Thread breaking strength

[Smitha T A]

Hello all,
On what are all the factors thread breaking strength depends?

Background: I'm referring to thread on spark plug which is fitted to engine's head. Task is to improve it's strength.

Thanks in advance

 

[Screwman1]

Get a copy of John Bickfords book: "An Introduction To the Design and Behavior of Bolted Joints". The will have a lot of information. Just some of the things that you have to look at at relative material strength, thread fit, thread length, torque, friction factors. A lot of work has been done on the spark plug threads and much of the problem with certain engine designs has to do with seizing from heat cycling and galvanic corrosion. The diameter of the internal hole is critical to spark plug torsional strength.

 

[chicopee]

Nothing like taking a course on machine design in which the subject of threads is covered.

 

[Tmoose]

This wouldn't happen to be a Ford Triton engine, would it?
Those spark plugs break the shell below the thread.

I'm not aware of other engines routinely breaking their spark plugs, or having them broken.