[Jurneyman]

I really hate to bring this up, but it sounds like there is the possibility of a wrist pin clip comming out,the noise could be increasing when the load is lower or off
the piston,when you are going downhill or crusin.The most comon reason for this
is when the c clip is put in backwards with the rounded side out.The flat side
must face out,the next most comon find is using the c clip in a groove
designed for a different or thicker clip,in this case two c clips may be used for convience,or laziness,whichever one applies,but even then the outside clip
of the two installed must have the flat side facing out,but the inside clip
should have the flatside facing the wristpin.This installation procedure is not
an option,I have found in almost every case the problem was not the c clip
but the way it was installed.

 

[Jurneyman]

good choice on the wrist pin clips,they are the way to go.I still am looking for
what might cause the noise when the motor is unloaded,did you check the
ideler gear bushing,shaft,and bolt,for tightness?Also the same for the dist gear,make sure it is tight on the shaft,with a good pin.Another thing to check is the generater drive gear,make sure it is tight,a friend forgot to correctly
tighten the nut and it came off trashing everything in the cam case.One more
thing you can check is the clearance between the cam lobe,and the dist.drive
gear when the motor is unloaded the gear can move back and forth to just
enough to hit.One more quick idea,did you block off the oil to the lifters,and
use pressed in lifter adapters.There really should be no problem with the 412 cam.I believe sifton used panhead lift spects,at the valve,so the shovel with
the lower rocker ratio would be less,this is why I used to recomend a little
more cam when changing from a pan to shovel,because what you made up in flow from the shovel you lost in lift and valve opening speed.