Identify 1920s (?) Douglas gear set

[cardan]

I have had several boxes of gears, shafts and selectors - all Norton/Sturmey-Archer I thought - in the shed for years. Time to sort it out. Lots and lots of Norton/SA (yell by pm if you need anything late 1920s-doll's head, including some close- and wide-ratio gears), but amongst it all was this Douglas 3-speed gear set.

From left to right in the picture, the gears are:
Mainshaft 16 19 23
Layshaft   21 18 14

Dimensionally it's similar to OB, but it has a spline on the output sprocket end of the mainshaft, rather than a taper.

What am I looking at?

Cheers

Leon

[cardan]

Looking at old posts, I see the teeth numbers match the "wide-ratio" gear set made by Doug for road-going SW5s, TTs and the like. https://www.douglasmotorcycles.net/aa-files/images/doug/2006/SW-gears/full_gearset_advert_e.pdf

But the mainshaft on my gears is only 1/2" (0.490" actually) inside the sleeve gear - seems a bit on the spindly side for a 500 ohv?

By the way, I get internal ratios for the gears as above of  2.16:1, 1.39:1 [Edit: not 1.36:1 sigh] (not 1.56 as given by Doug?) and 1:1.

If the gear set is for SG/TG/UG/VG boxes, perhaps we can make a table of the gear ratios/teeth numbers for the various boxes. With the gears is a 15-tooth (rather than 16t) sleeve gear, for a wider set of gears still. I found some ratios for the OC in an earlier post, but these are something different.

Cheers

Leon

[cardan]

I found some ratios for the OC in an earlier post, but these are something different.

The 15-tooth sleeve gear I mentioned, coupled with a 22-tooth layshaft gear would give:
Mainshaft 15 19 23
Layshaft   22 18 14
and ratios of 2.41:1, 1.55:1 and 1:1.

These are the internal ratios given in OC/27 handbook. Not sure what gearbox prefix this corresponds to.

Leon

[Hutch]

Leon,

I have looked inside a TG prefix gearbox (not mine) and the ratios are the same as you state above;

mainshaft  15 19 23
Layshaft    22 18 14

I gather this would be the wide ratio OC gearbox. It has a spline on the output sprocket end of the mainshaft.

If I get a chance I will get the measurement of the diameter of the inside of the sleeve gear for you for comparison with the one you have.

Cheers

Ian

[cardan]

Excellent! To which I can add:

QG ratios:
Mainshaft  16 19 22
Layshaft   20 18 15
and ratios of 1.83:1, 1.32:1 and 1:1
Yes, that combo is 16-20! (I note that Norton did similar things in their racing boxes - gear cutting is a mystery to me.) A very close ratio box, presumably for racing.

DT from parts list (presumably YG ratios):
Mainshaft  17 19 21
Layshaft   20 18 16
And ratios of 1.54:1, 1.24:1 and 1.1
As Doug has often pointed out, the ratios in this box were intended as choices to suit different tracks rather than for changing while riding. Useless in a road bike, or even a racing bike if the race has a standing start.

Beginning to make sense...

Leon

[cardan]

Thanks Doug for your marvelous document on Douglas gear ratios: https://www.douglasmotorcycles.net/aa-files/images/doug/2006/SW-gears/gear_ratios.pdf

A fun read! And now I understand why when I suggested some years back that the QG box had a 1.8:1 1st gear you were skeptical.

The 16/20 sleeve-gear pair in the QG box looks to be the real thing, with Douglas stampings. Since 16/21 is a "valid" combo (total of 37 teeth), is all the weirdness in the 20t gear? Or are there two different 16t gears - one for 16/20 and another for 16/21?

Cheers

Leon

[cardan]

From a seemingly-unmolested OB gearbox (PG8xx, so not an early example):

PG ratios:
Mainshaft  16 19 23
Layshaft    21 18 14
and internal ratios 2.16:1, 1.39:1, 1:1

Presumably there is a "standard" OC gearbox that uses the same gears? (Tempting to say the SG, even though it's listed as "OC close ratio" in The Best Twin.

