From: mthomas@venus.tamu.edu (Mark Thomas)
Newsgroups: rec.autos.vw
Subject: Re: [A] spark plug inserts: what's the best kind ?
Date: 29 Dec 1992 00:24 CST
Organization: Texas A&M University, Academic Computing Services
Distribution: world
NNTP-Posting-Host: venus.tamu.edu
Keywords: air-cooled   stripped spark plug thread   inserts
News-Software: VAX/VMS VNEWS 1.41    

kdrolt@athena.mit.edu (Kenneth D Rolt) writes...
>i have at least one stripped spark plug thread on my air cooled motor;
>the other cylinders might not need attention (yet).  i know about helicoils
>and how they work.  i have also seen at least two other types of spark plug
>inserts, one which requires tapping and then installing a new insert with a
>new spark plug (this type apparently doesn't expand into the new threads),
>and another one that does.  i don't recall the brand names (the non-expansion
>might be K-D).
> 
>has anyone any experience, good or bad, with any of these insert types (or
>others i have not mentioned)?   also, for any of the above insert types,
>is it recommended to use a loctite-type product as well?
> 

When one of the spark plugs seized up in an engine that used to
be in my 1970 Beetle, it was repaired with a K-D insert.  I dug
up the old package:  it was part #2128, 1/2" long 14mm spark plug
insert for aluminum heads.  The plug hole has to be tapped ("use
with K-D 2124 Tap K-D 2125 kit").  The inserts come with a
thread-locking compound which I guess is similar to Loctite's
"permanent" thread locking compound.

>
>FYI, the motor (and the head) is still in the car and i don't plan to
>remove either (until i need a clutch that is :)   -ken
> 

I had the insert first installed at a shop;  I'm sure they did
NOT remove the heads.  Removing the heads is strongly advised, so
you don't get the metal shavings (from tapping the holes) in the
cylinders.

If you're sure you don't want to remove the heads, after tapping
and reaming the hole and again after installing the inserts,
crank the engine for a while with the coil-distributer cable
disconnected and with the spark plug out, to try to blow out any
metal particles from the cylinder.

I used that engine for several years aftewards (several tens of
thousands of miles).

The big headache was that the insert usually came out when I
changed the plug!  This, despite using thread locking compound on
the insert and anti-seize compound on the plugs.  (I think the
shop may have used a subtly too-large tap.)  So, I had to replace
the insert when replacing the plugs.

I don't know if that's a usual problem, but I've heard that the
heli-coil method is better that the threaded inserts.

I'm still terrified when messing with spark plugs in those soft
heads.  I use a thread chaser to clean the threads and then crank
the engine before installing new plugs, then use anti-seize
lubricant when installing plugs (the tube I have is Permatex part
# 133A).

In the Bently manual, it says to replace the plugs every 12,000
miles, but I can't find any other info.  In other places, it says
to check the gap and wear every 6,000 miles.  The plugs are
always in pretty good shape after 6,000 miles (and even 12,000); 
since I'd like to reduce number of times I take them out, does
anyone have comments on the advisability of not touching them
except to replace them every 12,000 miles?

++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
Mark Thomas                         | The train ... traditional,
Evans Library, Texas A&M University |   yet environmentally sound  
(409) 845-5147 / FAX (409) 845-6238 |  
mthomas@tamvenus / mthomas@tamu.edu |              --Lisa Simpson
Newsgroups: rec.autos.vw