Home » Public Forums » GMCnet » Dead Cylinder
| Dead Cylinder [message #288614] |
Mon, 12 October 2015 22:53  |
bhayes
Messages: 263
Registered: March 2010
Karma: 1
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I took my GMC in to the shop today to have it looked over before some upcoming travel, and they informed me that the number 3 cylinder is dead. Thus far they've only disconnected the plug wire (didn't have any effect on engine idle) and did the paper-over-the-exhaust-pipe test (paper got sucked in). Tomorrow they're going to do a compression and leak down test.
The engine has about 15k miles on a rebuild which was done back in 2004. I'm hoping it is something simple, but it's not looking good. More to come....
Bryan Hayes
'76 Eleganza II
Salt Lake City, Utah
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| Re: Dead Cylinder [message #288616 is a reply to message #288614] |
Tue, 13 October 2015 00:11  |
roy1
Messages: 2126
Registered: July 2004
Location: Minden nevada
Karma: 6
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Wish you luck. My engine had 16000 miles on it when I did a compression check on it because it didn't idle smoothly. Turned out the #7 exhaust guide was badly worn destroying the seat. Pulled both heads and found 2 other guides also destroyed along with the seats? Shop said the combustion temperatures were likely too high and bronze exhaust guides would be a good idea. A real head scratcher for sure.
Roy Keen
Minden,NV
76 X Glenbrook
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| Re: Dead Cylinder [message #288619 is a reply to message #288614] |
Tue, 13 October 2015 08:12 |
kerry pinkerton
Messages: 2565
Registered: July 2012
Location: Harvest, Al
Karma: 15
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Could be anything from a bad plug or plug wire to a wiped cam lobe (doubtful) or other broken/worn mechanical part, blown head gasket, ect. I recently went through a similar problem and found an exhaust valve that had receded into the head. Note that in my case, compression and leak down tests did not show a problem AT CRANKING SPEEDS because the valve seated well enough to seal at cranking speed.
Kerry Pinkerton - North Alabama
Had 5 over the years. Currently have a '06 Fleetwood Discovery 39L
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| Re: Dead Cylinder [message #288643 is a reply to message #288614] |
Tue, 13 October 2015 13:27 |
bhayes
Messages: 263
Registered: March 2010
Karma: 1
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bhayes wrote on Mon, 12 October 2015 21:53I took my GMC in to the shop today to have it looked over before some upcoming travel, and they informed me that the number 3 cylinder is dead. Thus far they've only disconnected the plug wire (didn't have any effect on engine idle) and did the paper-over-the-exhaust-pipe test (paper got sucked in). Tomorrow they're going to do a compression and leak down test.
The engine has about 15k miles on a rebuild which was done back in 2004. I'm hoping it is something simple, but it's not looking good. More to come....
Looks like a bent push rod on the #3 exhaust valve, so something seems to be binding up that valve. They're getting me a quote to pull the head and have a shop perform a valve job. The question is whether I should have both heads done or just the one.
Bryan Hayes
'76 Eleganza II
Salt Lake City, Utah
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| Re: [GMCnet] Dead Cylinder [message #288646 is a reply to message #288643] |
Tue, 13 October 2015 13:46 |
James Hupy
Messages: 6806
Registered: May 2010
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do both heads.
Jim Hupy
Salem, Or
78 GMC Royale 403
On Tue, Oct 13, 2015 at 11:27 AM, Bryan Hayes wrote:
> bhayes wrote on Mon, 12 October 2015 21:53
>> I took my GMC in to the shop today to have it looked over before some
> upcoming travel, and they informed me that the number 3 cylinder is dead.
>> Thus far they've only disconnected the plug wire (didn't have any effect
> on engine idle) and did the paper-over-the-exhaust-pipe test (paper got
>> sucked in). Tomorrow they're going to do a compression and leak down
> test.
>>
>> The engine has about 15k miles on a rebuild which was done back in 2004.
> I'm hoping it is something simple, but it's not looking good. More to
>> come....
>
>
> Looks like a bent push rod on the #3 exhaust valve, so something seems to
> be binding up that valve. They're getting me a quote to pull the head and
> have a shop perform a valve job. The question is whether I should have
> both heads done or just the one.
>
> --
> Bryan Hayes
> '76 Eleganza II
> Salt Lake City, Utah
>
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> GMCnet mailing list
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| Re: Dead Cylinder [message #288686 is a reply to message #288616] |
Tue, 13 October 2015 20:00 |
George Beckman
Messages: 1085
Registered: October 2008
Location: Colfax, CA
Karma: 11
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roy1 wrote on Mon, 12 October 2015 22:11Wish you luck. My engine had 16000 miles on it when I did a compression check on it because it didn't idle smoothly. Turned out the #7 exhaust guide was badly worn destroying the seat. Pulled both heads and found 2 other guides also destroyed along with the seats? Shop said the combustion temperatures were likely too high and bronze exhaust guides would be a good idea. A real head scratcher for sure.
Roy,
Sorry to hear of the valve troubles, both on your part and Brian's.
