• Welcome to the new NAXJA Forum! If your password does not work, please use "Forgot your password?" link on the log-in page. Please feel free to reach out to [email protected] if we can provide any assistance.

Please help ID this knock - movie link attached

G

gone postal

NAXJA Forum User
Location
St. Augustine, FL
This is a continuation of this thread - http://www.naxja.org/forum/showthread.php?t=910495 - but I felt best to just start a new one to help diagnose the noise.

I tried using a hose as a stethoscope, but didn't have much luck. I honestly don't think it's an exhaust leak - sounds mechanical to me, but I've never had anything internal go wrong on an engine or an exhaust leak, so what do I know?!? I do have good oil pressure though:

new oil pressure sending unit - old one read 40 just about all the time
'91 HO 4.0 167k
60psi cold
At 210, I'm seeing 30 idle / 45-50 at 1500RPM cruise
At high 220s (overheating issue is next task) I'm seeing 20 / 35-40

Fresh 10W30 w/ half bottle SeaFoam in right now - only 20 miles on it.

Cameria is inches from the engine to ensure sound showed up. I started on driver's side and moved to pass. From the side of the engine, it sounds if it's louder towards the front than the rear. From the front of the engine, there is obviously fan noise, but it sounds just generalized. I'm guessing 2nd / 3rd cylinder area though. Any ideas?

http://www.andrewedwardsphotography.com/Random%20Photos/knock%20knock.MOV
 
Last edited:
Sounds like an extrmeley loose timing chain, that's pretty good oil pressure to be having a knock, but sounds like the timing chain is hashed, you could pull the oil pan though and start wiggling rods and the crank around and check for any play.
 
Yeah, I heard someone in another thread mention a timing chain can make a similar noise. I also heard water pump, wrist pin, etc.

The camera picked up more noise than I'd like - the rockers aren't that loud, but I guess that lil mic is pretty sensitive - definitely meant for usual 10-15' video action and not 6".
 
Sorry, I missed that part.

I'd pull the oil pan and see what you're dealing with.

But my guess is that you won't find a whole lot with that good of oil pressure.

If everything under the pan checks out, pull the timing cover, my guess is that the chain is about to break.
 
I have a Haynes & Chiltons, so I know I can get through the job, but are there any special tools required for this? Will I basically just need the chain & gasket? I don't know if there are any other wearable items in there. I'm obviously assuming that unless the cover & gears are chewed up, I'd be safe.
 
That's not a timing chain, at least compared to what mine sounded like. The sound is too dull...a stretched chain makes more of a mettalic tapping sound on the inside of the cover, and that rhythm is too fast.

Jeff
 
does the knocking get faster as the engine revs up? i'm gonna second the timing chain (possibly guides?) but I'd cehck your distributor as well. I've seen bent shafts make similar noises.
 
Well, noise is throughout RPM range. I'd say it gets faster w/ revs, but then again, the revs themself are getting faster, so I'm assuming it's something that is definitely mechanically linked.
 
I had someone who heard it tell me that (cracked or detached skirt) too! Not good, is it?

If I drop the pan to fix the rear seal, is that something I can feel as 'loose' from inside underneath?

And if it's true, how much time is left??


-Skip
 
I busted a piston skirt in a 4.0 once with a minor hydrolock. Compression went south in that hole and it made some noise, but not quite like in the video. Hard to tell with the mike that close.
At bottom dead center I could grab the bottom of the piston and move it back and forth easily. The steel strut in the middle of the casting was all that held it together. Easily found with the pan off- and if that's the problem I'd park the motor immediately.
 
I bought mine for $100 a while back.
Its a 93 that sounds exactly like that as well. When i rev it, the sound speeds up, it is a clackity knocking sound. Mine sounds as if it is coming from the top of the motor towards the firewall. But cant tell. I drive the damn thing almost everyday with no loss of power. All the gages are reading out great. The video that u posted has the EXACT same sounds my engine is making to the T.
Ill be keeping my eye on this thread.
 
JJacobs said:
I busted a piston skirt in a 4.0 once with a minor hydrolock. Compression went south in that hole and it made some noise, but not quite like in the video. Hard to tell with the mike that close.
At bottom dead center I could grab the bottom of the piston and move it back and forth easily. The steel strut in the middle of the casting was all that held it together. Easily found with the pan off- and if that's the problem I'd park the motor immediately.
Click to expand...

I don't like the idea of a busted skirt.

Engine knocked when I bought it last June. A few weeks ago, I took it muddin'. Slid off into the "deep" end of the hole, but was able to get out. During the process though, the engine had shut off - was hard to start - dieseled like crazy when I got it out. I checked the air filter - 2" water in box and filter was soaked. I was able to make it outta the woods, but it shut off again once I hit the main road and wouldn't restart. I let it sit for 15min. while we unloaded all my crap from my XJ into my brother's. I tried to restart one more time and it worked!! It was even quieter than when I entered the woods too!!

So, I may or may not have had a slight hydrolock - others have just suggested that I shorted the distr. w/ water. The engine seems to make good power though, so I don't know if I have a lost piston. I guess I can do a compression check too.
 
That almost sounds like a rod is bent alittle bit... It sounds too darn dull to be a chain. If you hydrolocked it, a bent rod is possible.... We blew a dodge ram 318 motor doing that...

My advice, drop the pan and take a look. With the pan down, you can check the skirts, you can check the rods, check for play at the bearing areas, AND you can get a sneak peak at the timing chain as well. You'll be able to get a finger in and there and feel how much slop is in the chain...

With the pan off, the bottom end of the 4.0 is pretty accessible. You can view and check out pretty much everything...

Let us know what you find out!

Justin
 
Last edited:
Just curious... I've been told that if you have to replace a piston, you have to do them all, then you have to bore it to round again and use oversize, then new bearings, etc. IF a piston cracked, and all else seemed acceptable (of course there'd be play in a 250k engine..) could you just replace the bad piston, in original size and be no worse off than if it just hadn't cracked???

What would be the bare minimum to get it back on the road? Not talking about making everything perfect, but wanting it to keep going until the next 'normal and expected' thing breaks, many more miles down the road.
 
I guess technically you could re-use your old rings and just replace the piston itself. Im pretty sure if you want to replace rings, you gotta do them all, and you gotta atleast hone the cylinders so that the new rings seat properly.

I doubt it would be very good to have super good compression in one cylinder and 250k mile compression on the others...

I dont know...if you want to keep the jeep, and you find a big failure like that, ide just rebuild the thing. My mom's 97 ZJ had an oil pump failure and I tore into it. ended up just replacing all of the main and rod bearings with standard sized stuff. Didnt find any wear on the 127k mile crank...so I figured Ide see what happens. So far its working perfect.

Ide pull the pan before you start worrying about replacing rings and all that jazz though.

J.
 
You must log in or register to reply here.

Similar threads

2
engine noise
Replies
9
Views
2K
Winterhawk
Winterhawk
G
98 XJ tick tick ticking!
2
Replies
29
Views
5K
straws
S
A
00 XJ - Low oil pressure at hot idle. Compression and analysis are good, what's next?
Replies
12
Views
2K
sixditchoffroad
sixditchoffroad
S
Warm Knock
Replies
2
Views
299
SFXJ125
S
W
Manual Trans not going into gear after warming up
Replies
15
Views
2K
cruiser54
C
Back
Top