Author Topic: TW24 Douglas restoration  (Read 4799 times)

0 Members and 1 Guest are viewing this topic.

Offline cardan

  • Master Member
  • ****
  • Join Date: Jul 2007
  • Posts: 1055
  • Location: Adelaide, South Australia
    • Leon's Vintage Motorcycle Page
TW24 Douglas restoration
« on: 06 Jul 2014 at 14:08 »

The TW24 is a pretty rare model; basically a 2 3/4 h.p. (350cc) Isle of Man model. It differs from its big brother the RA by having a sloping top tube frame, and carrying its oil in a compartment in the petrol tank rather than in an alloy reservoir under the motor. The TW cylinders are the same casting as the RA, but have 57mm bore (68mm for the RA). The cylinder heads are also externally identical, but the combustion chambers are machined to match the smaller bore. The rest of the motor/gearbox is identical to the RA.

The crank cases I'm using are numbered IE/1B 41. The table in Appendix 2 of "The Best Twin" lists prefix IE as "2 3/4 h.p. 1923 T.T. engine ohv, 57 x 68mm, 350cc". IE/1B is listed as "2 3/4 h.p. Williams Bros., Sydney City Council". Williams Bros. were the Sydney agent for Douglas, and were involved in racing in the major centres in Australia. I suspect "Sydney City Council" is a red herring: although the Council bought quite a few Douglases for various mundane tasks, I doubt they had much need of T.T. engines!

Numbers-wise, the cases are ideal: certainly 2 3/4h.p., a matched pair (match number A89 on each half) and delivered to the Australian agent Williams Bros. Condition-wise, there were none of the usual exit wounds, but they were a bit ratty where corrosion had ravaged the timing side. The front right engine mount was totally gone, rear right pretty tatty, the face of the timing chest was rotted, as was the face of the gear change lug - rotted right through in fact. On the drive side, the only corrosion was in the thin part of the case that covers the cam bearing, which was cracked and peeling.

The cases are now back in good order. The corroded parts have been machined off and new metal added where necessary for structural reasons (thanks Wolf and Seb - masters of the mill). Non-structural repairs use aluminium-filled epoxy and lots of hand finishing. Welding may have been possible, but given the rarity of the surviving metal I decided not to risk it.

The photos below are probably self explanatory: as acquired, on the mill, and the (almost) finished product.

Cam and followers next.

Leon

Offline Blackdodge1000

  • Member
  • *
  • Join Date: Oct 2010
  • Posts: 8
  • Location: Brisbane, Australia
Re: TW24 Douglas restoration
« Reply #1 on: 07 Jul 2014 at 03:23 »
Very nice.  Looking forward to seeing more progress photos if you have time to upload them

Offline graeme

  • Master Member
  • ****
  • Join Date: Oct 2004
  • Posts: 598
  • Location: Hobart, Australia
Re: TW24 Douglas restoration
« Reply #2 on: 07 Jul 2014 at 12:07 »
Great stuff Leon!
It certainly will be good to see such a rare model resurrected. I don't know that I've ever seen another pictured from recent times? I can't think of one, it would be interesting to know if any more have survived.
Cheers,
Graeme

Offline Dirt Track

  • Senior Member
  • ***
  • Join Date: May 2004
  • Posts: 212
  • Location: Hobart,Tasmania
Re: TW24 Douglas restoration
« Reply #3 on: 10 Jul 2014 at 06:25 »
G'day all.
Great thread.....looking forward to seeing the complete bike...in the meantime something to tease!
Howard.

Offline cardan

  • Master Member
  • ****
  • Join Date: Jul 2007
  • Posts: 1055
  • Location: Adelaide, South Australia
    • Leon's Vintage Motorcycle Page
Re: TW24 Douglas restoration
« Reply #4 on: 10 Jul 2014 at 07:37 »

Tease, tease, tease! Yes IE/1B 42 has survived as well, so Williams Bros. received at least two 350 IOM engines from the works in late 1923/early 1924.

Both engines, 41 and 42, had been updated at some time with 494cc (68mm bore)  cylinders and OB cylinder heads. Unfortunately 42 has been "fixed" with a hack saw and the RA gear change lug is gone from the top of the timing chest, but otherwise the engine is complete and looks like it could be a goer as is.  42 is a loose engine, and so far as I know there is no other TW in close to running condition.

I've spent several hours fettling the cam followers, tappet blocks and tappets of no. 41; getting close to something I'm happy with. Photos when I get the job done.

Cheers

Leon

Offline cardan

  • Master Member
  • ****
  • Join Date: Jul 2007
  • Posts: 1055
  • Location: Adelaide, South Australia
    • Leon's Vintage Motorcycle Page
Re: TW24 Douglas restoration
« Reply #5 on: 11 Jul 2014 at 02:15 »
The tappet blocks are in, and the tappets/cam followers glide freely in and out with little play, and are more-or-less vertical.

There was a LOT of fiddling to make this happen. On the RT/TW the brass tappet blocks are prevented from rotating by a double-ended steel pin, pressed into the cases between each pair of tappet blocks. You can see it on the right in the photo below. The steel pin engages with a slot machined into the outside of the tappet blocks, which you can see in the "loose" tappet block (that actually lives in the drive-side case, with the slot set to align with the pin). There is also a slot inside the tappet block, into which a pin, pressed into the shaft of the tappet shaft, engages on both sides.

