low compression on 1 cyl

kleake

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Got a few thousand miles on the full rebuild and starting to hear 1 cyl with low compression. As you crank it to start, if it hits that cyl you can hear an obvious low compression. When idling, it sounds like just a weak cyl, but while driving it all runs fine and you don't feel or hear any miss. I'm wondering if I have a valve that isn't seating all the way. Usually as things wear in, things get better, but this is definitely getting worse. Any quick things I should look at before assuming a valve issue and removal of the heads is in the cards again? I'm really getting tired of pulling the heads, this will make the 4th time in about 2 years if I have to do it.
 
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Geez. You need to find that voodo doll and burn it.

Why dont you pull the plugs and run a compression test? I can send you mine if youd like.

Also, you can get a boroscope in through the glow plug hole. I've done that several times while I had access to one.

If you did, you can visually inspect each cylinder, check pistons, valve seats, valves, etc. It takes some patience but it can be done.

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kleake

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Geez. You need to find that voodo doll and burn it.

Why dont you pull the plugs and run a compression test? I can send you mine if youd like.

Also, you can get a boroscope in through the glow plug hole. I've done that several times while I had access to one.

If you did, you can visually inspect each cylinder, check pistons, valve seats, valves, etc. It takes some patience but it can be done.

Sent from my SAMSUNG-SM-G935A using Tapatalk

I'm tellin ya, I would set that thing on fire in a second! lol

I'm figuring I will be pulling the plugs and doing a compression check to find the cylinder. I just have a bad feeling it's a valve not sealing because I can also hear it through the air box. It's not bad at the moment, but it's not getting better. I noticed it a month or two back, but I only drive this once a week or so unless I'm pulling the camper. After doing the tranny is the first time I noticed it when cranking it. If it is a valve not sealing, I don't think there is anything I can solve by pulling a valve cover unless the valve wore in and is now deep enough in the head that the rocker is keeping it open. I really don't see that happening, but i'm grasping at straws hoping a better solution comes to mind.
 

powerstroked08

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Might be a push rod that's bent. And as you keep running it its bending more causing it to make more noise. Most likely an exhaust pushrod of it is. That's why you can hear it through the intake.

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kleake

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Cut the oil filter open and check for metal

I can do that, but I sure hope I don't find any metal. When I changed the break in oil a few thousand back it looked good and clean. I didn't cut open the filter but I did drain the oil into a pan where any metals would settle at the bottom.

Might be a push rod that's bent. And as you keep running it its bending more causing it to make more noise. Most likely an exhaust pushrod of it is. That's why you can hear it through the intake.

I hadn't thought of a bent pushrod holding a valve open, but that could be possible. I would think I might hear a lifter tick if that was the case, but maybe not. The internals of the engine sound normal, it's only heard as a "thunk" sound through the intake and you can hear the exhaust isn't even, but no metal sounds anywhere. I'll try to do a compression test over the holidays and then dig into the valve cover to inspect. Bent pushrod would be a good thing to find!
 

powerstroked08

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Well what happens is the exhaust valve doesn't open enough with a bent push rod. So not all of the combustion pressure is relieved so when the intake valve opens it makes a "popping or thumping " noise because when the intake valve opens its popping the cylinder pressure back into the intake.

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kleake

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Also though, when it cranks over there is definitely 1 cyl with low/no compression so if it's a bent pushrod it's also holding a valve open a little.

And thank you, I'll see what I find and go from there.

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