You have zero compression in cylinder 8, and it isn't noticeable?

Is it idling rough at all? What does the #8 plug look like that you pulled out? Any blow by? Any water/coolant in your oil, or foamy junk on the underside of your oil fill cap?

I'll give my standard discalimer...I am not an expert, but I feel like sharing my experiences since I am in the middle of this as well. Someone will pipe in if I get too far off base .

I am working on a similar problem. After my truck overheated, I had 0 compression on #6. It was marginally driveable, but would die at idle engine speed. With the valve cover off, everything looked cool, the #6 valves seemed to be moving freely. I took the head off, and found that the exhaust valve had a slight bend in the stem really close to the face of the valve. So, the valve had enough range of motion to appear normal by eyeballing it, but it left about a 1/8" or so gap on one side when in the closed position, hence 0 compression. I was extremely lucky, as I had no damage to the piston, and no cracks or warps in the head (that's the cylinder head...my actual head is quite warped indeed). There is a nasty layer of carbon deposit on the #6 piston head, which I attribute to having to drive it 30+ miles with the exhaust valve open, and fuel spitting in there and not burning.

With any luck, the piston/chamber would be fine, and you have a bad valve, pushrod, spring, fulcrum screw, whatever, etc. You may have to remove the head to get to the problem. But first, it seems you have had the valve cover off...have you inspected the valvetrain components on #8? Anything look any different from the good cylinders? You can get the pushrods and valvesprings out without removing the head. Although being that it's #8, it's going to take some maneuvering.

I have started to take digital pics of what I am doing at various points of disassembly, to help me get the thing back together...let me know if you have to dive in, and need anything! ...or, maybe you can help ME!

good luck,

Bryan

 

Yes, it idles fine, but ticks very badly. The plug was very oily and wet. I had the header off and the tube for that cylinder was wet as well. With the valve cover off all seemed well, I had the pushrods out and they seemed fine. It's the back drivers side cylinder, I though the back passenger side is #8?

There is no sign of blow-by that I can notice, and no smoke. And it's weird, because when I drive home through the rockies it seems that the engine needs everything it has to get over some of the mountains. And the fact that I was running on only 7 and still had the usual power confuses me.

Removing the head is the last thing I feel like doing right now because it's not very fun. If I pull the rocker arm and valve spring off is there anything I can do to check the range of motion on the valve by hand.

And the ticking noise is what is confusing me the most.

Thanks for the quick reply, i'd be interested in the digital pics.

Jason

 

Correct me if I'm wrong, but if your plugs are oily, oil is getting into the combustion chamber. It could be a crack in the head, or piston/piston ring/cylinder damage (which would be bad), or it could be getting in because of a bad valve stem seal or valve guide (not so bad). How does the stem seal look? It will probably be hard to see under the spring.

Just a warning, keep in mind that if you take the spring off, you will have a hell of a time getting it back on, since you have no compression, and a compressor wont keep the valve up.

And about checking the valve's range of motion...like I said, I moved mine around, and thought it was good, but it weren't. Maybe there is some trick, but I don't know.

As far as the numbering...I might be wrong, but I thought the left bank was 5 through 8, that is, on the left side if you are sitting in the truck, on the right if you are under the hood cursing and whatnot.

Hey, do you have an air compressor? You might be able to figure out if your compression leak is up top or on the bottom if you can get some air into the spark plug socket....

As far as the pics, I don't think I have anything that will help you yet. I got farther than that before I started to worry about if I'd be able to get everything back together! I was actually worried more about all of the hoses, vacuum, and electrical connections. I am going to get the other head out tonight, and I'll get some pics together. Might not be much help, but who knows.

 

Well I removed the rockers, got a spark plug adapter and put 100psi into the cylinder chamber. And it all came out the exhaust port. Looks like I got the same problem as you. Did you just get a new head for it, or did you replace the valve? I assume the valve seat will be damaged as well.

 

Did you make sure that the cylinder in question was at top dead center when you hooked up the air? I'm pretty sure you need to do that to ensure that the valves are both in their highest position....

Bryan

 

No I removed the rocker arms so the valves were in fully closed position.

 

Oh yeah....duh.

Well, I decided thant I am going to remove both heads, and take them to a machine shop. You need to get the heads off to take the valves out anyway. From what I've read, it looks like it would cost $100-300 for a standard valve job if you bring the heads in yourself. I haven't called for quotes yet.

The seat may not be damaged, but they wear down over time -- 165,000 miles worth of time on mine.

Bryan

 

Oh yeah...I promised pics of ty tear down, and then hopefully the reverse! I've got both heads off now, and this weekend I'll get the pics up somewhere for you. I did get a few up to show from my original thread. They are here.

Interestingly enough, the right bank, 1-4, was worse as far as deposits than the cylinder with the bent valve. I am guessing it's because the PCV inlet is on that side. Overall I am happy with the condition...so far!

And again....if you have gone through the trouble to get the heads off, it would be silly to not get them done. I started this project right where you are, and after tons of research, and plenty of feedback from this forum, I have been completely convinced.

You probably already read it, but here's my original thread.

Stuck valve? What am I in for?

Bryan

 

Yeah I got the head off, broken valve. I made a new post in this forum. Pictures too.

I'm sure the noise i was worried about was cumbustion noise entering the exhaust. For the last yeah this truck has made an odd pinging under heavy load, so I expect the valve has been cracked for a while which was the pinging noise I heard.

I'm going to get both head done, or swap for some rebuilt ones.

Thank's for all the help.
Jason

 

Laka-

So how is your project going? I promised pics to you, and I haven't gotten to it yet.... Got busy with other things...

Bryan

 

Got a similar thing going here. #8 cylinder lost compression about 200 miles into a 1200 mile trip. No oil and water mixing, so I completed the trip on 7. Compression test suggests either the head gasket or a valve problem. Got it torn down to the heads now, they will come off tomorrow. I'll report what I find, maybe pictures, too.

 

Sounds exactly like my problem. Did it become loud also? There was a crack right where the valve seals in the head, not sure if that caused the whole problem.

My projects on hold until the weekend. (Working sucks.) I just need to pick up some lifters/plugs and some odds and ends and she's ready for re-assembly. Dont worry to much about pictures, I'm not too concerned about putting it back together. I swapped this engine in a year ago so I know where all the hookups etc. go. The old heads definitely could have used a valve jobs, so I how with these rebuilt ones I will feel some gain. I paid $470.00 CDN (after core $) for the 2 heads. One old head was cracked so no money for it.


Jason

 

No noise, just ran rough at low RPMs and used lots of gas.
Got the heads off today and #8 has a burnt exhaust valve and a crack in the head between the valves. Not sure which one caused the other, but I suspect they're related.

 

Are we working on the same truck here?

My head was cracked at the seat as well. Exact same cylinder as yours too. Hmmmmmm?

 

Yep, just about the same. Seems like that #8 cylinder gives alot of trouble. I'm routing my PCV line to the top of the manifold when I put it back together in case that is part of the problem.
Did you look into getting that crack repaired? I haven't made it to the machine shop yet so I don't know if that might be a possibility.