Re: [T3] Stripped Spark Plug

["Jim Adney" <jadney@vwtype3.org>]

On 28 May 2002, at 21:20, Keith Park wrote:

> This is EXACTLY what happened to me 14 years ago... I can tell you
> what NOT to do... DONT stuff it back in or try to put in a new one
> without removing the engine.  Its a helicoil thread insert... and
> stuffing a new one in there resulted in a plug that blew out and
> melted out the spark plug hole a couple days later ruining the head.
> 
> I hate to say it but Id NEVER use a helicoil on spark plug hole...
> there are those that swear by them but your occurance happens too
> often.  use a thread INSERT repair kit, although I find that the ones

I understand Keith's dislike after his experience, but his experience 
was not typical. Helicoil inserts seldom come out, and will never 
come out if installed correctly. The solid inserts almost always 
come out.

Both styles take some care to install, but the fact that the solid 
inserts come out with the SP almost every time you change plugs 
means that the outside threads wear a bit too.

The Heli-coil inserts are oversize, so they have to be squeezed 
down into the oversize threads you cut for them. This means that 
they are always tight in those threads and won't ever come loose. 
OTOH they have to be cut to length and installed carefully so that 
the first thread is recessed 1/2 turn into the head, and the last turn 
is not sticking out into the combustion chamber. 

I know people who can install these with the engine in the car, but I 
prefer to do it with the head off, so I can inspect it and redo it until 
it is exactly right. Done this way I don't think they will ever give any 
problems.

Another problem with inserts is the heat flow. Most people don't 
realize that most of the SP heat flow is actually thru the face of the 
body of the plug, not the thread. The Heli-coil allows this important 
interface to remain unchanged, while the solid inserts impose an 
additional interface. This is likely to make this plug run hotter.

Finally, the most important lesson here is to learn to take care of 
your SP threads. Always start the SPs in the threads by hand, so 
you can feel the threads. I always use a bit of moly lube on the 
threads to prevent seizures which will rip out the aluminum threads. 
DON'T USE standard anti-seize on these threads as it will 
eventually makes it's way to the SP tip insulator and foul the plug.

I have small tubes of an excellent moly lube for sale. One of these 
tubes is a lifetime supply. I use it on SP threads and burnish it into 
bearings when I'm rebuilding an engine. Everyone should have 
something like this available.

-
Jim Adney
Madison, WI USA

-------------------------------------------------------------------
Unsubscribe? mailto:type3-request@vwtype3.org, Subject: unsubscribe