Hi folks,
Was helping get a friends race boat ready for finals and in looking at plugs, we noticed some had been "kissed" by piston domes- first thought was rod bearings as once we saw one, we pulled the plug across from it- same crank journal , sure enough, it was kissed as well on the base/bottom of thread .
Started pulling the rest of the plugs- 4 plugs kissed, others were not across frpm each other- not likely to have lost that many rod bearing with engine good on oil- no noise.
So, I mic'ed the plugs thread length- the four that had kissed pistons were longer- to varying degrees- all the same number NGK race plugs.
Pulled a new box out- these were all closer, but not exact and none as long as the loner ones we had pulled out.

So : FYI, don't trust em- mic em.

Just sayin

Thanks for the heads up
What type of motor was this problem occurring in?

Maybe counterfeit parts ? NGK is a very good product , thanks for the info.CLICK LINK [video:youtube]https://youtu.be/2F9Cs-Bd8-U[/video]

Yep I check and ohm every plug on everything..........

540 chevy/ afr heads- 8 second index race boat- 1/4 mile

folks around here are reporting serious issues with consistency on NGK plugs.
Make sure you measure resistance as Dom suggested.
No, these are not counterfeits.
QC seems to be a current issue .
fyi

Are you indexing your plugs? I have to index my plugs or some have been re gapped for me!

Speaking of NGK, I had a set of 7 heat range plugs show up in 8 boxes recently too.

yes, we generally index on race engines.
Ones on that chebby- couple were "bumped" with index rings on them.

Perhaps all plugs vary a little in lengths and we just never realized it before?
who knows.

I will be checking lengths from now on for any engine with domes in it for sure.