Strange problem

While turning a corner in my '93 Miata, there was an ominoius POPP
followed by a loud THWACKA THWACKA THWACKA.
The problem was one of the plus had blown out with explosive force,
I put in a new plug and everything is fiune. The three other plugs
were snug and subseqiuent checks don't show any new loosening.
I'd be interested in theories.
My own is thart since the car is stored in bitter cold winter weather
--- 35 below --- the cycle of deep freeze and thaw caused expansion
and contraction that loosened the plug and that when I started driving
in the spring, it was only a matter iof time before it came right
out.
Would be interested if anyone has had a similar experience.
ds

"DS" > wrote in message
...
> While turning a corner in my '93 Miata, there was an ominoius POPP
> followed by a loud THWACKA THWACKA THWACKA.
> The problem was one of the plus had blown out with explosive force,
> I put in a new plug and everything is fiune. The three other plugs
> were snug and subseqiuent checks don't show any new loosening.
> I'd be interested in theories.
> My own is thart since the car is stored in bitter cold winter weather
> --- 35 below --- the cycle of deep freeze and thaw caused expansion
> and contraction that loosened the plug and that when I started driving
> in the spring, it was only a matter iof time before it came right
> out.
> Would be interested if anyone has had a similar experience.
> ds

I lost a plug in a similar manner -- different kind of car, but I don't see
the brand as a significant issue here -- and had to have a heli-coil
installed to hold the plug. The plug had come loose, and it damaged the
threads.

I also learned that I was supposed to use Anti-Seize on the threads. When I
installed the plugs, they felt tight, but the torque spec is not very high
and a bound plug can trick the torque wrench. I'd not have believed this to
be true before I witnessed the result firsthand.

Apparently the aluminum head and steel threads on the plug need to be
greased up a little with antiseize, or the plug might not seat well.

"Jeff Strickland" > wrote:

> I also learned that I was supposed to use Anti-Seize on the
> threads.

Always but be careful of this stuff!

I've used it for years on motorcycles, the normal procedure is to open
tube of Anti-Seize, put small amount on finger, wipe around the threads
of the plug, install plug, stand up (remember it's a motorcycle?), step
on tube of Anti-Seize which ruptures tube and squirts Anti-Seize for
surprising distances in all directions.

You'll also find the stuff is absolutely permanent on clothes, fingers,
motorcycle seats, floors, etc..



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DS wrote:
> While turning a corner in my '93 Miata, there was an ominoius POPP
> followed by a loud THWACKA THWACKA THWACKA.
> The problem was one of the plus had blown out with explosive force,
> I put in a new plug and everything is fiune. The three other plugs
> were snug and subseqiuent checks don't show any new loosening.
> I'd be interested in theories.
> My own is thart since the car is stored in bitter cold winter weather
> --- 35 below --- the cycle of deep freeze and thaw caused expansion
> and contraction that loosened the plug and that when I started driving
> in the spring, it was only a matter iof time before it came right
> out.
> Would be interested if anyone has had a similar experience.
> ds

I once had a well-used Corvair that had the same problem on three of its six
cylinders. The plugs would remain in place for a little while, but would
eventually pop right out. The situation worsened quickly. The solution was
to install helicoils.

It's possible that the plug was never installed properly; someone
accidentally neglected to tighten it down perhaps. Otherwise, I find it a
stretch to believe that the plug spontaneously unscrewed itself and popped
out. I think your problems with this cylinder are not over.

--
Dale Beckett

DS > wrote:

> My own is thart since the car is stored in bitter cold winter
> weather --- 35 below --- the cycle of deep freeze and thaw caused
> expansion and contraction that loosened the plug and that when I
> started driving in the spring, it was only a matter iof time
> before it came right out.

Probably a good idea to remove the plugs, re-apply antiseize compound
and re-torque them in the spring before driving the car.

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On May 12, 12:34*pm, "Jeff Strickland" > wrote:
> "DS" > wrote in message
>
> ...
>
> > While turning a corner in my '93 Miata, there was an ominoius POPP
> > followed by a loud THWACKA THWACKA THWACKA.
> > The problem was one of the plus had blown out with explosive force,
> > I put in a new plug and everything is fiune. The three other plugs
> > were snug and subseqiuent checks don't show any new loosening.
> > I'd be interested in theories.
> > My own is thart since the car is stored in bitter cold winter weather
> > --- 35 below --- the cycle of deep freeze and thaw caused expansion
> > and contraction that loosened the plug and that when I started driving
> > in the spring, it was only a matter iof time before it *came right
> > out.
> > Would be interested if anyone has had a similar experience.
> > ds
>
> I lost a plug in a similar manner -- different kind of car, but I don't see
> the brand as a significant issue here -- and had to have a heli-coil
> installed to hold the plug. The plug had come loose, and it damaged the
> threads.
>
> I also learned that I was supposed to use Anti-Seize on the threads. When I
> installed the plugs, they felt tight, but the torque spec is not very high
> and a bound plug can trick the torque wrench. I'd not have believed this to
> be true before I witnessed the result firsthand.
>
> Apparently the aluminum head and steel threads on the plug need to be
> greased up a little with antiseize, or the plug might not seat well.

The same thing happened to me over a decade ago on my '76 corolla in
my pre-miata days.