<VV> Stripped threads/plug holes

Sethracer at aol.com Sethracer at aol.com
Sun Nov 18 02:31:32 EST 2007

In a message dated 11/17/2007 4:26:28 PM Pacific Standard Time,  
utvairs at yahoo.com writes:

Is it  possible to repair the threads in a spark plug hole without removing 
the  head?  How difficult a fix is it? 

The guy I bought the car from  said he and his neighbor rebuilt the engine 
together.  Apparently his  strong-arm neighbor was putting things together on 
the passenger side while he  was on the drivers side -- because almost every 
bolt that goes into aluminum  on that side of the car is stripped.   Grrrr....


There are several different types of inserts. The helicoil is an actual  coil 
of shaped wire with the inner part of the coil shaped like a new set of  
stock-sized spark plug threads, and the outer edge like a similar thread but  
larger. You re-tap the threads in the head using a special tap that starts in  the 
plug thread size, to center the new cutter, and ends up having cut the  new 
size of threads in the head. Then you mount the actual helicoil on a tool  and 
screw it down into the new threads. When it has seated enough that it  doesn't 
stick out, you use a special tool - like a set of needle nose pliers -  to 
break off the leading thread/tab. Then pull the tab out of the hole. That tab  
is the part you DO NOT want to drop into the chamber. It is hard steel and will 
 tear things up in the chamber. Allowing the aluminum cuttings from the  
re-threading into the chamber should be minimized , and they may be  vacuumed out 
at the end. The Keensert, my favorite, is similarly installed,  and comes with 
it's own tap as well, It is a one-piece cylinder, inner and outer  threaded, 
that also has a set of locking pins that, after the insert is screwed  into 
place, are pushed down into place - (as with a tool and a hammer) -  this locks 
the insert into place. I have never had one of these come out, I  cannot say 
that about helicoils, although I haven't installed any. Several have  
"appeared" in my shop on various engines and some have latched to a spark plug  and 
pulled out. By the way, both types of inserts are available in all  sizes, not 
just for spark plug threads. - Seth  Emerson

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