Hi Gents
Have a SBM, has roller lifters, HS 1.6 roller rockers, heads are closed chamber W2 race heads. The cam card says for 1.5 rockers to set the clearance at 0.020” hot, what’s recommended for 1.6 rockers cold please

The clearance spec doesn't change. The thing to do is adjust a pair hot to the spec then let it sit overnight and check what the clearance is cold then set the rest to that.

I always add .002 - 003" to the hot spec for setting them cold. If you have aluminum heads, I'd use .003"-.004".

- EM

Lash those at .014" cold and you will be very close when hot. As the engine heats up, everything grows and it opens the lash a bit. I assume those are cast iron w2's?

divide .020" by 1.5 and that's the clearance at the tappet; .0133". multiply .0133 by 1.6 and use that number for lash clearance to maintain the same ramp clearance that the 1.5 setting had; which would be .0213".

Thanks gents, yes cast iron W2 heads, I will do the lash hot for sure, just needed a bit of a starting point to set them up cold for the first time

Crane cams use to have a cold lash chart in one of their older catalogs, they recommended adding .002 to the lash at room temps with iron heads and iron blocks, they also recommended using .006 tighter with aluminum heads on a iron block and using .012 tighter with aluminum heads on a aluminum block, that has worked well for me for a lot of years

Thats how I do mine as they call for .020 and I set them at .014 cold with my iron block and aluminum heads. Works great for me. Ron

This is correct, as well as what Cab states about expansion for iron and aluminum heads. So it's a 2 part answer factoring both the change in rocker ratio, and expansion, if you are trying to hit the cam card exactly.

For shaft mopars it also depends on the method used to set the lash.

I set the lash on the Intake side when the Intake is closed and the Exhaust is at max lift and vice versus.
VS
Setting lash when both Intake and Exhaust are closed

Ambient temp makes a difference; this weekend it was 112 in the trailer when I unloaded the car and set the lash - so I set it at .019 rather than .020.

If it had been 30 degrees then I probably would have set it at .017.

I think its all minuscule differences though at my level and more important to know where you set it last time so you can tell if things change.

I agree, i think its small peanuts. I tried those lash loops at the track when i had a 408 small block. Didn't see much if any gains with different small lash settings. I had open chamber w2's on it at one time and i do not remember the lash closing up with heat. The math that is suggested to get where you should be with your lash settings looks like the best advice here.

Iron block with iron heads and steel pushrods doesn't change the lash much from hot to cold, maybe .001 to .003

I had great results changing lash, but i had some serious head and cam limitations. Iron 906 heads,535 cubes, and a .590 solid cam. That motor was desperate for air! With lash spec of .028 i had room, and .014 intake and .012 exhaust lash really helped! BUT- it was the dual problem of very poor heads and small cam that made those settings produce big gains. W2 heads with a cam that is well matched would be hard pressed to see any change at the track. A dyno session would be needed to see small changes.