da_jokker

Hi all. Just recently became a Jeep owner. Stumbled on a 93 XJ with 55k original miles (supposedly). However, I'm pretty sure I have a #5 Rod knocking. I do plan on checking the flex plate bolts just to be sure but my stethoscope seems to place the sound just below the #5 right at the bottom of the block.

With only 55K I'm dumbfounded that something like this could happen. One of the things that got me into this was this rock solid 300K mile 4.0 engine I read so much about.. and to think I may have to replace the engine? Anyway, just wondering if anyone has any suggestions.

My plan is ...

1) check the flex bolts (just in case but the stethoscope was pretty quiet on the bell housing)
2) Maybe do an Engine Flush treatment
3) As part of #2, replace the oil. Trying to figure out which oil\weight might be the best chance of helping IF in fact it is a rod knock

I was reading about the possibility of dropping the pan and replacing the bearing on that one rod. Who knows, maybe I might find that the bearing is junk but there isn't any real damage to the crank so I can just pop in a new one and cross my fingers?


Also, I just did a tune up on it and while I was in there, I did a compression check. I'm really hoping my HF gauge is just crap because I only got 120 on all cylinders, but my #1 is actually lower at 100. I'd swear if I hadn't bought this from a little old lady who got it new when she was 70 and now she is 90 and can't drive... I would have thought someone swapped in a POS engine with 200K on it.

EZEARL

Just happen to be trying to keep a 5.0 '84 F-150 alive with a rod knock among other issues. The truck is strictly a temporary source of local transportation until they get another vehicle so not a lot of time,work,or money is going into it.. Anyways I recently found it about 3/4qt low on oil. Had a quart bottle of Lucas oil treat someone gave me. I top off the motor with it and drove around the house a bit. It was still knocking. Went out maybe 6hrs later and no knock. Next morning was right cool out. No knock. They stopped by yesterday. No knock. Got me baffled but it's working.

Turbo X_J

Aluminum chunks in the oil pan?

Tbone289

Good question. Why do you think it's rod knock and not, say, lifter clatter, for instance?

da_jokker

Good idea... I was thinking of the same thing... add some oil additive and just see what it does. I'm pretty sure that they just did an oil change before I bought it but I don't have any idea what kind they used.. but they did mention Synthetic.

da_jokker

I have not drained the oil. Debating that now but thinking of adding either an oil additive or an oil treatment before I dump out the existing oil.

da_jokker

I'm by no means an engine noise expert, but I can definitely hear the valve train, but with normal sounds. When you are under the hood listening, you can't hear the knock as well. It is much more pronounced when you step back (couple feet away). It is also a "single knock". I don't have a timing light to see if it is 1x per rev, but I just read something about pulling a spark plug wire and see if the sounds lessens...

So planning on doing that ASAP.

da_jokker

Something I was just reading that I would think would be promising is about something called Plastiguage. I would think that I should be able to drop the pan, pull the end-cap off #5 and use Plastiguage to check my clearance. Then replace the bearing with the appropriate thicker one, and be good to go (providing no severe damage to the crank or rod).

Could it really be that easy?

Turbo X_J

Possible broken piston skirt, chunky oil would indicate this.

Tbone289

If you rev the engine from idle in park, does the noise get louder as it increases RPM?

da_jokker

So just doing a normal oil drain would show this, or would I need to drop the pan?

da_jokker

No, actually I 'think' it gets a lot quieter or actually goes away. I say 'think' because I know I can't hear it but I wonder if it is not just from the engine getting loud enough to drown it out otherwise. Say it was only at idle and not under higher RPM's or load... does that point to something else?

dzywicki

When the piston skirt cracked on my '99, I had to pull the pan. It was broken off in a couple of chunks too large to fit through the drain hole. I was thinking this as a possibility too, but I think it would be lot louder than you are describing with your problem. Sounded horrible when it happened on mine.

To answer your other question about plastigauge. Once you drop the pan, you have easy access to all the connecting rod bearing caps.

One tip for dropping the pan. Use . jack under the front diff and jack it up. Counterintuitive, but it will move the axle forward and out of the way. Otherwise, it will look like it should come out but will not fit. You may also need to remove the oil pump to get the pan all the way out. For replacement, put the pump in the pan get it in the right spot, then put the pump back on and then bolt the pan up.

Cherojakee

If your mostly hearing it at idle, it may likely be a flex plate knock. A rod knock would get louder with rpms, while flex plate would be quieter.

Tbone289

Agreed. It could also be a sticking HLA (lifter). Lifter noise is usually much quieter by 1500 RPM. Rod knock will also get quieter if you disable ignition or fuel to the affected cylinder.