GLHS

Have a friend who continues to bend push rods on his 91.5. He says when they bend it is is always on the exhaust side and so far, a different cylinder each time. I think this is the 4th time. Last time it happened he had all the pushrods replaced and a Cummins shop told him his tappets were probably bad.
I personally have not looked at his truck but he says everything is adjusted correctly.
Truck has an estimated 300,000+ miles. Speedometer does not work.

Any ideas?

93John

The valves could be sticking.

1985cucv

or a bent valve i would definitly dig into it deeper rather than just keep putting new pushrods in

GLHS

If valves are sticking what is the short and long term fix?

dieselnut416

how can a guy tell if this is happening push rods/valves sticking/not closing i fired one last night and its smooth but has a thunk thunk noise that increases with rpm and its only herd in the exaust?

Riflemanusmc

If the lifters are bad, so is the cam. did your friend give you any detailed info as to how they came to that conclusion? Who has been doing the overhead, aka lash adjustment? Push rod seat in the top of the cam follower could be bad. They would be bigger in dia. with that many miles. Have him check and see if the cup the push rod sits in ontop of the follower has the upper edge's broken off. Letting the push rod slip off to the side, which would bend it. Are the getting bent between the top of the follower and where they go through the bottom of the head, I'm guessing? Too much RPM, or just normal driving? Could be a number of issue's. Have your bud dig alittle deeper and let us know. Taking the rear lifter cover off may shine some light as to what is going on by turning the engine over by hand. Hope this is of some help.

Riflemanusmc

If a valve is sticking, your going to have a miss. Hangs open too long and your going to bend it. The piston to valve clearance on a diesel is alot tighter than gas burners. Diesel valves are spec'd out in, valve reccesion or protrusion to the deck of the head. High mileage and loose valve stem to guide clearance will cause carbon to build on the stem, causing stuck valves.

Need95-00CTD

Has the cam or gear case ever been opened? Sounds like the valves are hitting the pistons. I just don't see them bending that often otherwise.

Riflemanusmc

As posted above, there are several things that will do it. Needs more troubleshooting...

jimbo486

are the push rods being seated in the tappets properly each time?

dieselnut416

how do you tell this?

GLHS

Think we figured it out.
I gave him about 4 scenarios of what it could be, and after he thought about it for a few hours he remembered every time it bent a pushrod he had been idling the truck for 1/2-2 hours. A couple times was when he was digging himself out or the snow (D350). The cold weather, too much idle time and his home brew bio fuel is more than likely the culprit of too much carbon deposits causing the valves to stick.

He seems certain now this is the problem and is relieved he does not have to tear into the engine to replace tappets and cam.

Thanks for the help.
Kurt

ofcmarc

1st rule of the north- Close the door......

Attachment 30001

2nd rule- Jack up the idle while idling for long periods of time. The oil will thicken in the cold and bend the push rods.

Just about every piece of equipment and or diesel truck up here has some kind of high idle device for that very reason.

At least you got it figured out......

TRENDZ

I bought a high mileage truck recently. It had a thumping noise in the intake. I knew it had some sort of valvetrane problems. I drove it home, pulled the valve covers, and found a bent exhaust pushrod. It was still activating the valve, but it had EXSESSIVE lash. I assumed the valve had been sticking, but it moved free at this time. I decided to remove the head at this point, as I didn't find anything to indicate a clear cause of the bent pushrod.
The first thing I looked at was the headgasket. The culprit cylinder(#3) had evidence of combustion leakage around the gasket's ring in that cylinder, although I would not call it "failed", and the piston bowl was wet. None of the other cyls were like this. At first, I thought the gasket had failed, leaked coolant into the cyl, and hydro-locked the cyl. Well, it turned out I was partially right. I took the valves out of the head to get an idea of what condition the seats/guides were in, and found the exhaust valve was not in as bad of condition as I figured it would be(it could have been saved) but the intake valve stem was bent.
There were no witness marks in the piston, or on either valve from contact with eachother.
I later found that the #3 injector was stuck open.
My assumption at this time is the injector failed, filled the cylinder with liquid fuel and the cam tried opening the valves against it. This is the only scenario I can come up with that explains all of the conditions I have found.

dieselnut416

logical