Knocking Noise

[thatxjguy]

There was about 1" of deflection in my MJ's timing chain when I rebuilt the motor. 0.5" is the replacement point.

I just got the timing cover off my LJ. Over 0.5" of deflection in the chain, rub marks on the cover, and one of the mounting tabs for the chain guide broke off causing it to slap against the inside of the cover. I do not know if that will solve my knocking noise yet, but I have fixed four different noise sources over the past two days.

What is the mileage? It's not easy to wear out a chain. A belt, I could understand.

 

[Mach2nh]

Its hard to tell with videos but i had a knock or tic sound that i had a hell of a time finding. I could hear it in the cab and outside. In the cab it sounded like it was low on the firewall but under the hood i couldnt pin point. It would speed up with rpms as well. Turns out it was the click from the evap purge solenoid on the pass side firewall.

 

[Alexia]

What is the mileage? It's not easy to wear out a chain. A belt, I could understand.

168,000 miles and my issues with power production started 30,000 miles ago.(The past few weeks it had difficult starting due to timing being off.) Jeep 4.0L timing chains usually are recommended to be replaced at 100,000 miles. Not necessarily needed, but to keep the engine running efficiently. I checked mine at 116,000 miles and it looked fine at that time.

 

[civic50]

Sounds a lot like a rod knocking. Going to a thicker viscosity oil may help quiet it down in the short term but is by no means a fix. Next time you change your oil drop the oil pan and give the rods a jiggle, find the one that's moving the most, remove the cap, plasti-gage the bearing to check the clearance,(check the FSM for your truck for tolerances). That will tell you how bad it is and give you a course of action. Good luck.

 

[Alexia]

Good luck, thatxjguy. My LJ is all back together and running with more power with all the bits replaced. However, it still knocks towards its death. It is definitely internal engine for mine. Hopefully you get lucky and it is not internal for your engine.

 

[thatxjguy]

Thanks for the best wishes, I certainly hope it's not a rod knock. This engine has been taken care of religiously as far as oil changes and and maintenance go.

This guy with a Comanche at 300,000 km has the same sound I do:

http://www.jeepforum.com/forum/f53/flexplate-knocking-more-2065857/

Looks like he took all his bearings out and they were all within spec. What confuses me is that the title says flex plate. I might just have to look into mine one more time.

 

[thatxjguy]

Alright, so regarding the sound in the bottom end...

I unplugged all of the fuel injectors one by one as the engine was running and the knock went away at cylinder 6.

So I believe the issue may be a rod bearing. I'm going to try rolling in new bearings to see if the problem goes away before I completely re-build the thing. Maybe it's not scored too bad yet.

 

[Hoooper]

yeah there are still a handful of possible causes, but rod bearing is a good start with that info.

 

[thatxjguy]

Knocking SOLVED!

I rolled in a set of new rod bearings today with the engine still in the chassis (super easy with my 6.5-inch lift), and wowwwwwww, cylinder 6 was really worn:

Cylinder 3 was also pretty bad, as was cylinder 5, but the others were alright. I replaced all 6 rod bearings just to be safe.

I feel much better without any knocking. The crankshaft looked great, pistons looked great, no wrist pin movement. I'm happy!

 

[Hoooper]

glad you found a fairly simple solution. How many miles did they have?

 

[thatxjguy]

glad you found a fairly simple solution. How many miles did they have?

Thanks, I'm happy too that I dropped $30 for bearings instead of $3000 for a new motor!

155k