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bent push rod and LOTS of question

bent push rod and LOTS of question
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neal90

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for brag
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1982 i6 keeping as stock as possible
Ok I have been trying to find/ fix a knocking sound that my jeep with a AMC 258 i6 / 4.2l . At first I thought it was piston slap because it went away when it was warmed up, but because of the inconcinnity of the sound and finding loos exhaust bolts i thought it was and still think its just a exhaust leek and i think i found out the hard way. The other day the jeep started to run real rough and lost all kinds of power but the knocking stopped :fear:, The jeep still ran. After looking around and doing a compression test the front cylinder and 0 compression. But the knocking is gone. So I took the valve cover of and there was a bent push rod. Well its unseated, so I took it of and it is bent a very little and there is also another rod that is stiff and dosent role around like the other. So my question is what caused it to become unseated and should all the push rods be able to roll around freely or will some be under tension because of the valve being open. And after all this does it sound to you all like the original problem of the knock sound to be a leaking exhaust gasket because it went away when the rod bent thanks far reading and all the help

Also the motor is SLUGGED up on the top end. Is there any safe way of cleaning this mess??
 
I've had a push rod pop out on a couple of jeeps, both times it wasn't bent so I just put it back in place. The only time it happened was at high rpm (that was higher than I feel a straight 6 should be run), So I just didn't do that anymore.
 
neal90 said:
Ok I have been trying to find/ fix a knocking sound that my jeep with a AMC 258 i6 / 4.2l . At first I thought it was piston slap because it went away when it was warmed up, but because of the inconcinnity of the sound and finding loos exhaust bolts i thought it was and still think its just a exhaust leek and i think i found out the hard way. The other day the jeep started to run real rough and lost all kinds of power but the knocking stopped :fear:, The jeep still ran. After looking around and doing a compression test the front cylinder and 0 compression. But the knocking is gone. So I took the valve cover of and there was a bent push rod. Well its unseated, so I took it of and it is bent a very little and there is also another rod that is stiff and dosent role around like the other. So my question is what caused it to become unseated and should all the push rods be able to roll around freely or will some be under tension because of the valve being open. And after all this does it sound to you all like the original problem of the knock sound to be a leaking exhaust gasket because it went away when the rod bent thanks far reading and all the help

Also the motor is SLUGGED up on the top end. Is there any safe way of cleaning this mess??
Click to expand...

The first two things in your write-up that are concerning: 1) a bent pushrod, and 2) the sludge. Can you post some pictures? How many miles on the engine? The sludge could be just lack of maintenance, but it also could be anything from a stuck/clogged PVC valve (again, maintanance) to a blown head gasket.

The bent pushrod is generally a symptom of a bigger issue. The most common is a worn and stretched timing chain, which if it gets bad enough, can cause the valve to hit the piston. The fact that the noise stopped and that you have no compression in the cylinder is not good :eek:...

Give us some pictures, and you may want to pull the timing chain cover and see how the timing gear marks line up - Sounds like you are about to get some teardown experience to me.
 
This is not good - 0 compression. :(

High RPM as Dune stated.

But why? Well with sludge sounds like the PO didn't change the oil very often. With that sludge it can cause a lifter to stick, combined with high RPM.

Or as Dune mentioned a badly worn timing chain that may have jumped a tooth or two.

The push rod can dislodge and in the right position, can cause the valve to hit the piston top bending the valve. A bent valve has to be replaced by pulling the head. Have the head cooked when you have the shop put in a new valve and re-seat the others while you've got it off.

To be absolutely sure it's a bent valve, put the cylinder at TDC and blow compressed air in the sparkplug hole. You should hear air in the intake or exhaust pipe depending on which valve is bent.

To check the timing chain, put a wrench on the crank bolt and move it back and forth watching the other push rods move. You're looking for slop the crank will rotate but the push rod doesn't right away.
 
Wouldn't it show 0 compression on the cylinder that the bent valve got dislodged??? Because the will stay open. Also I'm thinking the rod got bent and it is a very slight bend (the only way I could tell it was bent was by roiling it on a clean table you can't tell by just looking at it) And couldn't a realy sludgy motor cause a spring and valve to stick??
 
Correct 0 compression on the bent valve cylinder.

Yes to the valve sticking for lack of oil and maybe sludge.

Either way you should be considering a valve job.
 
should all the pushrods be able to spin nice and free. Or will some be under pressure from a valve being open and not spin freely??
 
Right some will be under pressure. Remember there is no adjustment for the rocker arms.
 
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