[T3] Weird Idle Dips

[jeffrey gunnarson]

Got that!
On Mar 2, 2012 8:05 PM, "Jim Adney" <jadney at vwtype3.org> wrote:

> On 2 Mar 2012 at 12:01, Gary Forsmo wrote:
>
> > A question has been rolling around in my head for several months.
>
> A fresh subject line would have been good here.  ;-)
>
> > IF (big IF, here) indeed the spark plug hole has been cross-threaded
> > at some time in the past, what is the correct remedy?
> >
> > While reading about HeliCoils, I came across other metal inserts to
> > repair spark plug holes.
> > E-Z Lok, http://www.ezlok.com/InsertsMetal/carbonSteel.html  &
> > Time-Sert.  http://www.timesert.com/html/sparkplug.html
>
> I prefer Heli-coils, and there are several reasons why.
>
> 1) All of these choices are made of steel or stainless, which expands
> less with temperature than alum. That means that solid steel inserts
> always get loose in the head as the head warms up. Because they are
> made oversize, helical inserts will "slip" in their outside threads
> to accommodate the change in size. This will make them tight when
> cold, but that's not a problem. But solid inserts get loose and will
> often come out with the spark plug, and you'll have trouble getting
> it off the SP to reuse, or you'll need to replace it every time you
> change plugs.
>
> 2) The spacing between the SP hole and the valve seats, inside the
> combustion chamber, is very small, and this is where most of our
> heads eventually crack. For this reason you want to use the thinnest
> insert you can get. Helicoils and Timeserts are both good choices
> here.
>
> 3) The most common style of solid insert has a flange on the face
> that prevents it from being installed too deep. This is what the SP
> seats against when you tighten it. It also means that when the head
> warms up and the insert gets loose, the SP is still tight to the
> insert, but the insert is really LOOSE in the head. This doesn't
> cause any noticable difference in performance, but that loose stuff
> moving around will eventually wear out the threads and require an
> oversize insert. That's why those inserts are made in oversize and
> double oversize.
>
> 4) When an insert comes loose, the heat transfer path from the SP to
> the head is interrupted. This makes the SP run hotter than it should.
> This can be a problem. Helicoils don't get loose in the head as the
> head warms up.
>
> 5) I don't have a lot of experience with inserts, but I've had
> several Helicoils and never had a Helicoil come out, and I don't see
> how it could possibly get pushed in. I have one car with a solid
> insert, and that cylinder is a real annoyance any time I have to deal
> with that SP. Of course there are people who can screw up anything,
> but you should be careful when starting ANY SP, regardless of the
> nature of the threads. If you just assume that the threads are OE
> aluminum and use proper care, you'll never have any problem.
>
> 6) The need for special tools is common to ALL of these approaches.
> Regardless of what you decide to use, you'll need the right tap and
> you'll need to do it carefully. Yes, Helicoils require a special
> insertion tool, but that's because they are oversize before
> installation. The fact that they are trying to expand after
> installation is what keeps them in place and makes them the right
> choice.
>
> --
> *******************************
> Jim Adney, jadney at vwtype3.org
> Madison, Wisconsin, USA
> *******************************
>
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