Help diagnosing engine knock sound (1 Viewer)

Joined
Jun 16, 2015
Messages
24
Location
Monterrey, MX
Hello all, I am aware the 3FE is a noisy engine, however, there is a clack/knock sound that has been getting more noticeable lately. I suspect the sound is valve related.

Perhaps someone can help me identify what is causing it to see what I need to work on.

Some information:
-1992 FJ80 3FE 182K
-Just checked valve lash, all in spec
-Compression relatively ok
-Pulled plugs one by one and no change in knocking sound
-Using a stethoscope i found out:
a) Noise is coming from the back of the engine (cylinders 4,5 or 6).
b) The exhaust manifold of the cylinders mentioned above produced the loudest knock through the
stethoscope. I could hear the knock in the block and head too, but definitely not as loud.
c) I removed the valve cover and the area between valves #10 and #11 in the valve rocker shaft
produced the loudest knocking sound (as loud as the exhaust manifold mentioned above).

-Knock is loudest between idle and 1500rpm.
-Visual inspection of valve train revealed no abnormalities (at least to my untrained eye).
-Knock is most noticeable when listening behind driver’s side wheel, under the truck (watch attached video), and it's much less perceptible when standing in front of vehicle with hood open.

VIDEO BELOW:



Thank you!

ml111
 
Joined
Mar 25, 2005
Messages
2,129
Location
Edmond, Oklahoma
That's a very impressive video. It does sound like a valve or two is not adjusted properly (too loose). I know you mentioned that they are within spec. I would try adjusting them with the engine running. You have already figured out how to keep it running with the valve cover off. A couple tips: break loose all the nuts and retighten snug, then do your adjustments and make sure your engine is idling as low as possible with AC off. What you will notice is if the adjustment is too tight, the engine will lope/miss. If it is too loose then the valve will tap. Set in the middle of the two adjustments and you will be good. On the 3FE and 2F that is the best way to make sure your valves are adjusted properly. You can also check with a feeler gauge when you are done just too double check your adjustments.
 
Joined
Mar 23, 2014
Messages
531
Hello all, I am aware the 3FE is a noisy engine, however, there is a clack/knock sound that has been getting more noticeable lately. I suspect the sound is valve related.

Perhaps someone can help me identify what is causing it to see what I need to work on.

Some information:
-1992 FJ80 3FE 182K
-Just checked valve lash, all in spec
-Compression relatively ok
-Pulled plugs one by one and no change in knocking sound
-Using a stethoscope i found out:
a) Noise is coming from the back of the engine (cylinders 4,5 or 6).
b) The exhaust manifold of the cylinders mentioned above produced the loudest knock through the
stethoscope. I could hear the knock in the block and head too, but definitely not as loud.
c) I removed the valve cover and the area between valves #10 and #11 in the valve rocker shaft
produced the loudest knocking sound (as loud as the exhaust manifold mentioned above).

-Knock is loudest between idle and 1500rpm.
-Visual inspection of valve train revealed no abnormalities (at least to my untrained eye).
-Knock is most noticeable when listening behind driver’s side wheel, under the truck (watch attached video), and it's much less perceptible when standing in front of vehicle with hood open.

VIDEO BELOW:



Thank you!

ml111
Sounds like valves to me ,double check your right at tdc and recheck clearance with feeler gauges , or adjust valves one at a time with it running,my 3Fe sounds exactly the same with a loose valve
 

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