Dart SHP Cam bearing failure

General engine tech -- Drag Racing to Circle Track

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ProPower engines
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Re: Dart SHP Cam bearing failure

Post by ProPower engines » Tue Oct 17, 2017 2:33 pm

I have seen the melted Durabond bearing issue in several engines in the past couple years year.
Even with the bearings with a single hole clocked correctly to promote oil wedge they melted.
These were both the std and HP non coated bearings. We switched to the HP coated bearings and the issue went away.
As mentioned there is bearings available with several holes drilled in them but I have had to drill others to provide adequate oiling to the cam journals.
In both stock blocks as well as aftermarket blocks there has been the same issue with melted bearings not specifically #4 but I have seen 3-4-5 have an issue.These were also not heavily loaded with higher spring pressures as well maybe 130/375 at most for spring loads but all have been chevy's
Again the coated HP bearings with 2-3 oil feed holes have provided better protection against the issue todate.

Now I just add the extra holes regardless or groove the bearing back if not available to provide a better oil supply
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Re: Dart SHP Cam bearing failure

Post by jsgarage » Tue Oct 17, 2017 3:37 pm

The only Chev cam bearing failure I've ever had came from very severe overheating- to the point of almost-piston-seizure.

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Re: Dart SHP Cam bearing failure

Post by MadBill » Tue Oct 17, 2017 3:56 pm

If coated bearings are substantially better, it suggests the issue is the lack of hydrodynamic lubrication during start up; one of the drivers for needle roller cam bearings.
Lets see, if seat duration is 300°, on average there will be 300/720 or 6.67 valves off their seats in a 2 valve V-8, with say an average spring force of 350# x 1.6:1 rocker ratio, so 350 x 1.6 x 6.67 = 3,735# total load on the cam bearings. Could be double that or more for a big high RPM application...
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