[Amc-list] Updated: Larger holes for pushrods with pressed rocker studs

["Dan Curtis" <d.curtis@xxxxxxx>]

Almost forgot to mention that AMC used the bridged rocker assemblies on the 
heads that had pressed rocker studs and larger pushrod guide holes.  The 
bridged rockers held the rocker arms in place, keeping the pushrods properly 
aligned.  If you have the pressed in rocker studs in your heads you will 
need the bridged rocker assemblies if you do not have a machine shop replace 
the rocker studs.

When I have an engine built for extra performance over stock, I always have 
the pressed rocker arm studs replaced with the screw in type.  The pressed 
rocker studs can sometimes come loose with heavy duty valve springs from a 
performance cam and valve train setup so I always have them replaced on any 
heads that I use on a built up motor.  When you have the screw in type 
studs, the guide plates can be put in at the same time as the studs are 
replaced.

Regards,
Dan Curtis
d.curtis@xxxxxxx
602-317-2018

----- Original Message ----- 
From: "Dan Curtis" <d.curtis@xxxxxxx>
To: <jshrewsberry@xxxxxxxxxxxxxxxxxx>
Cc: <mail@xxxxxxxxxxxx>; <eddiestakes@xxxxxxxxxxxxxxxxxxxx>
Sent: Saturday, February 10, 2007 8:52 AM
Subject: Larger holes for pushrods


> Shrews,
> The larger diameter pushrod hole you are experiencing is a common AMC 
> condition that is easily resolved with AMC or after market pushrod guide 
> plates.  I had a set of 74 401 heads on a 69 AMX 390 with roller rockers 
> and it had the guideplates installed under the rocker arm studs.
>
> The guide plates are a fairly inexpensive piece of flat metal with holes 
> aligned for both the rocker arm studs and the pushrods.  In older model 
> 50.6cc heads from early 1971 back to 1968, the pushrods guide holes were 
> precision machined into the head to keep the pushrods aligned with the 
> rocker arms. In the lower compression 58cc heads from late 71 forward, the 
> pushrod holes in the heads were larger and thus required the guide plates 
> under the rocker arm studs to be installed to keep the pushrods aligned 
> with the rockers.  They are required for both the newer roller rockers and 
> most stock  AMC late model heads and rocker arms.  I suspect AMC switched 
> to this design to reduce frictions and improve lubrication for the 
> pushrods in the guide area.  In the old "in cylinder head" pushrod guide 
> design, if the engine got too gunked up or the oil coked up from lack of 
> regular oil changes, the pushrods could get jammed in the pushrod guide 
> holes in the heads which would bend the pushrods and cause the engine to 
> run poorly or create a valve to be stuck open or closed which would either 
> give you a dead cylinder or even worse a valve and piston 
> collision..neither a good thing. The new design eliminated that potential 
> problem.
>
> I have a 75 360 on an engine stand in my garage and will pull a valve 
> cover today to see if I can find a part number on the guide plates.  You 
> may also want to go the AMC Forum and post an inquiry to see if anyone has 
> a set they are willing to sell or if one of the vendors like American 
> Parts Depot sells them.  I am sure any decent performance shop can get 
> them as well.  The machine shop that built assembled my 460 HP 390 put 
> them on that motor which is currently in my 68 AMX.  The other alternative 
> is to simply go the a bone yard and find a Jeep with a 360 or 401 and pull 
> the guide plates off of those heads.
>
> By the way, roller rockers should also require the guideplates due to the 
> end of the pushrod resting against the roller on the roller rocker which 
> is even less able to hold the pushrod in place than the indent on the 
> stock AMC rocker arm assembly.
>
> Regards,
> Dan Curtis
> d.curtis@xxxxxxx
> 602-317-2018 

_______________________________________________
Amc-list mailing list
Amc-list@xxxxxxxxxxxx
http://www.amc-list.com/mailman/listinfo/amc-list