Are the rocker arms on a 31 model 20 set on a taper shaft only or with a key?
Parts book shows what appears to be a taper rocker arm shaft with a key . The hand book gives no information on removal.
My exhaust rocker arm was replaced back in the 30's or 40's .No decompressor arm shaft etc .I suspect this was removed as the replacement arm ( later one I think) just hits the 5/16 rod I had inserted into the decompressor shaft hole.
They may have not cared where they set it as the decomp assembly has been removed.