Thread types on a Commando ?.

[Josh Cox]

Was wondering what are the common threads you'll find on a Commando ?.

Have done a search on this topic and found very little info other than the mention of cycle thread (BSC) in the barrells.

 

[L.A.B.]

Have done a search on this topic and found very little info other than the mention of cycle thread (BSC) in the barrells.

That's surprising?

The common thread types found on Commandos are:

Whitworth(BSW or "WW")
BSF
BA
CEI/BSC(BSCycle)
ME
BSP
UNF
UNEF
UNC
Metric (spark plugs and spin-on filter)

Many threads can be identified if the part number is known: http://stainlessbits.com/link12a.html

 

[Tintin]

Was wondering what are the common threads you'll find on a Commando ?

Rough guide: Frame and suspension UNF, engine mostly BSF (the timing cover bolts on mine were UNF IIRC) and some CEI thrown in for maximum confusion. Yes, you'll need WW and AF tool sets, a vernier gauge and a thread gauge to survive wrenching a Commando....



Tim

 

[L.A.B.]

(the timing cover bolts on mine were UNF IIRC)

Timing cover screws were originally 1/4W (20tpi) although they were changed to 1/4-20 UNC?

 

[Tintin]

(the timing cover bolts on mine were UNF IIRC)

Timing cover screws were originally 1/4W (20tpi) although they were changed to 1/4-20 UNC?

Yes, right, I just checked it and it is UNC.


Tim

 

[79x100]

The threads most commonly found on a project bike are the universal type known as "crossed" and "stripped"

 

[frankdamp]

I suspect the 1/4-20 UNC and 1/4 Whitworth are the only threads tha are intrerchangeable. I think just thread form (angles and so forth) are slightly different. I don't think any other thread system matches the "Cycle" threads, whcih were all 26 TPI regardless of diameter.

Whitworth wrenches are sized based on the diameter of the bolt, not the across-flats size of the nut. The old equation was a/f = 1.125x bolt diameter +0.25. Later it changed to 1.25x bolt diameter +.125. Most Whitworth wrenches fit either case, but very few are compatible with US a/f sizes or metrics. I don't remember what drove the nut sizes on Cycle-threaded bits.

 

[xbacksideslider]

Not that it occurred here, I just want to say that there is a tendency to run down Norton, and many other British marks, because of this issue.

It is worth noting that our engine's development finds its roots between the great wars.

Those engineers were actually closer to an earlier era when steam powered the world. They were close in time to those engineers who worked in an era when for the FIRST time questions such as what thread pitches might be, or ought to be. They had to answer questions such as what diameters and pitches would carry what loads and they did it while the science of metallurgy was in its infancy.

I cannot imagine what it must have been like before steam. I cannot imagine non-standard threads and arguments about what the correct thread should be.
To me, it is a pleasure to be able to reach into the engineering past by way of a Whitworth wrench and a BS thread gauge.

That tendency, to denigrate older machines on this point, betrays an arrogant ignorance of those great thinkers who came before.

 

[L.A.B.]

I suspect the 1/4-20 UNC and 1/4 Whitworth are the only threads tha are intrerchangeable. I think just thread form (angles and so forth) are slightly different.

Whitworth and UNC thread sizes from 1/4" to 1 inch have the same tpi, (except 1/2") although as you say the thread forms are different, so Whitworth and UNC threads are technically not interchangeable.

I don't think any other thread system matches the "Cycle" threads, whcih were all 26 TPI regardless of diameter.

1/4 Cycle and 1/4 BSF are the same pitch (26 tpi)-but they have different thread forms so one type can easily be mistaken for the other.

 

[splatt]

whitworth threads are 55* nf unc metric are 60*, ba threads are very close to metric threads, but are 55* to , from memory, I read somewere that the whithworth threads are a superior thread, but I'm not a design engineer so cant tell you why

 

[L.A.B.]

I read somewere that the whithworth threads are a superior thread, but I'm not a design engineer so cant tell you why

The Whitworth thread roots are radiussed, which I believe is supposed to resist fractures better than the sharply cut Unified thread.

http://www.boltscience.com/index.htm

 

[daveh]

While we are on this subject, can someone please tell me the thread form of the gearbox adjuster rod mounted on the cradle (Part no 062654)?

It looks UNF, but I need to be sure because I want to order some new nuts (but without taking the old ones off until I get the new ones). I have a Mark 1 850.