91 Honda blew out spark plug

My 91 Accord blew a spark plug out of the head. The threaded end was
still in place but the plug totally blew out. Anybody got any ideas
why?

 

Yep - I'm experienced <8^P

The aluminum head is not very forgiving of past cross-threading or
overtightening. Once I lost a plug that way I started using a torque wrench
and was amazed how little torque is used.

So - now what? The standard repair is to insert a helicoil in the damaged
threads of the head. It sounds a bit hokey but is a solid repair that should
last the life of the engine. It is normally done with the head on the
engine. The catch is that the hole has to be retapped to a larger size and
that produces a bunch of aluminum shavings. There are two ways of dealing
with that. The controversial (and probably outdated) way is to just let the
shavings fall into the cylinder and let them blow out the exhaust. In these
days of catalytic converters that doesn't sound like a good idea. Instead,
most people set the piston to bottom dead center on the beginning of the
compression stroke. They then fill the cylinder with shaving cream and tap
the head. When the dirty work is done, rotating the crank to top dead center
pushes the shaving cream and shavings out. The remaining shaving cream
doesn't hurt anything... assuming it didn't have silicones in it!

Expect between $100 and $200 US to have a shop do it, or to spend about $50
for a comprehensive helicoil kit for it. You might be able to find a better
deal on the helicoil kit.

Mike

 

1. if you mean that the plug disintegrated and part of it is still in
there, i'd have to ask what brand of plug it is so i can never buy one
like yours.

2. if it simply unscrewed and blew out, that's not usually so much of a
problem - they can often simply be screwed back.

3. if the head threads stripped, you can helicoil. it's a pain, but
easy enough to do with the right tools.

if it's #1, how much of the plug is still in there? if it's just the
metal outer, you can unscrew it with an easy-out and simply replace the
plug. if it left part of the core in there, the danger is the core
dropping into the cylinder. if that happens, you'll have to remove the
head. if you can post a pic of the plug remnant, it will help us advise
better. tinypic.com is free.