aero 250

[Tazmantic]

Hi all new here and new to the world of the Douglas, just bought my first classic bike a 1936 aero 250 was last on the road in 1985 so well rested and came from a London museum to the dealer that I bought it from not the most powerful I expect but there are a few reasons why I chose it.

I've had a little tinker and tho there is quite a few little jobs to do yet I've got it running so first question I'm not sure the carb is right? I seem to have got it to tick over ok but dies if I try to rev it quick I have to build the revs slowly I've had a good search and found that it should be a...

type:- 74/007
internal bore:- 21/32
Jet:- 60
slide:- 4/3
Needle position:-3
Float chamber:- 62/079

Mine has......

Type:- 274/027r
Internal bore:- 25/32
Jet:- 60
Slide:-4/3
Needle position:- 5
Float chamber:- 2a

Does this seem ok?? would the bigger bore cause it to run weak and that's why the needle is in position 5 because if I set to position 3 it don't seem to want to run. I have no idea what the needle jet or needle are or should be as no numbers.

Thanks in advance.

[cardan]

It's not often I get a good laugh from a motorcycle forum, but 274/027R caused quite a chuckle. It comes from (maybe amongst other things) a 1950-1954 249cc side-valve Indian Brave. That's a genuinely funny motorbike! Be assured it wasn't you or the Aero that caused the mirth.

Seriously, the 274/027R mixing chamber is for a 250 single, and you have a 250 twin for which a smaller carb would be better, since mixture is being delivered to one 125cc cylinder at a time. You could probably get the bike to run ok on it by fiddling needle, jets and cutaway in the usual AMAL way, and by not cracking the throttle open too quickly. It may even run better. That said, the 74/007 looks a bit different (with the holes in the sides of the throttle body and jet block) and might give a better-behaved response. The 274 body with no holes was not available before 1939.

Perhaps make do with what you have, while keeping an eye out for a more suitable carb?

Cheers

Leon

[Tazmantic]

Hi Leon,

Thanks for the reply and glad I can assist in the chuckle stakes 

I did think it was too big as that type well a 74/027 was listed for the 500/600 aero, so what carb should I be looking for? Is it the 25/32 that's wrong because the only Amal carbs I can find are 25/32 bore. Sorry I'm really new to Amal carbs 

Cheers Neil

P.s or is it the jet block that ? Mine has 25 stamped on top and 30T on bottom I don't know the bore size of that as not measured I measured the the diameter at the mounting flange 

[eddie]

Neil,
        The spec you have for the original carb was based on the fuel available prewar - we are now obliged to run on unleaded fuel, so need to make further adjustments. Post war Douglases running 274 carbs run better if the slide cutaway is reduced a little, and the main jet increased by 5 or 10 - then play around with the needle height to get clean running at about half throttle. The fact you can only bring the revs up gradually points to either a partially blocked drilling in the slow running passages, or the need for a smaller slide cutaway.

  Regards,
                 Eddie.

[Tazmantic]

Hi Eddie,

Thanks for the reply, I think the pilot way was blocked as it would only tick over if I covered the air inlet pipe so think that is ok now but might not be 😬 so how do the slide numbers work please? Would a 4/2 be smaller 🤷‍♂️ Also the next jet up they seem to list is a 70.

Cheers Neil

[eddie]

Hi Neil,
           Slide numbers - the first number is the physical size of the slide, and the second number is the size of the cutaway - i.e. the smaller the second number, the smaller the cutaway, and hence the richer the mixture. As an alternative, try richening the tickover mixture by winding the pilot air screw in ½ a turn to see if the pickup improves. Most of the 1930's Douglases have a bias on the inlet manifold because the carb enters from the back - this often results in the mixture not being split equally between the 2 cylinders, so a compromise has to be found - the end result is often one cylinder running smoothly and the other hunting a little.
      With regard to the main jet - when you have the bike on the road, having run it on full throttle, kill the engine and check the colour of the plugs - they should be a straw colour. If they are white, increase size of the main jet - this will make the engine run cooler.

  Regards,
                 Eddie.

[cardan]

Is it the 25/32 that's wrong because the only Amal carbs I can find are 25/32 bore.

Hi Neil,

The 250 Aero was probably the only 250 twin on the market in 1936, and there were be precious-few 125cc four strokes, so I'd guess the 74/007 - at 21/32" bore - was probably the smallest "full sized" AMAL available at the time. That makes it a rare carburettor, but at least not everyone is desperate to own one!

