Illustrated tour of the pre-war Douglas o.h.v. crankshaft

[Doug]

Illustrated tour of the pre-war Douglas o.h.v. crankshaft.


For those that have been playing about with the old Dougies for a while, but have not yet had personal experience with the pre-war o.h.v. machines, the following visual tour of the crankshaft might be of interest.  In time you are bound to hear stories about the unique assembly procedure for the o.h.v. pre-war engines; or how once worn out or damaged they can not be rebuilt.  And it is more or less true! 

Recently I was finishing up the assembly of a client's crankshaft, and took the opportunity to take some photos illustrating the sequence.  Then some other pictures from my collection, illustrating other problems that may be encountered should you be blessed with such a creature.  The crankshaft shown is for a Dirt Track model, essentially the last and strongest of the 82mm stroke crankshafts Douglas made.  The connecting rods shown are new manufacture (See advert), and not original Douglas components. 



The pre-war o.h.v. Douglas crankshaft is a two-throw crank, made of a single forging as seen above.  This presented a challenge to assembling the roller bearing big end bearings, which Douglas overcame in an ingenious way, subject of several patents. 



The first image shows the flywheel side connecting rod and counterweight installed, and the crankshaft is ready for the timing side connecting rod.



As the big end eye is not split, to allow an uninterrupted race for the bearing rollers to run on, the rod needs to be threaded onto the crank over the throws.  As you can see, the size of the throw and the diameter of the big end eye are optimized to their respective limits, it just passes! 



And so then around the second bend.



The rod is now in its final position, but the big end bearing is not installed. 



Here we see the connecting rod roughly centered on the crankpin, ready to receive the big end bearing.



The big end bearing is made up of two aluminum cages, slotted to carry ten Ø1/4x1/4" rollers in each half.  This is slid sideways past the haunch of the throw in to position.



Once in, it is pushed around to the inside of the throw to make way for the second half of the cage carrying the ten remaining rollers. 



This in turn is introduced.  And here a pause while it is explained one of the limitations of this design.  Obviously in a new or refurbished big end bearing you want no perceptible radial play in the bearing.  In reality this equates to a 0.001" running clearance.  This just allows you to slide the cage and its rollers sideways into place.  In time, wear occurs.  A worn connecting rod can be re-honed, but as there is no separate race one can only go a little bit before the surface hardness is compromised.  Worn rollers can be replaced with new oversized rollers, assuming you find them these days.  That leaves a worn crankpin, which can be re-ground.  BUT.  You can only reduce the diameter but a mere 0.003" or so before you run into trouble on assembly. 



That is because the haunch of the throw, shown as "A", and the crankpin "B" are pretty near flush.  If you were to grind the crankpin to a smaller radius, the rollers would have to 'step down' onto this surface as the cage was slid sideways into the connecting rod eye.  The first half of the cage is not a problem, but the second half only has a thou clearance, and you can not get the rollers to enter.  If it were close, you might drive the rollers in, but besides not doing the bearing any good; you will never again get it apart.  You may be able to force the rollers down a step, but as the next image shows, once in place there is practically nothing to grab onto to pry the rollers back up over that step! 



And here it is with the second cage in place.  For removal you only have the low hub on the side of the cage to grab onto with your fingernails, to wiggle and coax the cage out.  For added fun try it when everything is oily.  Least you think the solution is to reduce the radius of the haunch of the throw, I might point out that you would also have to reduce the width of the throw as well.  In turn, as the counterweight is a snug fit on this, new counterweights with undersize windows would need to be made.  Then there would be the issue of installing those, as the width of the throw is not only the same as the crankpin, but it is also identical to the main shafts, which the counterweights have to slip over...  Best not to go there.



As mentioned the counterweight fits snugly on the throw.  There is a registration groove indicated by "A" above that locates it.  This is a different crankshaft to that shown in the other illustrations, as I had already assembled that before thinking to take this and the next four images.  Also shown at "B" are typical roller 'tracking' and chatter marks that makes one wish you could re-grind the crankpins more than just a light 'lick'. 

The DT crankshafts are drilled for oil, but part way through the evolution of the model the factory added the gash at "C" on the leading edge of the center web to introduce a little extra oil alongside the connecting rod. 



Inside the counterweight we see the corresponding lip that fits the groove in the haunch of the throw. 



At the main shaft end of the throw is a V groove.  If it looks like it is not level, that is because it is cut on a 2º inclination. 



