1934-36 OW/OW1 models, a study in contrasts. This article first appeared in the LDMCC New ConRod magazine, Sept/Oct 2019 issue.
Roger Gibbard’s recollections in the previous issue about his OW1 brought to mind the numerous incongruities of the 1934-35 OW and OW1 models. It was a new model to replace the ohv F and G of 1931-32. Advertising showed the F/G would have continued into 1933, though that year the factory was so financially strapped that apparently only a few D33 models (600cc side-vale) were manufactured and sold and probably no F/G33 models. So it is all the more amazing that they came out with a new ohv model in 1934, though it was a mixture of something new and something old. Bear in mind, it would have had to been developed in 1933 with the manufacturing drawings released in Sept/Nov of that year. The efforts in 1933 are all the more impressive in that they not only introduced a new ohv model, but reintroduced an entire model range. The lightweights were just a freshening up of the 1932 range, but still would have required financial outlay beyond the ability to use up existing inventory. The heavyweights had some redesign work to eliminate the oil sump (legacy of the S6 models), a change to gear type oil pumps, and alterations to use the Lucas Magdyno rather than the BTH M2 magneto and separate BTH pancake dynamo that Douglas had been employing. There was also one entirely new model, the 2-stoke Bantam; though there is some indication this was intended to be a 1933 model offering and some may have sold alongside the D33.
The F31 & G31 model of 1931-32 that preceded the OW/OW1. 
The 1934 OW/OW1 model. 
1934 OW/OW1 showing the exhaust side. 
That the factory considered the OW/OW1 a continuation of the F/G can be seen in the use of the engine prefix code: 5/F for the 500cc and 6/G for the 600cc. Borrow from the F/G it did. Cylinders and heads with enclosed valve gear were carried forward without alteration. The crankcase was a different matter. The crankcase pattern, which since introduction with the 1924 OB/OW models had only received incremental updates, was discarded and replaced with an entirely new pattern. Coarser timing gears (16 vs. 18 diametral pitch) and a taller gear train allowed it also to utilize the Lucas magdyno. The timing chest joint changed to a more rectangular shape, and the engine now clamped onto frame tubes 4-3/4 inches apart. This was a break from the 6-1/2 inch spacing of the F/G with stretched back to the RA model of 1923. Why they changed this I don’t know; perhaps to preclude the practice of engine swapping that was keeping older models in use long after everyone else bought a newer bike! Internally, it used the same 82mm crankshaft as the F/G model, which were carried forward from the Dirt Track (DT). The two OW1s that I have also utilize the “IN.OP.20” camshaft seen in many DT engines and it makes for a very good road cam. The conrods are about 3/4 of an inch shorter than the DT and were inherited from the F/G. While the F/G models had the same stroke as the DT, it had a shorter cylinder, necessitating a shorter conrod. Whether they shortened the cylinder to make room for the valve enclosure or it was to utilize the conrod stampings from the aborted short-stroke DT (c1932) we shall probably never know.
Timing chest cover of the 1934 OW/OW1. 
Cylinder head with cast aluminum valve enclosure behind. The cylinder porting remained exactly the same as the Dirt Track but were not eased or polished. 
Detachable rocker arm perch shown sandwiching the inner half of the valve cover. The new perch design required slightly longer valve stems. 
The gearbox is basically the same as the final iteration of the 4-speed ‘box used on the Greyhound and Mastiff heavyweight side-valves (S6 descendants). The cluster is turned on its side and mounted up under the seat (standard practice since the OB/OW of 1924), so it had a new gear casing unique to the OW/OW1. As Roger mentioned, it was available in hand or foot change. Consensus is the hand change is much more reliable. The fault with the foot-change appears to be with the positive stop mechanism. The springs that return and center the shifting paws have to work in an arc shaped bronze housing, the end of which is externally visible on the cover, which creates a lot of drag on the springs. Initially (going by catalog pictures) the foot change lever was positioned absurdly high, about the level of one’s shin.
Early 1934 foot-shift model with direct and absurdly high pedal. Douglas updraft barrel carburetor. 
Revised foot-shift with remote linkage and pedal pivoting on foot rest. Amal updraft carburetor. 
By June of ’34, a lever pivoting on the foot rest and a linkage up to the gearbox was available. It is alleged that the cast aluminum primary chain case was also inherited from the F/G, but since the OW/OW1 frame was slightly taller, they cannibalized two, cut them apart and gas welded them back together! Yet there are problems with this theory. The factory drawing for the F/G primary casting survives, and it shows significant differences between the lower portion of the F/G casting and what is used on the OW/OW1. Also, there are alterations at the upper end too. Not only is the casting cut away to clear the secondary chain line, but there is a boss following the new opening. More than just sawing away at existing castings, additions were made to the pattern. So either there was a later changes to the F/G casting not documented, or the story about the factory altering obsolete castings is wrong.
