Author Topic: #5 cylinder exhaust valve not functioning properly.  (Read 3831 times)

Offline JuneBug

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#5 cylinder exhaust valve not functioning properly.
« on: March 26, 2014, 07:25:57 PM »
87 Chevy Silverado 350 5.7L TBI.  Had my truck in the shop replacing fuel lines. They told me that the exhaust valve in the #5 cylinder was not functioning properly but they wanted about 1000 to fix it.

They said exhaust valve does not close all the way. It sputters and knocks. I'm thinking bad valve. What else could it be.



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Offline bake74

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Re: #5 cylinder exhaust valve not functioning properly.
« Reply #1 on: March 26, 2014, 08:11:27 PM »
     Your valve could be bent, or broke same goes for the valve spring or the valve guide.  The shop would have to dig into that whole head, that's why the $1000.00 price tag, and if they were a good shop they would not do just the one side, they would want to do both sides.
     Exhaust valves do get burnt and can become brittle from consonantly being heated and cooled.
#1: The easiest and most obvious solution to any problem is 99% of the time correct.
#2: There is no such thing as impossible, it just takes longer.
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Offline JuneBug

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Re: #5 cylinder exhaust valve not functioning properly.
« Reply #2 on: March 27, 2014, 08:25:14 AM »
How hard is it to replace the valves myself?

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Offline Dan75k20

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Re: #5 cylinder exhaust valve not functioning properly.
« Reply #3 on: March 27, 2014, 10:24:15 AM »
Pull the heads and take them,to a machine shop it is not that difficult of a job

Offline JuneBug

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Re: #5 cylinder exhaust valve not functioning properly.
« Reply #4 on: March 27, 2014, 12:01:56 PM »
What exactly would I be asking them to do?

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Online bd

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Re: #5 cylinder exhaust valve not functioning properly.
« Reply #5 on: March 27, 2014, 12:10:49 PM »
87 Chevy Silverado 350 5.7L TBI.  Had my truck in the shop replacing fuel lines. They told me that the exhaust valve in the #5 cylinder was not functioning properly but they wanted about 1000 to fix it.

They said exhaust valve does not close all the way. It sputters and knocks. I'm thinking bad valve. What else could it be.

If you took it in for fuel line replacement, how did the shop arrive at an exhaust valve problem?  Does the engine misfire?  Did they run a compression check or cylinder leak down?  What were the results of their 'test' for the remaining cylinders?  There's more to this story.

For $1000 I would question the details on how they arrived at their conclusion.  What does "...not functioning properly..." mean exactly?  Be weary.
Rich
It's difficult to know just how much you don't know until you know it.
In other words... if people learn by making mistakes, by now I should know just about everything!!!
87 R10 Silverado Fleetside 355 MPFI 700R4 3.42 Locker (aka Rusty, aka Mater)

Offline JuneBug

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Re: #5 cylinder exhaust valve not functioning properly.
« Reply #6 on: March 27, 2014, 12:17:57 PM »
I'm am very weary. That is why I came here. I had put a 650 edlebrock carb and wanted them to tune it. They told me 650 was wrong size. They replaced with a 600 and replaced spark plugs and wires. Truck was sputtering and back firing. I believe they said they did a compression test. They said exhaust valve in #5 cylinder was not closing all the way. I barley got her home. When you press the gas she wants to die.

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Online bd

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Re: #5 cylinder exhaust valve not functioning properly.
« Reply #7 on: March 27, 2014, 02:07:13 PM »
So you converted it from TBI to conventional carburetion.  Did you decrease the fuel pressure at the same time to be compatible with a carburetor (~5 PSI)?

Was the engine sputtering and backfiring when you took it in to them, or was it just a routine maintenance type tune-up to accompany your carb change?  IMO, there's not enough difference between 650 and 600 CFM carbs to warrant the cost of a downgrade... re-jetting perhaps, but not replacement.

Bottom line - is the engine running worse since their "repairs?"  If it is, get a second opinion from a different local shop that is reputable.  You could have a problem with an exhaust valve, but I wouldn't proceed without verification and full confidence in the shop that is doing the work.  At the very least, they should be able to explain their reasoning, so that you are comfortable.
Rich
It's difficult to know just how much you don't know until you know it.
In other words... if people learn by making mistakes, by now I should know just about everything!!!
87 R10 Silverado Fleetside 355 MPFI 700R4 3.42 Locker (aka Rusty, aka Mater)

Offline JuneBug

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Re: #5 cylinder exhaust valve not functioning properly.
« Reply #8 on: March 27, 2014, 02:32:00 PM »
I got the truck from my mom. The engine had been replaced so I'm not totally sure what was changed. It has her distributer and is no longer fuel injected to my knowledge.  I'm not very knowledgeable about engines and tune up. When I took it in it was running rough but didn't knock and sputter. They informed me of the knock and sputter after they had tuned it.

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Offline JuneBug

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Re: #5 cylinder exhaust valve not functioning properly.
« Reply #9 on: March 27, 2014, 02:32:41 PM »
HEI distributer not her. Lol.

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Online bd

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Re: #5 cylinder exhaust valve not functioning properly.
« Reply #10 on: March 27, 2014, 02:45:52 PM »
Take it to a different (reputable) shop. 

Did they return your "old" carburetor?
Rich
It's difficult to know just how much you don't know until you know it.
In other words... if people learn by making mistakes, by now I should know just about everything!!!
87 R10 Silverado Fleetside 355 MPFI 700R4 3.42 Locker (aka Rusty, aka Mater)

Offline JuneBug

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Re: #5 cylinder exhaust valve not functioning properly.
« Reply #11 on: March 27, 2014, 10:33:30 PM »
Yeah they gave me the other one back. I live in Fayetteville Nc. I don't think we have any reputable shops here. Lol

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Online bd

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Re: #5 cylinder exhaust valve not functioning properly.
« Reply #12 on: March 27, 2014, 11:35:15 PM »
Here are some things you can do yourself that don't cost anything.  Check the firing order to make sure they have the spark plug wires correctly installed.  The 350 firing order is 1-8-4-3-6-5-7-2.  The driver (left) side cylinders are "odd" numbered 1-3-5-7, front-to-firewall.  The passenger (right) side cylinders are "even" numbered 2-4-6-8, front-to-firewall.  The following image originally posted by Irish_Alley in another Forum thread should help. 

But, be careful - the image illustrates the original factory wiring.  If the #1 plug wire isn't connected to the distributor as shown in the image, go ahead and check the firing order based on where the #1 wire IS plugged into the distributor, and let us know the distributor wiring is different.  FYI - the distributor rotor spins clockwise looking down from the top as indicated by the arrow.



You can also watch for arcing around the spark plugs with the engine running at night.  The shop may have broken a spark plug when they installed them.

And, check the timing if you have a timing light.
Rich
It's difficult to know just how much you don't know until you know it.
In other words... if people learn by making mistakes, by now I should know just about everything!!!
87 R10 Silverado Fleetside 355 MPFI 700R4 3.42 Locker (aka Rusty, aka Mater)