Knocking engine

[94f350]

So I think I have a bent pushrod in my engine (7.3 idi NA) because when I went to start it up the other day one cylinder had zero compression when it was cranking and when it started it knocked really bad. I shut it off and a few minutes later I went to start it again and it ran fine. Does anyone know what could've happened and if 7.3 idis are interference engines or not?

 

[Nero]

Pretty sure they are interference, and it could be a hydraulic cam follower that collapsed for a brief moment.

 

[Black dawg]

If it is running fine now, you probably were hearing compression pop back out the intake due to an exhaust lifter that wasnt pumping up for some reason.

 

[FrozenMerc]

They are absolutely interference engines. I can't think of a single diesel that isn't. Hard to get 21.5:1 compression if you have big enough pockets in the pistons to clear the valves.

Pull your valve covers, and turn the engine over a number of revolutions. Make sure all the rockers are operating correctly. It may even be a good idea to pull the push rods and roll them on a flat table to see if any where bent due to a piston helping to close one of the valves.

 

[94f350]

They are absolutely interference engines. I can't think of a single diesel that isn't. Hard to get 21.5:1 compression if you have big enough pockets in the pistons to clear the valves.

Pull your valve covers, and turn the engine over a number of revolutions. Make sure all the rockers are operating correctly. It may even be a good idea to pull the push rods and roll them on a flat table to see if any where bent due to a piston helping to close one of the valves.

So if my valve was held open do you think we're talking major engine damage or could I walk away from this?

 

[Nero]

If a valve got smacked, it typically would immediately not seal and always run like garbage.

 

[Black dawg]

So if my valve was held open do you think we're talking major engine damage or could I walk away from this?

If a valve made contact with a piston, you would have bent parts, and it would not be running fine now. What would cause a valve to be held open out of time?

 

[94f350]

Well it had to have been a valve open because it was cranking like one cylinder had zero compression. I can't think of anything else that could cause that randomly.

 

[Rdnck84_03]

Without knowing what the knocking sounded like makes diagnosis difficult. But with the fact you say it is running fine now I would guess that it was probably a fuel knock. Probably an injector sticking open.

James

 

[94f350]

Without knowing what the knocking sounded like makes diagnosis difficult. But with the fact you say it is running fine now I would guess that it was probably a fuel knock. Probably an injector sticking open.

James

But that wouldn't explain the weird compression issue though, also it was a very heavy knock, kinda sounded like rod knock

 

[Rdnck84_03]

Yea I missed the zero compression in the original comment. Collapsed lifter letting the pushrod dropout of the rocker can hold a valve open. Or a valve binding in the guide are what I have seen hold a valve open.

James

 

[IDIBRONCO]

If a lifter, for some reason, isn't pumping up, then it isn't opening the valve. If, for instance, an intake valve isn't opening, then there isn't any air getting into that cylinder to be compressed. Hence, low or no compression on that cylinder.

 

[94f350]

IIf it held a valve open then wouldn't I probably have bottom end damage from the piston hitting the valve?

 

[IDIBRONCO]

Yes you would. You may very well have a bent rod from that. Also, you'd probably have a bent valve too.

 

[FrozenMerc]

What lead you to the conclusion there was 0 compression in one cylinder when you first cranked it?