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Tight-Lash Cams?
I was surprised to find out that the valve lash recommended by my cam manufacturer is .012" (cold) for both intake/exhaust. This is a mechanical (non-roller) cam in a 427 FE with iron block/heads. My limited experience suggests that valve lash is usually in the .020" - .028" range.
What is it about some cams that allow for tighter lashes? What are the pros/cons? |
Redd,
Double check the instructions. That clearance may be for aluminum heads. |
Re: Tight-Lash Cams?
Quote:
What brand cam? On flat tappet cams, as the profiles get more aggressive on the opening ramps, it's necessary to reduce the valve lash to alleviate some of the initial clash between the lifter and its re-engaging with the camshaft lobe. The more aggressive cams do not have as much starting ramp on the opening side of the lobe and hence, requires less lash to insure that the opening ramp is not bypassed before doing some serious lifter pushing. As the original flat tappet cams for the Fe had softer or longer opening ramps, they would tolerate more lash in this area. Typically, I run the camshaft at the manufacturers recommended lash and then vary it ±.004" either direction looking for increased performance. I've been known to go even more, but the manufacturers caution against this. As a rule, if increasing the lash helps the vehicle to run better, then the camshaft has too much duration. If decreasing the lash shows an increase in performance, then the existing camshafts duration is too small. And you can effectively tighten one lash while loosening the other which will subjectively make the camshaft think it's more advanced or retarded. |
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