Originally Posted By: Chris142
Originally Posted By: OVERK1LL
Originally Posted By: Chris142
The old pushrod V8's (and v6's too I guess) would eat cams if idled too much. The cams were lubed from oil thrown off the rods and at an idle not much oil got thrown.
What?
There were many roller pushrod V8's, the SBF went roller in the Mustang in 1985.....
Oil is pressure-fed to the lifters, which regulate oil flow to the top-end. Oil coming down the lifter bores lubricates the camshaft lobes, the camshaft bearings are pressure-fed.
I'm talking non roller engines. This is why you break in a new cam @2000 rpm.
http://www.4secondsflat.com/Hydraulic_lifter_cams.html
"Because the camshaft and lifters are primarily lubricated by the splash of oil from the crankshaft, any RPM below 1,800 may result in insufficient lubrication and may cause cam lobe failure."
I don't completely agree with that article. That is because the cam is lubricated in two ways.
Many attempts at preventing flat-tappet camshaft failure in race engines have involved slotting the sides of the lifters to allow more oil to get on the lobes; one racing team even went as far as to put a tiny hole in the bottom of the lifter so that pressure-fed oil was put directly on the lobe.
While there IS spray from between the rods and crankshaft; the same oil that is sprayed on the sides of the bores, the camshaft benefits from also being lubed (on the lobes) from the lifter bores as well.
Oil selection, break-in procedure, spring pressure and a host of other things are all relevant to how long a flat-tappet camshaft lives for.
For example, the Ford 302, in flat tappet form, is not known for wiping cam lobes with the stock cam in it. No matter how much it is idled. Same goes for its larger 351 brother.
Situations where one typically does come across people wiping cam lobes is performance builds. Where of course higher spring pressure, more aggressive ramp-rates and potentially sub-par cam core material can all play a role.
In regards to the 2,000RPM thing, it is done for a few reasons:
1. Oil flow. Both spray and from the lifter bores.
2. Lifter rotation. In order to get the lifters to properly "spin" on the lobes, you must have the engine at a moderate RPM during break-in.