Why is the camshaft breaking?
 

I have broke two cams in the same engine within 10 hours. First time the distributor gear shattered, now the cam sheared off just in front of the disrtibutor gear. It is a roller cam made by CamMotion? The engine is a 572 ci blower 1000hp. Roller rockers with stud girdle and a rev kit (springs on the lifters). MSD Distributor looked fine and the gears on the cam looked fine. Engine builders and cam guys are saying they rarely break but can happen. Anyone have thoughts?

It sounds like a quality control issue at CamMotion to me. I've heard of them...but don't know much about them. I would call Gordon at Comp Cams, they are tough to beat. :cool:

Was reading a while back that roller cams with really high lift (.600++) are prone to breakage due to the small base circle needed to obtain the desired lift.
Look at it this way, a cam won't fit through the cam bearings if the lobes stick up higher than the bearing journal. In order to get higher lift the cam grinder uses a smaller base circle but scarifices material strength to do it. Combine that with the high spring pressures needed for high RPM use and anythings liable to happen.
Either that or the cam is binding in the rear bearing.

Iggy....maybe I'm off base here but.... If the cam is breaking in front of the distributor gear, then this is a part of the "rough" casting, not part of the machined (smaller base circle) journal. Therefore, there is no effect of the High lift problem you mentioned, ie: reduced journal size. How about excessive pressure on the cam due to valve springs "binding" or as you suggested- the rear cam bearing seizing???

While Iggy has some very valid points the camshaft should not be breaking due to "material issues". I run .785 lift with 330# seat pressures and 950# opening and have never had these sorts of problems, in over 50 hrs. While this cam might sound radical to some it is actually quite mild compared to Pro-stocker 10,000 rpm motors with over 1" of lift. ;) As Iggy suggests maybe its a bearing problem (although that would be evident in the oil filter) does the cam look likes its been hot? Otherwise, it really sounds like a quality control issue. my .10 cents:rolleyes: :)

Sometimes the gear on the cam isnt quit right I would check the gear pattern .. cam could be spaced wrong the intake could be out of allignment... distrirutor gear end play could be wrong.

Bearings are fine and the gears looked good on the cam and the distributor. I have also wondered and asked if the intake manifold was not aligned. Again the builders say not likely. I do not know the specs of the cam, however the engine guru is telling me it is a long duration with moderate lift. I think we are going to try another manufacturer at this point.

If its a tight cam, it would probably break at the timing gear end, not the distrib end. I doubt its a quality control issue. Most cam manufacturers buy the same blanks. Just ask Crane. This sounds like either an oil pump problem, or maybe the distributor is binding. Is it a sliding collar type distributor? Is the back of the cam contacting the block plug? Is the cam button too tight? I'd slide a cam and the distrib into the block, no timing chain,no push rods or lifters, and put the cam gear and cover back on. Bolt the oil pump on. Then see if you can spin the cam. With the pan off, you can grab it from between the bores. If its really tight, start removing stuff and trying it until it turns freely, or put the stuff on one at a time and try it.

Thee is also a possibility that the cam bores are not properly aligned, even a few thousandths is enough to cause failure.
Cam bearing clearance could also be an issue.

You are putting the cam button in arent you?
My cam has a .632 lift and never had an issue, I run cams with .700 and higher and never had one break in half
Dan

This is why I love this board. All very helpful suggestions. THANK YOU!:) :)