[Vwdiesel] Help - messed in the head...

[James Hansen]

What I'm getting at is that the valves move closer to the piston... reducing
the margin of error that the valves (cam) can be  out of perfect time and
still not tickle the piston.  I've never delved into the cam timing events
of the vw diesel, but the longer duration cams I work with do not allow much
room for error- the exhaust valve is just going closed as the piston is
reaching TDC of the exhaust stroke, and the intake is starting to open... so
if the whole head assembly moves closer to the piston, it follows that the
early opening of the intake (for scavenging) might result in tapping the
piston when the piston is at the top of the exhaust stroke.
What's in my head is that you are moving the valve face closer to the piston
when you surface the head... since the seat which is recessed, is coming
closer to the machined surface of the head by the thickness of the amount of
material removed,  the valve will be closer to the piston with all other
things being equal- unless the seats were machined deeper to compensate. The
piston protrusion measurement is assuming a stock head with stock distance
from valve seat to machined surface of head... by planing the head, you are
reducing this dimension, hence the valves are closer to the piston. From
what Loren sez, I guess it works, but I would think the tolerance for valve
timing error diminishes greatly.
hth
-James

-----Original Message-----
From: vwdiesel-bounces at vwfans.com [mailto:vwdiesel-bounces at vwfans.com]On
Behalf Of Gary Shea
Sent: Saturday, April 16, 2005 1:28 PM
To: Jim Arnott
Cc: vwdiesel
Subject: Re: [Vwdiesel] Help - messed in the head...


Thanks for the reply Jim.

I need to go have another look at that head.  The assumption I made is
that the piston protrusion is an issue because it's going to contact
something on the head -- valves or edge of combustion chamber -- if the
head is not kept far enough from the piston.

Slicing off the deck of the head moves the valves and edges of
combustion chamber (such as it is) closer to the piston.

So... that's my long way of saying I don't understand the logic of what
you're saying.  Oh, and I _did_ measure the protrusion (long before the
head work)   :)

    Gary

On Fri, 2005-04-15 at 19:21 -0700, Jim Arnott wrote:
> Shawn, Gary;
>
> The head doesn't determine the head gasket thickness, the piston
> protrusion does. You could cut 10mm off the head and not affect the
> protrusion a bit.  If it had a one notch gasket, replace it with a one
> notch gasket. (Or do it right and MEASURE the protrusion.)
>
> Jim
>
> On Friday, April 15, 2005, at 07:09 AM, Shawn Wright wrote:
>
> > On 14 Apr 2005 at 20:18, Gary Shea <shea at gtsdesign.com> wrote:
> >
> >> It sucks how letting anyone else touch part of your car leads to that
> >> part being screwed up :(  I'll never forget the place in Logan Utah
> >> that
> >> did an inspection on my Vanagon, knocked the press-on drums off with a
> >> sledge (before confronting the owner I quietly asked his son, who
> >> innocently acknowledged it), warped them beyond repair, denied doing
> >> anything improper, and when he finally agreed to replace them and gave
> >> me a ride back to my office, agreed with me when I told him that what
> >> I
> >> liked about Utah is how honest everyone was.  I could hardly keep a
> >> straight face on that one...
> >
> > It's been a few years since I had any work done by a shop, but they
> > screwed that up
> > too of course. In fact, I think at least half the shop work I've had
> > done in the past 20
> > years has had problems, and I've always tried to find a shop with a
> > good rep.
> >
> >> I had my TD head valve seats and guides done recently... I brought it
> >> in
> >> for the initial cleaning and had to come back later because I hadn't
> >> brought them the prechamber inserts.  Huh, the sealing surface of the
> >> head now has a big gouge in it... sigh.  Ok, so there goes the 1-notch
> >> gasket I already bought :(  I did get semi-lucky though, the guy
> >> called
> >> me when one of the prechamber inserts wouldn't stay in place.  He was
> >> afraid they would get pulled up by the cutting tool, just as yours may
> >> have.... he suggested we jbweld them in place, I gave him the go
> >> ahead,
> >> it worked.  I haven't dared to look at them closely since then :)  Nor
> >> have I had the courage to figure out the new clearance, if I can even
> >> think of a way to do it... they couldn't give me the exact amount of
> >> metal they milled off the head... it'll be at least a 3-notcher now
> >> though, based on what little information they could give me.
> >>
> >> So I know just how you feel :)
> >
> > I do have a spare NA head, are the prechambers the same on a TD? How
> > do I
> > remove them? I'm guessing tap them out with something in the injector
> > hole? I'm
> > already at a 3 notch gasket, so I hope this won't be a problem. I may
> > try to measure
> > the piston height, since I got them in last night. I was surprised how
> > much they stick
> > up.
> >
> > thanks for the info, I will try gather as much advice before I talk to
> > the shop.
> >
> "We need a revolution."
> "Keep saying that and we'll need a lawyer, assuming they let us have
> one."
>
> Jan Steinman <www.Bytesmiths.com>
>

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