Commando head to barrels studs - too short?

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Staytite

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Hi all,
I have just fitted the head to my 850 Commando. (Third time lucky - I'm becoming an expert!) However I feel that the three head
to barrel studs (067885) are a bit short. There seems to be only about 5/16" of thread for the sleeve nuts (063192) to go onto, and
the rear stud has only enough thread for about half the long nut at the back. I am not using washers as there would be even less
thread available for the nuts. I do not think I have put the studs in the wrong way round as I think the head end thread is different
to the nut end thread.

Has anybody else noticed this phenomemon?
Is it normal?
Has anybody tried making slightly longer studs?
(I realise longer ones probably make fitting the head even more difficult!)

Thanks
Staytite
 
Hi Ludwig,
Looks like you have done it all for me !!

Just to confirm.... It looks like your extended studs have the threaded portions increased at both ends.

I will increase the "head" end such that as much of the threaded hole in the head is filled, but leaving
a small amount to avoid bottoming out the thread in the hole.

I presume you extended the threaded portion for the nuts by 4mm. As you say any more makes the head
difficult to fit. At least it is an extra 4mm over standard.

Is the 4mm valid for both the two front and single rear studs?

Am I correct in my assumptions?

Thanks very much
Regards
Staytite
 
Staytite said:
the rear stud has only enough thread for about half the long nut at the back.
Click to expand...

I checked my own Commando, and I can feel the end of the stud with my finger, so it's more than half way through the nut.
 
ludwig said:
L.A.B. said:
.. and I can feel the end of the stud with my finger, so it's more than half way through the nut.
Click to expand...

No washer under the nut , I suppose ?
Click to expand...

None specified = none fitted.
 
ludwig said:
I prefer to think for myself instead of blindly repeating engineering mistakes .
Click to expand...


That makes me wonder all the more why you would actively promote the use of washers which have their own shortcomings when you say you do not want to repeat any perceived engineering mistakes?

Why use washers?
http://www.wds.com.au/pdf/why_use_flanged_nut.pdf

(And please, save the self-righteous attitude for your Sunday sermons.)
 
ludwig said:
L.A.B. said:
.. why you would actively promote the use of washers which have their own shortcomings..
Click to expand...

I am aware of the shortcomings of washers , but in this case ( rear cyl head nut) the sharp edges of the nut damage the barrel .
Click to expand...


The correct 076870 nut shouldn't really have any "sharp edges" that could dig in and damage the barrel.

Commando head to barrels studs - too short?

http://www.norvilmotorcycle.co.uk/067870.htm




ludwig said:
Maybe not so important with cast iron barrels , but I use alloy barrels and prefer to use 2mm steel washers there that I can evt replace if /when damaged .
Click to expand...

Yes if I were to use an alloy barrel then I would resort to using washers if I couldn't obtain any flanged nuts! :lol:
 
I noticed the swift edit! :wink:

Do you also fit washers under the crankshaft bolts/nuts then?
What about the conrod nuts?
 
L.A.B. said:
I noticed the swift edit! :wink:
Do you also fit washers under the crankshaft bolts/nuts then?
What about the conrod nuts?
Click to expand...

Can't remember what Commando con-rod nuts look like, but earlier dommie conrod nuts (for all-alloy conrods ) have what is almost a washer built into the nut....
i.e Until you look closely, you'd think they had a washer under the nut.

Doing it like this gives more thread onto the bolt, of course....
 
Rohan said:
Can't remember what Commando con-rod nuts look like, but earlier dommie conrod nuts (for all-alloy conrods ) have what is almost a washer built into the nut....
i.e Until you look closely, you'd think they had a washer under the nut.
Click to expand...

The parts books appear to list separate nuts and washers for the alloy cap Dominator rods, and that's what seems to be available at present (or at least from Norvil).

http://www.norvilmotorcycle.co.uk/crankbear.htm
Commando head to barrels studs - too short?
 
I thought I'd add this little tidbit that I remember reading in Machinery's Handbook. It is a common belief amongst engineers that the 1st and 2nd threads hold 75 - 80 % of the torque on fasteners. This is one of the few statements in the text that isn't backed up with geometric drawings and mathematical equations but is rather an acknowledgement of zeitgeist of engineers. Also mentioned but more as factual was that a nut should have sufficient thickness to equal the distance of the diameter of the stud or bolt it is fitted to.

I recall my roommates race bike in the 70's, in an effort to shave every possible gram off, every nut, bolt and stud was turned down in a lathe so when torque was achieved there was no extra length protruding past the nut. Further more every bolt and stud had been centre drilled and in steps for the larger sizes so there was just enough strength below the outer threads to support those threads. The heads of bolts and all nuts were turned down on the outer edges so you could just get a wrench on the inner side of them. The profile tapered out to the end of the threads so the threads weren't compromised. These fasteners retained a conical shape on the out facing ends. Bolt heads were also centre drilled in steps. They should have saved all the shavings and weighed them. The bike looked like swiss cheese but it won many races.
 
