The Stovebolt Site Forums The Shop Area Engine Shop Knock or not?

hi Guys, kinda new to the forum and could sure use some advise. My '54 235 with solid lifters has developed a noise when hot.

Here's what's going on...after running the engine for about 1/2 hour or driving at 30 mph for 15 or 20 minutes I hear a dull knock!!! I can't hear it at idle only at higher rpm's. Sounds like a small hammer pounding at about 2500 rpm.

I don't hear the noise when I first start the engine at any rpm, when the oil is cold and pressure is 30 - 60#. It doesn't have blow-by or smoke and the vacuum is strong.

After the engine warms up to 180 the oil pressure drops to about 18# at idle and 30# at 1500-2000 rpms. I checked the valve lash (COLD) and found intakes about .006 and exhausts .022. According to my manuals the valves should be set at .008 intakes and .020 exhausts. I assume this is HOT.

Would the valve lash get tighter as the engine gets hotter? Could a too tight valve lash or a bad rocker be making this noise?

I removed the oil pan too (it needed a new gasket anyway) and the screen was clean. I found a few very, very little fine metal particles and only one larger piece of metal shaped like a C about 3/8 inch long, a few thousands thick and a 1/16th wide at most. All the rods have very little play.

Sorry for being long winded but I want to give you as much info as I could.

What do you think? What would you do next? Any suggestions, thoughts you might have would be appreciated.

Was the "C" shaped piece ferrous?

Finding a piece of metal the oil pan will cause you to dream about it at night. This is usually not a good finding but it might not be the cause of your noise. This also might not be a bad thing - who knows, it might have been left there long ago.

After cold-adjusting the valve lash, it is imperative that you also carry out a hot adjustment.

Bobs54,

Valve train noise isn't usually a deeper knock to the ear...it's usually a clicky/clacky/tappy!

Wrist pins usually make a lighter noise at idle. What you are describing sounds like a connecting rod bearing to me.

If this is true, you should be able to make it knock at will. With the truck parked and hood open, you should be able to bring the RPM's up to say 1000, pop the throttle a little and let it go. If it is a rod, when it "relaxes" you should hear a rattle, or knock.

Sometimes you can pull plug wires and isolate the problem to a cylinder.

Keep in mind that everything from a water pump to a cam gear can make a knock which can be transmitted through the big iron block like a drum.

A bad rod bearing would certainly act up as the oil thinned and pressure was reduced.

Do some detective work with a rubber hose held to your ear as you run the engine. Good luck.

Stuart

I think so, it is magnetic.

Thanks for the great info/suggestions, Stuart.