25/32" is not a huge carb, so it may work OK with some tuning.

Cheers

Leon

[Dawn]

I remember from doing Stafford Show that Dave Pitt has a 1936 250 cc model.
I don't have any contact details but remember the bike being a 250cc

[Tazmantic]

Thanks for all the info looks like I will need to get a few bits and have a play 

Cheers Neil

[Aero]

Have you got the carb inlet pipe fitted that draws warm air from near the rear cylinderhead fins?
It seems to have quite an effect on carburation & my 600 Aero ran very weak without it.
It would be great to see some pics of your bike if you care to post some up

[Tazmantic]

Its fitted just not sure of the angle if that makes a difference, not sure where to put pics but here's one (sorry if that's wrong)

Neil

P.s wont let me upload pic...

[EW-Ron]

There is a 36 Aero on fleabay at the moment.
Cute little carb !, Nice little bike...




Image moved to server so it doesn't disappear - Dave 06 Mar 2020

[Tazmantic]

Oh no there aint, that's the one I bought 

[cardan]

And I was going to point out that the ebay bike also had the wrong carburettor!

Here are some options for the Type 74 AMAL. In fact there is one AMAL model smaller than the 74/001. By the way, roughly speaking, a 4/001 would have a bronze body, 74/001 alloy, and 274/001 alloy but with no air holes in the body.

Leon

[EW-Ron]

Oh no there aint, that's the one I bought 

And I was going to point out that the ebay bike also had the wrong carburettor!

I wondered about that.
And that.

Ihought I'd just throw it up there, and see what panned out...

I also checked out the little 274J Amal I have spare, but it seems to be about 23/32"  (?)
and quite an oval shaped bore.

[Dave]

P.s wont let me upload pic...

Hi Neil,

If you ever have any trouble uploading photos via the Attachment method, just send your them to the address shown in this topic and we'll add it to you post.

Dave


Updated details for emailing photos - Dave, 11Feb2021

[Tazmantic]

Thanks Dave

[graeme]

There are quite a number of 150cc four stroke bikes from the 30s, BSA, Triumph, New Imperial coming immediately to mind. Perhaps the carburettors for these would be close to the correct size for the Aero?

[Tazmantic]

Cheers Graeme, Ill keep my eyes out for carbs that come up.

Well got the aero out on the road today for my maiden flight (never ridden a hand change before) and yes it certainly wasn't break neck speed but seemed to trundle along quite nicely, do think the carburation needs tinkering with as seemed to run a bit better on about 1/2 choke ( tho I was trying it in all positions and was was tricky to tell as seemed better in different positions at different throttle positions) managed 42mph (according to gps on phone)(well off the 40mph speedo that's fitted think that needs some investigation too) not too bad I thought for a 1936 250 with a carb that probably needs tuning and a fat bloke on top..

[Tazmantic]

Hi all shortened version as just wrote essay and it didn't post

Want to remove flywheel but LDMCC have no pullers, I see one fabricated on a different thread I presume the holes they tap are the holes where the springs go??

also dynamo I know they don't produce much but it appeared to drain my battery out on a run and set to C yesterday I checked it today and found a soldered wire not attached to the com so resoldered it when spun by drill approx. 3000rpm produced about 10 volts no load, 5.5 volts with 5w lamp attached 6.5volts 3w lamp attached and this lamp looked brighter but once on bike would not make side lights come on with no battery attached and when battery attached and set to C the ammeter that's fitted didn't appear to show it charging.. does this sound abought right? could weak magnets cause a low charge as they did seem weak.

Thanks

Sorry cant attach pic again...

[Tazmantic]

Try adding thread link.

https://www.douglasmotorcycles.net/index.php?topic=5336.msg19325#msg19325

[Aero]

Hi Neil, not sure if your 250 has the same setup as my 600 but on those the flywheel is self extracting.
If you undo the central bolt at first it just undoes but if you carry on undoing it pulls the flywheel off the crank taper. Hope this helps

[Tazmantic]

Hi Aero,

Thanks for the info but I'm expecting mine will need a puller as it has the internal threads  will find out when I get a socket to undo the nut.

Also back to the Dynamo I've noticed that when the engine is running but switch is in OFF the BTH cut out clicks in and out as the voltage rises and falls (as it should) but when the switch is set to C the cut out clicks in but stays in due to the voltage from the battery holding the relay in so when the engine speed falls the battery discharges through the Dynamo windings.... SO should there also be a diode in circuit as I've read on a different thread or do people tend to just use these when the cut out is missing.

