toms roller rockers vs cam and valves from ta

Discussion in ''Da Nailhead' started by TAANK, Sep 17, 2007.

  1. TA Perf

    TA Perf Member

    The roller bearing will free things up abit. Take a pro mod engine with std cam bearings or any engine. Install the valve train then try and rotate it. Very hard to move. Now take the same engine and valve train combo, install roller cam bearings then try and rotate the engine. NIGHT and DAY differance. You will not even believe it. If roller bearing were not the ticket, there would be many after market roller rockers out there with out bearings just roller tips, but there isn't. So we decided to build what the industry expects.
    "What you get", 7075 alum billet rocker arm body's, dual torrington roller bearings, 1.65 true rocker ratio, 8620 gun drilled hardened shafts, machined nylon tubeular spacers, billet rocker stand towers with ARP studs. Rockers can be oiled factory stock or changed over to pushrod oiling. Qustions please just call.
  2. 1bolt

    1bolt Active Member

    Cam bearings are lubricated by oil pressure, so logically enough if you twist the rotating assembly when there's no oil pressure.......
  3. kitabel

    kitabel Well-Known Member

    Apparently, no one is interested.
    Fixed it.
    Last edited: Aug 26, 2009
  4. TA Perf

    TA Perf Member

  5. DaWildcat

    DaWildcat Platinum Level Contributor

    Where did this idea come from that babbit-type rocker arm bearings operate under the same "oil wedge" principle as crankshaft journal bearings??? You won't see any hydrodynamic wedge at all for the rockers to ride on with their back & forth sawing action, to get that you have to have full rotation. The best you can hope for is sufficient oil film to prevent excessive wear.

  6. kitabel

    kitabel Well-Known Member

    This is quite true.
    The analogy to a cam bearing is inappropriate - the roller bearing has the same friction when stopped as running.
    The higher plain bearing friction when stopped is due to the fact that the cam journals are "floated" by both system pressure and the wedge effect, neither of which works with the engine stopped. When the engine is running and the cam is in rotation and generating local oil pressure, the friction difference is greatly reduced.
    The rotation-induced oil wedge relies on speed differential (shaft vs. rocker ID) to produce local pressure. If one rotates, the pressure is a function of the speed (RPM shaft OD Pi 12 = speed in f/m), oil viscosity, clearance, and bearing width.
    Since a rocker only oscillates a few degrees (1.50" lever lifting .450" is about 17), the pressure is minimal, quickly bled off by the short "leak path" to the edge of each rocker or to the stand, and stops completely when the rocker reverses direction or stops.
    Pressure delivery to the shaft (or rocker, if pushrod oiled) is needed for plain bushing rockers, while needle bearings can live with just being "wet".

Share This Page