[T3] Spark plug blown out of #4 cylinder

Jim Adney jadney at vwtype3.org
Mon Jul 18 15:15:33 PDT 2011

On 18 Jul 2011 at 14:41, Norman Roush wrote:

> My '68 FI Sqbk blew out the spark plug from its #4 cylinder.  Why
> would this happen?  Car was running fine just before it happened.  It
> probably needed a valve job but would this affect the SP?

I don't think the needed valve job would have had anything to do with 
this. Either the SP was not screwed in all the way, or the SP threads 
in the head are damaged. You can test this by just tightening a new 
SP in that hole. If it tightens up normally, it's probably okay, if 
it slips and never gets tight, then the threads need to be repaired.

I prefer HeliCoil inserts for these repairs, but most mechanics like 
the solid inserts, which I detest. A good mechanic can install either 
one with the engine still in the car, but the best repair will be 
with the head off the engine. 

Maybe this is just a sign to get your valves done and the SP thread 
repaired at the same time.

In the future, be cautious when installing SPs. Always start them by 
hand, with an extension. That way you'll avoid cross threading them, 
which is what usually causes damaged threads here.

Jim Adney, jadney at vwtype3.org
Madison, Wisconsin, USA

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