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

RonR


1951 3600 with Clark flatbed, T5, 4.10 rear
1970 340 Duster
1990 5.0 V8 Miata (1990 Mustang Gt Drivetrain)
1964 CJ5