This is to receive a tapered cotter driven through a cross drilling in the counterweight, that wedges the counterweight onto the throw. 



This is a view of the inside aspect without the connecting rod, showing that the counterweight hangs over the inside face of the throw.  The center web is at the top.  The counter bore in the face of the counterweight receives the hub that protrudes from the side of the big end cage.  The floor of this counter bore near enough lines up with the inside face of the throw.  However since the cage is a 180º segment, it can span the opening in the counterweight.  This stops the cage from migrating sideways. 

This counterweight has had its lip built up with hard-face weld and machined back to reduce the end clearance on the connecting rod.  The counterweights are just mild steel and were not originally hardened. 



Here the counterweight is being introduced onto the throw.  They need to be a snug fit, else they will shuffle about and work the cotter loose no mater how tight it is driven in. 



And with the counterweight fully home.  The flare on the counterweight lines up with the eye of the connecting rod. 



And here we see another view of it.  Note that the slot in the counterweight is slightly longer than the throw.  This allows the lip to slide over the haunch till it drops into the groove.  This leave a gap (A) at the main shaft end, but it is of no consequence.  Also the throw is recessed into the counterweight.  It is eased back at the crankpin end; if it were not the connecting rod would be unable to be threaded around the bend onto the crankpin. 

As the counterweight itself can not be shifted, having one fixed position, the axial clearance of the rod is set by adding or removing material from the cheek of the counterweight.  This means assembling and disassembling the crank several times.  But no one said owning a pre-war o.h.v. Dougie was all beer and skittles!  Actually a few beers can help one's temper while working on one! 

The counterweights are stamped on the inside face "T" and "F" for timing and flywheel sides respectively.  They also have a number, which originally would match the number stamped on the crankshaft center web periphery.  Crankshafts were batch assembled, fitted, and balanced in the Douglas experimental department.  In fact the whole engine was built there before being sent out to the main factory for assembly into a chassis.  But by now it is rare to find matching numbers as counterweights have been hopelessly mixed up and interchanged over the years. 



The completed crankshaft assembly, rods tucked in.  Here you can see why these engines required short skirt pistons. 



And in its full 82mm long stroke glory!  This same assembly was used in the 500 & 600cc, and made to order 750cc size engines with the simple expedient of changing the bore size. 

Other faults to look for.  Any crankshaft that has been used in competition is probably sprung to a slight extent.  That caused by excessive rpm is in the plane of the crank throws and relatively easy to setup in the press to straighten.  Setting up is easy, by that is not to say straightening the crank is easy!  Even more difficult is correcting twist; from perhaps a catastrophic seizure.  These can be diabolical to rectify.  The crankshafts are incredibly springy, and you have to press them some 0.040" before they take a set.  It is a long process of trying to sneak up on 'dead-true', as you do not want to over correct and end up with it bent in the opposite direction.  All this bending reduces the fatigue life of the crankshaft. 



Here can be seen a crankpin that has been friction sawn nearly through alongside the center web, and the remaining bit broken off.  Note the fibrous nature of the original core material, which follows the serpintine shape of the crank.  They are incredibly tough buggers, or they would not have lasted as long as they did.  But they are not impervious. 

Any crankshaft being refurbished should be as a matter of course Magnafluxed to inspect for cracks.  I would be very much surprised if you did not find any!  Not to worry, they all are like that!  Most will be heat cracks from when the crankshaft was originally ground, either from pushing the removal rate or more likely using a dull grinding wheel. 



Very typical are these radial cracks on the face of the center web, indicated by orange Magnaflux residue pointed out by "A".  Using the side of the grinding wheel to 'face' the web as the factory did is prone to burning the metal and creating these cracks.  The cracks are typically very shallow, just a few thousands of an inch deep, and are nothing to worry about (not that you can do anything about it.)  After all if it were going to break it probably would have done so by now.  The exception would be if they go all the way in and touch the radius around the crankpin, which is a highly stressed area. 

"B" points out a groove worn by the side of the connecting rod big end eye.  If the big end bearing cage gets twisted or 'wracked' it will tend to work the rod hard over to one side or the other.  Perversely it always seems to be into the center web rather than the replaceable counterweight!  However these grooves can often be repaired. 

Another place micro cracks might be reveled are on the flywheel taper.  If they are axial, they are further examples of heat cracks during grinding.  Any circumferal or spiral cracks are cause for alarm. 

