Backfire at the carb

[eightOsix]

Frustrated! When I drove the truck a couple miles the knock came back. Same thing, the valve doesn't move, but the push rod and rocker do.
When I cold start the engine and check the valve movement the valve moves, but I determined that it does not move as much as the adjacent valves. So it seems that I have some valve movement with a cold/warm engine and then no movement when the engine gets fully hot. I didn't verify again with a compression test, but I am confident that the valve is fully closed and believe that the problem is downstream from the push rod - either the lifter or the cam. Also, the push rod doesn't rotate as fast as the others.
What to do? I need to verify the problem before I can move on.
Winter is here, expecting 3-5 inches of white stuff tomorrow, plus I lost the clutch on my 800, so now I have two down internationals.

 

[Robert Kenney]

Not many potential causes at this point in the game.
1) a lack of sufficient oil flow to the lifters, fed by the rear cam bearing..
Fix: engine comes out and cam comes out and bearings are installed. Along with a new cam and lifters. Based on your lifter photo of course.

2) flat lobe and lifter worn short so the oil feed port does not line up with the lifter.
Fix: engine comes out and cam comes out and bearings are installed. Along with a new cam and lifters.

I really can't see any other cause. Possible the oil filter is passing metal which is getting into the lifter. I doubt it though as the passage into the lifter is so small. Sorry.

 

[eightOsix]

Yeah, it looks like I'm sol with this motor. No way I can jump into that project with winter coming on. I thought I would try one more shot in dark and add some extra oil and run it one more time before parking it in the way back for the winter. Should do a compression check to evaluate the pistons and rings.
Have to evaluate the cost/benefit. I got the truck for free and probably have maybe $3k in it - windshield, tires and rims (that could go on my Scout), bumper, fuel system, springs and shocks, a crate of spray paint. Need to figure the cost of a new cam, bearings, lifters. Maybe new rocker shaft, and add in some extra for all the other fix-its that will need to be done along the way. I have never rebuilt a four stroke engine, so there will be a lotta' learnin' along the way.

 

[eightOsix]

Just want to report the final diagnosis after engine tear down.
Bad lobe on #7 exhaust cam, #4 and #1 cam bearings toast. #2 showing some wear.