If the cam follower on the foot of the tappet is to be truly vertical, several things should be in perfect alignment: the steel pin in the cases, the outside slot on the tappet block, the inside slot in the tappet block, the pin through the tappet shaft, and the hole drilled into the tappet shaft into which the pin is pressed.

This is the stuff of dreams. In practice the alignment is not perfect, and I had to try many combinations of tappet block, tappet, and orientation to get the slight misalignments to cancel rather than add. I rate the outcome as adequate rather than perfect or bad.

(The system for keeping the cam followers vertical was improved and simplified through the 1920s - the DT system is both simpler and  better.)

By the way, my motor is a bit like an ageing actress: it looks much better in natural light than it does when hit by the flash of the camera.

Camshaft is next.

Leon

Offline Doug

  • Administrator
  • ****
  • Join Date: Mar 2004
  • Posts: 3912
  • Location: Glen Mills, PA, USA
Re: TW24 Douglas restoration
« Reply #6 on: 12 Jul 2014 at 20:58 »
Leon,

It is not quite as bad as it seems.

Because the face of the tappets is only inclined at an eight degree angle, when that face is obliqued the error is not as great as the angle of rotation. For example: if the various pins and slots allowed the tappet to be rotated 5 degrees from the vertical (ideal) alignment, the angular error between the face of the tappet and the face of the cam (at the base circle) would only be 0.7 degrees. Assuming you have the early, 9/32 wide cam lobes, that equates to a possible surface deviation of 0.0034 inch. The cam probably flexes that much!

However, one does want the cam bearing evenly across the full width of the cam lobe. For longevity, if nothing else. In reality I expect the pressure of the valve springs cause the tappet to rotate an find its own optimum alignment against the cam lobe. As long as the cumulative error of the slots and pins do not hinder the tappet from doing so, the extra slop of such a system is not fatal.

Even the later system as used on the OC, DT, TT, etc. has a few degrees rotational freedom (and quite a lot when worn!) However since it is a simpler system of alignment, they did minimize the cumulative error. The tappet is more likely to be somewhere near vertical when it collides with the cam lobe!

-Doug


Offline cardan

  • Master Member
  • ****
  • Join Date: Jul 2007
  • Posts: 1055
  • Location: Adelaide, South Australia
    • Leon's Vintage Motorcycle Page
Re: TW24 Douglas restoration
« Reply #7 on: 12 Jul 2014 at 23:42 »
Thanks Doug, you've put my mind at rest. With the cam in place everything looks reasonably well aligned so I think what I have will be "good enough". One small problem is that one of the tappet blocks is slightly too long, or the tappet is slightly too short, so the foot of the follower does not run on the base circle of the cam. I'll take a lick off - only about 5 thou needed.

The "spectacles" are in place for the front tappet blocks. Unlike the later models, the brass blocks are full circles as are the recesses under the aluminium (aluminum to our American friends) "spectacles": all the alignment is done by the internal pegs.

The hole that spans the two crankcase halves to the right of the tappet blocks is for the valve lifter cable. Note that the front spectacle has its end machined off to to clear the cable entry. Of interest is the witness mark on the crankcase, showing that the cable holder is elongated in the vertical direction. I don't have this part, and I'd be interested to see an original if anyone has one.

Leon

Offline cardan

  • Master Member
  • ****
  • Join Date: Jul 2007
  • Posts: 1055
  • Location: Adelaide, South Australia
    • Leon's Vintage Motorcycle Page
Re: TW24 Douglas restoration
« Reply #8 on: 15 Jul 2014 at 10:25 »

It's a bit lame, I know, but this is one of my favourite RA parts: let's call it the magneto strap anchor. The magneto is held on top of the crankcase by a two-piece sheet metal strap, and these are the little doo-dads that anchor the straps and also locate the magneto base fore and aft. What really appeals is the pin that passes through a loop in the straps. Nuts and bolts are generally avoided if possible on the RA, and this pin + split pin arrangement is used where-ever possible. To keep weight down, the pins are usually drilled. Here the 38mm steel pin is drilled its entire length with a No. 30 drill - just over 1/8" - for a weight saving of about 1.5g per pin. Elegant.

The body of the breather that screws into the top of the crank case (on the right in the top photo) is made from aluminium. Another nice touch.

Leon

Offline Doug

  • Administrator
  • ****
  • Join Date: Mar 2004
  • Posts: 3912
  • Location: Glen Mills, PA, USA
Re: TW24 Douglas restoration
« Reply #9 on: 15 Jul 2014 at 12:18 »
Leon,

Those little weight saving touches seemed to have disappeared with later production of the RA series. As supplies were used up, they were replaced with components where they did not take as much trouble to pare away ounces. Particularly later as it became clear most RAs were headed for the dirt track rather than road racing, and robustness became more important than light weight. It also undoubtedly saved some time and therefore money in manufacture. Examples include on later machines non-scalloped brake flanges on the hubs and lugs on the frame and forks not fish-mouthed.

Offline cardan

  • Master Member
  • ****
  • Join Date: Jul 2007
  • Posts: 1055
  • Location: Adelaide, South Australia
    • Leon's Vintage Motorcycle Page
Re: TW24 Douglas restoration
« Reply #10 on: 19 Jul 2014 at 10:13 »

There are a lot of parts in this motor! Gathering, cleaning, fitting, worrying... it's a pleasure.

Leon