Re: rocker play

[jlandry@domain.elided (John A. Landry)]

When the truth serum kicked in, Kurt McDowell <gmcd@domain.elided> blurted
out...

>    Thanks so much so measuring your parts for me.

You're most welcome Kurt.

>     For future refrence: whenever you guys are re- doing valves dont wory
>about it if your boat-stye rockers/rods dont match the book's specs(for older stlye
>valves)
>. They will appear verry lose on the shaft.

There's one thing about rocker arm / rocker assemblies that does concern me
though.  Rik touched on this briefly and it's important to mention again.
While technically your rockers may be in or even near some sort of overall fit
spec, take a careful look at the rocker arm shaft itself.  If the engine has
any sort of high milage on it, chances are the shaft will be *severely* worn
where the rockers contact the shaft.  The wear pattern on the shaft will match
the contact surface of the rocker arm.  This wear can be deep enough to where
the oil channels stamped into face of the rocker arm bushing will be nearly or
completely blocked.  This would create a vicious cycle... you have severe
where between the rocker and the shaft... this results in lack of
lubrication... lack of lubrication leads to accelerated wear... which closes
off the oil flow even more... etc.  See the picture?

To top it off, the oil pressure naturally drops in the engine as the miles
stack up (due to the looser fit between engine bearings, etc.).  As a result,
I suspect lubrication to the rocker arm shaft is probably one of the first
places to suffer.  Think about it, the rocker arm assemblies are the highest
point in the lubrication system.  I'm concerned that this rocker on shaft wear
can progress to the point where, combined with lessened lubrication, the
galling of the shaft and possibly momentary seizure of the rocker could
result.  Because of the oil channels stamped into the rocker bushing, if the
wear is severe enough, it almost looks as though a sort of mechanical "stop"
is created between the shaft and rocker.  If you ever look at the wear
patterns on a rocker shaft with high milage, you'll understand what I mean.

I just wonder if the supposed "mystery" of why pushrods sometimes jump out of
their rockers on these IH engines without other obvious cause, is not somehow
tied into this extreme rocker shaft wear.  Many Digest members have admitted
that after they replace a pushrod, they can't find the cause.  Life seems to
simply go on.  Hmmmm!

So what can be done about it?  Well of course the shaft could be replaced if
you can find one.  I'm not saying they aren't available through current
Navistar heavy or light truck dealers or maybe Light Line of LA... I haven't
checked.  Heck, NAPA may be able to order one for all I know.  But as Digest
member Rik said, if you have access to both styles of rocker arm assemblies
(folded metal and boat), you can swap shafts between the two types to yield a
wear free contact point for the old rockers.  This is because the shafts
(which are functionally identical) must be turned over when swapping between
the two style rocker arms.  The boat style rockers assemblies must have the
oil holes on the rocker shaft pointed down, and with the folded metal it's
just the opposite... pointed up.

But if you don't have access to both types and you are contemplating buying a
second *used* set, I'd give serious consideration to buying the *opposite*
style from what you need to replace.  That way you can swap the shafts between
the two types and possible yield two good sets.  They won't be like new
because of the wear present in the rockers themselves, but at least you're
halfway there.

Merry Christmas,

John L.
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