Author Topic: Aero 600 Engine re-assembly (Read 6700 times)

Aero · « **on:** 26 Apr 2019 at 08:27 »

Hi, my names Mark, I'm from Shropshire & have just got hold of a 1936 Aero 600. Its in fair oily rag condition but needing a few jobs sorting. I've restored quite a few old bikes in my past but this is my first Douglas so may well need some help from you more knowledgeable folk. I've made contact with the club regarding getting the machine registered with the DVLA & hopefully by the time thats all sorted the jobs will be completed & we can be on the road before summers out. I'll post up progress & hope you can give me a guiding hand when needed.

Red · « **Reply #1 on:** 26 Apr 2019 at 17:23 »

Hi Mark

Welcome on board. I also have a Aero 600 which I bought about 8 months ago and I am still on a steep learning curve. Look down the list of posts and click on Douglas Aero1937. There are 5 pages of posts with a wealth of information on the Aero 600 and will probably answer many of the questions you may have. In the meantime I have attached a road test on the Aero 600 which you may find of interest

Aero · « **Reply #2 on:** 26 Apr 2019 at 21:51 »

Thanks for the links Red, they made good reading. I looked over some of your previous posts too & was wondering if you sorted your kickstart spring issue? I had my gearbox cover off today to see why my kickstart occasionally slips but its just the edges wearing on the pawls. I could take a pic of my spring if you still need to see what a 4 speed type looks like? (The return action on mine is still good)

Red · « **Reply #3 on:** 27 Apr 2019 at 09:43 »

Hi Mark

The club's spares has only just had some new springs made up for the 4 speed pre-war box. Another club member very kindly dismantled a couple of boxes he had in stock which had never been apart in the past 50 years or so and we were able to compare the return springs to get a good sample. I received my new spring in the post yesterday and it looks good and is identical to the broken one I removed from my gearbox, which had worked perfectly OK until it broke, so hopefully once I get it fitted that should resolve the problem. The slipping of the kick start when kicking it over seems to be a common problem and as yet I've not been able to resolve it. I tried fitting shims behind the worm drive to bring the gears closer in to mesh and whilst it may be slightly better it still slips on occasions. I think it is more a question of easing the lever down until you can feel the gears meshing and then continue pushing down to turn the engine over rather than "kicking it over" if that makes sense.

Roy

Aero · « **Reply #4 on:** 27 Apr 2019 at 10:41 »

Hi Roy, glad you have sorted the spring now & I'll try using the kickstart as you have described to see if it slips less. Do you by any chance have a link to the club spares list please? I'm looking for the oil pump drive gear (its the one on the pump itself) as mine has worn heavily. I emailed the club membership application form in a few days ago but still waiting to hear back at the moment.
Mark

Aero · « **Reply #5 on:** 27 Apr 2019 at 11:08 »

This is the gear I'm in desperate need of if anyone can help me in locating one?

eddie · « **Reply #6 on:** 27 Apr 2019 at 11:15 »

If I remember correctly, the kickstart in the late prewar 4 speed gearbox works in much the same way as that in the postwar Mark gearboxes (which, occasionally suffer similar problems with not engaging). On operating the kickstart, the quadrant initially turns the mating gear (which is mounted on a sleeve with helical splines) until it meshes with the ratchet - then it continues turn both the gear and the splined sleeve - thus turning the layshaft. The splined sleeve is loaded by a spring to cause some drag which causes the gear to ride up the helical splines - when the spring gets weak, there is less drag, and consequently less pressure to push the ratchet into engagement - hence, the kickstart slips!

Regards,
Eddie.

eddie · « **Reply #7 on:** 27 Apr 2019 at 11:20 »

Mark,
Can you add a few dimensions to the photo of the gear? I have a couple of gears like that from earlier models but am not sure if they are the same size as that in the Aero engine.

Regards,
Eddie.

Aero · « **Reply #8 on:** 27 Apr 2019 at 11:28 »

Eddie, the diameter across the gear teeth is roughly 31mm & they are just under 9mm wide. The height of the assembly is 28mm. Looking through posts on here it seems it might be the same pump as a 1932 B32 but I can't be 100% sure.
Thankyou for your help in this.
Mark

Red · « **Reply #9 on:** 28 Apr 2019 at 10:23 »

Hi Mark

I didn't reply to your earlier post as I doubt Club spares would have the oil pump gear you require and in any event Eddie had already been in contact with you. Hopefully Eddie will be able to help you out, but if not I am sure other members may have the gear, or if not a complete pump. It was fitted to a number of models. The new kick start spring is now fitted and works perfectly, so if any other members have a similar problem club spares do have a small stock.

Roy

Aero · « **Reply #10 on:** 29 Apr 2019 at 13:19 »

Eddie, I have just sent you a private message to see if you had any luck finding that gear. Thanks for the info on how the kickstart mechanism works. I've shimmed the spring up as much as possible so will see if that makes an improvement when the engines back together.

Roy, looking at the condition of my pumps shaft a complete replacement pump would likely make more sense, as mines in very rough condition, but just to get the bike back on the road I could make do with the gear until a complete pump is available. If anyone does have either they wouldn't mind parting with please get in touch.

Eric S · « **Reply #11 on:** 30 Apr 2019 at 08:47 »

I am delighted to read that the post about my work on my Aero helps others. It's nice that I can pay back to the community.
Here is the link : https://www.douglasmotorcycles.net/index.php?topic=6434.0

I still have to work on the kick but glad I can get a spring shall I need it. As it has been replaced earlier in its life, it probably have the wrong one.

