They are not stretch bolts on the Twin spark. You do not need to change them.
yeah they are they are. hence why they have to be torqued to a specific torque and then tightened in angles.
Torque to yield (TTY) bolts, also commonly referred to as angle torque or
stretch bolts, are used in many of today's modern engines predominantly for
cylinder head bolts but also main bearing and big end caps.
Compared to conventional type bolts, TTY bolts offer the engine manufacturer
a number of advantages including greater flexibility of design, reductions
in component costs, more accurate assembly and reliability of seal. Engines
designed utilising TTY head bolts require fewer head bolts to achieve the
desired clamping loads then those using conventional bolts. With fewer bolts
the engine manufacturer has more flexibility in cylinder head and block
design as well as reducing the cost of the engine.
Whilst TTY bolts are attractive to the engine manufacturer, there are
disadvantages to the engine repairer. For the most of us it would be
unthinkable to replace a conventional head bolt unless the bolt was damaged,
i.e. stripped threads, the bolt head was rounded off, the shank was severely
corroded or pitted.
Conventional head bolts simply just did not wear out. Torque to yield head
bolts however, by the very nature of their design, do wear out and should
NEVER be reused.