Date: Wed, 27 Sep 2000 18:18:49 -0500
Reply-To: John Rodgers <inua@HIWAAY.NET>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: John Rodgers <inua@HIWAAY.NET>
Subject: Re: How long to do a valve job and replace the seats?
Content-Type: text/plain; charset=us-ascii
If the compression is good, but oil consumptions is high, the suspicions would
be that the valve guides are wearing out. On every intake stroke a worn intake
guide will allow excess oil to be drawn through the guide to go into the
combustion chamber with the fuel air charge. The oil is "consumed" in the
combustion process.
I've a lady friend who allowed her little Mitsubishi Precis to run the oil down
until the oil light came on. She tried to drive it to a gas station. Toasted the
valves. The engine has good compression, lots of get-up-and-git, but now the
valve train is very noisy, and her oil consumption is off the scale. She burned
the guides and valve stems...not enough lube when she let the oil get to low.
I believe if I had your van, I would simply be a religious fanatic about keeping
the oil level up, the oil changed and proper filter installed.
I have long suspected that older engines would do better on more frequent oil
changes. Nothing to back this up, but just some things I know about wear and oil
wearing out.
Oil is made of long chain molecules, and part of the process of wear in the
engine is for the engine parts to break these long chains. The longer you run
the oil, the more contaminants it picks up, and the more the chains are broken
into pieces. And as the oil chains are broken they lubricate less and less. So
it makes sense to me that newer oil would do a better job. Of course filters
help, but even so, newer is better. Of course modern engine oils are designed to
resist all that, but they still break down over time as they are are cycled
through the engine over and over..
Good luck
John Rodgers
88GL Driver
1980 VW Westfalia \"Pokey\" wrote:
> I guess I am OK then. The engine is strong, compression is at manufacturers
> specifications; 130, 130, 125, 130. According to Bentley, the requirements
> for a new engine are 131 PSI and there is a 40 PSI range. Pokey does have a
> moderate appeitite for oil, but it is more a function of some small leaks
> rather than "consumption" per se.
>
> Thanks,
> Chris Gronski
> Toronto, Ontario,
> '80 Westy "Pokey"
> '87 Chevrolet Sprint (Ice Racer)
> '91 Pontiac Firefly Convertible
>
> ----- Original Message -----
> From: "John Rodgers" <inua@hiwaay.net>
> To: "1980 VW Westfalia \ Pokey\" <pokey@VANAGON.ORG>
> Cc: <vanagon@GERRY.VANAGON.COM>
> Sent: Wednesday, September 27, 2000 3:55 PM
> Subject: Re: How long to do a valve job and replace the seats?
>
> > Chris, since you have no coolant to worry about, there are three things to
> be
> > concerned about on the top end of the engine. Valve stem/guide wear, valve
> > face/seat errosion, and cylinder/ring/ring lands wear.
> >
> > In the aircraft industry, on the average general aviation airplanes that
> run
> > flat 4 and 6 cylinder opposed aircooled engine, a differential compression
> test
> > is done that will tell if the engine needs a top overhaul...ie, valve job,
> and
> > rings. If oil consumption is high, then it's time, no matter what. But if
> oil
> > consumption is relatively low or modest a different approach was taken.
> >
> > The compression test is done static. The engine is rotated to top dead
> center on
> > the compression stroke. This ensures that both valves are closed. The
> propeller
> > is held so the incoming air pressure doesn't kick the engine over and
> hurts
> > someone. Then compressed air is pumped into the cylinder to a
> predetermined
> > pressure. As I recall, it is 100 PSI. There are two gages that are read.
> The
> > input pressure, and the pressure that is held by the cylinder. Cylinder
> pressure
> > down to 70 psi is OK. At 60 PSI it's time to overhaul the cylinder. If on
> > examinig the spread of pressures betwen cylinders it is disparate, ie not
> fairly
> > uniform, it's time to look at over hauling all cylinders. You don't want
> an
> > engine running with uneven pressures all over the place, hard on the
> engine.
> > Power would be erratic.
> >
> > During the compression tests, aircraft mechanics listen to the engine
> under
> > pressure. If a cylinder is going or gone, there will be a characteristic
> hissing
> > sound internally. Listen to the exhaust pipe. If it is loud, then exhaust
> valve
> > is leaking. If soft,(you can't hear it as good through the induction
> system) it
> > is intake valve leaking. If neither, but you can still hear air loss,
> it's
> > rings that need replacing.
> >
> > Now I'm not sure how one would apply the differential compression test to
> a flat
> > VW engine, but a standard compression test would tell a lot. If you turn
> the
> > engine over, and the gage won't hold pressure, then your pre-emptive
> strike
> > approach to the head maintenance certainly would be appropriate.
> >
> > Good luck
> >
> > John Rodgers
> > 88GL Driver
> >
> > 1980 VW Westfalia \"Pokey\" wrote:
> >
> > > I have 187,000 KM / 115,000 miles on my air-cooled and I'm thinking
> about
> > > pro-actively doing a valve job, replacing the valve seats, and replacing
> the
> > > valve cover gaskets while I'm at it. How long should this take? Should I
> > > just wait until 150,000 miles or is it worth doing now? Pokey is going
> away
> > > for the winter shortly is it better to wait until spring?
> > >
> > > Thanks,
> > > Chris Gronski
> > > Toronto, Ontario,
> > > '80 Westy "Pokey"
> > > '87 Chevrolet Sprint (Ice Racer)
> > > '91 Pontiac Firefly Convertible
> >
> >
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