Failed plug

I have since found another engineer who also thought sparkplug blanks
were indeed machined from screw stock (i. e. resulfurized or leaded
free machining steel alloys). That would still suggest a possible raw
material fault. I certainly wouldn't want any plugs made from that
particular bar.

Be sure you save it. I'll bet you could exchange that plug with its
manufacturer for a new one...........!

They already offered that. I am more interested in getting an opinion from
them. My mechanic had them look at an oil filter that had a problem, and he
said they actually took a close look at it and let him know what the problem
was. I hope they are as helpful on this.

"nrp" wrote in message
ups.com...
I have since found another engineer who also thought sparkplug blanks
were indeed machined from screw stock (i. e. resulfurized or leaded
free machining steel alloys). That would still suggest a possible raw
material fault. I certainly wouldn't want any plugs made from that
particular bar.

Be sure you save it. I'll bet you could exchange that plug with its
manufacturer for a new one...........!

Be a little careful - they might "accidently" lose it!

These longitudinal crack-like defects are called sulfur stringers and
sometimes we found them in poor quality resulfurized free machining
steels. It makes the steel very brittle - especially when the
temperature is elevated, and that's why they machine so easily.

I'm not a metallurgist - which is what you really need for a valid
opinion.

If this is what has happened though, as a mechanical engineer I am
appalled - from both a design and especially from a quality monitoring
standpoint.