There are a few dimensional constraints that are unavoidable no matter
who makes Roller Rockers!
After-all, we're not recreating the entire cylinder head; our rockers
need to fit within what is available for the stock head.
Certainly the entire, (shaft, pedestal), assembly could be easily
manufactured; but you would still be limited by a number of things,
(geometry-wise). The shape of the head, the location of the valves, the
location of the pushrods, the clearance available under the valve cover,
and a number of others I'm sure I have missed.
As "stock" replacements the rockers should fit and operate within the
same envelope as the originals. It should not be necessary to purchase
any additional custom items, (unless of course it is known prior to
installation), in order to install the rockers.
If anything has been changed, all bets are off! It is impossible for any
manufacturer to be able to cover all contingencies.
The drawing available by following this link,
http://web.tampabay.rr.com/tr6tech/shop%20drawings.pdf
,is one of a set that I generated for the shop. It is a PDF file so you
will need to have the acrobat reader loaded. View it at 100%, and pan
with the "hand" for the best resolution.
The upper left view shows two critical dimensions! 1.210" & .265".
1.210" is the distance from the centerline of the rocker shaft to the
centerline of the valves. The vertical offset value of .265" controls
whether or not the rocker sits parallel to the valve stem when on the
dwell side of the cam.
The auxiliary view shows two more important dimensions: .230" & .280".
The .230" dimension is given from the rocker surface that contacts the
pedestal. It controls the location of the roller tip in relation to the
valve stem tip. From the centerline of the roller tip it should be .280"
in order to provide proper pushrod orientation.
At the top of the sheet, the center view, a dimension of .750" is called
out. If the rocker is too wide at this location, it will not fit within
the end pedestals which trap the rocker.
There are of course many other dimensional call-outs that fully define
the part. The dimensions discussed are critical to the proper fit of the
rockers.
These are constants that anyone designing stock replacement rockers will
have to deal with!
Provided that the rocker is parallel when off of the cam, the amount of
off center travel for the roller tip, (as it travels through an arc of
19.5 degrees), is negligible, (.008-.012").
Jim Swarthout
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