Washers and nuts on mid 1920s Douglas

[cardan]

I'm getting fasteners organised for the RA/TW engine. The bolts that hold the crank case halves together are 5/16-25 tpi, with domes and pinned heads. The studs that hold the cylinders and heads on are also 5/16, BSW where they screw into the cases and 25 tpi at the top end.

By scrounging in countless tins and ice-cream containers I have a selection of 5/16-25 nuts in two hexagon sizes: 3/16W and 1/4W. The cylinder head nuts really need to be smaller (3/16W) to get a spanner on them, but I am assuming that the crank case bolts use the larger hexagon nut?

There are various 5/16 washers: mostly thicker flat washers, and some thackeray (double-coil spring) washers. What style of washer, if any, did Douglas use in the mid 1920s under crankcase nuts? Under cylinder/head nuts?

Thanks

Leon

[Doug]

Leon,

There were at least two 5/16-25 hex nuts in use at that time. #z385 was a tall nut of 7/16 inch across the flats, used for the OHV cylinder head nuts. This allowed just enough room for a thin ring spanner. According to the K29 spares list (DT model) this was also to be used for the crankcase half bolts too. There was also a 5/16-25 nut #711 that was 0.525 inch across the flats (5/16 Whitworth wrench opening) that was used for things like the magneto clamp studs, cam follower clamp studs, etc. However I have seen plenty of these used on crankcase halves as well. The smaller hex seems most needed on the two bottom studs where the nut sit in a counterbore. These part numbers date back to the 2-3/4hp era.

In conjunction with one or both of these was used part #735, a 5/16 heavy flat washer, that was 0.072 inch thick and about 0.620 inch diameter. This was used for the crankcase half bolts. Another washer #4990 was used for the cylinder studs, and was presumably thicker yet. This also (part number usage) from the K29 spares list.

I have made a run of about 500 each of the afore mentioned nuts and washers (except #4990 for lack of a verified example) in alloy steel, but I have yet to get around to listing them in the spares offered section as they ended up being a bit pricy and I do not expect them to sell! 

Unusually comprehensive spares lists for the 3-1/2hp Sports survive that would help throw some more light on this matter. Especially since it came just before and the K29 model just after, bracketing the RA model as it were. Unfortunately Douglas chose to (unusually) renumber all the parts for that model even though I an sure some of the hardware remained identical. So the fact that the 3-1/2hp Sports mentions which washer is used with the cylinder head is of little use without a cross reference. It might have also helped with the usage of the Thackery washers, which were Douglas' favorite when a shake-proof (?) washer was needed. The only place I can think of off the top of my head that I know these were used were with the engine mounting clamps. In the DT era the bolt heads were drilled for locking wire anyway, so the Thackery washers were superfluous.

-Doug

[cardan]

Thanks Doug. Based on your comments I have sorted the nuts more carefully; threads and hexagons. Most of the small, tall nuts are indeed 7/16" AF, however eight are 0.445" AF (3/16 W). They look original and are definitely 25 tpi, so it looks like at some stage there were similar but different tall nuts. Also found the thick washers, and the 5/16-25 nuts with 1/4 W (0.525") hex.

Next step is to put a complete set of fasteners together...

Leon

[cardan]

Hi Doug,
Just a note on the thick flat washers. From the witness marks on the crankcases, and photos of period and surviving bikes, I'm sure the washers under the crankcase nuts are smaller than those you mention. I found one that looks likely: 0.562 (9/16") OD and 0.068" thick - about the same size as the points on the hex nuts. Pretty sure these were used with the 1/4W-size nuts (0.525") for the crankcase bolts.
Leon

[Doug]

Leon,

Bear in mind my observations are based on the DT; a slightly later machine. Quite possible they were using something smaller on the RA; they were quite fanatical about saving weight at that time. And there is that smaller 3/16 Whitworth hex nut that you observed, that does not seem to have been utilized on later models.

In the illustration that you attached, it does indeed appear that they are using the 5/16 Whitworth hex nuts on the upper crankcase. I have seen this too on the DT, but by the time I get them they are quite the dog's breakfast so it is difficult to draw positive conclusions! Nor do I believe that just because the DT spare list say a certain washer and nut were used, that the factory built all DTs that way.

-Doug

[cardan]

Thanks Doug. On the same theme, do you know the specification of the bolt (technically hex-head screw) that holds the half time pinion on the end of the crank? It's hard to measure.

