When shimming the cam towers to restore the cam height after head milling, it's
also important to check the cam wiping pattern on the rocker pads. It may
require
thicker lash pads to restore the proper rocker arm geometry and wiping pattern.
You don't want the cam lobes running off the end of the rocker pads. I think
it's
good practice to check the wiping pattern after any head work. Don't assume the
machine shop checked it if they built the valve train. A valve grind job can
change the geometry too.
Cheerios,
Gary
Thomas Walter wrote:
> Rick,
>
> On any OHC engine, it would be a good idea to always check the top
> of the head for warpage.
>
> You're correct that the top sealing area of the gasket and top of
> the head are milled. Should be obvious that the towers, and rocker
> adjusters, are all removed to allow the top of the head to be milled
> flat.
>
> Look at a feeler gauge, check the thickness of a 0.020" blade. A gasket
> could still seal with 0.020" warpage to it. Now look at the camshaft...
> while it MIGHT be able to withstand a 0.020" "bend" in it, it will not
> last for long. I've seen snapped camshafts due to a warp in the top
> of the head.
>
> Once both top and bottom are surfaced (milled flat), you should install
> some cam tower shims. I picked up a set from Stan Chernoff.
>
> This is just one of those "little" things to remember when you are
> having the head redone.
>
> Cheers,
>
> Tom
>
> >I have seen several posts about milling both the top and bottom of the U-20
> >head. Tom's, point about the posts keeping the cam fairly well aligned got me
> >to thinking... when the top of the head is milled, is the sealing area for
> >the valve cover and the cam tower area cut? In my twisted world, they both
> >warp the same. If they are, how would know how much was taken off off a used
> >head? I assume you measure the total thickness from the bottom of the head
> >to the area where the valve cover seats. Also, I have had other aluminum
> >heads cut (Nissan L20B springs to mind) and never had my machinist mention
> >the top. Should it just be checked, or is milling the top and bottom of an
> >aluminum head a hard and fast rule? Or just the U-20? Can't imagine that.
> >Never know about these things!
> >
> >
> >Rick Stayner
>
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