13289 - SOHC M30/M40 (Wasted Head) Front Frame Engine Bolt Set (1/2"x20 tpi) - Stainless Steel

Product no.: 0727 13289

Not in stock

£21.00
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This is the 13289(Norton part number) 1/2" x 20 Engine Bolt set - but as fitted to SOHC Norton International Model 30 and Model 40 models, with the rounded head profile as would be expected on roadgoing International models. 

As well as saving a small amount of weight over the 'rounded head' type, they also look very pretty. The set is CNC machined from stainless steel with the correct 'reduced Hex' head and profile, 2 stainless washers and reduced Hex wider nut

It is hard to be definitive about when Norton started fitting these 'wasted head' bolts - they are definitely visible in the 1948 Spare Parts catalog.  Please note that some original pictures of SOHC Manx Norton models indicate this bolt was also drilled through the centre to further lighten it.  We do not do that with these bolts as it can result in a weakened bolt if used on roadgoing bikes - however you can do it yourself if you so wish (I have done it in the past on my own racing bikes), but note it is important not to drill all the way through the bolt, you should stop just short of where the thread starts. 

The set consists of hex head bolt, deep nut and two washers - CNC manufactured by ourselves in Stainless Steel. It is as used on all rigid and plunger framed SOHC models from 1930's/50's.  The set comes fitted with standard size stainless steel washers.  We do occasionally get reduced outer diameter 0.5" washers (Item 0662), but as these are not always available we list this item with standard size washers

As there were so many variations of Norton SOHC engine bolts, the table below will help assist you confirm if you are ordering the correct bolt, and you may find this bolt will also fit your bike model for another application :

Norton Engine Bolt Attribute Table:

No:

       Attribute Type:  

   Attribute Description                      
 1

          Model Type:

   M30/M40 Racing Models (ie to fit early Manx)
 2

          CC/Model:

 

 500cc and 350cc SOHC M30/M40 Models

 3

         Bolt Shaft Diameter:

   1/2" shaft diameter
 4

         Bolt Shaft Length:

   4.230"/107.5mm (UH to end of thread length)
 5

         Head Type:

 

 Norton 'Wasted Head' Type

 - as fitted to racing M30/M40 SOHC models

 6

         Spanner Size/AF Dia

   3/8" Whit Spanner : 0.705" AF Hex.  

 7

         No req'd per engine:

   1 per engine
 8

         Bolt Radial Position:

 

 Approx 10.00pm

 (if crankcase is clock face from timing side)

 9

         Approx Nut Depth:

   0.430"/11.0mm
 10          Material:  

 Stainless Steel

 11

        Thread Type:

  1/2" x 20 tpi
 12

         Notes:

   Kit consists of hex head bolt, 2 washers, nut.

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). 

Therefore - when comparing the length shown in the table above to your own engine, you need to take into account the width of the engine casting, engine plates and the height of the nut.  Also, any brackets that you may fit under the bolt head - I have tried to base the length of bolts on not having additional brackets unless I know they were standard (the nuts are normally extra width though and can be narrowed slightly if necessary, or one of the washers omitted

Remember that in some cases, bolts were fitted where there may have only been an engine plate on one side - i.e for the rear of the engine on most SOHC engines, the bolt immediately above the magneto platform has an engine plate only on one side, while the bolt under the magneto has an engine plate on both sides - which is why I make 2 versions of these bolts.  Norton did not bother originally, fitting the same length bolt to both)

'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 tpi3/8" x 26 tpi7/16" x 20 tpi1/2" 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.

In most cases, orginal 'New Old Stock' Norton bolts were used as templates for these bolts - although being practical - it is very hard to tell what is absolutely original or nut for each engine! - there were so many bolt variations and lengths over the years, with some engines seemingly using different lengths and shaft diameters for the equivelant engine by the year.  It is worth noting particularly that pre 1948/49 350cc cranckcases are physically smaller than the equivelent 500cc crankcase - but they standardised them in 1949

Therefore - please check your own engine to check which ones you require before purchasing, and double check the fit before final tightening - in case you need to return.  We hope you understand, we will not accept returns if you have marked the finish of the hex or shafts as we will not be able to resell.  Email us on our normal sales@racingvincent.co.uk if you need any more information before ordering.

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!

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