Despite the reversed positions of the shafts compared with the later boxes, the internals of the PG look pretty much the same. This PG has the internal detents for the selector - see the photo at the top of the thread. There is a captive spring-and-plunger in the top of the gear case that does the indexing. The housing for the spring projects through the top of the casting as a dome on the outside. Also, there is a complete "bridle" around the sliding gear, and a taper for the sprocket. The QG has no internal indexing, "fingers" to engage in the sliding gear, and spline for the sprocket.

Both the PG and the QG boxes have the 1/2" mainshaft inside the sliding gear - I guess even the later boxes have this?

Does anyone happen to know the ratios in a UG box?

You'd have to think that the alphabetical designators for the various boxes were chronological: PG, QG, (ignore RG - used for EW), SG, TG, UG, VG, (ignore WG 600 EW and XG D28) and YG. While OBs were in the range, they didn't need a sporty gearbox because the RA was the sports/racing bike (with an MG gearbox). QG was likely the racing box for the 1925 TT in June (in March 1925, Rudd's racer used a PG-like box, with the mainshaft at the back, and Clew suggests QG for 1925 TT). It could also have been the "standard" box for the early OCs, but not with the very close ratios that live in the surviving QG I examined - see above.

That's why I like "SG" for the standard OC box, despite Clew describing it as "OC/26 close ratio". Does the SG have internal indexing???

[Edit: Just to be clear, I'm thinking that my mystery gear set - same ratios as PG, same bridle mechanism as PG, same indexing mechanism as PG, but with spline for the sprocket and the shafts rearranged - is likely "road going OC". Possibly stamped SG.)

Leon

[cardan]

Go ahead! Fill in the gaps or provide alternate suggestions:

BGGRs (Best Guess Gear Ratios): (first, second, third)

PG     2.16     1.39     1     Standard OB, mainshaft at back
QG     1.83     1.32     1     Close ratio racing box, 1925 TT etc
SG     2.16     1.39     1     Standard OC
TG     2.41     1.55     1     Wide ratio OC
UG        ?        ?         ?     Sports close ratio, 1926 TT etc.
VG        ?        ?         ?     Competition gears (extra wide ratio)
YG     1.54     1.24     1     DT (these ratio also listed for 1929 two-cam racer, but surely too close to use?)

[EW-Ron]

Thanks Leon, about what I thought.

Rather than clutter up the thread with irrelevant SA stuff, may I rephrase
the question to are these 3 speed gearsets being discussed a 'crash' box ?
Not having yet experienced the joys of vintage motoring...

[cardan]

[Hi Ron, I'm putting this in parentheses so we don't get into trouble! E1V is the prefix for the part numbers relating to a 4-speed Sturmey Archer box. In this case, I'm not sure if this is the part number for the case, or the gearbox number itself. Cheers, Leon]

[Hutch]

Leon,

Good progress on the list of gearbox ratios!. Just a thought; the 1927 OC brochure lists the gearbox ratios (shown in the attachment) and these are the same as the ratios in the TG gearbox I have seen (also seemingly unmolested). From this would it be more accurate to say that the SG gearbox was a "close ratio OC" rather than the "standard OC" ? It might be that the TG gearbox was the "standard" OC box and the closer ratio SG was an option?.

Cheers

Ian

[cardan]

Hi Ian,

I don't know!! But you make a good point.

I see I have to change my notation. Let's call the SG "mid ratio" (neither close nor wide) rather than "standard", to avoid confusion.

That way we can say that, in 1927 at least, the OC came standard with the TG (wide ratio) gearbox.

My alphabetical/chronological argument suggests the SG came after the QG (mid 1925) and before the TG. The SG is a candidate for the first gearbox fitted to the OC. It may, or may not, have come standard with the 1926 OC.

