Is the cam gone?
Thread Starter
Drifting
Joined: May 2002
Posts: 1,546
Likes: 5
From: Sacramento California
Is the cam gone?
Hi,
I have been helping a buddy of mine with his project 71 Ls5. The car is really clean as far as the frame, birdcage, etc and is a nicely optioned car.
The problem is that the PO claimed the engine to be freshly rebuilt, and by the looks of it, it is, but after a fresh battery and fuel we cannot seem to get the valves adjusted where they don’t clatter. It also loses power at around 3800 RPM. We have tried setting cold (using the published method of adjusting at base circle) and the same warm, also while running doing the loosen until the clacking noise, tightening till the noise goes away and ¼ turn, and again at ½ turn.
Were thinking the PO didn’t break in the cam correctly and now it might be on the way out.
Now it’s time to ask the experts about this before tearing the engine down, only to discover we missed something simple.
Comments, ideas, similar experiences?
I have been helping a buddy of mine with his project 71 Ls5. The car is really clean as far as the frame, birdcage, etc and is a nicely optioned car.
The problem is that the PO claimed the engine to be freshly rebuilt, and by the looks of it, it is, but after a fresh battery and fuel we cannot seem to get the valves adjusted where they don’t clatter. It also loses power at around 3800 RPM. We have tried setting cold (using the published method of adjusting at base circle) and the same warm, also while running doing the loosen until the clacking noise, tightening till the noise goes away and ¼ turn, and again at ½ turn.
Were thinking the PO didn’t break in the cam correctly and now it might be on the way out.
Now it’s time to ask the experts about this before tearing the engine down, only to discover we missed something simple.
Comments, ideas, similar experiences?
Melting Slicks
Joined: Jan 2003
Posts: 2,877
Likes: 13
From: Doha
St. Jude Donor '08
I had exactly the same problem a while ago, a ticking noise and the engine will be out of breath at about 4K rpm, I re adjusted the rockers at the TDC of each cylinder while engine was cold (1/2 turn after zero lash) and took it for a test drive, engine woke up and I could rev it past 5K rpm very easly and it pulled harder also, but the tocking was still there so I re adjusted the rockers once again but while the engine is fully warmed up and running this time, I used a stethscope and carefully listened to each rocker and started tightening it until noise is gone, now its much better and the engine seems much stronger than before. BTW, its also a '71 LS5.
Race Director
Joined: May 2005
Posts: 10,674
Likes: 122
From: Millington Illinois
St. Jude Donor '08-'09
Hi,
I have been helping a buddy of mine with his project 71 Ls5. The car is really clean as far as the frame, birdcage, etc and is a nicely optioned car.
The problem is that the PO claimed the engine to be freshly rebuilt, and by the looks of it, it is, but after a fresh battery and fuel we cannot seem to get the valves adjusted where they don’t clatter. It also loses power at around 3800 RPM. We have tried setting cold (using the published method of adjusting at base circle) and the same warm, also while running doing the loosen until the clacking noise, tightening till the noise goes away and ¼ turn, and again at ½ turn.
Were thinking the PO didn’t break in the cam correctly and now it might be on the way out.
Now it’s time to ask the experts about this before tearing the engine down, only to discover we missed something simple.
Comments, ideas, similar experiences?
I have been helping a buddy of mine with his project 71 Ls5. The car is really clean as far as the frame, birdcage, etc and is a nicely optioned car.
The problem is that the PO claimed the engine to be freshly rebuilt, and by the looks of it, it is, but after a fresh battery and fuel we cannot seem to get the valves adjusted where they don’t clatter. It also loses power at around 3800 RPM. We have tried setting cold (using the published method of adjusting at base circle) and the same warm, also while running doing the loosen until the clacking noise, tightening till the noise goes away and ¼ turn, and again at ½ turn.
Were thinking the PO didn’t break in the cam correctly and now it might be on the way out.
Now it’s time to ask the experts about this before tearing the engine down, only to discover we missed something simple.
Comments, ideas, similar experiences?
Last edited by 63mako; Mar 10, 2010 at 11:02 AM.
Thread Starter
Drifting
Joined: May 2002
Posts: 1,546
Likes: 5
From: Sacramento California
I got to thinking it might be the springs. He said it had been rebuilt, but the car sat for several years after that, and i'm thinking a couple of springs that were compressed during that time might be a little weak.
