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91 GMC 5.7 Engine smoking
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mikkos
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Aug 15, 2010, 6:45 AM
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91 GMC 5.7 Engine smoking
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Hi all I am new here
I have a perplexing problem with my GMC k1500.
It appears my 5.7 GMC engine starting smoking after sitting for a few months. I have checked the compression and reading between 150 and 160 on all cylinders. However, when I removed the plugs the two cylinders on the passenger side closest to the firewall do not appear to be a tan color more of a dark grey but not oil soaked. Engine idles ok. When I step on the gas pedal smoke goes not totally away but becomes significantly less, it is when I let off the gas pedal it smokes a lot. It does not have the heavy blue smoke but it smells a little like burning oil. I am not sure if I overlooked something simple or not but any help would be appreciated.
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Hammer Time
Ultimate Carjunky
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Aug 15, 2010, 7:21 AM
Post #2 of 14
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Re: 91 GMC 5.7 Engine smoking
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That engine is pretty notorious for wearing valve guides and the sitting around would dry out the valve seals so I would suspect your looking at a valve job now. Replacing the valve seals may give you temporary relief but the problem will likely return.
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mikkos
Novice
Sep 5, 2010, 5:57 PM
Post #3 of 14
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Re: 91 GMC 5.7 Engine smoking
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I went to do the valve seals and made an adapter to pressurize the cylinders. I place the cylinder to TDC and I hear air leaking. It did this on two cylinders I tested 1 of the cylinders I mentioned in the previous post and one of the ones that the spark plugs was burning perfect. Am I missing something here. What pressure shoud I charge the cylinder with to prevent the vales from falling into the cylinders. Very confused. Any help you could provide would be of great value to me.
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Hammer Time
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Sep 5, 2010, 6:03 PM
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Re: 91 GMC 5.7 Engine smoking
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TDC isn't as important as making sure you are on the compression stroke. If you just watch the valves and make sure they are both closed you will be OK. The air pressure will probably force the piston back down anyway. Having it at TDC will catch the valve if you drop it though. I use full pressure which is usually over 150PSI. Once you back off the rockers you know they are closed anyway. The leaking could be just burnt valves.
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mikkos
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Sep 5, 2010, 6:21 PM
Post #5 of 14
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Re: 91 GMC 5.7 Engine smoking
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Thanks again, this is the first time I am doing valve seals so I am a little nervous. I will suck it up and give it a shot.
Thanks again
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Hammer Time
Ultimate Carjunky
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Sep 5, 2010, 6:26 PM
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Re: 91 GMC 5.7 Engine smoking
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Make sure you use a magnet to remove and replace those keepers. You really don't want to drop any. Once you compress the spring a little, tap the top of the compressor with a small hammer to break the spring away from the keepers.
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We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.
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Sidom
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Sep 5, 2010, 6:55 PM
Post #7 of 14
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Re: 91 GMC 5.7 Engine smoking
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You could put some rope in the cyl & carefully rotate it until it's tight.... This will hold the valves up.
Of course it's critical to make sure you are coming up on the compression stroke before you start this...
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mikkos
Novice
Sep 6, 2010, 10:12 AM
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Re: 91 GMC 5.7 Engine smoking
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Well the oil drain port was plugged closest to the firewall. So I was able to unclog that. After getting both the intake and exhaust valve springs off the exhaust valve seal was completely broken and the others are really hard and brittle. The Flat O Ring was missing on the exhaust, and on the intake valve it is broken. The other thing I noticed is the Valve Stem oil seals are the umbrella type but the intake one has little compression rings around it that must hold it tight to the Valve guides. The replacements I have, do not have these compression rings. DO I need to have the seals with the compression rings??? I am assuming I can buy the flat O-Rings as well at NAPA or somewhere like that.
Would that oil drain port being plugged cause more smoking? I read on another post that this was another persons trouble and just unclogging that oil drain port relieved most of the smoking issues.
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Hammer Time
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Sep 6, 2010, 10:15 AM
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Re: 91 GMC 5.7 Engine smoking
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It's all in the quality of the parts you buy. If you can find FelPro brand, they will probably be the best seal to use.
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We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.
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Sidom
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Sep 6, 2010, 11:03 AM
Post #10 of 14
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Re: 91 GMC 5.7 Engine smoking
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You sure want those ports free. It would have to be clogged pretty good to get standing oil sitting on the seals but if that was the case it would definitely make it smoke more.....
You need to take HTs advise here and get the right parts. This is a lot of work to try a cheap short cut that doesn't work out. I know the feeling, you got it apart and just want to get it back together. But if you can possibly wait......get the right quality parts... It'll be better in the long run.....
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mikkos
Novice
Sep 11, 2010, 2:25 PM
Post #11 of 14
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Re: 91 GMC 5.7 Engine smoking
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Thank you for the advice and tips. Just finished and startd it up and it's ot smoking anymore. I think it was a combination of the plugged oil drain port and the fact that the umbrella seal was missing onthe valves closest to the firewall. All is good for ow.
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Hammer Time
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Sep 11, 2010, 2:44 PM
Post #12 of 14
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Re: 91 GMC 5.7 Engine smoking
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Your probably right. Glad to hear you got it resolved.
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We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.
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mikkos
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Sep 12, 2010, 3:15 PM
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Re: 91 GMC 5.7 Engine smoking
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Thanks all,
Especially HammerTime, people devoting their time to assist others is greatly appreciated, and not easy to come by. SO thanks alot.
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Hammer Time
Ultimate Carjunky
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Sep 12, 2010, 3:19 PM
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Re: 91 GMC 5.7 Engine smoking
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We really appreciate the rare thanks that we get here. Thank you
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We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.
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