Cheers

[Aero]

Any chance of a pic of your flywheel, as it may be the outer "clutch adjusting" nuts internal threads that you are seeing. With that removed the flywheel bolt proper is exposed.
I've read that the output of the BTH generator is so feeble it is quite acceptable to remove the cut-out from the circuit without any detrimental effects. There is no diode in circuit as standard its a DC generator, although I guess others could possibly have fitted a zener diode in parallel with the generator to limit the voltage.

[Tazmantic]

The threads are defiantly on the flywheel as I've looked with the adjusting nut removed.

Thanks

[Aero]

Still need a pic, as those threads could be where the retaining ring screws in. This is what the flywheel bolt bears on when it extracts

[Tazmantic]

Flywheel

[Aero]

Looks very similar to mine but it seems the threaded ring that fits into those threads is missing, and that is what the shoulder of the flywheel bolt bears on when its undone & self-extracts. I don't have a diagram but sure theres one in these pages somewhere

[Doug]

Here is a picture of the flywheel nut and the ring nut for the 600 Aero:



I don't know if the 250/350 Aero had this ring nut, as the flywheels are not the same between the lightweights and heavyweights. The flywheel would have the internal thread regardless, as previously it was used with an extractor tool. The method with the ring nut is as follows- When the jam nut is screwed in tight against the flywheel nut (straddling the hex portion), it jams it. When backed off a few turns it allows the flywheel nut to be unscrewed. It then bears against the jam nut and extracts the flywheel from the crankshaft taper.

-Doug

[Tazmantic]

Thanks for the info guys, I'm now thinking looking at pics that mine is not a 250 flywheel as mine has 4 pins that protrude through not 2 like other 250s I've seen..

[Doug]

Oh, it is probably a 250/350 flywheel, but the four, large drive pegs is certainly odd.

-Doug

[Tazmantic]

Don't like the word ODD 

[Tazmantic]

So got the flywheel off today, it wasn't self extracting but to be honest the nut wasn't that tight so with a bit of gentle levering and several gentle taps of the hammer it came off ( maybe it can be identified as don't look like others I've seen in here) and Im thinking ive found several lets say discretions with it  pictures will show this..(and excuse the incorrect names for items)

Firstly I notice a washer between the thrust bearing and the cog (I'm presuming its wrong as it would stop the thrust bearing getting any grease and by the groove init that's crooked)

There is what looks like a piston ring against the engine block spacing off the plate with 3 rollers

When I removed the back plate there was washers spacing this off (think this is because the lip on the inside of the back plate touches the friction plate (shiny area can be seen in inside edge so thin that's what's been driving it  )

And finally there was no grease in the bearing at all (im lucky ive not knackered it) there is a groove in the flywheel retaining nut but once its tightened up no grease will go through.

Oh also the flywheel appears to be brass??


Pictures to follow as never works from my computer...

[Tazmantic]

Pics

[Tazmantic]

Any ideas guys? is this a 250 flywheel with extra pins?

Ive noticed that when it releases the bottom does not push out as much causing a bit of drag, it appears the gap between the release arm and the clutch is slightly bigger at the bottom than the top 

[Eric S]

It shares some parts and design with latter 600 Aero. Check the quality of the cone surface on the crankshaft and for any play in the crankshaft by pushing on the cone portion. As I said earlier I had the same symptoms and this is where I had problems. You may want to remove these points from your list.

[eddie]

Neil,
        From the photos, it looks as if you have a couple of problems.
         Firstly, the washer for the thrust race looks as if it is made from soft steel, and the balls have worn a track in it. A bearing stockist should be able to supply a new, correctly case-hardened thrust washer that can be adapted.
         Secondly, the rollers on the clutch release have flats worn on them and need replacing - this is probably the cause of the plate tilting as it lifts.

        Also, when re-assembling the clutch, check the lengths of the springs. If they vary, arrange them in pairs of equal length, then fit the equal length springs opposite one another - this will also reduce the tendency for the plate to tip.

  Regards,
                 Eddie.

[Tazmantic]

Hi Eddie,

Thanks for the reply I'm thinking that washer is an extra that was fitted to remove slack as there is already a hardened washer between the thrust washer and the pressure plate (pic attached)

Yes they are quite worn how are these removed? and where do I get replacements 

I will check the springs they do vary a little bit for sure.