Leon

PG     2.16     1.39     1     Fitted as standard to OB, mainshaft at back
QG     1.83     1.32     1     Racing close ratio, fitted to June 1925 TT bikes, etc.
SG     2.16     1.39     1     Mid ratio
TG     2.41     1.55     1     Wide ratio, fitted as standard to 1927 OC
UG        ?        ?         ?     Sports close ratio, 1926 TT etc.
VG        ?        ?         ?     Competition extra-wide ratio
YG     1.54     1.24     1     Extra-close ratio, fitted as standard to DT (these ratios also listed for 1929 two-cam racer)

[cardan]

Maudes Motor Mart sold Douglas motorcycles directly to the public, but also supplied "the trade withing the London area and in Devonshire and Staffordshire". In November 1925, Maudes advertised no fewer than six variants of the newly announced OC/TT models:

Model OC 596cc Solo
Model OC 596cc Combination (i.e. bike and sidecar)
Model OC Solo Sports (elsewhere said to have aluminium pistons, vs cast iron on the standard OC)
Model OC TT Solo (i.e. IOM TT, presumably a 596cc)
Model OC 600cc TT Combination
Model OC 500cc TT Solo (i.e. IOM TT)

My guess is there would be different gearboxes on different machines. Say TG on the "cooking" combination, SG on the Solo Sports, UG on the 500 TT Solo... 

Leon

[Hutch]

Hi Leon,

Yes "mid ratio" could be a good way to describe the SG gearbox to save confusion between it and the closer ratio versions.

Just to add another option on the OB front, from The Instruction Book of the Douglas Motor Cycle O.B. & O.W. Models April 1925 they list that optional wide ratio gear sets were available from the factory. These appear to be the same ratios as the later OC TG prefix. No clues as to whether Douglas used a different prefix than PG for these wide ratio gear sets. So the "standard" OB gearbox was "mid ratio" and the optional box was "wide ratio" - opposite to OC?!

A quick look at the LDMCC Machine Register 2014 lists a TG gearbox with the serial number TG 258, attached to an OC. So it appears that at least 157 TG prefix gearboxes were made for the OC. If we use the usual Douglas practice of starting at serial number 101, and that maybe 300 or so OCs manufactured, TG prefix gearboxes would have been on approximately 1/2 of the OCs manufactured? This could be possibly explained by the number of OCs leaving the factory with sidecars attached compared to sporting solo machines??

I had a look for SG prefix gearboxes in the machine register but my quick scan didn't reveal any listed so I cannot deduce any further information from that other than they are possibly scarcer than the TG variety! I agree that, obviously, closer ratio boxes would have been supplied on the more sporting variants of the OC.

I have seen a picture of the OC-TT (cannot find it at the moment), but from memory it does look a little bit different from the cooking version of the OC .......:-)

-Ian

[cardan]

Thanks Ian: nice info.

There is at least one mistake, and I hope there is another! The obvious mistake is in the bottom table, where the column "1st 2nd 3rd" should read "3rd 2nd 1st". I'm hoping there is another mistake in the 2nd gear for the solo OW (350 ohv). As it stands the ratios would be 2.19, 1.20, 1 which would be pretty weird. Let's assume 2nd gear for the solo OW is an error: it's pretty likely that ALL sliding gears are 19T, coupled to 18T fixed on the layshaft.

So, yes, there was a wide ratio option for the OB/OW, with ratios as per the TG box. It looks like the OB (solo and sidecar) and the OW (solo) all used the "mid ratio" 2.16 1.39 1 gears, with the wide ratio gears fitted to the OW in sidecar form, and otherwise to special request.

(Note there are some rounding errors because of the "fractional" ratios in the OB/OW tables.)

