[tcb] Re: Speaking of Valves
- From: "w.wood" <evil.scientist.boo@xxxxxxxxx>
- To: tcb@xxxxxxxxxxxxx
- Date: Mon, 25 Jan 2010 22:02:06 -0500
it's heat and pressure related. even when an engine has very little
leakdown (piston rings, valve guides etc.) there's still a lot of pressure
that builds up in the crankcase. In a stock ACVW the 3/4 side also get a
lot of oil slosh (windage) into the valvetrain area which further causes
some pull when it drains back in. This means that the air inside those
covers is also less dense than the air outside the valve covers. all it
takes is enough pressure differential and heat and you'll pull a gasket.
I used to think it was just bad gaskets or warped covers but venting those
same covers and alleviating the crankcase pressure helps solve the problem.
If you don't want to vent the covers then a little permatex works wonders.
Just be prepared to do a little scraping between gasket changes.
On Mon, Jan 25, 2010 at 12:49 PM, sammie smith <bugcollections@xxxxxxxxxxxxx
> wrote:
> Here is a good tech question for you Will or any other ingenious VW
> engineer/mechanics that want to chime in.
>
> What causes the valve cover gaskets to "suck" in, i.e., sometimes work
> loose on the bottom and move up into the rocker chamber, which of course
> causes tremendous oil leakage. Happened to a VW mechanic friend of mine a
> while back on his daughters car and she ran it out of oil with all of the
> resulting burned up engine problems. Valve cover gasket had "sucked"
> resulting in loosing all of the oil in the engine.
>
> I know how to prevent it: have talked about that before; but what causes
> it. Got into an academic discussion with another VW mechanic friend about
> how is it possible to "suck" a valve cover gasket. Normally there is
> positive crankcase pressure and the pressure through the push rod tubes
> should keep a positive pressure inside the valve cover/rocker assembly
> resulting in the pressure to attempt to "push" the valve cover gasket
> outwards, which of course it can't do because of the lip around the valve
> cover. Have talked to one old VW dirt track racer who ran big stroker
> motors on the dirt tracks where there was a lot of acceleration/deceleration
> of the engine and it he says it was a common problem which they usually
> cured by welding some tabs around the inner side of the gasket channel.
> Have had it happen to me and it is a rather common occurence in the VW
> engine.
>
> But what causes it? For the engine to "suck" a valve cover gasket there
> has got to be at least some time when there is a negative pressure (vacuum)
> in that chamber. With my knowledge of the flat-four, 4-cycle engine, I
> don't know how that is possible.
>
> The only thing I have been able to deduce is that it might be possible
> under extreme engine deceleration for the piston on the down-side
> compression stroke (since it has no positive pressure on that stroke under
> deceleration) to have a vacuum so severe that it sucks pressure through the
> valve guides and creates a vacuum in the valve cover chamber. But I don't
> really think that is possible.
>
> Comments?
>
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