Sunday 14 November 2010

STILL LEARNING ABOUT THREADS


I refitted the engine release valve stem and body – see photo. In the process of attaching the clip one of the screws sheared off leaving a few millimetres of thread inside the hexagonal stem body which can not be removed. These ‘screws’ are 3/16 BSF x 3/8 bolts (why are very small bolts called screws ?)  This size of screw could not be found online but in the process of searching I discovered that 3/16 BSF is interchangeable with 2BA thread. (32 tpi  and 31.4 tpi respectively.) So I searched my electrical bits box and found a 2BA screw which after cutting to length fitted perfectly. Just one problem. Having fitted the new screw into another threaded hole in the hexagonal valve stem body the clip and lever are no longer in the correct  position when fully screwed into the engine casing. Moreover the stem appears to be seized inside the body when it should act like a piston inside a cylinder when the decompressor lever is applied. For now I’ll leave as is and address this problem when the restoration is complete and ready for fine tuning to fire her up.  
(Part descriptions as referred to in the Atco spare parts list,courtesy of the OLMclub)

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