You mill out the plug hole from the outside so that the sparkplug goes
deeper into the cylinder and the spark gap is not shrouded.......ideally you
then index the plug to face the chamber....the milling is about .25"
My machine shop was initially nervous about doing it as he was worried about
the remaining strength.
Paul
-----Original Message-----
From: healeys-bounces at autox.team.net [mailto:healeys-bounces at
autox.team.net]
On Behalf Of Bob Spidell
Sent: Wednesday, September 21, 2011 8:08 AM
To: warthodson at aol.com
Cc: ardmorebusiness at xtra.co.nz; healeys at autox.team.net
Subject: Re: [Healeys] cylinder head questions
I couldn't get from Chris' page what the 'solution' is; mill out the plug
hole, or the inside of the chamber?
Bob
--------------------------------
Bob Spidell - San Jose, CA
----- Original Message -----
Chris & Mark,
Thanks for the information. I checked my two 960 heads & they both have the
plugs recessed in the combustion chamber as per Chris' information &
photographs.
If this is a machining mistake it is still a mystery why they never
corrected
it. And why the BJ8 is the only model a greater advance.
Gary
Chris and Gary,
also have an original works head. It too has the AEC 721 number
ast into the top.
s an aside, I was told long ago that the heads were made 'after
ours' when production had stopped for the day. They were apparently
ade from recycled diff. heads that had been melted down.
've not done a side-by-side comparison of the 721 and the 960 or
lue-printed either of them, but I have been told that there is also a
light difference in the squish area in the heads, the 721 being
onsidered the better designed one.
ne of our racers here in NZ actually replaced the 960 on his BJ8 with
he 721. He reckoned it gave him a marginal improvement in
erformance. I don't know how scientific his analysis was . . . that
as back in the 70s.
Cheers
ark Donaldson
uckland. NZ
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