There is one other readily visible fault with these crankshafts that typically renders it unusable, and that is a bad flywheel taper.  These always were a bit marginal in surface area, and as the horse power increased, the situation only got worse.  If you have a good taper, make sure it fits the flywheel perfectly and keep the nut dead tight.  And check it several times during the course of the season to make sure it stays tight! 



If you do not, they tend to fret the taper, as seen in this example.  Also they are prone to chipping out along the edge of the keyseat, as the taper is case hardened too.  This example exhibits fretting, metal transfer, galling (when the key sheared), and chipping.  Actually the chipping is minor, I have seen far worse.   



It is not uncommon, if the flywheel becomes slightly loose for it to hammer back and forth on the key, and a spiral crack to develop from the top corner of the Woodruff key seat.  Magnaflux was not required on this example!  Woodruff keys are not particularly brilliant if trying to avoid stress concentrations.  At this point the crankshaft is in imminent danger of breaking, allowing the flywheel to go belting off in a kinetic catastrophe.  And it is not an old legend, it really does happen. 

If the fretting is not severe the taper can be re-lapped or a light pass taken with a grinder.  As it is a shallow taper it does not take much before the flywheel moves sideway sufficient to foul the crankcase.  Then remedial action needs to be taken with the flywheel hub, like a re-sleeve.  The taper need not be completely cleaned up.  It is more important that it be a lap fit on the flywheel.  You should be able to dry wring the flywheel onto the taper such that it sticks tight on its own accord, and requires a tap with a mallet to jar it loose.  The first taper shown above was successfully cleaned up to about 90%. 

Welding up the tapers has been tried, but the crankshaft is a heat treated 5% nickel alloy that is unforgiving.  Eventually the shaft breaks anyway at the end of the weld zone.  Also the taper surface is more susceptible to fretting in a soft condition, and is difficult to keep tight.  Hard chromium plating has been tried, but besides the low coefficient of friction, a taper so repaired broke right where the plating stopped after two seasons use. 

The spiral crack in the example above was precipitated by the taper being built up with weld (using nickel rod) and then the hammering of the poorly fitting taper. 



Here we have a crankpin where the surface is starting to break up; the term used is brinell.  As the case hardness depth is only about 0.040", the pressure of the rollers traversing the surface 'kneads' and massages the hard skin over the relatively softer core.  (Much like what happens to asphalt at the traffic light where large trucks brake heavily.)  In time this breaks up the interface between the two and flakes of the case break away leaving pits.  These particles are naturally very hard, and on their way to the sump get run over by the rollers and crushed, adding more dents and dings to the rollers, connecting rod, and crankpin.  The crankpin shown is probably just a little too far gone to reclaim by a light grind.  Unfortunately this is all too common, as the severe quench process Douglas used resulted in a very hard case and tough core, but a rather shallow case depth with abrupt transition. 



Connecting rods are not immune from brinelling either, especially where the load is the heaviest.  This rod is scrap. 



The other problem afflicting crankpins is forgetting to oil them.  Either on the earlier engines forgetting to give the hand pump a stroke every now and then, or on the mechanically lubricated version forgetting to put oil in the tank or open the drip valve on the sight glass.  Note the face of the adjacent center web is also torn up. 

There is no current viable repair for this kind of crankpin damage.  Perhaps some day a brave soul will attempt to weld one of these crankshafts up.  But like the crank taper, it will be quite an involved process to have it done properly.  Spray welding will not work (hard thin skin is bad, remember?)  The crankpins need to be machined down a 1/8" to remove the carbon enriched surface, then built up with a nickel chromium alloy similar to the composition of the crankshaft (akin to SAE 9310 or En 39c.)  After rough machining this needs to be case hardened again.  That means heat treating the whole crank, and distortion is bound to occur, and a straightening session will be required.  Then finish grinding.  As the main shaft journals accuracy and flywheel taper will likely be compromised in all this heating and quenching, they too will need cutting down and welding up so that they can be reground at the same time.  All this is technically possible to do, albeit very expensive.  The unknown is how the core grain and fiber structure is going to interact with the weld zone, especially at the highly stressed transition between throws, crankpins, and center web.  It will probably be all right, but who wants to be the first to try it in their engine? 

Douglas Kephart, Glen Mills, PA, USA
© Jan 2005

[Dave]

Nice one Doug... a champion post!

[Ian]

Doug, very interesting post - thanks. I have one difference with mine - the big ends are separate rollers with riveted on plates to hold them in place. I guess the DT was a later update.

