2F Knocking noise at idle? (1 Viewer)

This site may earn a commission from merchant affiliate
links, including eBay, Amazon, Skimlinks, and others.

78crzr

78crzr

Joined
Apr 6, 2003
Threads
104
Messages
755
Location
Tomball, TX
Well, took the 40 out today for the first time since the carb. rebuild. I'm getting a knocking noise while idling. The engine supposedly has 107,000 miles, but for all I know it could be 207,000. The title was mileage exempt. I've owned it for about a year and put 3,000 miles +/- on it and never heard the knocking sound before. Any ideas what it might be?

I'm also noticing some smoke upon taking off from stops. Didn't notice this before the Jim C. carb rebuild, although I'm very doubtful the carb has anything to so with the smoke. I'm wondering if it is head rebuild time, or total engine overhaul time? :eek:
 
Does it speed up and get louder with an increase in the engine RPM's?
 
Can't really hear it at anything more than idle. Guess I need to pop the hood while idling and bip the throttle and see. Any ideas either way?
 
Well, if it does not increase intensity with engine RPM's, and you have strong oil pressure, I would not worry about it, as I have known a few 2F's that have had a low 'knock' sound at idle, and ran for years, and are still going, without any problems...But generally speaking, a steady knocking from the engine is not a good thing...You could have a rod bearing that is starting to lay down on you, but without dropping the oil pan, and dropping the rod bearings, you will not know if it is something in the bottom end, of course, unless it lets go while running, in which case, you will know EXACTLY what it was...

Good luck!

-Steve
 
Mine has knocked constantly since I got it 12 years ago. Never had a problem with it. It seems to scare most people but hasn't bothered me. (though I am still swapping for a 4.3)
 
Get a 4 foot long dowel and put it against various parts of the engine while it is running (don't stick it in the fan blades!). Put the other end of the dowel up to your ear and you will hear the knock. This is a poor man's stethoscope.

I have a similar knock and have identified it as coming from the timing gears. With the dowel method, you can (sortof) tell whether an engine noise is coming from the top end or bottom end and approximately where along the length of the engine. Push the clutch end and see if the noise changes as some tapping, knocking noises can come from the clutch.
 
I had a similiar knock from my F. After dropping the oil pan I found it was just a loose weld on one of the baffles in the pan. The baffle was just tapping the oil pump strainer. Not sure of all the lower end differences from the F to the 2F but it might be a similiar gremlin
 
my first thought was a loose rocker-pushrod. After reading the other posts, I also remembered the swb has a knock in the timing gears. Been there for 8+ years now, ever since I took out the grenaded fibre cam gear and put a steel one in! Too lazy to put a matched new set in.

Ditto on the dowel stethescope suggestion.
 
I know this thread is super-old... but just bought a 2F with a bunch of miles on it, and the owner said it is making the same noise at idle. He thought it might be the fuel pump, but was unsure. Its getting torn down but just curious if anyone figured it out...
 
The 2F I had before my FJ40 rebuild had a similar knock at idle - sounding almost like a diesel. Jim C. said it was most likely a worn place on the cam shaft at the fuel pump. We swapped in a rebuilt 2F and I don't know if Jim C. did an autopsy on the old one.
 
Im getting a knocking noise at idle, sounds like it is coming from the back on the engine near cylinder 6, lower down in the engine if not close to the timing gears. Knock stays constant at idle and knocking increases with revs. At idle, it gets louder and quieter at random. Thoughts?
 
While it's running and knocking, pull the spark plug wires (wear gloves), one by one, reattaching each one as you go down the line so that 5 cylinders are always in play at any given time. If the knocking quits, you may have found a cylinder with out-of-spec bearings or some other tolerance issue. You also might monitor oil pressure (with a real gauge) vs. knocking sounds to see a correlation.
 
Oil pressure is great, stays great though all rev ranges. Ill try the spark plugs and get back to you.
 
I like to use a long screwdriver or something similar as a stethoscope to help isolate internal noises.
 
Pulled all the plugs, signs point to cylinder number 6 as the culprit of the knocking. What is the fix?

Any way it could be timing? Have not had that adjusted since the engine was new about a few thousand miles ago.
 
Last edited:
If you really think it’s #6, you should drop the pan NOW, while there’s still a chance to save the motor. It is possible to polish the crank in the truck and replace a rod bearing. There is a VERY old thread from @Romer that describes the whole ordeal. But he and @nuclearlemon and a couple of other cruiserheads from Rising Sun saved that engine.

I have done it once or twice myself.
 
You must log in or register to reply here.

Similar threads

cims1970fj40
Idle Cut Solenoid
Replies
2
Views
584
ToyotaMatt
ToyotaMatt
R
Clunking noise
2
Replies
36
Views
1K
RevISK
RevISK
arep831
Slow idle help
Replies
6
Views
463
arep831
arep831
nmemtp01
1978 FJ40 metallic engine noise
Replies
4
Views
299
franklin40
franklin40

Users who are viewing this thread

Total: 2 (members: 0, guests: 2)

Share this page

Back
Top Bottom