Excessive distributor gear wear from billet cam
12-05-2012, 02:36 PM
#52
Budman
Going on the assumption that your camshaft is a genuine GM steel core it would be made from a 51xx alloy which is induction hardened. While technically it is a steel billet core, there is a difference between this core and a core that is traditionally referred to as a “billet” core. The billet cores we use are all 86xx alloy which are carburized. A carburized heat treat is significantly deeper than induction hardened treat. That’s an important factor when considering regrinding a camshaft.
It would appear your gear failure on the induction hardened core could be either of the following elements.
1) The gear you used was not a Melonized gear.
2) There was an improper wear pattern on the cam after the first use which caused premature degradation of the new gear. If that’s the case there is the potential to continue to fail any additional gears you put back on the cam.
You may also be looking at some secondary issues down the road from regrinding an induction hardened camshaft. If the hardened layer of the camshaft has been compromised during the regrinding process this could lead to a failure at some point down the road. When the hardened layer becomes too thin you run the risk of penetration as the substrate layer beneath it begins to yield. As it does so, the stresses can result in spalling or failing a camshaft lobe at some point down the road.
We are currently using a gear manufactured for us that is hardened steel, treated, gear compatible with cast/induction hardened/carburized cores.
Bob
Going on the assumption that your camshaft is a genuine GM steel core it would be made from a 51xx alloy which is induction hardened. While technically it is a steel billet core, there is a difference between this core and a core that is traditionally referred to as a “billet” core. The billet cores we use are all 86xx alloy which are carburized. A carburized heat treat is significantly deeper than induction hardened treat. That’s an important factor when considering regrinding a camshaft.
It would appear your gear failure on the induction hardened core could be either of the following elements.
1) The gear you used was not a Melonized gear.
2) There was an improper wear pattern on the cam after the first use which caused premature degradation of the new gear. If that’s the case there is the potential to continue to fail any additional gears you put back on the cam.
You may also be looking at some secondary issues down the road from regrinding an induction hardened camshaft. If the hardened layer of the camshaft has been compromised during the regrinding process this could lead to a failure at some point down the road. When the hardened layer becomes too thin you run the risk of penetration as the substrate layer beneath it begins to yield. As it does so, the stresses can result in spalling or failing a camshaft lobe at some point down the road.
We are currently using a gear manufactured for us that is hardened steel, treated, gear compatible with cast/induction hardened/carburized cores.
Bob
Pulled the cam and I have severe spalling on 5 exhaust lobes. That explains where most of the crap came from, although I am still not convinced this is what trashed my oil pump. The damage in there looks like it was from much larger chunks than what I would expect to see from cam spalling. Glad I didn't try to run it any more than I did.
12-07-2012, 03:33 PM
#54
Patri, I had five lobes affected, all on the exhaust side. All 16 lifters looked fine, rollers were smooth when I checked them. When I first saw this, since it was on the ramp instead of across the nose of the cam, I thought I had been lofting my lifters across the nose of the cam. However, the spalling is on the opening ramp, not the closing. Looks like they did not properly heat treat the surface after the regrind. Since I was going for more lift, the material was removed from the base circle blending up into the ramp. That probably explains why the nose of the cam looks OK - heat treating is still intact there. They also increased the duration on the exhaust side by a few degrees and slightly tightened the LSA, which probably made matters worse.
Like I said, Bob called that one on the nose - wish I had talked to him before my build. Expensive lesson learned!
Like I said, Bob called that one on the nose - wish I had talked to him before my build. Expensive lesson learned!
12-10-2012, 03:32 PM
#56
Registered
Patri, I had five lobes affected, all on the exhaust side. All 16 lifters looked fine, rollers were smooth when I checked them. When I first saw this, since it was on the ramp instead of across the nose of the cam, I thought I had been lofting my lifters across the nose of the cam. However, the spalling is on the opening ramp, not the closing. Looks like they did not properly heat treat the surface after the regrind. Since I was going for more lift, the material was removed from the base circle blending up into the ramp. That probably explains why the nose of the cam looks OK - heat treating is still intact there. They also increased the duration on the exhaust side by a few degrees and slightly tightened the LSA, which probably made matters worse.
Like I said, Bob called that one on the nose - wish I had talked to him before my build. Expensive lesson learned!
Like I said, Bob called that one on the nose - wish I had talked to him before my build. Expensive lesson learned!
More like heartburn.
