Damaged rocker update - A/C question
Thread Starter
Heel & Toe
Joined: Jun 2010
Posts: 20
Likes: 0
Damaged rocker update - A/C question
I got the Grand Sport back together yesterday and fired it up today. This was the LT4 that had the rocker arm come off #6 exhaust valve. After weighing in everyones opinion I decided to trust the cylinder leak down test and the test I did that showed .011 runout of the valve head by pushing it down until it hit the piston. I figured .011 runout was not that bad and besides, the leak test showed exactly the same amount of leakage, 9% (cold engine), as #4 cylinder. I removed the intake and replaced that lifter with a new one in case that was the problem, and also replaced the spring, retainer, and keepers, along with the rocker arm. I flushed several quarts of oil into the head and valley and then changed it. Ran the car today for fifteen minutes and changed the oil again. Car runs awesome, just as before, EXCEPT, when I kicked the A/C on there was a very noticeable vibration and drag on the engine. I only ran the A/C a couple of times before this rocker arm incident, but I don't think it acted this way, at least I didn't notice it then. Maybe I am just very sensitive to anything now after the repair. Is it possible I may have a vacuum line crossed or something? Any ideas? Thanks in advance.
Le Mans Master
Joined: Jul 2007
Posts: 5,043
Likes: 8
From: Tampa Florida
Glad to hear the damage wasn't too extensive.
AC pressure problem? Check the pressures with a manifold gauge set to see if anything is off or if the system is just short cycling.
Make sure you reattached all the hardware on/around the AC area after you completed your head work.
Check the accessory belt to see if it is showing signs of excessive wear.
AC pressure problem? Check the pressures with a manifold gauge set to see if anything is off or if the system is just short cycling.
Make sure you reattached all the hardware on/around the AC area after you completed your head work.
Check the accessory belt to see if it is showing signs of excessive wear.
Thread Starter
Heel & Toe
Joined: Jun 2010
Posts: 20
Likes: 0
Glad to hear the damage wasn't too extensive.
AC pressure problem? Check the pressures with a manifold gauge set to see if anything is off or if the system is just short cycling.
Make sure you reattached all the hardware on/around the AC area after you completed your head work.
Check the accessory belt to see if it is showing signs of excessive wear.
AC pressure problem? Check the pressures with a manifold gauge set to see if anything is off or if the system is just short cycling.
Make sure you reattached all the hardware on/around the AC area after you completed your head work.
Check the accessory belt to see if it is showing signs of excessive wear.
Le Mans Master
Joined: Dec 2006
Posts: 5,139
Likes: 482
From: H-Town Texas
I remember your original post. Made me pull the valve covers just to check the rockers.
I can't recall though, didn't you say the p.o. put a hotcam in it? I've had experienced, read and heard that the hotcam is not very a/c friendly. But, a/c does cause a bit of a drain on all cars. It did on my LT4 prior to came change and even more so afterward.
I can't recall though, didn't you say the p.o. put a hotcam in it? I've had experienced, read and heard that the hotcam is not very a/c friendly. But, a/c does cause a bit of a drain on all cars. It did on my LT4 prior to came change and even more so afterward.
Melting Slicks
Joined: Feb 2005
Posts: 3,204
Likes: 4
From: Midland Georgia
St. Jude Donor '06
AC vibration...
I got the Grand Sport back together yesterday and fired it up today. This was the LT4 that had the rocker arm come off #6 exhaust valve. After weighing in everyones opinion I decided to trust the cylinder leak down test and the test I did that showed .011 runout of the valve head by pushing it down until it hit the piston. I figured .011 runout was not that bad and besides, the leak test showed exactly the same amount of leakage, 9% (cold engine), as #4 cylinder. I removed the intake and replaced that lifter with a new one in case that was the problem, and also replaced the spring, retainer, and keepers, along with the rocker arm. I flushed several quarts of oil into the head and valley and then changed it. Ran the car today for fifteen minutes and changed the oil again. Car runs awesome, just as before, EXCEPT, when I kicked the A/C on there was a very noticeable vibration and drag on the engine. I only ran the A/C a couple of times before this rocker arm incident, but I don't think it acted this way, at least I didn't notice it then. Maybe I am just very sensitive to anything now after the repair. Is it possible I may have a vacuum line crossed or something? Any ideas? Thanks in advance.
Last edited by jakers; Jul 16, 2010 at 08:19 AM.
Thread Starter
Heel & Toe
Joined: Jun 2010
Posts: 20
Likes: 0
I remember your original post. Made me pull the valve covers just to check the rockers.
I can't recall though, didn't you say the p.o. put a hotcam in it? I've had experienced, read and heard that the hotcam is not very a/c friendly. But, a/c does cause a bit of a drain on all cars. It did on my LT4 prior to came change and even more so afterward.
I can't recall though, didn't you say the p.o. put a hotcam in it? I've had experienced, read and heard that the hotcam is not very a/c friendly. But, a/c does cause a bit of a drain on all cars. It did on my LT4 prior to came change and even more so afterward.
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Le Mans Master
Joined: Dec 2006
Posts: 5,139
Likes: 482
From: H-Town Texas
Yes, he put a Hotcam in it. The A/C was fine, I didn't notice any power loss or vibration before I removed the intake. It feels like someone pulls off a plug wire when I turn the A/C on now. I think I don't have something back together right or its something with one of the numerous switches or sensors. I've seen talk of having to reset the IAC, how do you do this? Or maybe the MAP sensor.