Backfire at the carb

[Steve Grant]

just to be clear, the rocker and the pushrod both move when the engine is rotated. The valve does not.
I did a compression test on the #7 cylinder and found that it held 115#. So the valve must be closed!
Loosened the stand bolts enough to remove the pushrod. Perfectly straight.
Tried my new removal tool, but you have to hold the collet with a wrench to expand it. Maybe a crows foot wrench would work, but what a pita. Tried a magnet and "Bob's your uncle" the lifter came out of its bore, but then it dropped. After a few hectic minutes I was able to fish it out using a flexible flashlight in the adjacent pushrod bore, a retrieval tool and a magnet. I thought I had lost it into the bowels of the engine.
Attached is a pic of the lifter. It was pretty much clean - just wiped it off. If the bottom is supposed to be flat it doesn't look good. It's dished about .016.

Just watching the video from the point of view of where you filmed it looked like the push tube wasn't moving. That lifter looks pretty dished.

 

[Steve Grant]

really don't need the rope. Piston at tdc and the valve can only drop about 1/2". Actually good to be able to move it up and down while working it loose.. Air will help while replacing the keepers.

I got the rope idea from bill usn-1 on the binder planet site. I wouldn't think that putting rope inside the cylinder would bent the valves especially when they are closed anyhow. Just trying to help.

 

[Robert Kenney]

Hey steve I have no problem at all with the rope tool. It's a good suggestion. Used that my self a few times. I also know that being able to vertically work the valve to free it is helpful so tdc is good.

 

[Robert Kenney]

the lifter didn't want to collapse on the bench.
Got the lifter apart. I was trying to be careful but the spring clip still got away from me. Fortunately it stayed on the bench after hitting the bill of my cap.
Is there a need to disassemble the check ball/spring?
I have posted a pic of the parts. Shouldn't there be some sort of o-ring? Want to make sure before I put it back in the engine.

No oring only metal parts.. Yes pull the cap spring and check valve off to clean it good.

After thinking about the compression test it could be that the valv shut at low speeds but hangs at speed.. The lifter is badley dished but so long as there is still some preload it should be able to move teh valve and run well enough not to pop.

 

[eightOsix]

Today I reassembled the lifter. I didn't take the check ball apart, but cleaned and blew it out. While assembling I could push on the check ball and see/feel it pass fluid. I believe the lifter was clogged with a small metal flake that I found on the shop towel that was under the assembly while cleaning. See the pic.
Slid the lifter back in with a magnet, installed pushrods, torqued the stand bolts. When I turned the engine over the valve moved. Installed the valve cover and started her up. Then she died. Out of freaking gas!
Once I got some fuel and let it warm up I was pleased that the engine idled smooth - smoother than before, and sounded strong. Vacuum held steady at 13.5 and oil pressure 15. I could check the valve through the oil filler.
Revved the engine and held it at 3800 with no knock or backfire. Next will be a test drive.

 

[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.