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Dommy distributor housing fixings

Submitted by robert_tuck on Mon, 05/07/2021
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Heavy Twins

I have been hearing the occasional rattle from inside the Timing cover, Its been many years since I looked in there so I took the cover off to check the chains.  All looked fine except the dissy chain has a bit too much slack (memory says it was ever thus!.)  The nuts that hold the Housing to the back of the case are some form of early socket like an allen head but with  multiple facets . Nothing fits any ideas??.  Otherwise its going to stay slack. Can't be good for the advance and retard unit ,probably why the tickover is a bit uneven.

Submitted by george_farenden on Mon, 05/07/2021

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Hi Robert, 

From your description, it sounds like a Torx bolt, but to my knowledge these are only made in metric sizes. Also you say 'nut', then describe as like an allen 'bolt'..

If it is indeed a nut, is the shape like in the pictures I have attached? These are of 'E' sockets and are in imperial sizes, but I feel these are more modern than would have been used on a 99. Anything like what you have?

Regards,

George

Attachments
20210705_1R.jpg
20210705_2R.jpg

Submitted by robert_tuck on Mon, 05/07/2021

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Phill s list describes them as 12 point allen nuts . I have boxes of torx bits but these are different , and probably imperial too. May have to make a bit to fit .

Submitted by robert_tuck on Mon, 05/07/2021

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HI Mikael,   I have a huge box of 6 point  allen keys  Imperial and metric , none fit.  Built in 1959 its surprising that Norton were so advanced in their thinking , perhaps too advanced!  a bit like the posidrive screws they used on the rear fully enclosed  chaincase. Most of us had not seen a posidrive screwdriver up till then. Its back together now, slack chain an-all . Still  ,it would be nice to get the bit/key for next time. I bet Hudson would have had the info in his head,  

Submitted by philip_hannam1 on Mon, 05/07/2021

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The studs used for holding a Magneto / Distributor in position are supposed to be 5/16" x 18 BSW. The opposite studs ends having 5/16" x 26 CEI threads.

However, my equivalent thread tables show that 5/16" x 18 UNC has a close enough thread pitch to fit in the cases.

In which case a full-length 5/16" x 18tpi stud might fit. Robert mentions nuts that look like sockets with multi-point socket heads. Supposing these are actually  5/16" x 18 UNC Torx bolts???

A similar fitting change was made on the Commando cylinder head when the rocker spindle end-plate bolts changed from 1/4" x 20 BSW to 1/4" x 20 UNC.  Try playing spot the difference with Atlas head rocker  fittings?

Submitted by robert_tuck on Tue, 06/07/2021

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I have seen "somewhere" !!  a fuller description of these 12 point  allen socket head sleeve nuts, But can't remember where. .   

Submitted by mikael_ridderstad on Tue, 06/07/2021

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Wonder what caused Norton to use these nuts for some years, until replacing them with ordinary hex nuts. Anyhow, as far as I know there is two different types of 12 point screws/nuts. The triple square ones (XZN) which I've only seen in bigger dimensions. And the double hex ones. Of course point angle is different. Don't know if any of these where made in imperial sizes.

Submitted by robert_tuck on Tue, 06/07/2021

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Thats the type George , only I can't imagine they would be metric  .I did try the modern splined bits but no go. I have a memory  ( 25 years ago) of managing to get  an Allen  key to grip a little ,just enough to lightly tighten them .  I'm sure they were not the same as used to fit a mag .

Submitted by george_farenden on Wed, 07/07/2021

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Hi Robert,

Is it worth sacrificing a flat blade screwdriver by grinding the end to fit? A gentle 'persuasion' into the nut and a strong twist might get it moving? Alternatively,  sacrificing the next size up Torx bit? Chamfer the end and same gentle 'persuasion' as before? Both have worked for me with rounded off allen bolts.

As to replacement, if 'correct' nuts aren't available,  would something like clutch spring screws/nuts work?

