The Stovebolt Site Forums The Shop Area Engine Shop Engine knock, very slight.

The 1951 truck's 57k mile original 216 in my tagline is quiet. I run the valves at the Chevrolet min. clearance since it's not a real work truck the majority of the time and the just switched to summer 20w50 oil cushions the vast majority of normal sounds. Of late, as in the last 200 miles I've been hearing a low frequency very slight sound. Last evening after driving the four mile round trip to feed the horses I slowed the idle down to around 450 rpm, and did the following:

Pulled plug wires to try and isolate the sound to a cylinder. No change from pulling wires.

Used an old shovel handle as a stethoscope, the noise is in the front half of the engine. With the wood handle to ear, you can easily pick out the lower frequency noise from the tappets.

And then the new noise went away.

At this point I see one of two options, pull the pan and check main and rod clearances, last time I checked with Plastigauge about 15,000 miles ago everything was within specs.

Or, just let it go for a bit and see if it gets a little more noticeable, at the moment I'm likely the only one that would notice it.

One last question, anyone ever had a fuel pump make a noticeable knocking sound? I've had engines you could hear the mechanical pump working at idle, I'm thinking that "could" be what's going on. Of course why did it just start out the blue.

Thanks for any thoughts.

RonR

Ticking sounds are almost always valve train related while knocking is lower down. Can’t recall a fuel pump making noise.

I have encountered knocking fuel pumps. When the rocker-arm pivot pin gets loose they will knock, aside from leaking oil.

Twenty/fifty motor oil is a heck of a lot thicker as you pour it out of the bottle than is 20/20w. If you're not working the engine hard I would stick with the factory-recommended 20/20w, if you can find it; straight 20 is probably fine. You don't say where you are but unless it gets very hot I'd stick with SAE20. These old engines ran rather tight clearance on rods and mains and quite low oil pressure (15psi) hot and running. That's not enough to push much oil through if it's thick oil.

You say clearances were fine 15,000 miles ago and unless you've abused the engine in some way I wouldn't think it would have changed since then. I would just run it and see if the noise returns or gets worse.

Rod knocks have a tendency to create a double-tap noise when a spark plug is disabled. Main bearings are more likely to cause a lower frequency "thump" type knock that doesn't change with or without spark. A main bearing knock will also make a "thump- thump- -thump" noise during acceleration that goes away or diminishes noticeably once a steady speed is achieved. I've seen several engines get an "in the frame" rebuild over a noisy fuel pump. A broomstick, dowel rod, or a long screwdriver held against the pump housing at idle will usually pinpoint the noise pretty reliably. Try removing the fuel pump, blocking off the hole in the block, and running the engine on a gravity fed fuel tank.
Jerry

A clue. The rogue sound is at half the engine rpm. I counted and got 44 in 10 seconds, or 264 in a minute. I didn't have a tach hooked up but that's going to be half speed. So, if my logic is sound and a cylinder fires once ever two revolutions, it's likely piston, or rod (big or little end) related. That said, I'm still surprised I didn't detect a change by pulling plug wires.

RonR

A fuel pump also operates at half crankshaft speed, since a lobe on the cam actuates it and camshafts turn at half speed.
Jerry

I used 3 different listening devices (1" dia. oak stick, 3' long 1/2" extension and short length of water hose, wood is best) to try and get a better handle on an exact location in the block. Not much luck, but I did pretty much rule out the fuel pump. Now that said, it's an easy thing to pull the pump and put a plate over the hole to do a real test. May very well add that to the list.

One odd observation I mentioned in the original post, after a bit at low rpm the knock goes away. Happened again today, however bring the rpm up to 1500 or so and it's back, let it idle for 10 minutes or so at low rpm and it goes away.

RonR

Just a thought, did ya look for an exhaust manifold leak? Couldn't change the noise killing cylinders via spark plug wires, and seems repetitive. Not to mention, comes and goes?..

You've probably got a misaligned oil spray tube that's starving a rod for oil at speeds above idle. I have an aiming fixture that's used with a water hose or a solvent tank pump to bend the nozzles for a correct squirt into the rod dippers at running speed.
Jerry

Thanks all for the help. The Plan. I'm going to (in the next few days) pull the pan and use water to see if all the sprayers are spraying the same. I don't have a way to do a proper spray tube alignment adjustment, but perhaps I'll spot an anomaly if there's one spot. Then drop caps looking for obvious signs of distress. I'll also be breaking out some green plastagauge.

If an obvious issue isn't found and that includes the wiggle, push/pull rod test on the wristpins......we'll see what happens next.

I do have a purchased as good, 1959 261 that's cast in the 1954 mold setting in the shop. Before I do a serious amount of work on the 216, or actually anything beyond pulling the pan I'll go as far as necessary into the 261 to make sure it's ready to put back in service. Been needing a good excuse to put in on the engine stand and get it in the truck. Just didn't want to do it right now. Other projects on the top of the list need serious attention. Guess it's good to have a job though.

RonR

Glenn, I've had exhaust leaks that made a slight serious sound before and agree they can be a cause for concern. However when you listen with something touching the block to ear, it's definitely a low frequency metallic sound from deep in the engine.

The above said, if I discover your suggestion is spot on, I'll buy the boiler makers as we toast to your psychic abilities!

RonR

I had a fuel pump make a odd knocking noise in a Ford FE engine. What happened is one of the springs failed and was hung up inside the arm. When it finally spit it out it dropped into the pan, and got sucked into the pump, stopped the pump and then the shaft broke stopping the dist from turning. Not sure how it got past the screen, but it did.

Same thing happened to a friend of mine with a 351M.

Not sure if this helps, but mechanical fuel pumps suck at times.

If they don't, there's no way to get the fuel to flow!
LOL!

Jerry

I had a similar noise on my 270. Deep low sporadic thunk noise from front of engine. Pulled belt off to eliminate noise from alternator and water pump. Noise stopped.
Turns out the harmonic balancer was a little loose on the shaft and the wobble would intermittantly cause the noise. Replaced balancer and noise is gone.