[s-cars] S-car head repair

[Tom Mullane]

Charlie,

I admit that my experience is mostly with 2 valve per cylinder VW/Audi
engines where valve/piston contact is generally NOT near the edge of the
piston.  But I would think that any damage that would cause this type of
ring problem would be obvious and severe.  No?

Tom
----- Original Message -----
From: "Charlie Smith" <charlie at elektro.cmhnet.org>
To: "Tom Mullane" <tmullane at snet.net>
Cc: "Audi S Car List" <s-car-list at audifans.com>; "Charlie Smith"
<charlie at elektro.cmhnet.org>
Sent: Wednesday, December 18, 2002 11:30 AM
Subject: Re: [s-cars] S-car head repair


> Earlier, Tom Mullane wrote:
> >
> > It sounds to me like the two visibly bent valves were damaged when the
car
> > was not running.  The belt was off, so the cam was fixed and crank was
> > moved. Two open valves were damaged.  Running the engine probably
resulted
> > in some additional contact between the pistons, the town bent valves and
the
> > head, but the other valves should not have been touched.
> >
> > Take the offer, fix the car, and get on with your life.  The last thing
I
> > would want, if I were you, is to have them start removing pistons.  This
is
> > not a race car; a couple of marks on the top of a piston or two should
not
> > affect the drivability or life of the car.
>
> Tom -
>
> I can tell you from personal observation, valves touching the pistons
> like this can cause the top ring groove in the piston to get 'squished'
> and thus tighten up on the top piston ring.  The ring won't seal and
> will end up breaking, causing score marks on the cylinder wall.  This type
> of valve to piston impact can also cause cracks in the piston, which can
> lead to the piston breaking apart.
>
> Also, if the valve head is bent, it has caused the valve stem to bend
> into an "S" shape.  When this "S" shaped valve stem enters the valve
> guide, it will probably screw up the valve guide.  I have seen valve
> guide inserts split from this cause, and I have seen cracks in the head
> when the guide holes are bored directly into the head.
>
>     - Charlie
>
>
>   Charlie Smith   charlie at elektro.cmhnet.org  614-471-1418
>   http://www.elektro.com/~charlie      Columbus Ohio   USA
>   http://www.elektro.com/~audi     photos & technical info
>
>   95 S6 Quattro  -  24 PSI, RS2 6 speed, and other features
>   97 Dodge Ram   -  35 PSI, 4x4 w/Cummins turbo diesel
>
>
>