NGK Spark Plug MAR9A-J: Ducati Monster 1200-821, SS 939, HM 950-939-821, Multistrada 1200-1260, Panigale 899-959-1199-1299. Diavel/X

An over-torqued spark plug can suffer from severe stress to the Metal Shell which in turn can distort the spark plug's inner gas seals or even cause a hairline fracture to the spark plug's insulator...in either case, heat transfer can again be slowed and the above mentioned conditions can occur.

The spark plug holes must always be cleaned prior to installation, otherwise you may be torquing against dirt or debris and the spark plug may actually end up under-torqued, even though your torque wrench says otherwise. Of course, you should only install spark plugs in a cool engine, because metal expands when its hot and installation may prove difficult. Proper torque specs for both aluminum and cast iron cylinder heads are listed below.

Spark Plug Type Thread Diameter Aluminum Clyinder Head (lb-ft.)

Flat seat type (with gasket)

18 ø mm - 25.3~32.5
14 ø mm - 18.0~21.6
12 ø mm - 10.8~14.5
10 ø mm - 7.2~8.7
8 ø mm - 5.8~7.2