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)

I supposed that valve lash is most important during break-in. Having researched valve lash for mechanical flat-tappet cams, there is an obvious lack of consensus and numerous opinions. I have two Y-block cams (three, counting the one in the engine). .019 lash seems to be the most common setting (I'm assuming that's hot). However, Schneider recommends .012-.015 cold. Howards recommends .022 (again, assuming that's hot). Some people claim that lash increases at temperature, requiring a tighter cold setting (that could explain Schneider's recommendation). Others suggest the opposite. And then there's the consideration of all iron vs. iron & aluminum/all aluminum (not Y-block). Is it a street-driven or race-only? Something so simple shouldn't be so complicated. 

Ted has said that tight-lash cams usually have aggressive ramps and tend to be noisy. The tighter lash quiets them down. Also, a narrower difference between advertised duration and duration @ .050 is an indication that the cam has aggressive lobes, but they can act like a smaller cam, which explains the lower advertise duration. For instance, Oregon Cams has a grind/w advertised duration of 248; however, the duration @ .050 is 219. My Schneider cam has an advertised duration of 258, but duration @ .050 is 214. The Howards cam advertised is 255/@ .050 is 220. Mummert's 312+ advertised 258/@ .050 is 218.

I suppose that a too-tight lash could accelerate cam & valve train wear, cause burnt exhaust valves, and valve/piston clearance issues if clearance is marginal. Of course, if lash is excessive, we'll hear it. 

While the iron heads with a solid lifter camshaft prefers adding 0.001-0.002” to the lash measurement for a cold engine, aluminum heads tend to like the opposite but to a greater degree.  Aluminum heads for the Y prefers the lash adjustment to be decreased on the order of 0.005–0.006” for a cold engine to compensate for aluminum expansion or growth as those heads come up to operating temperature.  The aluminum heads expand upwards a considerable amount when the engine is heated and although the valve stems and pushrods will decrease the valve lash on the order of 0.001-0.002”, the valve lash will still increase 0.005-0.006” due to aluminum expansion.  If running a choppy camshaft with aluminum heads, it will be much lumpier when cold versus when the engine is heated regardless of the valve lash setting simply due to the decreased valve lash when the engines are cold versus the increased valve lash when the engines are at operating temperature.

My experience with the E4 camshafts has those camshafts being more drivable using 0.019-0.022” hot lash versus the recommended 0.015” that’s on the cam card.  The E4 in my 272 is crowding 200K miles and most of those miles are with the valve lash in excess of 0.020” which gets rid of a pesky hesitation issue that’s prevalent with using the smaller lash numbers.

Lorena, Texas (South of Waco)

😊 For a perfectionist this topic could be a mind blower 😵‍💫. My 312 is a street driven E4 set to .018 cold. The idle is quiet but tappet click is audible cruising at 2K RPM, zero hesitation. It’s a sweet running motor, I just want to keep it happy. Many thanks to all 🙏.

1955 312 T-Bird Warwick, NY

Ted, this ties in with my more recent post regarding cold vs Hot lash. Could the cam LSA have something to do with the hesitation to which you referred in your 272? Does your E4 cam have the 108 LSA or 112? I'm just wondering if a wider LSA prefers a tighter lash.

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)