[DeTomaso] FW:  Rocker Stud angle question

Doug Braun doug at silicondesigns.com
Thu Jan 3 18:57:46 EST 2008


Jack,

Dan Jones provided a post yesterday of a Ford drawing
http://www.bacomatic.org/gallery2/v/hidden/dan/dan-cars/album04/album24/pgs_
28_37_File_2_Page_05.jpg.html (and my own measurements confirmed) that the
rocker stud bosses are not tilted to the same 9 deg 30 minute angle towards
the lifter valley that the valve stems are.  They are only at the same angle
as the valves when looking at them from the point of view of the intake or
exhaust ports; these two smaller angles are listed in the picture here
http://www.bacomatic.org/gallery2/v/hidden/dan/dan-cars/album04/album24/pgs_
4_7_File_5_Page_2.jpg.html.

The cutter I have isn't from Isky; it's #41860 from Manley and yes it does
index on the existing rocker stud boss hole.  I visited the Isky site but I
couldn't find their cutter; do you know the part number?  For the Manley
cutter I have, you have to drill the rocker boss hole out first to letter
size "U" (0.0368").  This is coincidentally the hole size needed prior to
tapping the 7/16NC14 threads needed for the larger non-positive stop type
rocker studs.  I plan on using roller rockers (not stamped type Boss
rockers) so I'll be taking care to do this machining as accurately as I can.

Since the cutter won't index on the hole until I drill it out, I could just
use an electric hand drill to progressively drill out the existing 5/16
threads up to size "U" and then let the cutter index on the larger hole but
I think a better way would be as follows:

I intend to place the cylinder head flat on the milling table and tilt the
mill head in two planes to the Ford spec compound angles for the intake
bosses. I'll install 5/16 bolts (with their heads cut off) into the intake
rocker bosses and see how well a Jacobs chuck on the milling head indexes on
the bolt shanks and readjust the milling head accordingly to get a good
average of the 4 rocker boss angles.  This all assumes that Ford took as
much care in drilling accurate rocker stud holes as they did milling the
pedestal shelves.  I'll then drill each hole, use the cutter to reduce the
pedestal heights by .300" , then tap each hole to 7/16NC14.  Then I'll
repeat the whole process at the different angles needed for the exhaust
rocker bosses.  What do you think?

Doug Braun
blue 73L #5505

Original Message-----
From: detomaso-bounces at realbig.com
[mailto:detomaso-bounces at realbig.com]On Behalf Of JDeRyke at aol.com
Sent: Thursday, January 03, 2008 2:29 PM
To: doug at silicondesigns.com; detomaso at realbig.com
Cc: kenn_green at yahoo.com; asajay at asajay.com; forestg at att.net;
jab at cisco.com
Subject: Re: [DeTomaso] FW:  Rocker Stud angle question


In a message dated 1/2/08 1:40:52 PM, doug at silicondesigns.com writes:

> My goal is to machine the rocker stud bosses for 7/16" non-positive stop
> studs.  My reasoning is that I have free access to a milling machine and I
like
> playing with this kind of stuff.  The Manley
> cutter was $70 and their 42277-16 stud set is only $50.
>
Is that the cutter that pilots on the existing tapped hole in the bosses?
Boss rocker studs are at a compound angle to the horizontal- also known at
the
time as poly-angle valves. They are at 4 degrees 15 minutes of angle in one
plane and 9 degrees 30 minutes of angle in the second direction. Photos of
this
are more confusing than informative. All the mechinists I know that have
done
this mod dial-indicate the flat area between the 'ears' on each pedestal and
cut
the pedestal down accordingly. This is extremely time-consuming to do
correctly with lots of opportuninty to do it wrong, which is why most use an
Isky
pedestal cutter- much faster for often more accurate results. And extreme
accuracy is not needed unless you use full roller rocker arms; there's
enough slop in
stock rocker pivots to absorb some mistakes- especially if you use big-block
Chev ball-pivot rockers.
Note also that stock Boss intake & exhaust valves have different stem
lengths
which will tip some rockers at more angle than others, just to throw another
number into the mix. Good luck- J DeRyke






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