Head bolt torque - JEM0002-6

·         Stuart Spencer

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I see in JEM0002-6 that the head torque entry in table 10 has changed to red and indicates only 34NM. There used to be an initial and subsequent torque. The subsequent torque is also still referenced on page 67. I recently checked mine and did to 34NM assuming that there is only one torque now, is this correct? If so the reference on page 67 needs updating. If there is a different torque for subsequent checks, is it now a problem that I have torqued to 34NM?

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·         Doug Smith

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Hi Stuart,
The system of 24 / 20 lb.ft torque settings came in a few years back as a part of a package of mods intended to reduce the amount of work that needed to be done at an average service.

Going by my rusty memory the intent was to reduce the rate at which heads recessed when operated at higher temperatures. Lower torque = less tension load on the head = slower deformation when the head was hot = more stable head sealing. The higher initial torque was to provide better sealing while the engine was new / running-in and then, once it had settled down the torque could safely be reduced.

In practice it never really made any measurable difference and did cause some confusion around service time so it's been scrapped; 24 lb.ft (34Nm) is now the standard number again, for initial and all subsequent checks.

Regards,
Doug.