Hi, i'm a bit confused:
i'm searching information about 45 cilinderheads Iron & Aluminum and compression markings.
in Palmers book: on page 201
he refers to 3 types of iron heads marked 4.5 for high compression,
marked 5.5 for medium and 6.8 for low compression
however i own 3 couple iron heads, 1 pair with narrow sparkplug hole ( should be Servi-car: later years and low compression and 2 pair with the 18 mm sparkplug hole from Ex-police motorcycles
all are marked 6.0 (for howfar i can deciver the corrosion)
also some people around here (well known with old Harley's) are talking about : 6.0 for high compression, 5.0 for medium and 4.5 for low compression.
concerning the aluminum heads: medium compression are marked 5.0 (as i found on some military heads and also the numbers : 119-39 F and 119-391 R)
and marked 6.0 for high compression (which i don't have)
but my confusion is about these Iron heads
please: let me see clear.