Because the shop said combustion temperatures were too high I thought it might be time to talk about causes of that issue.
Not necessarily in any order and I am not claiming that I am an expert or the last word on the subject. I would also like to thank Matt Colie, who has helped me understand these things to a greater degree and has filled in gaps in my "shade tree" knowledge.
1. Lean mixture at the wrong time.
a. lean mixture at very light loads lowers combustion temperatures. (less fuel and more cool air)
b. even "good mixtures" (14.7:1 is perfect) when pulling a 11-12K vehicle up a slight incline can raise combustion temps 100-150 degrees in seconds.
c. not rich mixtures at 1/2 to wide open throttle. (Caused by the power valve not working in a carb or Power Enrichment not set correctly in Electronic Fuel Injection or lack of sufficient fuel, usually caused by an ailing fuel pump in carbs and mal adjusted fuel pressure in EFI.
2. Lean mixtures to only some cylinders
a. May be a leaking intake gasket, or a major vacuum leak, perhaps the power brake hose (large) often mounted on the back of the manifold. (This could be the booster leaking as well but I would imagine you would have terrible brakes.) Intakes could leak at any or all of the 8 cylinders, where it mates with the head.
b. Perhaps a crack in the intake. (Original's did this before block off relieved the temperatures.)
3. Freak problem. We saw a 403 with a warped intake. The final analysis (thanks again Matt) was that a plug got to warm or just went to pieces. The electrode broke off up inside the plug. The electrode dropped to the plug ground and welded there. (too much heat). At this point the plug had a gob of metal that was hot enough to weld. Intake valve opened, ready to fire gas and air entered and hit the hot metal. It touched off the incoming mixture and the flame front flashed back up the intake. Intake valves are not like exhaust and flame was too much and it tuliped. (the head sucked down, pulled by the stem.) Matt said this all happened in split seconds. Now the valve did not seat properly and the cylinder began to fire weakly. Temperature went down, and the engine limped on. Matt said, "The owner should have bought a lottery ticket." The valve head could have popped off and that would have ruined a piston, if not whole cylinder.
I tell this because there was more lessons to be learned. Inspection of #6, the offending cylinder, showed casting "teats" here and there. After grinding those smooth, that engine has reduced its tendency to ping and knock. I know Dick Patterson grinds these little guys off and even touches up plugs. Glow plugs are for model airplane engines, not gasoline engines.
Also learned, plug #5 was blackish, with good compression. Why? it follows #6 in the firing order and the mixture was mucked up by #6 sending fire up the intake.
4. Carb jet or EFI injector problems feeding one side of the intake. However, this should only cause problems in 1/2 the engine. Remember the left side of the carburetor does not feed the left side of the engine, exclusively. (Left does 1, 7, 2 & 4)
5. Check the distributor weights and vacuum advance. If either is not working the spark is not advancing or is retarded. Retarded spark = hot cylinders, valves and water temperatures. Again this would effect all cylinders.
6. Too advanced spark causing excessive knock or ping. This causes hot spots, terrific concussions to moving parts... like being hit with a hammer.
So, look for goobers that might get hot and glow. When the intake comes off, inspect carefully. Look for signs of oil in the intake caverns of the heads or seeping under the gasket. Check all vacuum hoses and related devices. Check the engine timing and the distributor.
Nothing worse than fixing a problem only to have it reoccur.
I am sure others will have other bits of help in the heat in cylinder problems.
'74 Eleganza, SE, Howell + EBL
Best Wishes,
George
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| Re: Dead Cylinder [message #288704 is a reply to message #288619] |
Wed, 14 October 2015 00:52 |
bhayes
Messages: 263
Registered: March 2010
Karma: 1
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kerry pinkerton wrote on Tue, 13 October 2015 07:12Could be anything from a bad plug or plug wire to a wiped cam lobe (doubtful) or other broken/worn mechanical part, blown head gasket, ect. I recently went through a similar problem and found an exhaust valve that had receded into the head. Note that in my case, compression and leak down tests did not show a problem AT CRANKING SPEEDS because the valve seated well enough to seal at cranking speed.
Kerry, I believe this is exactly what is happening with mine. The technician mentioned something about the compression and leak down tests not showing a problem, which prompted him to remove the valve cover to look further. What did you end up doing in your case?
Bryan Hayes
'76 Eleganza II
Salt Lake City, Utah
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| Re: Dead Cylinder [message #288707 is a reply to message #288704] |
Wed, 14 October 2015 05:32 |
kerry pinkerton
Messages: 2565
Registered: July 2012
Location: Harvest, Al
Karma: 15
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Senior Member |
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bhayes wrote on Wed, 14 October 2015 00:52...
Kerry, I believe this is exactly what is happening with mine. The technician mentioned something about the compression and leak down tests not showing a problem, which prompted him to remove the valve cover to look further. What did you end up doing in your case?
Bryan, I did both heads and installed block off plates on the crossover like Rob mentioned.
