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F-Head question

60CJ5

60CJ5

Member
Joined
Jan 29, 2003
1960 F-head, was rebuilt about 20 years ago and has been running like a champ. HOWEVER, last weekend while driving up a pretty steep hill, I started hearing a knocking sound. Drove it about 40 miles today (Hwy at 50 mph) and only hear the sound when the motor is under load (up hill or acceleration in 3rd) When sitting still the engine makes no noise (for a f-head) I can rev it up and there are no knocks. Driving around the neighborhood on flat land and the engine sounds like it is running great.

it is hard to tell if it is a metallic sound or maybe a pop out of the exhaust or something. I am really baffled in that it only does it under load.

Any thoughts on what it might be? It's going to have to run regardless because it is the get away car for my son's wedding next week.

him in it 10 years ago
cj.jpg
 
60CJ5 said:
Any thoughts on what it might be?
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How's the oil pressure? "Knock under load" suggests a main bearing, or possibly a rod bearing. Not good. Use a stethoscope on the lower parts of the motor to define a location.

Alternatively... since you don't hear it when sitting still, maybe just the exhaust pipe hitting the frame or body? Engine or transmission mount rubber?

Get out and get under! Take a look, shake stuff.
 
If you had a failed rod bearing, it would be loudest under load.
No knock at idle?
What's your oil pressure?
A bad bearing would leak oil and I'd expect it to show up in the oil pressure.
Not the F134 guy!
However, these engines have a very long stroke, the rod velocity is high, and rod bearing failure seems common.
If it's a rod bearing, it will only get worse.
 
forgot to add, there is no apparent loss of power and no leaks

I dont have an oil pressure gauge but the dummy light is not coming on.

Was wondering about a mount, maybe when the engine is torqued something is moving
 
at idle, it sounds great. my neighbor actually came over while i was checking things out and said, "it sounds great, I don't hear anything"

dont hear it when starting out through 1st and 2nd gear but once in 3rd and under load it is very much there.
 
Indicator light won't come on until you have near zero oil pressure.
Not very helpful.
An analog oil pressure gauge can be installed in the Jeep, or used as a diagnostic instrument.
I have this one as a test instrument and it works well.
Mine came with fittings and tubing.
 
just have to get it up a mountain to my son's wedding venue and through next weekend and ill be free to do whatever on it.
 
I will look for a real gauge but just not going to have a lot of free time this week. I may tow it to the venue
 
Ignition timing might be off, and/or the advance mechanism might be locked up or not working properly. Might be hearing detonation.
 
Note that the torque of the engine moves the engine and exhaust when accelerating.
The engine strains on the mounts.
You could look for somewhere that the engine or exhaust is hitting the body or frame under load.
You may be able to load the engine while standing still and hear the knock.
Brake on, third gear, heavy throttle, slip clutch - that sort of thing.
 
60CJ5 said:
I am really baffled in that it only does it under load.
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As said, that could be timing. And detonation (which will destroy an engine). Check it, including advance operation, after setting your points accurately. When was the last time you did that?

Vehicles from this era were not 'maintenance-free." They were designed to be tuned to spec more or less annually.

I would not be climbing any mountains, or making long highway drives "at 50 mph" with an F-head, until you resolve this issue.
 
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I agree completely with the don't drive until I figure it out BUT it was a risk I had to take. I don't have a trailer and I had to get it here for my son's wedding.

I adjusted the valves last summer and checked the timing (it has an electronic ignition) I would guess that it only had a couple hundred miles on it over the past year.

in general, except for a rattle, it sound like this is going to end up be something major.......
 
A great fix to any Fhead issue is a v6. Seems to take care of all the issues!

My F head made all sorts of mechanical noise. I ended up just driving it and not caring. Worst thing that can happen is you throw a rod or spin a bearing..

If it self destructs or you preemptively pull it, you have to make a decision. Fix what is already antique at a large cost or go modern and significantly cheaper.

Check the easy stuff, put a oil pressure gauge on it, see what happens and drive it till it stops if it’s no easy fix.

Last time I did this I ended up with a 4.3 v6 and it has made my jeep more useful, fun and able to easily drive in everyday traffic along with the brakes and steering upgrades…

So it depends on how you look at those issues.. problem or opportunity?
 
47v6 said:
A great fix to any Fhead issue is a v6. Seems to take care of all the issues!

My F head made all sorts of mechanical noise. I ended up just driving it and not caring. Worst thing that can happen is you throw a rod or spin a bearing..

If it self destructs or you preemptively pull it, you have to make a decision. Fix what is already antique at a large cost or go modern and significantly cheaper.

Check the easy stuff, put a oil pressure gauge on it, see what happens and drive it till it stops if it’s no easy fix.

Last time I did this I ended up with a 4.3 v6 and it has made my jeep more useful, fun and able to easily drive in everyday traffic along with the brakes and steering upgrades…

So it depends on how you look at those issues.. problem or opportunity?
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This.

Just our experienced, but jaded opinions from a few people who tried to give the F-head more chances than it deserved…

The F-head is a novelty at best. It’s great if you want a Jeep to start up a few times a year to plow snow, move some firewood, or drive back roads once in a while to a car show, but propelling itself down a road is not its specialty. It’s not easily or reliably modified to make any more power than it already has, and in today’s world of distracted lunatics, that’s putting the driver and their surroundings in an elevated level of danger.

Check the timing, put some heavy oil in it and drive it till it dies. In the mean time, put your thoughts and savings towards a powerplant that makes more sense moving forward. If you’re set on the F-head, it’ll be cheaper to find a good running used one to drop in than to properly rebuild the one you have.

Good luck! I hope it’s something simple.
 
That was my thought when I started the drive yesterday. "If it blows up, a V6 is in the future" I really like the idea of being stock but the Jeep is a modified stock now, 11" brakes, dual master, electronic ignition, 2 barrel carb. The f-head works for my need except for the fact I live on top of a mountain so I have a pretty steep 2 mile climb every time I take it out. 2nd is too low and 3rd is too high.

Not that I'm going there yet, but how hard and expensive is the V6 swap for someone that doesn't weld.
 
update: I'm even more confused now. Took it out for a spin around the subdivision which has some ok hills. Could not get it to knock at slow speed in any gear on flat ground, while pulling hills, and starting on a hill. But when I got up to 45 in 3rd and give it gas, it would start knocking.

I did find a broken exhaust mount that is letting the pipe hit on the transfercase crossmember. I tried just pulling it into place with some heavy wire (until I can get to town to get a replacement mount) and need to get it back out to see..... just have a hard time believing that was the issue because of how rhythmic it sounds when it happens and it does not sound like it is coming from under the jeep.
 
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