[Doug]

Ian,

Yes, the earlier crankshafts went through various configurations of big end bearings.  That shown is for the Dirt Track and seems to have come out in 1928, when a patent was applied for the tapered cotter securing the counter weights.  

I do not have a good picture of the earlier rod connecting rods and bearings to illustrate, but there are at least two variants.  One has the side plates (big washers) riveted through the eye of the connecting rod.  The other has the washers riveted through the two segment roller cage.  In both cases I think you should find the crankpin is stepped, or of two diameters.  The one the rollers running on 0.896/0.897" diameter verses 1.1918" diameter for the DT and later style crankshafts.  

-Doug

[Ian]

Yes - mine has the stepped crankpin and the sideplates are riveted through the eye of the rod. Unfortunately I didn't take pictures of it before installation !!

[Doug]

Here is a patent illustration of the earlier version with the side plates riveted to the roller bearing cage.  The patent was applied for Oct. 1920, and granted Feb. 1922.  

There is a patent for the side plates riveted to the big end eye of the connecting rod, applied for Mar. 1917, and granted Oct. 1917.  But the illustration is not a good example, and I am still looking.  

Despite the earlier patent date, I think the side plates riveted to the rod was revised and used after they gave up on the plates riveted to the cage.  Right up to the time they switched to the DT style crankshaft circa 1928.  Catalog illustrations of the RA circa 1923 show the washer riveted to the cage.  Illustrations of the OC/TT engine circa 1925-26 show the washers riveted to the connecting rod.  I will try scanning those and if they turn out o.k. I will add them to this post.  

-Doug

[Ian]

Most interesting thanks Doug. Looks from your picture as though the crankpin was not stepped on the earlier ones either !! Mine has the stepped pin but the rollers are not in a cage at all but just held in place by the riveted plates - I think that must be the purpose of the step - they are a single row. From the look of the cage in the diagram it has two rows of rollers which would require the full width.

[Doug]

Ian,

Yes it is stepped, but not very noticeably; the large diameters being quite short.  A bit out of proportion and artistic license needs to be taken into account.  This same cage design is shown clearly in the April 1925 OB&OW handbook.  

The Patent illustration shows a wide crankpin surface, and I have seen a crankshaft like this.  There were grooves worn by two tracks of 1/4" wide rollers widely spaced apart with an unworn space in the center obviously occupied by the cage.  

However drawings for the 1925 OB and 1926 TT models show a crankpin Ø0.897" by 0.483", which would seem narrower in proportion to that shown in the 1922 Patent.  Also the shoulders, or larger diameters, on each side of the crankpin journal proper are more prominent.  It is possible they ran one wide roller in this groove, but the general practice of the time was for the roller length not to exceed the roller diameter.  Plus some room needed to be left for the cage with either a central bar or a pair on each side.  This would seem to be at odds with the cage shown in the OB handbook (being too wide), unless they used really narrow rollers.  I do not think they did, but I do not have an explanation either.  I suspect the narrow crankpin race was still double row of rollers side-by-side.  Possibly a different cage design or just a crowded assembly.  Perhaps this was the crank were the washers were riveted to the eye of the connecting rods and not the cage?  If this transitioned into use late 1925, it could explain the old illustration in the handbook.  

There are some patent drawings of stepped crankpins with a single row of rollers running in a narrow groove.  But these are even earlier than the Patent drawing shown above, circa 1919-1920.  Most illustrations that I am finding that show anything of the connecting rod on the pre-war o.h.v. show a rod wide enough for two rows of rollers, even the first 3-1/2hp Sport model of 1921.  

Yes, you should have taken a picture as what you have sounds a bit unusual.  

-Doug

[Dewey]

Doug - I know it's an old thread I'm viewing but I've also been soaking up everything I can find out about Douglases since I got started on the Fulton engine. I'm really impressed by the presentation you've made here and wanted to ask - what process did you use to get those parts so mirrorlike finish? Aqua Blasting?

Dewey

[Doug]

Dewey,

Block sanding with progressively finer grades of silicon carbide paper with a light oil lubricant and lots of elbow grease. I stop at 600 grit, which gives a satin-matte finish. The impression of a mirror finish is just a trick of the lighting.

-Doug

[carl denton]

what fits what?

