SBC 406 Cam Broken
Thread Starter
Racer
Joined: Dec 2005
Posts: 368
Likes: 4
From: . New Zealand
SBC 406 Cam Broken
A speedway modified engine I built 3 yrs ago has just broken the cam shaft at about #6, at first I suspected the usual #6 contact clearance issue, but this has been fine for some time now, and I know it had good clearance. It runs a gear drive so can't blame chain stretch. The cam is a Comp Cams 12-515-5 259/262 @ 0.050" .550/.570".
Anyone else have this happen?
Anyone else have this happen?
Racer
Joined: May 2006
Posts: 257
Likes: 0
From: Tampa by way of MIAMI! FL
Is it a flat tappept or roller? I've heard their is something different about the oil these days that kills a Hydraulic Flat Tappet. I think it has something to do with the Zinc content IDK for sure.
Thread Starter
Racer
Joined: Dec 2005
Posts: 368
Likes: 4
From: . New Zealand
This cam is a flat tappet mechanical cam, it is broken because its sticking out the back cam bearing about 3/4".
The rods are Scat 4340 I beam and were clearanced properly to the #6 lobe. I have not disassembled the engine yet, the owner has shelved his racing this season, so he wants me to repair it during our winter (June to August). The engine sat for 2 seasons unused, because of owners health issues, so I had him re-lube the cam when he restarted it, it seemed to be ok for his first race meeting, then this. He is using our Shell equivalent of Rotella T, so it should not have been a lubrication issue.
The rods are Scat 4340 I beam and were clearanced properly to the #6 lobe. I have not disassembled the engine yet, the owner has shelved his racing this season, so he wants me to repair it during our winter (June to August). The engine sat for 2 seasons unused, because of owners health issues, so I had him re-lube the cam when he restarted it, it seemed to be ok for his first race meeting, then this. He is using our Shell equivalent of Rotella T, so it should not have been a lubrication issue.
Le Mans Master
Joined: Aug 2000
Posts: 6,362
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From: Brazos TX
Cruise-In IV Veteran
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I had a Comp cam break in half but it wasn't their fault. The cam was in the engine when a valve head broke off and destroyed the cylinder head. When the engine was rebuilt the cam we reused. Well, 15,000 miles later the cam snapped in half. When talking with Comp about it they said that sometimes the cams can be damaged in shipping. If they are dropped they can have problems later but I don't think that is what happened to mine.
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Is it a P-55 cam core? They are a hardened one that is really good as far as wear resistance goes. Many circle track folks spec them......but they DO have more of a tendency to do just what you said...break in half. Usually they are replaced before they break as part of maintenance program.
JIM
JIM
Thread Starter
Racer
Joined: Dec 2005
Posts: 368
Likes: 4
From: . New Zealand
You're probably right, but I won't be able to strip it until next year. According to the driver it went onto 7 then stopped, so it does sound ominous.
Rod