Leon

[Doug]

Leon,

I only have one sample to analyze. It has a major diameter of 0.378 inch, 28tpi, left-hand thread. Despite being a smidge over 3/8 of an inch, it is a sloppy fit in the crankshaft. I do not know if this is due to the crank thread being oversize or the pitch diameter on the screw being undersized.

Getting into the DT era the screw became 7/16-20 LH.

-Doug

[cardan]

Thanks - 3/8"(ish!) and left hand I had been able to figure, but 28tpi I would have not guessed! I will try that first.

Leon

[Doug]

Leon,

Yup, a perfect match on the 28tpi pitch gauge. But 28tpi? go figure. Does not match up to any thread standard that I know, so must be another Kingswood special. 

-Doug

[Jim]

Hello,

 3/8 by 28 tpi common on TSs, the wheel nuts have it as do the nuts that hold the gearbox on and the screw into the crankshaft is also, but they are all right handed, I find that 1/8 bsp is an alternative, it`s a smidgeon bigger but works for me,

 regards Jim

[Doug]

Jim,

I do not know the 2-3/4hp models very well.

That is a thought. I just looked up BSPT, and a 1/8 straight pipe thread is 28 TPI, and has a major diameter of 0.383 inch. Sounds like a possible match for the crankshaft pinion screw. I will see if I can find a tap and try it in the crankshaft as a gauge.

-Doug

[Bob M]

Hi Jim & Doug,
Why not have a 3/8 x 28 tap made? This isn't the expensive exercise you may think as really all 3/8" taps are made on the same base stock item so a special tap only means grinding a common blank 3/8" tap to your particular needs.
For that matter Jim, as you live in Victoria why not just wander along to Goliath taps in Brunswick and ask if they have a 3/8x 28 tap? I've always been gobsmacked at what they stock.
I've had a couple of taps made, the last being 5/16x20 and it although it wasn't cheap it wasn't impossible either and the tap will last for life.
Cheers, Bob

[Doug]

A left-hand 1/8 BSPT is probably not a stock item. But having taps made as Bob says it not terribly expensive. If you order a dozen you can get the price down to about US$35, TiN coating included. However since it is the hex head screw that Leon needs, it can be screw cut in the lathe.

-Doug

[Jim]

Hello Bob,

                  thanks for the tip about Goliath, another good place for odd size taps and dies is Tracy Tools in the UK,
and Doug,  I found a left hand 1/8 bsp tap on UK ebay, god knows what they are for, regards Jim

[Chris]

Hi all
I have always used a 1/8" BSP tap for the thread in the end of the crankshaft for 2.3/4hp models up to 1926 but they are definitely normal right hand thread. I obtained 3/8" x 28tpi taps and a die from Tracy Tools many years ago and they have been invaluable in making new studs and cleaning the holes for the gearbox mountings also wheel spindle nuts. Chris.

[Doug]

Doug,  I found a left hand 1/8 bsp tap on UK ebay, god knows what they are for, regards Jim

It boggles the mind! Jim, was the seller location near Kingswood? Perhaps a former neighbor picked up some ex-Work stock...      Would not that be something, genuine Douglas tooling. I believe the straight pipe threads were used on early electrical conduit, but still cannot see a purpose for a left hand thread BSPT.

What is also interesting was that Douglas was using 1/8-28 BSPT in right and left-hand for the same purpose (crankshaft pinion screw) on two contemporary models. Since the pinion is keyed, the chance of the screw backing once tightened out is nil, so I am not convinced there was the need for a left-hand thread.

-Doug

[chris mac]

I don't know very much about Douglas yet, but I can tell you that LH pipe threads are used in repair couplings where one thread is RH and the other LH, The two pipes are threaded appropriately and the coupling can then pull up without disassembly.
" Commonly" used in Gas piping where unions are not allowed except at equipment

[cardan]

I found an original screw for the RA/TW half time pinion. I also measure a smidge over 0.375" - 0.382 or so - and yes it's 28tpi, left hand, and screws in nicely. The hexagon is 7/16 BSW, and being RA the screw is drilled out for most of its length.

Leon

[Alan]

Just a comment, but many years ago I took some Douglas bolts etc rather optimistically into a nut and bolt shop..
The vintage sales assistant looked bemused until he suddenly found an equally vintage set of thread gauges...he found matches
with British Military ( I think Royal Navy???..came to me last night..he actually said "British Admiralty Standard or British Standard Admiralty) threads from the 1910 to 20's..Did a quicky search and an "Admiralty Thread" did once exist and was used for instrument assemblies.....Maybe a false lead, but possibly Douglas copied these ?