Author Topic: Drive ratios on the 2 3/4 hp  (Read 4159 times)

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Offline Lat Fuller

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Drive ratios on the 2 3/4 hp
« on: 19 Sep 2016 at 05:39 »
Hello members who may be able to help:
I have restored a 1917 2 3/4hp model W.   I have used the original parts as it came to me.   Having got it running, I have found the gear ratios appear to be too high.   It gets along at a good 15 mph in 1st gear at the slowest engine speed.   I am aware of the adjustment to the front pulley, and have unscrewed the pulley to its maximum, but it is still too fast, and will not climb a small gradient.   I got to thinking that perhaps the front drive sprocket on the flywheel is too large.   The drive sprocket is 18 tooth and the clutch sprocket is 54 tooth.   Can anybody tell me is these are correct ?  (I am sure this is the original clutch).
Any suggestions would be greatly appreciated.

Offline RockDr.

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Re: Drive ratios on the 2 3/4 hp
« Reply #1 on: 19 Sep 2016 at 10:30 »
Hi Lat,

Before giving an answer, what type of gearbox do you have fitted, 2 speed with clutch or without, or  3 speed flywheel clutch. Also what type of chain do you have fitted... 1/2" x 3/16"or 1/4" x 5/8"?
 
My 1920's TS' have 31T and 17T for a 2 speed clutchless flywheel with a 1/4x5/8 chain according to Douglas 2.75HP manual.
Looking at the spare parts book the 3 Speed 1915-1919 has a 30T Drive wheel of 3/16" width.
Hope someone else with more knowledge or info can jump in




Offline glenn

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Re: Drive ratios on the 2 3/4 hp
« Reply #2 on: 19 Sep 2016 at 11:08 »
Hi,
I have a 1924 TS 2 3/4 hp with a 2 speed gearbox and was wondering if anybody has an assembly diagram for one of these ?
Cheers,
Glenn

Offline RockDr.

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Re: Drive ratios on the 2 3/4 hp
« Reply #3 on: 19 Sep 2016 at 12:58 »
Just a cut away

Offline RockDr.

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Re: Drive ratios on the 2 3/4 hp
« Reply #4 on: 19 Sep 2016 at 13:04 »
Not sure if this helps.....but anyway

Offline Lat Fuller

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Re: Drive ratios on the 2 3/4 hp
« Reply #5 on: 20 Sep 2016 at 01:46 »
Further to my question on ratios:   This bike is fitted with a 2 speed gearbox, and has a plate clutch.  I am using 1/4 x 5/8 chain.   Thanks for the gearbox diagram - and I can't see how I could have changed anything in the gearbox when I overhauled it: it only fits together one way, and I have 1st and second gears working.

Offline eddie

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Re: Drive ratios on the 2 3/4 hp
« Reply #6 on: 20 Sep 2016 at 06:51 »
Lat,
      You have obviously covered the most likely causes of your problem, so there must be something stupid that is causing the bike to be overgeared. This may sound daft, but have you tried running it in both gears? - have high and low ratios got swapped over? If you are selecting low gear but getting high gear, check the lever at the bottom of the vertical gearchange rod - if it has been fitted 180 degrees out of place, you will still select both gears, but get high gear when selecting low on the gearchange gate (and vise versa).

  Regards,
                Eddie.

Offline Lat Fuller

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Re: Drive ratios on the 2 3/4 hp
« Reply #7 on: 21 Sep 2016 at 00:41 »
Hi Eddie
Yes thanks for that.   I know what you mean because initially I did get the linkage the wrong way around and the gears were reversed ! (I felt very foolish over that).   But that is not the problem here now. I have come to the conclusion that the drive sprocket on the flywheel (18 tooth) is too large, and the London club have a 16 tooth which I am in the process of ordering.   This will only make an 11% reduction, which does not seem enough, but I have to try....  rgds Lat

Offline cardan

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Re: Drive ratios on the 2 3/4 hp
« Reply #8 on: 21 Sep 2016 at 06:05 »
Hi Lat,

It's easy to measure the overall gear ratio in top gear, which takes into account both the primary drive and the belt.

Put the bike on the stand, and remove the plugs (or get a friend to lift the valves). Select top gear. Rotate the rear wheel one complete turn (valve to valve) and count the number of times the engine rotates. (A bit of tape on the rim of the flywheel makes counting easier).