Thread Starter
Drifting
Joined: May 2002
Posts: 1,546
Likes: 5
From: Sacramento California
Paul -
Yes it has good oil pressure, and the oil looks good (not metalically)(if thats a real word)
My buddy is currently in Arizona and won't be back until next month. The car is in my shop in North Highlands.
I will check out the valve springs and turn it over slowly and see if each valve is opening the same.
Where is your shop? I live across the street from Carmichael (Mission and Robertson)
Yes it has good oil pressure, and the oil looks good (not metalically)(if thats a real word)
My buddy is currently in Arizona and won't be back until next month. The car is in my shop in North Highlands.
I will check out the valve springs and turn it over slowly and see if each valve is opening the same.
Where is your shop? I live across the street from Carmichael (Mission and Robertson)
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Burning Brakes
Joined: May 2008
Posts: 860
Likes: 0
From: Stratford Ontario
If the cam is gone you will see an irratic pulse on a vacuum gauge.You may even get popping through carb or exhaust under load.Be carefull adjusting rockers, you don't want the pistons closing the valves or they will bend.Good luck
Safety Car
Joined: Mar 2007
Posts: 3,652
Likes: 49
From: Bridgewater nj
Also you can watch the rockers while its running and see some rockers aren't moving the same amount. Another thing is, if your cam has over .500 lift you need long slot rockers. If not they crack in the cup and lose the pivot point.My 427 cam got wiped too!!!
1st Gear
Joined: Mar 2010
Posts: 1
Likes: 0
Is the cam gone.
You might want to look a push rod top and bottom, the old style ones look like a ball at the top and some are even dome shaped, with age and ware they crack and split. Most rebuilders just put them back without checking them, when the pushrod rotates under stress it can make the crack open and close like a clam, the noise will be sporadic. Someone else also posted if a cam is wiped it will pop thru the carburetor which is correct. I just hope for your sake you don't have a solid lifter or roller cam, they are not adjusted the same way as a hydraulic cam and will make some noise.....
Thread Starter
Drifting
Joined: May 2002
Posts: 1,546
Likes: 5
From: Sacramento California
The good news I'm getting here is, there is no popping or backfiring through the carb
Former Vendor
Joined: Nov 2006
Posts: 2,482
Likes: 3
From: Carmichael ca
Paul -
Yes it has good oil pressure, and the oil looks good (not metalically)(if thats a real word)
My buddy is currently in Arizona and won't be back until next month. The car is in my shop in North Highlands.
I will check out the valve springs and turn it over slowly and see if each valve is opening the same.
Where is your shop? I live across the street from Carmichael (Mission and Robertson)
Yes it has good oil pressure, and the oil looks good (not metalically)(if thats a real word)
My buddy is currently in Arizona and won't be back until next month. The car is in my shop in North Highlands.
I will check out the valve springs and turn it over slowly and see if each valve is opening the same.
Where is your shop? I live across the street from Carmichael (Mission and Robertson)
Heel & Toe
Joined: Mar 2010
Posts: 22
Likes: 3
I would adjust the rockers while running and warmed up.
I used a steel valve cover with 1/3 of the top cutoff and some rocker clips to keep the oil from squirting all over the place from the pushrod end of the rocker. Valve cover with the valve cover installed to keep the oil from dripping over the sides of the head. All rockers exposed for easy adjustment and no messy oil drips.
With each valve, back off until you hear a slight clatter, then turn 1/4 tighter.
Go on to the next valve so the previous lifter adjustment has time to adjust to the new setting.
Go down each of the (8)valves 1/4 turn each until you complete the (1)turn from zero lash.
Check your GM Service Manual as believe it is (1)turn from zero lash so the 1/2-3/4 turn might not get rid of the clatter.
Hope this helps.
I used a steel valve cover with 1/3 of the top cutoff and some rocker clips to keep the oil from squirting all over the place from the pushrod end of the rocker. Valve cover with the valve cover installed to keep the oil from dripping over the sides of the head. All rockers exposed for easy adjustment and no messy oil drips.
With each valve, back off until you hear a slight clatter, then turn 1/4 tighter.
Go on to the next valve so the previous lifter adjustment has time to adjust to the new setting.
Go down each of the (8)valves 1/4 turn each until you complete the (1)turn from zero lash.
Check your GM Service Manual as believe it is (1)turn from zero lash so the 1/2-3/4 turn might not get rid of the clatter.
Hope this helps.
Instructor
Joined: Jan 2008
Posts: 208
Likes: 0
From: McDonough GA
A vacuum gauge is your best friend on troubleshooting things like this.
The gauge will get you pointed in the right direction.