Kerry Pinkerton - North Alabama
Had 5 over the years. Currently have a '06 Fleetwood Discovery 39L
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| Re: Dead Cylinder [message #288738 is a reply to message #288718] |
Wed, 14 October 2015 15:44 |
Bob de Kruyff
Messages: 4260
Registered: January 2004
Location: Chandler, AZ
Karma: 1
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thesmith wrote on Wed, 14 October 2015 09:31Im curious, does the 403 have the "Crossover" thats on the 455?
Pete
kerry pinkerton wrote on Wed, 14 October 2015 06:32bhayes wrote on Wed, 14 October 2015 00:52...
Kerry, I believe this is exactly what is happening with mine. The technician mentioned something about the compression and leak down tests not showing a problem, which prompted him to remove the valve cover to look further. What did you end up doing in your case?
Bryan, I did both heads and installed block off plates on the crossover like Rob mentioned.
Yes the 403 does as well but is less prone to cracking than the 455.
Bob de Kruyff
78 Eleganza
Chandler, AZ
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| Re: Dead Cylinder [message #288743 is a reply to message #288733] |
Wed, 14 October 2015 16:18 |
bhayes
Messages: 263
Registered: March 2010
Karma: 1
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Matt Colie wrote on Wed, 14 October 2015 12:12
Bryan,
Something made that pushrod bend. Don't put it back together unless you find out what happened.
Two good possibilities are:
The exhaust valve seized in the guide. This will leave scuff marks on the valve stem.
Hydraulic lock on cranking. This could also be with fuel and #3 is a prime candidate. If the head bolts there seem loser that others, you may be right.
Good Luck
Matt
Matt, I talked with Dick Paterson earlier (and I must say that I was in complete awe of his knowledge). If I understand correctly, iron valve guides can sometimes cause the exhaust valves to seize due to the heat these engines generate.
I'm getting the GMC back this afternoon from the shop. They want quite a bit to do the work, so I'm having them put it back together. I'm going to pull the valve cover off to inspect things myself. I'm going to try to determine if there are any scuff marks on the valve stem, if the stem is bent, and to see if I can get a good range of movement out of the valve. Some have said that if the valve checks out, at least from the top of the engine, then I should put a new push rod in and see what happens. (That's if I heard them correctly, of course.)
If things don't check out, then Dick gave me some great recommendations on some of the parts I should have a machine shop use when rebuilding the head.
Bryan Hayes
'76 Eleganza II
Salt Lake City, Utah
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| Re: Dead Cylinder [message #288771 is a reply to message #288614] |
Wed, 14 October 2015 20:00 |
kerry pinkerton
Messages: 2565
Registered: July 2012
Location: Harvest, Al
Karma: 15
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Senior Member |
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You're probably right Mark. I had forgotten it was an exhaust valve. I was thinking about small engines after dropping off the EV6010 and remembered that happened to me on a new Kolher with old gas. I don't see how it could do anything to an exhaust valve/pushrod either.
Kerry Pinkerton - North Alabama
Had 5 over the years. Currently have a '06 Fleetwood Discovery 39L
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| Re: Dead Cylinder [message #288777 is a reply to message #288771] |
Wed, 14 October 2015 20:39 |
C Boyd
Messages: 2629
Registered: April 2006
Karma: 18
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On the intake side it is a liquid mixture, out the exhaust it is an unburned sticky mess.
kerry pinkerton wrote on Wed, 14 October 2015 21:00You're probably right Mark. I had forgotten it was an exhaust valve. I was thinking about small engines after dropping off the EV6010 and remembered that happened to me on a new Kolher with old gas. I don't see how it could do anything to an exhaust valve/pushrod either.
C. Boyd
76 Crestmont
East Tennessee
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| Re: Dead Cylinder [message #288782 is a reply to message #288614] |
Wed, 14 October 2015 21:34 |
bhayes
Messages: 263
Registered: March 2010
Karma: 1
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Got it back home from the shop. Here's the write-up from the technician:
--------------------------------
The customer brought the motor home in for an oil change and timing adjustment. After the oil change was performed, the technician was going to set timing when he discovered the engine had a misfire. Additional diagnostic time was approved to try and determine the misfire cause.
The technician experienced backwards flow in the exhaust system related to the misfire. He believes there is an exhaust valve issue. A compression test was performed and all cylinders tested normal cranking compression at 125 psi. But cylinder 3 remained "dead". The technician performed a running compression test when the engine was cold, and the reading was 65 psi. A normal reading for 125 psi cranking compression.
The technician then got the engine warm and ran the running compression test again. This time the results were 25 psi. The running compression test failed. The technician removed the valve cover, rocker arms, and push rod for cylinder three. Nothing about the valve spring or valve looked out of the ordinary, but the push rod is bent, most likely from an intermittent exhaust valve hanging up on cylinder 3. The cylinder head will need to be removed for further diagnosis. A cylinder leakage test was also performed on cylinder three when the rocker arms were out, but that test showed normal as well.
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Bryan Hayes
'76 Eleganza II
Salt Lake City, Utah
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