In message <9312091456.AA25690@tin.monsanto.com> Larry E. Snyder
lesnyd@monsanto.com 314-694-3626 writes:
>
> The verdict is in. Compression on cylinder #6 on my GT6 is 0. Engine is
> broke.
>
> I'm taking the day off tomorrow to pull the head. Since I'm driving to KC
> early Saturday, I have the opportunity to stop by VB and purchase any parts
> I need. Some folks have told me that if I freshen up the head, I should
> also do the rings, but the prospect of pulling the engine does not appeal
> to me at this time. This is all speculation, since I don't know what my
> problem is anyway. If it's a ring or piston, then I'll have to pull the
> engine anyway. If it's a valve, I have the option of redoing the head and
> putting it back on.
>
> Now, I've replaced LOTS of stuff on this car, but I've never done that
> kind of engine work. When I pull the head, exactly what am I looking for?
> I presume if one valve looks obviously different from the others, something
> is wrong with it...
You are most likely dealing with a burnt valve. When you look at the underside
of the valves you will probably see a chunk missing out of the edge of one of
them. Zero compression can be caused by a number of things but you only
mentioned symptoms of a burnt valve. A hole in the piston would cause all kinds
of blow-by. A crack in the head or block or leaky valve gasket often affects 2
cylinders and commonly puts lots of frothy air bubbles in the radiator, water in
the oil or oil in the water. If your compression in the other cylinders is
close to being even and within the manual's spec for the engine, don't worry
about doing rings. If the other's are out of spec, your already doing 1/4 of
the work for a ring job & you might as well do it.
Go to a good automotive machinist and don't be shy of asking dumb questions.
They do this all the time, so follow their advice.
>
> Also, at this time I think I'm going to go ahead and put in hardened seats
> and guides.
Using hardened seats is an excellent idea in this day & age, and certainly new
valve guides if your machinist tells you they are worn. I didn't catch the year
of the GT6, but it may already have hardened seats. Having owned air cooled
VWs, I just replace all the exhaust valves with new ones. Its the same
philosophy that has people throw away perfectly good throwout bearings whenever
they split the engine from the transmission. The part's cheap compared to the
labor involved in R&Ring a head.
>
> How much should a machine shop charge to do a head? When I take the head in,
> what do I leave on it? Do I leave the valves and springs on it? I assume
> I leave the rocker assembly at home.
This varies by area and machine shop. Call a couple of places and ask. Give
them the assembled head without the rocker arm assembly. Ask them to magnaflux
the head (no use having work done if it has a crack) and to check the mating
surface for trueness (if its not completely flat, they can machine it flat).
They will clean the head & disasemble the valves & springs for you. They can
check the valve guides for wear, Or you can just go ahead & tell them to put in
a new set of bronze valve guides. If the engine has a lot of miles on it, you
might consider springing for a new set of valve springs. They will do the work
and hand you a reassembled head that you can bolt back on.
The trick is in torqueing down the head. You want to sneak up on it from the
center outward to both ends in stages. Retorque the head after about 300 miles
then again at about 1000. Check your manual for torque sequence (remember do it
in stages dont put all the torques on each bolt one at a time).
>
> Do I sound enough like a neophyte? I feel kind of stupid about this, and can
> use all the advice anyone wants to give!
>
> Thanks,
>
> Larry
Larry, don't worry we are all neophytes doing something for the first time. I
keep asking dumb questions to this group all the time.
Best of luck!
TeriAnn
TeriAnn Wakeman One of these days, I'll be old enough that
twakeman@apple.com people will stop calling me crazy and start
LINK: TWAKEMAN calling me eccentric.
408-974-2344 TR3A - TS75519L, MGBGT - GHD4U149572G, 109 - 164000561
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