Re: rocker play

[Kurt McDowell <gmcd@domain.elided>]

John,
    My shafts are within specs so i'm not going to worry about it. Do you know of any
advantages of new vs old style rockers? I'm sure getting a a new shaft machined
would be pretty straightforward as long as the diameter of the rod is standard.
    -Grant McDowell (Kurt is my brother he set up the computer)
ihc-digest@domain.elided

John A. Landry wrote:

> 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.
> --------------------------------------------------------------------------
> jlandry AT halcyon DOT com      |
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