Soft Cam Lobes?
Thread Starter
Pro
Joined: Jan 2005
Posts: 539
Likes: 3
From: Twin Cities Minnesota
Soft Cam Lobes?
I have a 76 and someone told me that around that year GM used a softer metal on the cams (lobes) on a L48 engine. They wear down which causes a loss of power from not opening enough. Anyone have any info on soft cam lobes? Anyway to tell if cam lobes are wore down without complete disassembly? I realize my poor L48 engine is pretty gutless, and I will do some to correct that in the future, but need to run what I have for now. 
Thanks for the help
Thanks for the help
Tech Contributor
Joined: Aug 1999
Posts: 14,382
Likes: 6,402
From: At my Bar drinking and wrenching in Lafayette Colorado
GM did have some cam failures related to soft cams. But when the cam fails, there is no doubt that you have suffered a massive failure of some type: When the cam lobes wear down, they immediately chew up the bottom of the lifters. The chewed up lifters them shave the lobes right off the cam, making the cam lobes on the affected cylinders completely inoperative. You end up with a distinctive miss, often associated with popping out the exhaust or popping up through the carb. If your engine is running on all 8 cylinders with no irritating miss, your cam is okay.
Drifting
Joined: May 2004
Posts: 1,258
Likes: 0
From: Huntsville Alabama
[QUOTE=lars] You end up with a distinctive miss, often associated with popping out the exhaust or popping up through the carb.[QUOTE]
does it sound like an exhaust leak or does it sound different will the sound get louder when you reve the motor.
does it sound like an exhaust leak or does it sound different will the sound get louder when you reve the motor.
Safety Car
Joined: Oct 1999
Posts: 4,101
Likes: 10
From: NorCal
To elaborate a bit, when the cam lobe and coresponding lifter wear enough to start "going flat" it happens real fast, like within a few hundred miles, and they wear down to nothing (zero lift). The resulting performance is unmistakeable, so if your engine runs good, that is not an issue.
It was a real problem on the SB in the 70's - 80's, but I'm not sure why, and I know some folks here have had problems with some Comp Cams products.
Hans
It was a real problem on the SB in the 70's - 80's, but I'm not sure why, and I know some folks here have had problems with some Comp Cams products.
Hans
Melting Slicks
Joined: Jan 2004
Posts: 2,672
Likes: 1
From: New Cumberland PA
Originally Posted by lars
You end up with a distinctive miss, often associated with popping out the exhaust or popping up through the carb.
Melting Slicks
Joined: Jun 2003
Posts: 2,802
Likes: 241
From: Niles, MI
I had a '67 Impala with a 283 that wiped a couple lobes. As Lars stated it started popping through the carb.
I've talked with an old engineer who used to work at GM. He stated that the cams were flame hardened in an unattended operation. I think there was a gas fired burner for each lobe. Sometimes the flames would be extinguished and it wouldn't be caught immediately. Those lobes where the flame was extinguished would be soft.
I've talked with an old engineer who used to work at GM. He stated that the cams were flame hardened in an unattended operation. I think there was a gas fired burner for each lobe. Sometimes the flames would be extinguished and it wouldn't be caught immediately. Those lobes where the flame was extinguished would be soft.
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Racer
Joined: Aug 2005
Posts: 308
Likes: 0
From: Salem MA
in my other car hobby (volvos) aftermarket cams are not treated in the same way the OE cams are. and the aftermarket cams slowly wear down over time. its because they arent hardened enough (or some other similar metal treatment). but as it turns out OE volvo cams are harder than american cams and basically never wear. and aftermarket cams are made the same way american cams are. so its probably the cam went from better than normal to what most people consider normal around your year. so dont worry about it too much.
Le Mans Master
Joined: Mar 2004
Posts: 7,503
Likes: 1,511
From: Little Rock AR
The L-48 is pretty gutless even when all the cam lobes are still there. 
I tore my '80 engine down to repair a bottom end problem and give it an overhaul. The miles were about 45K and the bores were still perfect. The cam had a lobe or two that had worn enough to be seen with the naked eye. The engine did not have any of the classic worn lobe characteristic "popping" sounds when running. In fact it ran great that way. Just something to think about.
-Mark.
I tore my '80 engine down to repair a bottom end problem and give it an overhaul. The miles were about 45K and the bores were still perfect. The cam had a lobe or two that had worn enough to be seen with the naked eye. The engine did not have any of the classic worn lobe characteristic "popping" sounds when running. In fact it ran great that way. Just something to think about.
-Mark.
