maxbraketorque maxbraketorque is offline
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Re: Can I have some opinions on this knock?

Factory service manual says 120-150 psi with max 30 psi variation. You're in there, but barely and on the low side.
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  #17  
Old August 30th, 2021, 21:56
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Patrick S. Patrick S. is offline
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Re: Can I have some opinions on this knock?

I had a difficult time seen the flexplate crack. Take another look with a powerful flashlight. Look closely at the area by the bolts that go to the crankshaft. Keep us posted.
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  #18  
Old August 31st, 2021, 13:35
GravyDavey GravyDavey is offline
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Re: Can I have some opinions on this knock?

Thanks. I'd like to run a leak down test at least on cyl 3 and 6.

I also picked up a good condition OEM flexplate. Debating on whether to tackle that job this weekend or not.
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  #19  
Old September 5th, 2021, 08:03
GravyDavey GravyDavey is offline
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Re: Can I have some opinions on this knock?

I got the transmission off yesterday, and wouldn't you know that the aforementioned good condition oem flexplate that I picked up looks nothing like the flexplate in my jeep. The timing windows are completely different. I haven't pulled the old flexplate off for inspection yet. I hope to get to that later today.

Mine is 88 4.0, and the one I picked up is supposedly out of an 87. I'll post up pics later when I get a chance. I'm curious what jeep the flexplate I have came out of.

While I have it apart, I figured that I'd go ahead and replace the seal at the input shaft. Is that seal commonly referred to as torque converter shaft seal? I only see one option on RockAuto.
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  #20  
Old September 5th, 2021, 09:53
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jeep ride jeep ride is offline
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Re: Can I have some opinions on this knock?

l always called them front transmission seal.
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  #21  
Old September 5th, 2021, 10:17
RCP Phx RCP Phx is offline
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Re: Can I have some opinions on this knock?

Quote:
Originally Posted by GravyDavey View Post
Mine is 88 4.0, and the one I picked up is supposedly out of an 87. I'll post up pics later when I get a chance. I'm curious what jeep the flexplate I have came out of.
The 87-90 is the same so it sounds like you definitely have the wrong one.
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  #22  
Old September 6th, 2021, 17:46
GravyDavey GravyDavey is offline
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Re: Can I have some opinions on this knock?

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.

Last edited by GravyDavey; September 6th, 2021 at 18:00.
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  #23  
Old September 6th, 2021, 19:35
Unclewolverine Unclewolverine is offline
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Re: Can I have some opinions on this knock?

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.
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  #24  
Old September 6th, 2021, 20:03
GravyDavey GravyDavey is offline
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Re: Can I have some opinions on this knock?

Wouldn't you be able to hear a rod knock with throttle? This knock goes away at 1200-1300 rpm.
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  #25  
Old September 6th, 2021, 23:28
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8Mud 8Mud is offline
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Re: Can I have some opinions on this knock?

Quote:
Originally Posted by GravyDavey View Post
Wouldn't you be able to hear a rod knock with throttle? This knock goes away at 1200-1300 rpm.
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.
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  #26  
Old September 6th, 2021, 23:36
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8Mud 8Mud is offline
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Re: Can I have some opinions on this knock?

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.
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  #27  
Old September 7th, 2021, 06:20
Unclewolverine Unclewolverine is offline
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Re: Can I have some opinions on this knock?

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.
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  #28  
Old September 7th, 2021, 09:31
GravyDavey GravyDavey is offline
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Re: Can I have some opinions on this knock?

Thanks everyone. With the compression numbers that I have, I think I'll just shoot for a rebuild at some point.
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  #29  
Old September 18th, 2021, 06:42
GravyDavey GravyDavey is offline
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Re: Can I have some opinions on this knock?

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.
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  #30  
Old September 18th, 2021, 10:49
Unclewolverine Unclewolverine is offline
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Re: Can I have some opinions on this knock?

That's normal.
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