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Valve lash : solid cams vs. hyd cams w/ solids

Discussion in 'Street/strip 400/430/455' started by Bigpig455, Dec 11, 2022.

  1. Bigpig455

    Bigpig455 Fastest of the slow....

    I've never quite gotten straight why when we run a solid lifter cam, a common recommended lash is .015-.020, and when we run solids on a hydraulic cam, we typically run .003-.005 (or 0 as Brian Trick has recently suggested). I'm sure if has to do with lobe profile and ramp, etc.. but can somebody explain in real simple terms for this dumb ass? It seems to me we should be able to run all solids at 0, and increased lash on an aggressive love would just beat the hell out of the lobe and valve seats, despite the cam grind but I'm obviously wrong.....
     
    Bigpig455, Dec 11, 2022
    #1
  2. LARRY70GS

    LARRY70GS a.k.a. "THE WIZARD" Staff Member

    LARRY70GS, Dec 12, 2022
    #2
  3. Bigpig455

    Bigpig455 Fastest of the slow....

    Thanks Larry but I didnt see where it answered my question. A solid lifter LT-1 cam requires .024-.030 lash, I can run solids on a hydraulic cam with as little as .002 or maybe even zero lash (which makes sense to me) ..what specifically about the grind of the Chevy cam requires all that empty space and doesnt that empty space hammer away at the lobe ramp as the valve opens? Why is .004 not going to work on that cam?
     
    Bigpig455, Dec 12, 2022
    #3
  4. LARRY70GS

    LARRY70GS a.k.a. "THE WIZARD" Staff Member

    Actually, you answered your own question. It depends on the specific cam profile, and the combination. What about that Chevy profile makes it different? Not sure. Maybe JW could answer that.



    "Successfully running solid lifters on a hydraulic profile requires some amount of valve lash (a solid lifter cannot run at zero lash or be preloaded). This lash effectively reduces cam duration, especially at low lift off the valve seat (see table below). With less duration, peak torque and power occur at lower rpm than would normally be the case for the given combo when running a hydraulic lifter. In other words, the cam acts smaller.

    Exactly how much lash is necessary varies with the specific cam profile, as well as the material used to make the block and heads. Too little lash and you could burn a valve; too much and the valvetrain gets very noisy. Generally, the amount of hot lash will vary between 0.004 and 0.015 inch. These tight hot-lash settings may cause problems with aluminum blocks and heads, which see considerable thermal expansion between cold-start and normal operating temperature, so running solids on a hydraulic profile is problematic with all-alloy engines. Aluminum heads on an iron block usually work out OK, with lash expanding about 0.012 inch from cold to hot. With iron heads, expect about 0.008-inch growth.





    Too little lash and you could burn a valve; too much and the valvetrain gets very noisy. Generally, the amount of hot lash will vary between 0.004 and 0.015 inch. These tight hot-lash settings may cause problems with aluminum blocks and heads, which see considerable thermal expansion between cold-start and normal operating temperature, so running solids on a hydraulic profile is problematic with all-alloy engines. Aluminum heads on an iron block usually work out OK, with lash expanding about 0.012 inch from cold to hot. With iron heads, expect about 0.008-inch growth.


    The more aggressive the lobe, the tighter the lash needs to be. The tighter the lash, the more you need to pay attention to thermal expansion problems. For example, Comp Cam's classic Magnum hydraulic-roller grinds usually run fine with solid lifters at 0.0120.014-inch hot lash. But its newer, more aggressive Xtreme Energy hydraulic rollers get very noisy over 0.0100.012 hot lash, so for them Comp recommends tightening up the lash to 0.0060.010 hot.

    One way to home in on what lash your combo likes is to first set the valves at 0.004-inch cold, warm up the engine, and recheck the lash hot. Fine-tune lash settings within the preceding recommendations if the valvetrain is too noisy. Once satisfied, let the engine cool down again and recheck the lash. In the future you can accurately cold lash the motor. —Marlan Davis"
     
    LARRY70GS, Dec 12, 2022
    #4
  5. BrianTrick

    BrianTrick Brian Trick

    Nobody is a dumbass. Nobody was born with all the knowledge.
    Yes,I run zero lash when I run solid lifters on a hyd cam,due to the original design/intent of the cam.
    That .024-.030 sounds very loose for a solid/solid. Mine are usually .016-.018.
     
    BrianTrick, Dec 12, 2022
    #5
    dan zepnick likes this.
  6. Bigpig455

    Bigpig455 Fastest of the slow....

    Thanks guys - and even the Chevy guys agree that the factory spec is too loose, they run considerably tighter.

    I found this explanation of where the 30/30 clearances for a solid lifter Z28 302 came from, and it's probably as good a technical explanation as I'll ever get but I still can't get my mind wrapped around it,. It does explain why .030 is theoretical, and why some lash will likely be necessary on the exhaust valve as the stem may see thermal expansion at a greater rate than the block/deck/heads..but it doesnt explain why a lash like .004 on this cam would be unsuccessful, maybe hold the valve open etc..it does explain why too loose is damaging but in my mind the tighter the better?


    Clearance Compensation
    The difference between "hot" clearance (i.e., at engine idle speed) and cold clearance on a cast iron pushrod engine is negligible, so clearances can be set cold, which is much more convenient. When running hard, such as at sustained WOT (wide open throttle), the exhaust valve head heats up considerably. About 80% of exhaust valve cooling is through the seat, but the stem temperature will increase also, which causes the stem to grow and decrease running clearance. This is why exhaust ramps are typically higher than inlet ramps - to allow for more stem growth while maintaining some running clearance to ensure that the valves seat fully. Since the intake valve is cooled by the incoming fresh intake charge, its temperature and clearance will remain more consistent over the entire engine operating spectrum.
    The factory 0.030-inch/0.030-inch (intake/exhaust) clearances are derived from multiplying the 0.020-inch maximum height of the ramp above the base circle by the theoretical max lift ratio of 1.5. However, the actual as-measured lift ratio for the stamped OEM rocker arm at the lash points is actually about 1.37:1 (not the design ratio of 1.5:1, which is a theoretical max lift measurement, or the actual as-measured max lift with factory stamped rocker arms, which is about 1.44:1). The desired clearances in this procedure are therefore derived by "factoring" the OEM recommended clearances by the ratio 1.37/1.5 to compensate for the actual as-measured rocker arm ratio of 1.37 at the lash point. That number is then rounded down slightly to result in the cold clearance number. The clearance ramp, which is exactly 0.020-inch high on the lobe, is all taken up at 1.37 x 0.020 = 0.0274-inch clearance. Rounding down yields the desired 30-30 cam clearances of 0.026 inch/0.026 inch for this cold procedure.

    Using the 0.030-inch clearance with the valve closed is too loose - the ramp ends/begins before the 0.030-inch clearance is taken up, resulting in the valve being lifted off and returned to the seat at greater than ramp velocity. This will contribute to valve seat recession, and can cause valve bounce at the seats at high revs - it will also be noisy.



    http://www.camaros.org/302valves.shtml
     
    Bigpig455, Dec 12, 2022
    #6
    chrisg likes this.

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