Andy Ramm wrote:
> Is it OK to put a 18V head on a non 18V motor? I
> assume pushrods and tappets would have to be changed,
> anything else?
Scott Gardner replied:
> You will also need to fit the pre-18v pistons, since
> the combustion chambers of the 18V head are smaller
> than the old head. If you used the old pistons, you
> will probably end up with an unworkably high
> compression ratio.
Michael S. Lishego replied:
> Won't you also have to use the rocker assembly that
> works with the head? I know that some heads used an
> offset rocker stand while others used a straight one.
> I've seen both; it seems that the only difference is
> where the oil galleries line up. Am I correct in
> this assumption?
> I have 1967 block. With a 1970 (18GH motor number)
> head. The head is a 18-L with shallow chamber on my
> 67 block.
Scott ... fitting the 18V head to an earlier engine,
with the original 8.8:1 CR pistons, would increase the
CR to approx 9.5:1 ... streetable, especially with a
fast road cam.
Mike ... yes, you need to match the rear rocker
pedestal to the head ... the change in rear rocker
pedestal, from 'inline' to 'offest', occured in
conjunction with the introduction of the Zeinth-Stomberg
for the "federal market" in '75 ... the heads with the
'offset' pedestal will have the water take-off at the
back for the automatic choke.
John ... to my knowledge the 18GH head retained the
original 43cc combustion chamber ... it was not until
the introduction of the 18V engine, in '72, that the
size was reduced to 39cc ... but the "18 L" casting
mark would indicate that its the later shallow head.
Andy ... to summarize: Fitting an 18V head to an
earlier engine will substantially increase the CR.
You will need the later (18V)pushrods and tappets,
to check the rocker pedestal, and to add the cutouts
to the block face (to provide clearance for the
exhaust valves) ... some might argue that the later
isn't required, but the folks at Abington thought it
was necessary else they wouldn't have incurred the
expense ... the last thing that you need is to have
the exhaust valve contact the head ... besides the cuts
will provide slight increase in power.
Note ... commencing with the 'rubber bumper' heads, in
'74 1/2, the intake valve reverted back to the size
found on the 18G series ... so, if you fit one of the
'rubber bumper' 18V heads you may wish to fit the larger
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