[Amc-list] Larger holes for pushrods

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

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 

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