Let us know the result.

Leon




Offline Lat Fuller

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Re: Drive ratios on the 2 3/4 hp
« Reply #9 on: 22 Sep 2016 at 01:48 »
Hi Leon
Thanks for your input.   Yes I have got the engine turning 8.4 turns with one revolution of the drive wheel in low gear, and 6.5 turns in high (at the widest drive pulley setting).  This is roughly as per a manual, and it is still too fast.   I have a 16 tooth sprocket on order, which will reduce it a bit more, but enough ?     Regards Lat

Offline cardan

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Re: Drive ratios on the 2 3/4 hp
« Reply #10 on: 22 Sep 2016 at 03:13 »

Hi Lat,

6.5:1 is a pretty low top gear - that is the motor will be revving at a decent clip at a given speed. Sounds fine for a revvy little bike like a 350 Douglas. Going from an 18 tooth sprocket on the motor to a 16 would take the gear ratio down to more than 7:1 which would be very low geared indeed.

For comparison, on my direct drive bikes (no clutch or gears) I use about 4:1 on big twins, 4.5:1 on a sporting 500 single (1914 Rudge), and about 5.5:1 on a gutless 1909 375cc single. I think my single-speed FN four is about 6:1.

I think 6.5:1 is fine and should get you up most main road hills. In flat country, I'd be thinking a taller top gear would be fine.

Perhaps some other veteran 2 3/4 owners could report their top gear ratio?

Cheers

Leon

Offline Ian

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Re: Drive ratios on the 2 3/4 hp
« Reply #11 on: 22 Sep 2016 at 04:30 »
I will have my TS out in the next few days getting ready for the Douglas Rally - will look at the gearing on that. Got to be VERY careful with gearing on these as they are easy to over-rev with drastic consequences !

Offline cardan

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Re: Drive ratios on the 2 3/4 hp
« Reply #12 on: 22 Sep 2016 at 07:08 »
... they are easy to over-rev with drastic consequences

Yep. A 26" wheel has a circumference of about 2.07m, so turns 482 times each 1km. At 60km/h (1km per minute, 35mph), the back wheel is turning at 482 turns per minute. If top gear is 6.5:1, the engine is turning 6.5 times faster than the back wheel: 3130rpm. Quite fast enough.

Many years ago I was passed on a long down hill by a 1914 Douglas. Just down the road it had stopped with a conrod out the side of the crankcase. Holes in the crankcase are not a good look.

Leon

Offline eddie

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Re: Drive ratios on the 2 3/4 hp
« Reply #13 on: 22 Sep 2016 at 09:52 »
Hi All,
          I have just checked out the gear ratio on the 1913 TT model. High gear is 5.8:1. I cant see the engine sprocket to count the number of teeth (will sit down later and work it out!), but the gearbox sprocket has 29 teeth, and the pulleys are 6" dia on the gearbox and 19" on the rear wheel. On 5.8:1 the TT bike will easily reach 60mph (cruises happily at 50-55mph on level ground) - I might frighten myself later and work out what speed the engine revs to! I read somewhere that the factory reckoned the standard 2 motor was good for 4,500 rpm!
  I am of the opinion that an engine is better built a little on the 'loose' side to make it free running, if it is to achieve those speeds with plain bigends and splash lubrication.

 Regards,
              Eddie.

P.S.   According to my maths, it seems that the engine sprocket must be 18 tooth.
« Last Edit: 22 Sep 2016 at 10:00 by eddie »

Offline cardan

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Re: Drive ratios on the 2 3/4 hp
« Reply #14 on: 22 Sep 2016 at 10:22 »

Hi Eddie,

Scarily fast! Is the motor any different from the standard 2 3/4? Does it have the little fins on the cylinders around the inlets?

Lots of people who have made derogatory comments about 2 3/4 Douglases - I can only think they've never ridden one. One of motorcycling's genuine delights.

