SOHC E4268 7/16" x 20tpi BSC Rear Frame Bolt - Stainless Steel

This is the distinctive E4268 7/16" x 20 tpi BSC short engine bolt that was used to bolt the rear engine plates to the upright frame tube on most 1930s - 1950s Norton frames.  These are CNC machined by us in stainless steel (with linished flats). 

Frames using upright gearbox's used two nuts per frame, later flat gearbox frames used 4 nuts per frame.  They were also used to close off the bottom of the rear plunger shaft on Gardengate frames (fitted with a thick washer, to lock them to the frame)

As can be seen from the third photograph, where our bolt is alongside an original 'New Old Stock' Norton E4268 bolt, ours are identical in thread, hex size and head shape to the original  - other than ours are just machined in non rusting stainless steel and look a bit nicer!

Bolt Table Legend and Useful Information: 

AF = "Across Flats', i.e the diamter in inches of hex bar between the two opposite flats - this is the diameter the spanner gap needs to be - we use the correct 'British Standard' bar, as fitted to all Norton single cylinder motorcycles originally, to fit BSW spanners. 

UH = 'Under Head' Bolt Length, i.e. when measuring the length of the bolt shaft - dimensions are taken from the distance at the base of the hex head to the end of the threaded shaft.  It does not take into account the height of the hex head, or the slightly rounded chamfer at the end of the threaded shaft, which are additional.  (Please bear in mind length is nominal - there may  be 1 or 2 mm variation because of batch variation). 

'Rounded Head'/Reduced Hex Head : Norton's used a distinctive rounded dome on many of their larger engine bolts - these are replicated exactly on our bolts, as the photographs show.  This style of head was used on many Norton bolts of the '30's-'50's. 

In addition many engine bolts had an AF (Across Flats) diameter that was less than normal commerically available bolts for a given bolt shaft size - the rationale for this was that there was not much room around complex castings, therefore you needed to be able to get access with a smaller spanner.  To allow for this, many of the engine bolts with these 'reduced head size to shaft diameter' bolts also had a deeper depth of hex as well, to provide as much spanner to hex contact as normal bolts - reducing the chance of 'rounding' the hex when applying a lot of pressure with spanners and providing as much thread on the nuts as possible - but important with the pressure required of engine bolts.  We have replicated these deeper heads, with reduced hex diameter to shaft as per the originals, not only giving that authentic look, but ensuring the nuts .  To our knowledge this type of bolt/nut is not  had, as well as a smaller hex (reduced head) than is normal for a commercially available 7/16" bolt.  They are very distinctive and I always struggle to find these when restoring or building a project Norton.

Bolt Radial Position In Relation To Crankcase:  In the table above I show the radial position of the engine bolt listed here, in relation to the crankcase, if looking on the Timing side of the crankcase as a Clock Dial.  Therefore, the front engine bolt closest to the front down tube and on the horizontal datum line with the mainshafts would be - 3pm, hope this makes sense!  I expect most owners used to Norton single engines try and work out in their head the relative positions of engine bolts in the same way. Clock times are approximate!

Thread Type:  Engine Bolts on Norton engines tended to come in most of the standard British Whitworth diameters, with the following common thread types, where TPI means 'threads per inch':  1/4" (shaft diameter) x 26 tpi (Threads per inch), 5/16" x 26 tpi, 3/8" x 26 tpi, 7/16" x 20 tpi, 1/2" x 20 tpi.

Most thread profiles were originally BSC (British Standard Cycle), but please note that 7/16" x 20tpi is also a UNF standard thread size and none of the tooling manufacturers will now make the BSC profile tooling - therefore we manufacture this size nut/bolt in UNF profile.  These nuts may fit on original bolts, but can be slightly tighter.

Overall, these bolts are high quality, CNC machine finished engine bolt sets manufactured to look just as the original Norton items, but in non rusting stainless steel, with original Norton dimensions and profiles.   We linish the hex faces on the bolt heads to ensure crisp finishes and we hope you find the will give that finishing touch to any restoration - or just clean up the look of your oily rag, ride to work Norton!