[Doug]

Carl,

The one on the right is DT. Looks like the taper has been welded up and re-machined. These repair have a reputation for snaping off at the end of the weld, allowing the flywheel to belt off into the crowd. Middle looks like OC and TT/I.o.M. engines just before they switched to the DT type. It would still have used the conrods with the riveted plates to retain the rollers. It too appears to have been welded on the taper, as well as having been extended for reasons unknown. One on the left looks like later OB or maybe early OC. Again, the flywheel taper has been built up/altered.

-Doug

[carl denton]

hi Doug

thanks so much for your help got a DT that I have been collecting parts for , so I have 3 cranks and not one of them is any good for my engine then . I keep looking at all the articles related to this engine . got so many of the small parts to fined or fabricate . the crank on the left has not had any mods done to it just a very small taper on it . what is the threaded hole and two small pins for about were the bob weight fits ?

[Doug]

What is the threaded hole and two small pins for about were the bob weight fits?

There is a stuffer block that goes there that fills up the full-radius opening in the counterweight.

-Doug

[carl denton]

I don't suppose you have any images of them or even know of any . Would that crank work in my motor?

[Doug]

No, I had a look before posting but didn't find an example to use as an illustration.

You would have to use the associated rods that go with that crankshaft big end design, the type with retaining side plates riveted to the big end eye. Not having any example to measure, I do not know how the length and other dimensions compare to the typical DT long stroke rod. The earlier cranks had 25mm bearing journals before switching (not sure exactly when) to 30mm.

Problem is the crankshafts were rapidly evolving, possibly several times a year. So you end up saying 'early OB' or 'late OB' because even during it's two year run they did not use just one crankshaft design. It started out using the RA style big end cage; or at least that is what they intended based on published literature. How many, if any were made that way is unknown. Then the side plate design riveted to the conrod with loose rollers. The last OBs might have had a crank that was starting to have some of the DT features in counterweight attachment. I think the DT cage was the last improvement to be introduced c1928, and then the design was pretty much static until the end of ohv production in 1935.

-Doug

[Hutch]

Hi Carl and Doug,

Here are some pictures of OB stuffer blocks (the one shown with the individual counterweight has been welded to it by someone in the past - I guess it means you cannot loose it :-) - a bit rough tho'..... ) and comparison of OB and DT conrods, for 600cc and 500cc respectively. I have not come across stuffer blocks with locating pins yet- only ones with the countersunk screw that holds the counterweight onto the crank and the stuffer block in position. I can measure the rods / take more detailed pictures if required.

-Ian

[carl denton]

hi hutch
photos are so helpful looks like I am going to have to get some made and the screws and bolts I knead . what is the taper like on the OB fly wheel my one looks like its a very big taper on my one , in fact you can only see it when you measured it . have you had to get and big end bearings and plates in Australia ? did not think they made that many types of crank and rods for a DT would be good to see the flat on your crank were the filler plate fits in the bob weight . if I use the OB crank got to fined a pair of rods both of mine are different .

on a side note aren't you a friend of Harrold he has a few Douglas bikes . he moved back to Queensland from WA a few months ago . 

yours carl.   

[Hutch]

Carl,

I started my OB project by "happy" accident. I obtained a job lot of 2 3/4 HP parts and amongst them were a few wheels. I thought 2 of them were CW, as that is what they looked like in the pre-sale pictures supplied by the vendor. Turns out they were OB and not CW. No worries I thought, I can sell them on pretty easily. Then I had the silly idea that I should start a project out of them.......:-).

It took me a while to find a cache of OB parts to go with the wheels and amongst these were some well worn OHV engine bits. All of these require quite a bit of work to be usable and some are scrap unfortunately. But I did manage to get few of the harder to get parts that are specific to the OB. I have found out that good, usable OHV parts are quite hard to come by, in particular bottom end components. Just about every thing I have has had a very hard life (speedway, possibly beach racing etc) or has not been stored well.....

I have so far found 2 OB cranks and one is scrap due to corrosion and the other is possibly usable but I have not finished pulling it apart yet. When I do I will measure the flat stuffer block dimensions for you. The OB crank taper is 25mm by 5 degrees and a DT crank is 30mm and 5 degrees. The flywheel (for use with the flywheel clutch) shown in the picture is for a 350cc engine and has the 25mm taper. which suits the OB crank. I have a 600cc flywheel for the OB (different to DT, no flywheel clutch, and SW5/6 with flywheel clutch) but it is suitable for use as a pattern only due to corrosion.