Cheers Neil

[Tazmantic]

Sorry Pic wont upload again but if you look in one of the pics already posted you can see the washer on top of the thrust bearing and arm

Cheers

[eddie]

Neil,
        In the top photo, the clutch operating arm has a hardened thrust ring let into it. The cage with balls presses against it - then there should be another thrust ring to complete the thrust bearing assembly - I think the soft steel washer has at some time been used in lieu of a hardened washer - also, looking at the fifth photo, it looks as if the bearing has run direct against the end of the hub of the pressure plate at some time - the wear looks deep enough for the bearing cage to have rubbed on the end of the hub - maybe, the soft washer was inserted to gain some clearance. Also in photo 5, the odd wear patches on the pressure plate give the impression that the pressure plate may be distorted and will need some careful attention to get it running true again.
   When the clutch plate is slid onto the pressure plate, the hub of the pressure plate should protrude further than the hub of the clutch plate - then when the thrust bearing lifts the pressure plate, the clutch plate will be free to spin.
   Something else that may need investigation is the clutch linings - they look to be new, so are they the correct thickness? Do a dummy build of the flywheel assy - put the pressure plate and clutch plate into the flywheel and screw on the backplate without any spacer washers - the pressure plate/clutch plate should still be free to move about a 1/16" (so that the pressure plate can lift and free the clutch plate). Once you have established that the flywheel assembly is built correctly, you will probably have to re-shim the release assembly to get the orientation of the operating lever correct - this will likely be a trial and error job.
  As Doug has said - there is something odd about your clutch/flywheel - normally, the smaller capacity engines didn't have the drive pins through the flywheel - that type of clutch was only fitted to the larger capacity OHV machines, so your clutch has probably been 'owner modified' at some time.

  Regards,
                Eddie.

[Tazmantic]

Hi Eddie,

Hopefully I can upload the pic that shows the thrust washer that was also fitted (well I'm presuming its the thrust washer as it does have a ring mark (not groove just a mark) that lines up with the bearing balls) I'm just thinking its been put together wrong in the past, don't know why the end of the pressure plate is damaged on the face but when the washer is against this it appears to be ok and I think the odd wear marks are because the clutch plate was running out but I have now straightened this up.

Yes it looks like the friction material has been replaced and it is too thick if I don't use the washers as spacers for the backplate it just binds up (don't know how thick the clutch plate should be) as for being owner modified I think your right, the lugs that go through the flywheel will only line up one way if production made would of thought it would fit anyway.

Going back to the 3 rollers on the clutch release how are these pins removed? it looks like they are peened over on the back.

Cheers Neil

sorry no pic again... wont work from computer or phone.

[Ken Rogers]

Hi Neil could you tell me the diameter of the 20 balls in the thrust race please as I am looking to make one.regards Ken

[Doug]

Neil,

If I remember right, the posts for the three cam throw-out rollers are riveted over on the inside. But I never pressed one apart to see how much. Either make new posts too and re-rivet, or an alternative would be to cut the head off and drill and tap the axis of the post for a button head allen screw.

-Doug

[Aero]

They aren't riveted over much so press out fairly easy. Holding everything whilst pressing it out is the awkward bit. I believe a roller (10mm?) cut from a link in a heavy motorcycle drive chain makes a good replacement for the existing roller.

[Tazmantic]

Thanks for all the info guys..

Ken ill try measure them tomorrow.

Doug sounds like a good idea of an allen bolt didn't think of that.

Aero cheers for that just need an old bike chain 

I did have another look today and found the flywheel wasn't running true (out by about 1mm) so of coarse the back plate would of been running out of true too, managed to straighten it a bit but its still out (might have another go but don't want to break it) which has made it a bit better but to get it to release I do still have to have the release arm in contact with the thrust bearing all the time.. the investigation goes on 

[Tazmantic]

Hi Ken,

Sorry for the delay they are 3/16" hope this helps

Neil

[Ken Rogers]

Many thanks Neil thats all I needed .regards Ken

[Cliffy73]

Hi I'm just in the middle of restoring my 1936 250 Aero. Having trouble finding engine parts. I'm currently waiting for all the chrome plated parts to come back. The tank is the next job to do. Can anyone tell me what decas it has and where they go. Cheers.

[Red]

Hi Cliff

Having just helped my son restore his 1936 Aero 500, all you need is item 13 in the club's list of transfers - one on each side of the tank. They are now available in vinyl and are much easier to use than the old water slide transfers.

Roy

[Cliffy73]

That's great thanks. Does yours have a headstock and chain case transfer?