I was driving my 71 c20 up a steep grade at low speeds and noticed a clattering from the engine. I pulled the valve covers and noticed the #6 exhaust valve was only lifting about a third as much as the rest. I tried tightening the rocker an eighth of a turn and the motor wanted to stall so I backed it off to where it was. Other than the noise and a little bogging going up the hill, the truck runs really well with good power at highway speeds and on flat terrain at lower speeds. I drained the oil and ran it through a coffee filter, shined a flashlight on the oil, and checked the drain plug and bottom of the drain pan for metal. There was nothing but oil. I didn't pull the filter and cut it open. So my question is wouldn't there be metal in the oil if it was a flattened cam lobe? Could the problem be a collapsed lifter? What else could cause the lack of lift?

 

Check the lifter or possibly a flat cam lobe.

 

This^^^^^^ Is it a SB or BB

 

It's a original stock 350. Is there a way to see the Cam lobes without pulling it? I know you can see some of them on a 455 through the valley.

 

If you pop the intake and run the cam and pull the lifters you'll find it. What oil have you been running in it?

 

15-40 diesel, but I haven't had the truck long. It only had only been driven about 1,000 miles since 2005 based on the receipts that came with it.

 

Difficult to tell then. Engine may need to come apart to diagnose.

 

Yeah I expect at least the intake will need to come off and the lifter pulled to inspect. I know what to look for if the bottom is worn. I don't have experience with a collapsed lifter. Is it easy to tell if it's collapsed?

 

If it's collapsed it will not have the plunger near the top of the lifter.

 

Is the bottom of the rocker torn at the pivot ball? Is the pushrod bent? If both are ok it is most likely a bad cam lobe.