Cold valve lash settings

The Isky E4 camshaft in my ’55 Customline is ground on 108° lobe centers. When the lash is shortened or tightened up, the amount of overlap is increased which lowers the vacuum signal. Overlap is simply that period of time that both the intake valve and exhaust valve on a particular cylinder are open together. That lower vacuum signal is what is making for the hesitation issue. While an air bleed adjustment to the carburetor could have helped to solve that hesitation issue, it was simply much easier to make the valve lash adjustment. If the carburetor has ‘fixed’ air bleeds (which most do), then modifying the air bleeds accordingly can get complicated.

Increasing the valve lash shortens up the duration which in turn decreases the amount of overlap. This subsequently increases the signal to the carburetor. When having that same camshaft ground on a wider lobe center (110° or 112° versus 108°), the amount of overlap present at the same valve lash setting is reduced which provides a higher vacuum signal. When using the E4 camshaft in the Y powered automatic equipped cars, I’ll typically order the E4 camshafts ground on 112° or 113° lobe centers. Some of the rumpiness of the camshaft is reduced but low rpm idle and vacuum are better for the automatic equipped vehicles. The same 4-6° of advance is still applied with most of those camshafts regardless of the degrees of lobe centerline that the camshafts are ground on.

Lorena, Texas (South of Waco)

Author	Message
Ted	Posted 3 Years Ago
Co-Administrator Group: Administrators Last Active: Yesterday Posts: 7.4K, Visits: 205.0K	312YBlock (5/15/2022) Ted if I could go off topic for a moment, my 312 has an E4 cam. The Isky website says set valve lash to .015 hot, what would be a good cold setting. Rather than answer this in a non-related thread, this topic deserves its own post. With an iron headed and unheated engine, I will typically set the valve lash 0.001”-0.002” more to compensate for both pushrod and valve stem expansion when the engine is at temperature. Lorena, Texas (South of Waco)
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Ted	Posted Last Year
Co-Administrator Group: Administrators Last Active: Yesterday Posts: 7.4K, Visits: 205.0K	The Isky E4 camshaft in my ’55 Customline is ground on 108° lobe centers. When the lash is shortened or tightened up, the amount of overlap is increased which lowers the vacuum signal. Overlap is simply that period of time that both the intake valve and exhaust valve on a particular cylinder are open together. That lower vacuum signal is what is making for the hesitation issue. While an air bleed adjustment to the carburetor could have helped to solve that hesitation issue, it was simply much easier to make the valve lash adjustment. If the carburetor has ‘fixed’ air bleeds (which most do), then modifying the air bleeds accordingly can get complicated. Increasing the valve lash shortens up the duration which in turn decreases the amount of overlap. This subsequently increases the signal to the carburetor. When having that same camshaft ground on a wider lobe center (110° or 112° versus 108°), the amount of overlap present at the same valve lash setting is reduced which provides a higher vacuum signal. When using the E4 camshaft in the Y powered automatic equipped cars, I’ll typically order the E4 camshafts ground on 112° or 113° lobe centers. Some of the rumpiness of the camshaft is reduced but low rpm idle and vacuum are better for the automatic equipped vehicles. The same 4-6° of advance is still applied with most of those camshafts regardless of the degrees of lobe centerline that the camshafts are ground on. Lorena, Texas (South of Waco)
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Cold valve lash settings

Cold valve lash settings

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