Cheers

Leon

PG     2.16     1.39     1     Fitted as standard to OB, mainshaft at back
PG?    2.41     1.55     1    Wide ratio, fitted to OW sidecar, and option for OW/OB
QG     1.83     1.32     1     Racing close ratio, fitted to June 1925 TT bikes, etc.
SG     2.16     1.39     1     Mid ratio
TG     2.41     1.55     1     Wide ratio, fitted as standard to 1927 OC
UG        ?        ?         ?     Sports close ratio, 1926 TT etc.
VG        ?        ?         ?     Competition extra-wide ratio
YG     1.54     1.24     1     Extra-close ratio, fitted as standard to DT (these ratios also listed for 1929 two-cam racer)

[cardan]

in the mid 1920s, Harold Hicks campaigned a 596cc ohv Douglas outfit for the factory. He dragged it around all manner of trials, including the Scottish Six Days Trial and the International Six Days Trial.

In the 1925 Scottish, a reporter for The Motor Cycle watched him climb one of the observed hills:

"H. M. Hicks (596 Douglas s.c.) changed neatly to bottom gear right on the funny bone of the "elbow", then seemed rather annoyed with the high revolutions of his o.h.v. engine."

I suppose the bike was an OB (he rode an OC in 1926), but from the description I guess he was using the VG "extra wide ratio, competition" gears! He would have appreciated the ratios in the 1926 ISDT where tough observed climbs were combined with speed tests.

At a guess, the VG gears could be the TG ratios, but with EITHER (a) a 14T sleeve gear (as Doug points out, perhaps just marginally possible as there needs to be a dog on the back of the gear) to give 2.70 1.73 1 OR (b) a 13/24 pair for first to give 2.71 1.55 1.

There are certainly 15, 16 and 17T sleeve gears. Has anyone seen a 14?

Cheers

Leon

[cardan]

Here's why option (a) for the VG gear ratios is unlikely. The attached photo shows two of the three-known sleeve gears: 15T on the left and 16T on the right. There is a 17T version.

Note that on the 15T version it has been necessary to cut into the dog drive. 14T might be just possible, but not a strong design at all.

My best guess for the VG gears ratios is option (b) 2.71, 1.55 and 1:1. I'd be pleased to hear the actual ratios if anyone knows them.

Leon

[cardan]

Here's a description of the 1929 IOM TT Model - the Dixon twin-cam design. I doubt many were sold. The over-all gear ratios of 7.91, 6.36 and 5.12:1 translate to internal ratios of 1.55, 1.24 and 1:1, same as the YG (DT) box.

These are pretty close ratios, but for a fairly flexible twin they might be OK for most road racing. Not much fun for up-hill hairpins, or rallying in modern traffic.

Leon

[cardan]

And finally to answer the original question...

The spring-detent indexing and the straight operating lever are (I think) only found on the OB gearbox. When the shaft positions were reversed for the OC/TT models, the space where the springbox screwed in was used for the cast-in adjuster, and the change lever was curved and oriented in the opposite direction.

The spline for the output sprocket is not very OB, but may have been used on very late OB boxes, or the shaft may be a later replacement.

I think the gearset is late OB, albeit the same as later boxes with the same ratios.

The photo below shows the OB configuration (left) and the OC/TT/DT configuration (right).

Cheers

Leon

[cardan]

ANd the mystery gearset in the same orientation.

[cardan]

For comparison, some mid-1920s non-Douglas standard, close ratio, and racing gears:

1.82    1.29    1   "the order of the day" for the 1923 TT ("Technical Aspects of the TT Races", Motor Cycle, 28 June 1923)
1.63    1.28    1    close ratios in Sturmey Archer CS gearbox, up to end of 1925 (12-pitch gears)
2.66    1.33    1    standard ratios in Sturmey Archer CS gearbox, up to end of 1925 (12-pitch gears)
2.16    1.33    1    close ratios in Sturmey Archer CS gearbox, 1926-on (10-pitch gears)
2.65    1.47    1    standard ratios in Sturmey Archer CS gearbox, 1926-on (10-pitch gears)

And the Douglas ratios:

PG     2.16     1.39     1     Fitted as standard to OB, main shaft at back
PG?    2.41     1.55     1    Wide ratio, fitted to OW sidecar, and option for OW/OB solos
QG     1.83     1.32     1     Racing close ratio, fitted to June 1925 TT bikes, etc.
SG     2.16     1.39     1     Mid ratio
TG     2.41     1.55     1     Wide ratio, fitted as standard to 1927 OC
UG        ?        ?         ?     Sports close ratio, 1926 TT etc.
VG     2.71?    1.55?   1     Competition extra-wide ratio
YG     1.54     1.24     1     Extra-close ratio, fitted as standard to DT, 1929 TT Model (two-cam)

Perhaps someone knows the original ratios (or teeth if you don't want to work it out) in a UG [edit: not QG as I typed] gearbox? Can anyone verify the VG ratios?