The OW/OW1 primary chain case with numerous repairs! 
So new patterns for the engine a gearbox and probably new patterns for the primary! The primary cover was a sheet metal pressing. I am not certain if this was the same as the F/G; but it looks like it is. The F/G used a cross-over transmission (modified from the DT) with the final drive on the right, but the 4-speed that the OW/OW1 acquired from the heavyweight side valve range had the chain line entirely on the left-hand side. That would not necessarily precluded the use of left over F/G primary components, as it would just mean cutting a slot for the final chain to exit. The primary chain case is one of the weakest links of the OW/OW1 models. It needed to be quite thin to stay out of the way of the roller chain and fit between the flywheel and crankcase. Also the attachment at the upper and lower end was something any designer should have been ashamed of! The upper end attached to a false back that went behind the sprocket. This allowed the case to be removed without disturbing the sprockets. So far, so good. But the back plate attached to the gear case by just two small countersunk screws places not very far apart and lacking stability. Further aggravating the situation is they are practically lined up with the gearbox mounting studs, so are only tapped in about 5/16 of an inch into typical low-tensile Kingswood aluminum. The attachment at the lower end is not much better with a lot of the casting ‘skeletonized’ to clear various objects such that what is left is fragile and prone to fracture. The entire primary appears to be a last minute thought.
OW/OW1 gearbox (hand-change). Mounting holes for the primary chain case false back are circled. 
Primary chain case off for repairs, again! The primary false back remains attached to the trans. 
The OW/OW1 was the first ohv model Douglas to have the chain line entirely on the same side. This required some alterations to the F/G frame. The rear lugs are laterally symmetrical (or very close) so swapping them side to side is not a problem. With a tube and lug frame, changing the offset for the rear stays to clear the chain is no problem either. However, because the OW/OW1 frame is slightly taller, the angles of the chain stay triangle are slightly different. The rear axle lugs (part #8032 & 8033) had been introduced with the I.o.M and OC model back in 1925-26 and they did not see fit to change them now. The sockets for the tubes are bored at a slight angle to the lugs! Going up and forward from the rear axle, the gearbox platform is different in that it springs directly forward from the level of the cross tube. Traditionally on the DT, TT, OC models, etc. it swept downward slightly so the gearbox hung closer to the rear cylinder. This change in gearbox platform casting was introduced with the F/G, so the OW/OW1 reused that same casting. The F/G in turn seems to have gotten the idea from the short-stroke DT chassis that also had a shorter, and lower frame. While the same idea, the casting on the short-stroke DT is not exactly the same in detail and unique to that model.
The OW/OW1 had a new saddle tank with inset instrument panel common across the entire 1934 heavyweight range. The catalog specification states the tank is chromium plated, with Douglas super-marine blue panels lined in gold. The formula for the blue had changed from previous years, causing it to show up as very pale in black & white photography. So much so that Douglas saw fit to comment on it in the trade magazines at the time, assuring readers that in reality the blue remained the same shade as before. In the past it has been stated that none of the tanks were actually plated but rather painted black. However period photos and survivors with known province show that some indeed were plated. In the 1935 catalog illustration, the tank is shown in the alternate scheme of black rather than chrome, the paneling remaining as previously stated. Even though it is stated the finish is chrome, with no mention of an alternate finish. Most of the big side valve models seemed to have the black & blue scheme, though occasional exceptions of a plated tank are known. The reality may have been chrome was an optional extra, or choosing black enamel effected a discount, but no information has been found to clarify. The 1935 petrol tanks were different (across the range) as they had additional reinforcing to the mounting points. These reinforcing plates are visible from underneath the tank. It is believed that these tanks were made by another firm for Douglas.
1934 OW/OW1 petrol tank showing modification for twin front down tubes. Tank was originally chromium plated. Design shared with Z1 model. 
While this petrol tank is from a 1936 single down tube model, no instrument panel, it shows to good advantage the four reinforcing straps added to the 1935 big twin mounting bosses. 
Addendum: The reinforcing straps may not have started until 1936. Some 1935 models do not seem to have them. One difference between the 1934 and 1935 petrol tanks is the mounting of the instrument panel. The 1934 has the instrument panel screws threaded into two posts that are attached to the instrument panel well floor. 1935 tank have the instrument panel screws threaded through two heavy sheet metal tabs welded to the fore and aft instrument well walls.