L.A.B. said:
The parts books appear to list separate nuts and washers for the alloy cap Dominator rods, and that's what seems to be available at present (or at least from Norvil).
Click to expand...

From that angle, its hard to tell if the shape of the Norvil supplied conrod nut is the same as the genuine item. Also, the original washers that go under the conrod nuts are extremely thin, where the Norvil ones look thicker.
Commando head to barrels studs - too short?
 
RennieK said:
I thought I'd add this little tidbit that I remember reading in Machinery's Handbook. It is a common belief amongst engineers that the 1st and 2nd threads hold 75 - 80 % of the torque on fasteners. This is one of the few statements in the text that isn't backed up with geometric drawings and mathematical equations but is rather an acknowledgement of zeitgeist of engineers. Also mentioned but more as factual was that a nut should have sufficient thickness to equal the distance of the diameter of the stud or bolt it is fitted to.
Click to expand...

Does that mean that a nut with only 2 threads in it could take 75 % of the torque of a full nut ? I'll let someone else experiment with that one....

And what about these tall nuts, does that mean they can't take more torque than standard ones ?
 
RennieK said:
<snip> Further more every bolt and stud had been centre drilled and in steps for the larger sizes so there was just enough strength below the outer threads to support those threads. .
Click to expand...

Can't recall the exact details, but aren't bolts that are centre drilled actually stronger than solid ones ?? Something to do with the circular shape spreading the stresses. Surface finish of the drillings has something to do with it though...

(maybe thats for the same quantity of material, so a larger hollow bolt is stronger than a smaller solid bolt ? Is it ??).
 
Rohan said:
Does that mean that a nut with only 2 threads in it could take 75 % of the torque of a full nut ? I'll let someone else experiment with that one....
Click to expand...
No.
Rohan said:
And what about these tall nuts, does that mean they can't take more torque than standard ones ?
Click to expand...
Basically, yes.

http://www.ohiocae.com/bolt.htm

http://www.ajaxfast.com.au/.../Technica ... hreads.pdf

Higher Order Analysis
Ajax Fasteners has conducted a comprehensive Finite Element Analysis (FEA) on a generic bolted joint.
This analysis revealed some interesting facts regarding the micro level distribution of stresses [3]. In
summary, it was found that the threads are not equally loaded and at typical applied load (65% Proof
Load) the first engaged thread (closest to the head) will carry up to 33% of the applied load. The
ensuing threads will carry  27%, 20%, 12% and 8% respectively. Any extra threads engaged do not
carry any load.
 
rpatton said:
Higher Order Analysis
Ajax Fasteners has conducted a comprehensive Finite Element Analysis (FEA) on a generic bolted joint.
This analysis revealed some interesting facts regarding the micro level distribution of stresses [3]. In
summary, it was found that the threads are not equally loaded and at typical applied load (65% Proof
Load) the first engaged thread (closest to the head) will carry up to 33% of the applied load. The
ensuing threads will carry  27%, 20%, 12% and 8% respectively. Any extra threads engaged do not
carry any load.
Click to expand...

Interesting.
It would be interesting too to see what practical research they based this analysis on ?

First thoughts are that if the first thread was that heavily loaded, it should deflect enough that the load trasnfers to the 2nd thread etc etc. Perhaps strain gauges fitted within a multi-part nut may show something ?

So will a nut with only 1 round of thread withstand being torqued to 33% of the torque of a complete nut ?

Straying into theoretical territory here...
 
Rohan said:
[Does that mean that a nut with only 2 threads in it could take 75 % of the torque of a full nut ? I'll let someone else experiment with that one....
Click to expand...
It'd take a wing nut to try that.

Rohan said:
And what about these tall nuts, does that mean they can't take more torque than standard ones ?
Click to expand...
They should be able to take more "over torque" (as the 1st threads let go the following threads come into effect).

Maybe that's why the book just kinda threw that one out there with out substantiating it, there are many variables to consider:
1 - Threads are formed in a variety of different alloys.
2 - Fine Threads = stronger - VERSUS -Coarse Threads = weaker (but less turns for faster on/off).
3 - How the threads were made in the 1st place, Rolled Threads are stronger than Cut Threads.
4 - When Threads are more than 2 pages long, there is little more being said. (well I got away with my wing nut joke so... :lol:

to continue, there must be a sliding scale for any given situation. There does seem to be a general consensus that the 1st threads carry the brunt of the load.
 
While on the subject of those Norvil bigend nuts for dommies, I'd be a little nervous that these nuts are not nice and black - showing that they have been heat-treated and are hi tensile. Very hi-tensile in fact they need to be.

So are they ????

Commando head to barrels studs - too short?
 
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