Dead cylinder

[TucsonHooligan]

Cylinder 3 has 15 lbs of compression. Started running like crap about a week ago, checked everything else, i.e. plugs, plug wires, carb tuning, etc, then hooked up a compression tester and found the culprit. Long story short, what are the most likely causes and the easiest fix? Whats my next step in all this is what I basically need to know.

 

[bubba22349]

Dose yours have solid lifters? Than it might just be the valve clearance tightened up. Easy to fix pull valve cover and reset them all. If not solids than likely it’s a burnt valve or a loose guide. You can maybe see a bad guide by pulling the valve cover and pushing on it though not easy the fix still would be to pull the head for both of them.

 

[Frankenstang]

Another one you can see by pulling the valve cover is a stuck valve (likely stuck open...probably more easily detected watching the valve train while someone cranks her over a little), that one might/might not involve pulling the head. I was able to free one on mine by working it lightly with a light hammer to free it up then, plunging it back & forth several times and adding a little lube on the guide top under the umbrella seal. Originally happened a good while back after a 'very long sit', but re-reared it's ugly head over the winter very briefly after a not very long but longer than normal sit..and went corrected itself after a few minutes of warm-up. Seems those valve train & crank assemblies have a tendancy to come to rest in certain spots more frequently than others. I'll probably end up running some sea foam green or atf through the crank case for a clean up...should've already done it
Good luck

 

[woodbutcher]

Says he hooked up a compression tester,and found the culprit.Besides what has been mentioned so far,a blown HG or cracked head has not been mentioned.
HOPEFULLY,it is nothing but a stuck or burned valve,or bad/stuck lifter.Simple fix,however still might require removal of head.
Did engine overheat before problem showed up?If so,he is possibly looking at blown HG or a busted head.If it was my engine I would pull the head just for good measure.Takes a little longer,and a little more money and effort.However it will be cheaper in the long run.
Good luck.Have fun.
Leo

 

[TucsonHooligan]

Thanks guys! I'm gonna dig into it this evening, pull the valve cover and see what I can see. No overheating problems prior to this, so I'm not thinking blown head gasket. I'm leaning toward a stuck valve, but that may just be wishful thinking on my part. I'll update after I get the cover off....

 

[falcon1963]

Put compressed air in the dead cylinder & see where the leak is.
Easy diagnosis, air out the intake, air out the exhaust And or air out of the crankcase.
Do that & you will find your problem.

 

[TucsonHooligan]

Couldnt get a pump to shoot compressed air thru, but I removed both the rockers so the valves would be close and checked the compression. Still the same, 15. Does this mean my rings are bound or what?

 

[jahearne]

What does your oil look like? any contamination?

 

[Frankenstang]

Not having two cylinders reading low would seem to rule out a HG leak/blown between two cylinders, but there is still a chance for a HG leak limited to a single cylinder...had that one happen too Blew a section of the HG out on the passenger side of one cylinder on the gasket (non oil/water passage side)...sounded like an exhaust leak but didn't have as poor a running condition and loss of power as a stuck valve (that's probably dependent on the size of the leak). And burnt valve is still very possible. falcon1963's approach would likely be my next step IIWIYS (given the right connections/tools)...might see if you could rig up the connections and hook a compressor to it running say 60-80psi out, so the leak could be more easily detected
(EDIT: I would think too low psi out would make it harder to track down) . Likely the most logical next step short or pulling the head, kinda like a leak down although you already know the dead cylinder. Shame it didn't turn out to be as easy as a stuck vavle...good luck!

 

[TucsonHooligan]

Oil looks fine, not odor of gas. Sigh. What a PITA. Gonna see if I can find a way to get compressed air pumped thru it as per Frankenstang and others suggestion.

 

[oldgrezmonke]

I removed both the rockers so the valves would be close and checked the compression. Still the same, 15.

You can't run a compression test that way though the number should have been different ; the valves have to open and close in their normal pattern . You should replace the rocker arms and adjust for a valve clearance of .016 then retry the compression test . Regardless it does sound like a burned exhaust valve .

 

[jimlj66]

When you did your compression test, did you squirt motor oil in the dead cylinder? From an oil can, squirt 4 or 5 pumps of oil down the spark plug hole, crank the engine a few spins and re-test that cylinder. If it is a bad valve, you will see little or no increse in compression. If it is a broken/stuck ring your compression will come up untill the oil is worked out of the cylinder.

 

[TucsonHooligan]

Will try both of those suggestions this evening. I think I got a bad compression tester. It's a loaner from the parts store and it seems to be missing parts and not working properly. I'll just suck it up and buy one.

 

[69.5Mav]

Any Progress to report

 

[TucsonHooligan]

Status the same, still no compression. Can't do anything else short of pulling the head, so I'm just gonna drive it gently while I get my other vehicle on the road, then do a rebuild on it.