Leon

Offline eddie

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Re: Drive ratios on the 2 3/4 hp
« Reply #15 on: 22 Sep 2016 at 10:57 »
Hi Leon,
             Outwardly, the 'TT' engine looks identical to the standard 2 unit. Internally, the only parts that I know have been replaced are the pistons - when Trevor Phillipps owned the bike, he got a respected member of the LDMCC to provide new pistons. The back piston was removed and used as a pattern for modifying a pair of Mark type alloy pistons. When the time came to fit them, it turned out that the bike had originally been fitted with odd pistons - higher compression in the front! Anyway, the bike has run almost faultlessly since the Mark pistons were fitted in the early 70's. The only other difference from standard is the camshaft which has wider and higher opening than any of the usual '5' series cams - the only identifying mark being a 'C' stamped on the face of the gear.
  As I said earlier, it is quick - in one years Pioneer Run when the weather was a 'bit damp'- so not too many 'moderns' to get in the way, it covered the first 46 miles in just under 1 hour 20 minutes - then I had to stop for fear of getting into Brighton in less than 2 hours (thus risking exclusion for speeding!). I think it was that year that a spectator on a Honda informed me that I was cruising at 55mph on the A217 towards Reigate.

Regards,
             Eddie.

Offline Lat Fuller

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Re: Drive ratios on the 2 3/4 hp
« Reply #16 on: 23 Sep 2016 at 00:18 »
Thanks Leon, Ian and Eddie for that information.   I am not sure what to think.   Yes I am very aware of not over-reving the engine having seen how flimsy the con-rods look etc.! Yes this all looks correct thanks, but perhaps it is because I live in a very steep and hilly valley.   I had better take it out on the trailer and try and find a level road to see how it feels.
I have noted in one of my manuals that the ratio can be adjusted from 8 3/16 to 9 3/4 on the drive pulley in low gear, which all follows with your information - and I have it at the widest setting.   
What I was not sure of was what sprocket should give these ratios (it does not mention the sprocket size in any of my manuals).  The parts book shows the option of sprockets 16, 17,18 tooth, which got me thinking in this area.   Also the three speed gearbox goes up to a ratio of 14 1/16 in low gear (but I don't have a 3 speed gearbox).
Thanks again for your inputs.
Best regards Lat

Offline ian scott

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Re: Drive ratios on the 2 3/4 hp
« Reply #17 on: 23 Sep 2016 at 00:40 »
Ian. What speed do you ride your 2&3/4 at in top gear?

I've been limiting myself to 50 - 55 km/h.

Offline cardan

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Re: Drive ratios on the 2 3/4 hp
« Reply #18 on: 23 Sep 2016 at 00:51 »
I've been limiting myself to 50 - 55 km/h.

You're a good person Ian. Eddie is officially bad! :)

Leon

Offline Ian

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Re: Drive ratios on the 2 3/4 hp
« Reply #19 on: 23 Sep 2016 at 03:07 »
Just checked my TS - gearing is about 9.3 and 6.5

We cruise around 45MPH max

Offline Black Sheep

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Re: Drive ratios on the 2 3/4 hp
« Reply #20 on: 23 Sep 2016 at 05:27 »
My 1913 2 3/4 cruises at about 35 mph on the flat, no wind. In favourable conditions it will see 45 mph but that seems a mite quick, especially with the patent anti-lock Douglas brakes. A friend who rode it before I owned it said it had been clocked at 52 mph. Don't think I will try that. One thing it does not like is strong headwinds combined with any upslope. Low ratio and patience required. 

Offline Ian

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Re: Drive ratios on the 2 3/4 hp
« Reply #21 on: 23 Sep 2016 at 06:26 »
Yes - 60kph (about 37MPH) is much more comfortable - the 45MPH is the absolute max I think I have had it at. Agreed - hills or headwinds require patience !

Offline cardan

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Re: Drive ratios on the 2 3/4 hp
« Reply #22 on: 23 Sep 2016 at 10:32 »

Lat,

There's no substitute for a flat road to try out a new bike, particularly one of lesser power. I rebuilt a 1914 211cc direct-drive Radco for a friend, and the first rides on it helped me to identify hills I didn't know existed. The neighbours probably wondered about my sanity when I was out in the street in front of my house with a spirit level and a ruler, measuring the gradient! I have some quite roads about 5km from home that are ideal for first rides.

Good luck - let us know how you get on.

