#8 dead cylinder
Thread Starter
Racer
Joined: May 2007
Posts: 370
Likes: 0
From: Cherry Hill N.J.
#8 dead cylinder
I'm in the process of giving up!!!!!!!
Over the last few months I have had an ongoing problem with a rough running engine and dead miss at idle.
The problem began suddenly after running well for years.
I have checked wires, replaced plugs, replaced lifters(2 were not pumping up) disassembled carb and cleaned (only 2 years old),replaced distributor cap & rotor.
On adjusting valves I noticed #8 exhaust valve spring seemed to be loose.
Would a weak valve spring cause a miss at idle. Engine does run better after 2000 rpms.
I checked with vacuum gauge and the needle fluctuated at idle but steadied at higher rpms.
I think that indicates bad valve guides.
And ideas are welcome.
Thanks in advance`
Over the last few months I have had an ongoing problem with a rough running engine and dead miss at idle.
The problem began suddenly after running well for years.
I have checked wires, replaced plugs, replaced lifters(2 were not pumping up) disassembled carb and cleaned (only 2 years old),replaced distributor cap & rotor.
On adjusting valves I noticed #8 exhaust valve spring seemed to be loose.
Would a weak valve spring cause a miss at idle. Engine does run better after 2000 rpms.
I checked with vacuum gauge and the needle fluctuated at idle but steadied at higher rpms.
I think that indicates bad valve guides.
And ideas are welcome.
Thanks in advance`
Pro
Joined: Aug 2007
Posts: 707
Likes: 31
From: Pitman NJ
Did you do a compression Check?
If it happened all of a sudden, I think something broke... like maybe a valve, valve spring, or rocker arm. If this happened, you could get a miss.
As far as you valve guides being bad, this would happen over a longer period of time, and not cause a problem all of a sudden.
I'm sure others will chime in....
I also see that you are not too far from me.
If it happened all of a sudden, I think something broke... like maybe a valve, valve spring, or rocker arm. If this happened, you could get a miss.
As far as you valve guides being bad, this would happen over a longer period of time, and not cause a problem all of a sudden.
I'm sure others will chime in....
I also see that you are not too far from me.
Team Owner
Joined: Jan 2006
Posts: 37,637
Likes: 3,117
From: Crossville TN
How did the electrode on the plug [in #8] look? Was it different from any of the other plugs? Do the pushrods on #8 look like they are providing the same valve "lift" as the others? Is the miss only at idle, or is it just masked by the higher revs of the motor? Put a timing light on that plug wire (and on one or two of the others) to see what the 'spark' is doing on each of those cylinders.
Thread Starter
Racer
Joined: May 2007
Posts: 370
Likes: 0
From: Cherry Hill N.J.
#8 dead cylinder
Spark is same as other for #8.
My problem is the exhaust valve spring seams "softer", there is not the same resistance as other valves to my pushing down on them with my finger.. #8 valve can be moved downward.....the spring doesn't hold it closed.......could this be causing rough idle....
I'm doing compression chech and leakdown check tomorrow.
My problem is the exhaust valve spring seams "softer", there is not the same resistance as other valves to my pushing down on them with my finger.. #8 valve can be moved downward.....the spring doesn't hold it closed.......could this be causing rough idle....
I'm doing compression chech and leakdown check tomorrow.
Le Mans Master
Joined: Jan 2000
Posts: 8,918
Likes: 27
From: New Hill NC
Spark is same as other for #8.
My problem is the exhaust valve spring seams "softer", there is not the same resistance as other valves to my pushing down on them with my finger.. #8 valve can be moved downward.....the spring doesn't hold it closed.......could this be causing rough idle....
I'm doing compression chech and leakdown check tomorrow.
My problem is the exhaust valve spring seams "softer", there is not the same resistance as other valves to my pushing down on them with my finger.. #8 valve can be moved downward.....the spring doesn't hold it closed.......could this be causing rough idle....
I'm doing compression chech and leakdown check tomorrow.
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Melting Slicks
Joined: Jul 2006
Posts: 2,288
Likes: 489
From: Salmon Arm, BC
You should be able to go to your local machine shop, or performance warehouse and pick up a "better than stock" Z28 type spring set for about 20-30 bucks. If I was you I'd change the whole set asap.
Drifting
Joined: Aug 2005
Posts: 1,682
Likes: 3
From: League City TX
There are several vacuum hoses that connect to the intake runner that feeds the #8 cylinder.
If one of these has a leak in the system, the cylinder will run lean and result in a dead miss at idle.
If you noticed anything that runs off of vacuum start to malfunction around the same time as the miss started, it could be a sign.
Have you tried capping the vacuum ports?
If one of these has a leak in the system, the cylinder will run lean and result in a dead miss at idle.
If you noticed anything that runs off of vacuum start to malfunction around the same time as the miss started, it could be a sign.
Have you tried capping the vacuum ports?
Team Owner
Joined: Jan 2006
Posts: 37,637
Likes: 3,117
From: Crossville TN
If you've had a valve spring failure on #8, it's just a matter of time that the others begin to fail, as well. Stock valve springs are not an expensive item and changing them out is a PITA (if the heads are on the car). Just change them all and replace the valve seals while you're at it. It's a "do good" move that you won't regret.
Thread Starter
Racer
Joined: May 2007
Posts: 370
Likes: 0
From: Cherry Hill N.J.
#8 dead cylinder
Guys
I think we've got it.......Removed exhaust valve spring(the one I replaced before) and found the replacement spring had broken.
That is what happens when you overlook the obvious.
Had same symptoms again and assumed it must be something else....
I'm in the process of replacing all other valve springs and I hope I can get it back together without any more problems.
Thanks again for everyones help....
I think we've got it.......Removed exhaust valve spring(the one I replaced before) and found the replacement spring had broken.
That is what happens when you overlook the obvious.
Had same symptoms again and assumed it must be something else....
I'm in the process of replacing all other valve springs and I hope I can get it back together without any more problems.
Thanks again for everyones help....