Knock

I am the proud owner of a 1958 A120 which has been on the road for about the past 10 months. It ran pretty well for about 7 of those months then got to where I was downshifting to go up hills I never had to downshift for before. As I don't have much in the line of diagnostic equipment I took it to a reputable shop and they said it was timing and retimed it at that time. It ran pretty well again until the past couple of weeks when I seemed to lose power overnight. One day it was running great and the next, literally, it is running poorly, ie. no power, and making a knocking noise it never made before. I started it and the noise was present so I pulled the spark plug wires one at a time to see if I could identify where the problem is and could not find any noticeable difference and the noise was present through all 6 spark plugs. Any suggestions? I need to get this guy back on the road so I can go get some water, we're really dry here in Santa Fe.

I do driveability diagnosis and I'm amazed at how many people don't recognize a miss.
Is the engine missing on one or more cylinders?
A misfire will definitely make low power.
When you pulled plug wires (I would've done that, too without equipment) did the engine react the same on all six?
In other words, run equally each time (but WITH a noticeable reaction) on all six?
Any overheating problems? Unexplained coolant loss? Did it run low on oil recently?
The knock...same intensity at all times? Comes and goes? Changes with throttle application?

Once it cools a bit you need to pull sparkplugs and play "one of these things doesn't belong here" ala Sesame Street and report if the business ends of the plugs all look the same.
OR do you have a wet, oily one?
Engine smoke warmed up? What color?

Beg, borrow, steal or actually buy a compression gauge and a vacuum gauge and give us a report.
A timing light would be a great idea, too.
I love these old trucks but DEPENDING on a fifty or sixty year old piece of machinery to help you sustain life might be unreasonable.
Time to get a newer back-up vehicle.
Preferably in this millenium.

As one who "depended" on my '42 K-7 for transport I would disagree with that last statement. Do you think people didn't depend on these daily when they were younger? The do require maintance at a rate that no new vehicle does, however. If you are the turn the key and forget it type then an older vehicle would not be the best choice.
The knock can be anything from carbon to a bad bearing or piston. Carbon in the combustion chamber can stay glowing red hot and ignite the new mixture prematurely giveing a sharp knock that doesn't go away even if that plug is grounded or dis-connected.
Try to isolate the noise to top end, bottom end or middle (cyl) Bottom end noise is bad and you shouldn't contiune to operate it or you risk the whole engine. Top end might be cured by new plugs or de-carbonizeing the head. Middle could be piston slap or wrist pin but neither of these would likely result in low power.
I find simple compression tests to be fairly useless. Cranking speed and throttle opening can greatly effect readings, makeing a good engine look bad. A cyl leak down test is far more telling but requires test equpment most do not have nor is readly avaiable. It is worth the time and money to have someone do it tho, it can pinpoint if and where compression loss is happening.

First off, thanks for the quick response. I love that about this site. Now, to the questions. When I pulled the plug wires there was a slight loss in revs but no one was more than any others. No overheating problems nor loss of coolant. I check oil and coolant pretty much every time I intend to drive more than 5 miles. I've had lots of older vehicles over the years and even though I don't know much I know that much at least. The noise changes with throttle application but a very deep noise occurs when I put it in gear and let the clutch out and when I shift to the next gear and subsides when I get up in speed on flat ground.

I stand by my statement.
This stuff is OLD CB!
Not everyone on the planet has your road-side diagnostic skills!
If nothing else the original wiring in this stuff and the non-availability of parts pretty much makes these old trucks a hobby for 99% of us.

Easy way to find out what area the noise is coming from.

Grab a long handled screwdriver or long steel bar, rest it on different positions on the engine with it running and place the other end to your ear you will easily pick up were the noise is, just be carful not to get it near any electrical leads.

Trevor

Of course I like CB's carbon diagnosis...
You can try one of the many decarbonizers.
Or the ol' "pop bottle full of water trickled down the carburetor while it runs..you have to keep it running with your hand on the throttle.
The alternative would be to remove the head and manually remove the suspected carbon...who wants to do that?
However, in my world DEEP engine noise usually means something catastrophic. Sorry.
Rod knock, piston damage, spun bearing...
I surely hope it all works out fine for you.

First off, thanks for the quick response. I love that about this site. Now, to the questions. When I pulled the plug wires there was a slight loss in revs but no one was more than any others. No overheating problems nor loss of coolant. I check oil and coolant pretty much every time I intend to drive more than 5 miles. I've had lots of older vehicles over the years and even though I don't know much I know that much at least. The noise changes with throttle application but a very deep noise occurs when I put it in gear and let the clutch out and when I shift to the next gear and subsides when I get up in speed on flat ground.

Are you sure it is coming from the engine? This is a manual transmission, perhaps Clutch is gone. Just my thoughts. Rod knocks rarely go away.

lloyd