WOW! I think I finally figured out how to reply to all the messages that fill
up my e-mail! Hope this works! I'm sure this info is common knowledge but
anyway.. One of the weak points of the 2000's is the head/ cooling system, the
fan clutch is worthless, and the heads are fragile and often not properly
torqued. Once overheated and warped, the unaware owner/ machinist is likely to
just mill the bottom face of the head, This results in a curvature of the top
surface of the head. The old school method to properly effect this repair is
to bolt the head to a surface plate to insure it is flat,heat the head until
it is pliable, and cool it slowly to make it as true as possible. Next mill
top and bottom surfaces as little as possible to make sure both surfaces are
parallel, shim cam towers so that the over stressed cam chain tensioned
doesn't have to take up too much slack,and finally line bore the cam towers.
Obviously this is not a cheap fix, and not many shops have the equipment or
the knowledge to do this properly! Also, it is important to consider the
thickness of the lash pads to maintain proper valve lift/ rocker arm geometry.
One of the old rules is not to loosen the cam tower fixing nuts, as this will
put the bore that the cam turns in out of alignment. If properly repaired and
maintained, the U20 motor is very reliable, but 40 years of inept repairs are
sometimes difficult to remedy!
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