Hi Robert
Not sure there is one specified but I would go for 15 ft/Lb from guessing the diameter. That is the same as the Oil pump and also the cam chain fixings.
Problem with little screws and big (long) unwieldy torque wrenches is you loose the lack of 'feel'....I would use the appropriate ring spanner and use two fingers and a thumb to tighten it. Then the length of the spanner gives you feedback.
Stuart.