Good luck,

George.  

 

Submitted by robert_tuck on Thu, 08/07/2021

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Hi George.  A sleeve nut with a shallow hex head would have been a better solution. If I had a lathe I would make some from a bit of hex bar.  A good mate has a lathe -----------.In the meantime a ground down 7 mm allen key may be the solution. I have had a close look and the issue is there is only about 2mm of engagement with the key, a 1/4" does fit but any wear at all means no go.A 12 point 1/4" allen key would do it.The nuts are recessed into the housing so no reason for them to be so short. If I can get them out I could cut a screwdriver slot accross them.

Submitted by robert_tuck on Thu, 08/07/2021

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Got one out,  They are 1/4 BSF 12 point allen nut.  The reason they are such a pain is because the stud end comes through the nut and restricts the key  engagement to about half what it could be. A simple solution will be to fit a washer under the nut. Next question ,   is that all that holds the housing on ? 2 allen nuts ? ,or is there something under the dissy that needs Houdini to access it.

Submitted by howard_robinson on Thu, 08/07/2021

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Hello again Robert - Those internal double hex nuts are !/4 inch BSCycle (26 tpi).  Two are used at the top in the recesses in the mount,  for the 18D2 distributor,  each with a small 1/4 inch thick  washer. (The washers have a small o/d - maybe 3/16 inch washer but with a 1/4 inch hole?  I personally use 1/4 inch spring washes adjusted with two pairs of pliers to stop the springing.)  The bottom nut is usually a standard 1/4 inch BS Cycle nut again with a thick washer.  If you're not careful undoing the nut (if you can get at yours) you can undo the stud from the case instead and then you're in trouble.  I have a specially altered spanner that allows me to undo it - most people don't. Unlike the suds for fitting the magneto the studs for the distributer are parallel (1/4 inch) all the way to the collared end that screw into the cases.  Good luck, Howard

Submitted by robert_tuck on Thu, 08/07/2021

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Hi Howard , It may be that they changed things as time went along , my Allen nuts are stamped with !/4 BSF.   I found some small spring washers and eased the internal diameter out to make them an easy fit . I'm sure I once  had a spanner that would get at the lower nut ,but not now !.In the end I used the official aprooved woolwich method as detailed in the service book.   A mallet !. I think last time I removed footrest and oil manifold to get in there. A locktited nut inside the timing case as on some mag bikes would be much easier to work with.The extra depth that the washer gives allows a new key to do the job ,but only just.

Submitted by philip_hannam1 on Thu, 08/07/2021

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Both 1/4" BSF & BSC threads are 26tpi. The slight difference in thread angle is next to impossible to make out.

Submitted by paul_nicholls on Fri, 09/07/2021

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The 2 studs that have the allen nuts are waisted which allows the housing to be adjusted by rotating slightly around the bottom stud. Enough to adjust the drive chain.

Submitted by howard_robinson on Tue, 13/07/2021

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Hello again Robert -  I don't believe the studs are waisted as Paul suggests.  The nuts are 1/4 inch and the holes in the dynamo housing mount are 5/16 inch.  So there is already plenty of movement to adjust the drive chain.  On a magneto the nuts are 5/16 inch so the studs are waisted down to 1/4 inch to permit the movement required for adjustment.  If they are indeed waisted what diameter remains of the stud - 3/16 inch ?  I suspect a previous owner must have done it rather than buy a new chain.  Cheers, Howard

Submitted by robert_tuck on Tue, 13/07/2021

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Hi Howard, I doubt I will ever find out.  To get to the bottom nut is a real struggle. With the top 2 allen nuts loose its possible to lever the housing back by levering against the case. Getting it to go forward required the service department  mallet !.I must have achieved something as the rattle has gone. The motor runs too dirty for my liking ,so thats my next target . A breather that keeps the internals at a negative pressure should help the head drain oil and reduce oil  getting down the inlet guides.

 


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