Cheers

Leon

[Doug]

Leon,

QG is listed by Jeff Clew as 1925 TT gearbox for the 4hp class and the solo OC. It does not specifically say if it is close-ratio or not. For a big open road course like the TT (rather than a closed circuit), I don't know how close a racing box would be to be most useful. Jack Nelson had an example of a QG box; though after all this time who knows what ratios may have been installed.

So the wide (TG) and close (SG) were alternate ratios for the OC and the QG as the standard. (Jeff Clew calls the SG as a close-ratio rather than mid-ratio.)

I believe the UG box, besides being used in the 4hp class of the 1926 TT, was the standard box for the SW5. However I have not seen any info as to what prefix code gearbox was actually fitted, or what the SW5 ratios really were. The circumstantial 'evidence' is based on them being suitable for a sporty model like the SW5, showing up on some extant examples, and conveniently surplus from the 1926-28 TT/I.o.M. models.

There are no unassigned prefix codes around PG for a wide-ratio version, unless Douglas did something like PG/A. They did do this occasionally to squeeze in more variants after the fact, the RG/ series for the 350EW being the most extensive example.

-Doug

[cardan]

Hi Doug,

I've learned a couple of things from fiddling with this stuff: (1) When the EW came in, particularly when it had some early production problems, EVERYTHING at Douglas was thrown at it, and the other bikes weren't very important, and (2) for the ohv bikes, there was a gearbox for every occasion!

Because of (2), I think it's best not to associate a particular gearbox prefix with a particular model, but instead with a particular bike. Sure there would be a "usual" gearbox for a particular model, but I reckon there would be variety in what was delivered.

The UG remains a bit of a mystery. There already seems to be range of ratios available from QG, SG, TG, VG and YG, it's hard to imagine what else was required! If I had to guess, I'd say close ratios between 2nd and top (very racy), but a lower first gear for better sport and road riding. Perhaps we will see.

I like the PG/A... suggestion. Does anyone have a PG/A, PG/B... prefix gearbox?

Cheers

Leon

[cardan]

Here are the ratios for the RA - IOM TT Model. They come from a document prepared by Douglas to help entrants in the 1923 TT.

The gearbox prefix is MG.

Mainshaft 17 19 21
Layshaft   21 19 17

Giving 1.53   1.235   1:1

Note that these ratios are almost identical to the later YG ratios, but are obtained using different gears. The pairs in the MG gearbox have teeth adding to 38; pairs in later boxes usually add to 37.

Summary of Douglas ratios:

MG    1.53     1.23     1     Fitted as standard to RA for the 1923 TT. Gearbox clamped to crankcase.
PG     2.16     1.39     1     Fitted as standard to OB, main shaft at back
PG?    2.41     1.55     1    Wide ratio, fitted to OW sidecar, and option for OW/OB solos
QG     1.83     1.32     1     Racing close ratio, fitted to June 1925 TT bikes, etc.
SG     2.16     1.39     1     Mid ratio
TG     2.41     1.55     1     Wide ratio, fitted as standard to 1927 OC
UG        ?        ?         ?     Sports close ratio, 1926 TT etc.
VG     2.71?    1.55?   1     Competition extra-wide ratio
YG     1.54     1.24     1     Extra-close ratio, fitted as standard to DT, 1929 TT Model (two-cam)

Leon

[Rob]

Leon,

to add another gear box into the mix I have recently stripped down a "FG" gearbox with the following layout.

15  19  23
23  19  15

Rob