oil consumption-valve guides Re: [Shotimes] Power steering and AutoRx

[Leigh Smith]

It's all a question of which item wears out first. Seal or guide. That
varies greatly depending on useage, etc. Valve guides do wear out on
high-mileage motors. You can't tell by looking at them. The valve stem must
be checked for "rocking" at about 1/4 in valve lift (mid stroke).  Virtually
any clearance is too much, since the typical spec is very tight, llike .001
in or less. I have seen valves that rocked 1/4 inch!!! (Non-SHO) Both the
guide and the valve stem wear, but usually the guide is worse. Since this
requires virtually complete engine & cylinder head dissasembly, they are not
typically checked except at rebuild time. And many machine shops won't even
check them, they'll just automatically go ahead and put in new ones (more
$$$). I have seen 60k mile engines with guides that were shot and 185k
engines that spec'd as-new. Too many variables to generalize.
Once the guides are shot, no valve seal will last long. They help for a
while, then "puff" again. I've heard guys say "that engine needs valve seals
every 6 months...." NO ... it really needs new valve guides.
However, It is possible for a valve seal to dry out and crack or leak. Why?
Heat most likely. If the guides are still tight, new seals alone would be
all that is required.
Personally I have not dissasembled and checked out a set of high mileage SHO
heads. Has anyone else? What were the guides like? I could get access to my
old ones and have them checked & measured , if anyone is interested. Since
they are presently in the high school auto shop as demo items, it shouldn't
be too hard.
The easy "fix" is to put on new seals first, if you get puffing. Leave the
heads on the motor, and save some bucks. However on a SHO, that job would be
a major PITA, a lot of labor $ unless you DIY. If they don't last long, then
pull the heads, and have a good machine shop do 'em right.
BTW the guide clearance has much more to do with oil consumption than valve
seals, so much so that some engines do not even have a valve seal on the
exhaust valve.
Lee




----- Original Message ----- 
From: "Ian Fisher" <dataflash@yahoo.com>
To: "Donald Mallinson" <dmall@mwonline.net>; <shotimes@autox.team.net>
Sent: Wednesday, April 13, 2005 3:48 PM
Subject: oil consumption-valve guides Re: [Shotimes] Power steering and
AutoRx


> Actually, this brings up a question that I wanted to
> ask. I've heard for awhile that the valve guides wear
> over time which causes oil loss. After having my heads
> rebuilt and bronze guides installed, I'm wondering if
> its not the guide seals that are the problem. My
> guides looked fine. If there ever is a next time I'll
> probably just replace the seals and leave the guides
> alone.
>
> Ian
>
> --- Donald Mallinson <dmall@mwonline.net> wrote:
> > And if the oil use was due to bad valve guides, the
> > typical problem with
> > extreme oil use in the SHO V6, then no oil or
> > additive is going to help.
> >
> > Don Mallinson
> >
> > Ron Porter wrote:
> >
> > >My '94 had leaky valve seals. On the original Mobil
> > 1 that the POs used, it
> > >went 800 miles to a quart. Castrol got that up to
> > 1,600 miles/quart. About
> > >every 3-4th cold start, I would get a puff of
> > smoke.
> > >
> > >After the long drive to CA & back on fresh Castrol
> > MaxLife, the long hours
> > >of running hot really seemed to help. The puff on
> > startup went away, and I
> > >only went through 3 quarts for the whole 5,500
> > miles or so. Which I thought
> > >was great considering the high temps, track time,
> > etc.
> > >
> > >The MaxLife oils seem to work better for crank seal
> > leaks (like my '95 had),
> > >but it does OK on valve seals...or well enough to
> > forego the expense of
> > >changing the seals.
> > >
> > >Ron Porter
> > _______________________________________________
> > Shotimes mailing list
> > Shotimes@autox.team.net
> > http://www.team.net/mailman/listinfo/shotimes
> >
>
>
>
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