Since the OW/OW1 was a full duplex frame, the petrol tanks for it required an alteration at the front to clear the splayed down tubes. This it shared with the 750cc 1934 model Z1 side valve, whereas the model Z (600cc) used a single down tube. The fit is a little tight with the head stock, suggesting they arrived pre-altered rather than done at Kingswood. The head stock was different from the previous F/G; the F/G used the same separate upper and lower castings as the DT, and indeed the castings dated all the way back to the RA model of 1923. Or according to catalog illustrations that is what they intended to do. The OW/OW1 used a one-piece head stock lug with taper roller bearings top and bottom, and presumably it was also shared this with the duplex front down tube Z1 model. It is bored to a very thin wall between the bearings and at least two are known to have fractured at this location. At some point very late the F/G changed from the loose balls for head stock bearings (a.k.a. DT), to taper roller bearings and the front fork from the S6 model. Perhaps when they finally ran out of the venerable DT girders! (Side note: these girders were introduced with the RA; and the RA, OB/OW, G/H28, DT/SW5 and initial F/G 31 girders are all very similar but each are slightly different and they are not fully interchangeable.) Further sustaining evidence is the factory changed the F/G31 head stock part way through the program is the factory frame drawing shows the update to the head stock but they did not get around to penning in the new part numbers. Like the head stock it replaced, it was a 2-piece design so it is not the same one subsequently used on the OW/OW1. With the new head stock, the OW/OW1 acquired new forks, but these were shared across the 1934 heavyweight model range. The S6 style forks were discontinued for the heavyweight side valve models. If remaining stock were used up on a cheaper model (common Douglas practice), it did not show in the 1934 catalog. As already mentioned, the lower part of the fame had new, narrower spacing for the engine mountings.
The 1934 heavy weights had a new style mudguard, a deep c-section with a narrow, high rib, which of course the OW/OW1 shared. This must have been too expensive, as by 1936 model range they were back to the old profile they had been using since the twenties!
1935 rear mudguard, showing the correct profile, stays, and chain guard for 1934-35.
The detachable rear section unique to the 1935 models only. 
Wheel rims were chromium plated. The spokes and the center well were painted black and a blue pinstripe each side. This is another detail where experts disagree. I was told the pinstripe was gold, but I have the original rims for my 1934 OW1 and they are certainly Douglas blue. Whether the blue pinstripe was unique to the OW/OW1 I do not know, but it would seem more likely they used the same inventory of rims on all the heavyweight models. They were using a gold pinstripe by 1936, such as on the 500/600cc Aero side valve models. Presumably the blue pinstripe carried through on the 1935 OW/OW1 models unchanged from ‘34. My 1935 OW1 has the rims have been repainted in a hideous turquoise color (as with the rest of the bike) and it is doubtful any evidence of the original color remains underneath.
The 1934 OW/OW1 specifications.
Cover of the 1934 OW/OW1. Except it is a 6D light aero engine shown! 
An interesting bit of trivia is that the brochure for the 1934 OW/OW1 does not show an OW/OW1 engine on the cover but rather a 1932 6/D light aero engine. It can be identified by the propeller flange and the timing chest mounted AC fuel pump just visible on the far side. As such, it was based on the F/G crankcase which was not the same as the OW/OW1. Part of the brochure talks about Douglas’ certification for aero engines so perhaps the felt the substitution was acceptable. They do not say it is an OW/OW1 engine, but on the other hand they do not say it is not!
While the OW/OW1 was the successor to the F/G models, the F/G designation was dropped and they were cataloged in 1934 as OW and OW1. What ‘OW’ might have stood for and how they arrived at that designation in not certain. Other models that year had a letter/numeric designation.
X, 150cc 2-stroke with magneto lighting
X1, 150cc 2-stroke with dynamo lighting
Y, 250cc
Y1, 350cc
Y2, 500cc (based on 350cc crankcases, i.e. a continuation of the C32)
Z, 600cc
Z1, 750cc
So the “W” of OW does fit in with this ‘end of the alphabet’ pattern, as does the appending of a number one to differentiate between the larger and smaller displacement. Also, the model W had been the top of the range 2-3/4hp model back in the belt-drive era that had morphed into the CW, or all-chain drive W. So perhaps OW was the ‘Overhead-valve W’. Officially in the catalog, the model designation was printed O.W. and O.W.1.
The last OW model was the 350cc counterpart of the 1924-25 600cc OB model. The OW/OW1 continued in the 1935 model range, now additionally called the “Speed Special”. The other models acquired names too and a numeral five was prefixed to the model code (Except for the OW/OW1!). So we have:
OW, “Speed Special”, 500cc ohv
OW1, “Speed Special”, 500cc ohv
5X, “Bantam” 150cc 2-stroke with magneto lighting
5X1, “Bantam” 150cc 2-stroke with dynamo lighting
5Y, “Comet” 250cc
5Y1, “Cotswold” 350cc
5Y2, “Blue Chief” 500cc (new model, subsequent basis of the 500/600 Aero of 1936)
5Z, “Wessex” 600cc
5Z1, “Powerflow” 750cc
“Endeavour” 500cc transverse, shaft drive.