Cheers

Leon

Offline psjc

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Re: Drive ratios on the 2 3/4 hp
« Reply #23 on: 23 Sep 2016 at 14:20 »
Following this discussion with avid interest as I'm just in the process of pulling apart a recently acquired 2 and3/4 HP Douglas and was wondering how to dismantle the gearbox amongst other things. I very nearly didn't buy it because there were several oddities about the bike despite the previous owners swearing blind that it had never been interfered with and was definitely 1913.

So imagine how tantalised I am by the throw away comment from Leon in the string above which says something along the lines of 'are there any small fins on the inlet tract? ' since my engine has said fins and I was really nervous that these are an indicator of something much later. It has no frame number in the obvious place but fins all over the inlet tracts. What have I got chaps? Is the gearing likely to be as suggested or is this one something else?

best regards

Shaun in Ealing

Offline graeme

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Re: Drive ratios on the 2 3/4 hp
« Reply #24 on: 23 Sep 2016 at 23:24 »
A photo of your engine would help Shaun
I suspect your engine may have later barrels fitted, rather than the special TT ones (very rare!) that Leon mentioned, a photo would definitely tell us the story
Cheers, Graeme

Offline psjc

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Re: Drive ratios on the 2 3/4 hp
« Reply #25 on: 24 Sep 2016 at 09:01 »
All may be beyond my computer abilities but herewith two photos I hope. Now have the gearbox in pieces and am slightly flummoxed as to how to withdraw the two magneto type bearings which are at the bottom of a blind recess in the case. Any wise words? Also unsure as to how the mainshaft comes apart. There are two spacer/washers at either end of the square section. I assume these come off in the same direction i.e. away from the drive pulley taper? My shaft has a lot of wear just inboard of the drive taper. A new one seems in order but there's a lot of work in it if there is a quick and dirty solution already developed. Any advice please. The bike itself came from an auction here in the UK about a fortnight ago and can still be seen on the DVCA website results page if the photos don't upload. many thanks in advance for any help/advice.

Am in Tasmania in a month with the VCCA rally so perhaps might sight some of your rarities in the flesh?

best everything

Shaun in Ealing

Offline cardan

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Re: Drive ratios on the 2 3/4 hp
« Reply #26 on: 24 Sep 2016 at 09:27 »

Well I'm interested.

Here's a photo of Harry Bashall on a 1913 racer, with the little fins around the inlet valves where the roadsters were bald. Not to be confused with later TS barrels that had substantial finning in this area.

I'd go carefully with this bike for the moment Shaun, in case it turns out to be something very interesting. Is there any back story for the bike?

Cheers

Leon

Offline cardan

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Re: Drive ratios on the 2 3/4 hp
« Reply #27 on: 24 Sep 2016 at 09:54 »
Top to bottom:
Veteran
Vintage
Bashall 1913
Shaun's bike

Unfortunately, it looks as if the barrel is vintage roadster rather than 1913 works?

Keep an eye out for those little fins at an angle to the main fins.

Cheers

Leon


Offline Lat Fuller

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Re: Drive ratios on the 2 3/4 hp
« Reply #28 on: 10 Oct 2016 at 03:39 »
I thought I would put this final note into my above notes about the drive ratios on my 1917 2 3/4 model W.
Thanks to all members who contributed to solving my problem - which I have now done.
Bear in mind, as I said before, that I used all the original parts on the bike, as it had stopped 40 years ago.  I am not sure how the owner then managed it with the high ratio, except that perhaps he lived in very flat country, and somewhere along the line he had had to put in a new flywheel sprocket (and could not get the correct one). The parts book quoted 3 sizes, 16, 17 and 18 tooth.   My bike had an 18 tooth as stated before.   Whilst I live in pretty hilly terrain, first gear was still much too fast.  I had a drive ratio of 9.5 to 1 in low gear, and the bike could barely climb a gradient of 1 in 9.  I was fortunate enough to find a 16 tooth sprocket in the club parts department, which I have just received and fitted.   This now gives a low gear ration of 11 to 1.   Well this is now about right, and the bike will now pull up my hills okay.
I know this all looks as if I may have now under-geared everything, when one looks at the information supplied above, but I still have the facility of being able to close up the drive pulley on the belt drive to increase the ratio should I find myself in flat country.
I could find nowhere in any manual any indication of the correct sprocket for the cork type clutch setup, but I am now happy that I can ride the bike comfortably on a reasonable road.

 

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