In period pictures of OB machines I have noticed a few use the 350cc flywheel instead of the 600cc one - maybe for better acceleration as they are lighter? I will use the 350cc one until a usable 600cc one turns up.

I have not chased rollers and keeper plates etc. yet as I have  not confirmed that I have a usable crank as a starting point. I am also possibly short one rod - but we will see what I can resurrect out of what I have. I also have still got a lot of other parts to source for the OB, but we will persist  - I guess I am a sucker for a challenge!

Yes I know Harold well. He kindly helped me out by bringing some bike parts over to this side of the country in his trailer when he returned from  W.A. Harold is concentrating on non-Douglas projects at the moment but will probably be back onto them as soon as the others are completed.

cheers

Hutch

[carl denton]

hi
the taper on my OB crank measures 28.10 at the big end and 27.10 at the small end . the crank is in good condition luckily fitted the bob weights over the weekend. I do have two rods for it both the same length but different designees . as you can see both my DT cranks have big problems but I do have two good rods for them just my luck . got both size clutch fly wheels luckily . looking for the round cover that the decompressor fits in on top of the motor think I could make the parts that go in the side of the motor by the barrel . bit like you my DT started with a frame then a gearbox and so on .
not that I need another Douglas to build , when you talk to Harrold again just ask him how many bikes I have got on the go O and tell him he still has not called me back .
would be good to see what the proper blocks look like I will make some up then .

yours carl.
 

[Hutch]

Hi Carl,

I managed to get the OB crank apart. It was an interesting learning curve as the screws that held the bob weights onto the crank resisted my initial puny attempts to get them out....for a little while that is, until I got a bit more aggressive with them! ....I will have to source some new ones now or make them, shouldn't be too hard.

Anyway I can now measure up the stuffer block for you. Turns out my crank has the two little pins to locate the stuffer block like yours so I now know what they look like! A plus is that the crank looks like it can be refurbished but alas - it looks like I only have one possibly usable conrod out of 4 600cc ones I have. Two different designs tho'. I will post some details when I have taken more pictures.


cheers

Hutch

[Hutch]

Carl,

Sorry in the delay in getting some dimensions of the stuffer blocks for you but I have been quite busy with work lately. I did these pictures in a hurry so I hope they are adequate for you? I can take some more measurements of them if needed. It looks like the pins locate the blocks accurately and the end that is closest to the big end rollers could possibly have been ground to the correct length when the journal was machined? That is why I didn't put a dimension on the drawing for this, and the length of the block is approximate. So I think you will have to machine it for the correct length to suit your crank?

The small pins are a tight-ish thumb push fit into the crank. The radius on the block looks like 19/32" or about 0.594" to 0.598" but will double check that for you.

Cheers

Hutch

[Hutch]

Carl,

Your strange collection of cranks got me thinking about what they might have been used for. This is an extreme long shot, but quite a while ago I came across this newspaper article on W A Heinz's helicopter project (I had misplaced it so had to search for it again in Trove!). Given your location, it does not seem beyond the realms of possibility that those cranks may have been used for this project? If there is a connection then those cranks may be a piece of Australia's aviation history if his helicopter ever got off the ground! :-)

I will send you a PM when I get a chance.

Cheers

Ian

[Hutch]

-Ian

[Hutch]

Sorry to hijack the thread momentarily but Mr Heinz was not alone in his endeavours in 1948! :-) You would not want to be  a very tall pilot!

http://www.redbackaviation.com/early-australian-experimental-helicopter/

Edit:- Add bio of W.A. Heinz;
https://www.carnamah.com.au/bio/william-adolphus-heinz

cheers

ian

[SteveW]

In the Milntown Collection in the Isle of Man is the 1923 TT winning Freddy Dixon banking sidecar outfit, although I understand the RA machine is not the actual winning machine. The outfit was last used about 15 years ago in a TT parade but unfortunately one of the pistons disintegrated and seized the big end on that side.

I have read with interest the details, and complexity of the RA crank, and refurbishment of the damaged crank seems all but impossible. Manufacture of a new, simpler 'pressed up' crank has been investigated, as the engine will never be run 'in anger' again, but to have it run is our aim.

However, my query is, did Douglas fit a crankshaft of the RA dimensions, albeit a bolt-up or pressed-up type, to any model?
I am one of number of volunteers looking after the Milntown bikes and cars and do have access to some precision engineering facilities on the island. Any advice would be much appreciated.