The 1935 OW/OW1 catalog specifications.
Timing side of a slightly adulterated 1935 OW1. 
The OW/OW1 was dropped from the 1936 catalog, though given the slow sales surely a few left overs were still available if a customer inquired for one. For a model that was only cataloged for two years, they did not get a lot of mileage out of some of the new patterns and designs that were incorporated; especially when you consider the years in production (with incremental alterations) of the preceding components like crankcases and gearbox patterns.
The 1935 OW/OW1 did have some minor differences from the 1934 models. The ’34 models did not have an airbox (as the F/G models did). The airbox returned for ’35. The carburetor was an updraft barrel type device manufactured by Douglas. It was not a very good instrument, personal experience talking! While the catalog specifications only say “Douglas single lever”, i.e. an automatic type suitable for twist grip operation, drawings for the 1935 airbox show it could be machined to suit either this or an updraft Amal like used on the S6 models. When the later was fitted, an unsightly notch along the rear edge had to be cut out of the airbox to clear the Amal flat bowl.
The exhaust system changed from the traditional two-into-one pattern with an S6 style silencer in 1934, to a dual exhaust system using a pair of cast alloy silencers as used on the Endeavour, Blue Chief, and certain other 1935 models (and subsequently the silencer was used on the Aero models from 1936-38). At the rear and in common with other ’35 heavyweights, was a detachable rear section of the mudguard. I hesitate to say quickly detachable! One still had to unbolt the rear stays and the chain guard. So far as I know, the knock-out rear hub option for certain heavyweight models of 1935 (like the Blue Chief) was not offered on the OW/OW1 models.
The OW/OW1 cost £58- in 1934, same price for either the 500 or 600cc. The electric lighting was £5-15s-0d extra. In 1935, the price jumped to £63-15-0.
1934 OW1 hand-shift model. Not 100% authentic. 
I know of nine 1934-35 OW/OW1 survivors, with possibly a tenth (though maybe in an Australian landfill) within and without the London Douglas Motor Cycle Club (LDMCC) registry. Numbering started at 101 and the highest number recorded is a frame at FR129. Batch production is evident as all the engines and gearboxes are also numbered in a similar range, though none were paired up with matching numbers. Surviving engines run from 6/G102 to 6/G119 and the transmissions G/106 to G/113. The presence of a K/101 gearbox (a 1935 prefix) suggests the numbering was ‘reset’ to 101 for the transmissions. This change in prefix and numbering may be due to the change from an involute to a stub tooth form, though my ’34 box looks like it has stub teeth. Regardless, the frames and the engines did not change prefix and the numbering for them is assumed to be sequential spanning 1934-35. This does bring up an anomaly in the engine prefix codes in Jeff Clew’s book “The Best Twin”. There it states the 1935 OW/OW1 engine should have a I/5 or I/6 prefix, for 500 or 600cc respectively. This is not borne out by surviving examples, which while they have the 1935 airbox, continue with the 1934 engine crankcase prefix code. As a slow seller (more on that momentarily), they may have had plenty of engines from the 1934 batch in stock that just needed fitting of a new timing cover/airbox to updated it to a 1935 model. Since the frame/engine/gearbox numbers do not match exactly, it is hard to say when they switched over from 1934 to 1935. The OW1 in the H&H auction (July 30th 2019, so will be over by the time you read this) has engine 6/G110 with a ’35 airbox and gearbox K/101 (’35 prefix). Frame is FR114. All the ohv valve engines were reputedly assembled in the experimental department (Source: former employee Eddie Withers) and then brought out to the general assembly area to be mated to a chassis. So it could be the tenth or fourteenth one off the line depending on how you look at it, assuming they were even in numerical order! Nor could one even say that it is the first one with 1935 features, as the next ’earlier’ survivor is FR109, 6/G106, F/104 (1934 features); so there is a gap of uncertainty. But it does suggest there were only around ten or so OW/OW1s made in 1934; give or take. Then there are 1935 models up to frame FR126, suggesting a further sixteen or more (give or take!) Perhaps eighteen, as there is one known example of a “I” prefix engine; 75/I 101. This is a 750cc OW1 (listed in Jeff Clew’s book as 75/1) in frame FR129. Presumably this was a final ‘one-off’ to a customer order (larger cylinders and piston), and as the highest frame number recorded likely represents the top end of the frame numbering range. So twenty-eight potential frames with about ten made in 1934 and the remainder in 1935 is my best estimate.
©19Jul19, Doug Kephart, Glen Mills, PA, USA
Corrections & revisions. 11Nov19
Addendum added about petrol tank. 10Oct21
