That is what I thought initially at the track. Tear down showed the valve stem broke at its end then bounced around killing the plug before it lodged itself into the exhaust seat sideways. Funny thing was no cel for this type of failure.

 

Facts:

- a properly tightened spark plug will not back out or come loose under ANY situation...track, drifting, or unrelenting abuse.
- that is 100% the fault of the last guy that touched the spark plugs, and ALL the damage you see is from the plugs backing out due to improper torque.

- torque wrenches are for those who do not have a well earned feel for the fastener they are working on, and torque settings are a GUIDE.

- torque wrenches are for CRITIAL applications, and spark plugs are NOT ONE OF THEM. Spark plug torque is not critical (within one foot lb) but it is of great importance...TIGHT!!!!

As of now, there are about 35 incorrect torque settings in the Honda Repair Manual, dated 2009.

 

You are 99% right.

A loose plug caused ALL the damage, 100%.

But it is not the plugs fault, it is the individual who put them in.

I still need to do a pull test, and I will post an EXACT torgue for an NGK ORIGINAL plug in an S2000.

 

While i was at the dragon billman checked the tightness of the spark plugs on every car he worked on, all but one if i recall has loose spark plugs. Now that is scary!!

Bill where can i find all the proper torques for those 35 incorrect ones?

 

Agreed. I'd love to make a list of them so I can keep personally. Billman's knowledge is unsurpassed!

 

I have to admit I'm confused here. How does a loose plug lead to damaged valves and pistons?

I could see if you break a valve retainer and drop a valve into the cylinder it could strike the spark plug and damage it and the coil pack but I'm having trouble seeing the reverse happen. Wouldn't a loose spark plug lead to gas blowing by the spark plug and blowing the coil pack off? Once that happened there would be no more spark in that cylinder.

 

Which Cylinder?

My motor a couple years ago had a few seasons on it and did much the same. Pulled the head and found cylinder 4 absolutely destroyed. Spark plug was in pieces in the cylinder, piston was melted and cylinder wall was beat to death.Put a new motor in it and she ran fine till I sold that motor. Still no idea what happened in #4. And The car had OEM plugs in it.

 

I guess it is possible to damage coil even tough I have hard time believing. Coil is bolted down and sealed effectively making that area under it chamber if there is leak past plug.
Question is how much can leak by plug that is hand tight like my was. It is not like plug was hanging on one thread or blown out.
My guess is plug negatives broke due to ignition/detonation and probably got jammed between valve and seat which in turn can break retainer and valve drops in.
I will know more once I get head of, hopefully in next couple weeks.

 

I was following you when this happened and have it on video. I can upload it and send you a link.

 

Thanks, I would like that. If there is something to see, like nice smoke bomb, you can post it here also