As for the oil pump, the guy that repaired the cone on the crankshaft has bought a small company that makes pinions. He may be able to help. It will be costly for a single part or to rebuild the pump... The guy is a biker and willing to help.

Aero · « **Reply #12 on:** 01 May 2019 at 09:23 »

Eric, your article is very good for reference & the multitude of pics are very helpful too. There is not much info out there on our Aero 600 models so this forum is invaluable when trying to fathom an issue out.

I noticed from your pics that the large primary drive sprocket which fits on the gearbox should contain a cush drive, and is located by two woodruff keys, which alerted me to the fact mine is definitely a cobbled together affair, with just one keyway & no provision for the cush drive. I was hoping that the welded on sprocket on mine was just some previous owners way of renewing an original assembly with worn out teeth but it looks like somewhere in the past the original cush assembly has been lost and a simple solid hub has been substituted. I will obviously have to take a lot of care with my gearchanges until I can source a genuine replacement.

A kind member is sending me an oil pump so hopefully I can get my machine on the road this summer, if the DVLA can issue me a registration number in time.

eddie · « **Reply #13 on:** 01 May 2019 at 09:55 »

Mark,
Don't worry about your sprocket having just one key in it! The power should be transmitted by the taper being a good fit (usually lapped in with grinding paste) - not by the shear strength of the keys. Fitting 2 keys usually adversely affects the fit of the taper as they have to be precisely positioned to prevent them holding the taper off to one side, so leaving one out is probably the better bet.
If you need to renew worn teeth on the sprocket, have the old ones turned back and get a new ring cut from a 'plate wheel' (available from most bearing stockists) welded on - don't worry about the teeth being in a 'soft' condition - they wont wear out any quicker, in fact, probably the opposite!

Regards,
Eddie.

Aero · « **Reply #14 on:** 02 May 2019 at 08:44 »

Eddie,
thats good to know about the keyway. Just the cush drive left to worry about now!

On a separate matter can anyone tell me if this assembly order for the generator drive gear & oil pump scroll drive that fit onto the crank looks correct?
The generator drive gear fits over a tapered bronze cone, and when everything is assembled it spins freely on it, with virtually no resistance, so I would hazard a guess something akin to a shim or similar is missing to preload the gear, causing some grip, or maybe general wear means it now needs to be shimmed?

Aero · « **Reply #15 on:** 02 May 2019 at 10:16 »

Also it seems the cam timing is way off.
On the inlet side the timing marks are around a quarter turn of the sprocket out, whereas on the exhaust side its a couple of teeth off. I did previously have the engine running for a short time though so I'm puzzled how it ran so well with such a discrepancy?

Doug · « **Reply #16 on:** 02 May 2019 at 15:56 »

Mark,

From the looks of you generator drive arrangement, it would seem you have the 1937-38 type engine. This had the timing side main shaft extend right out to a plain bronze bush in the timing chest. The 1936 models had the main shaft stop short; the oil pump worm idled on its own stud in the timing chest, driven by a face dog (which was also the crank shaft nut). I have a 1936, and it can be seen here:

Forum member Eric S is working on a 1937-38 type; lots of pictures:
https://www.douglasmotorcycles.net/index.php?topic=6434.msg23959#msg23959

I have not seen a handbook for the 1936-38 Aero models, but I do have a 1938 (non-illustrated) spares list. It lists the following:
18307 Timing pinion
18931 Coned hub for generator pinion
18929 Sleeve between coned hub and generator pinion
18944 Spring for generator pinion
18930 Washer for spring
18213 Oil pump work
18309 Key for generator pinion and worm (presumably they mean the cone)
18310 Key for timing pinion
18099 Lock nut
18211 Locking washer.

Presumably the spring is a wave washer, given the restricted space available. Douglas had been using such on the 250/350cc engines to keep the engine rotary breather valve disk against its face, as can be seen here:

I suppose the change from the 1936 to the 1937-38 engine was to reintroduce some sort of slip clutch between the dyno and its drive, as they use to have on earlier models that were driven off the magneto gear. Using a bronze cone to drive is very similar to the friction tapping heads used by machinist in things like radial arm drill presses. Though the proportions do not look very generous.

As for the timing problem, the tappets are installed the wrong way, as you may have already noticed from the image earlier in this post. The faces of the tappet should be vertical. This kept the timing events truly at 180 degrees, even though the tappets are at an angle. Lacking a handbook, I don't have the timing figures for the Aero, but I would be very surprised if they differed much from the 600 EW, which shared the same layout. Figures seen here:

-Doug

Aero · « **Reply #17 on:** 02 May 2019 at 17:31 »

Doug,
many thanks for taking the time to share your knowledge. I can see from your picture now that the outer tappets are in the wrong places, and unfortunately after taking the cams out I can see that the inner tappets are also swapped around, which I assume means removing the front cylinder to remove their guides, as they can't be removed otherwise?
By the way my engine is a 36 & same as design as Erics, but near the end of that year, as its a 6/M. I noticed his is a 6L so I guess theres a chance they may have changed to our longer crank nose length & associated parts near the end of 36. My frame is also a 36 as it bears the AE prefix and not the same prefix as the engine as on the 37 models onward.

I'll have to quiz Eric on how the generator gear is tensioned, as it looks like the spring you listed may fit around the spacer that is fitted between the timing gear & coned hub, perhaps pushing that washer into contact with the generator gear so it is forced into the cone.

Mark

Doug · « **Reply #18 on:** 02 May 2019 at 18:03 »

Mark,

The window in the base of the cylinder should be big enough to knock the tappet guides out without disturbing the cylinders. Nor do you need to completely remove them; just enough that you can wiggle them at a slight angle and slip the tappet free.

Come to think of it, I have seen the existence of a 1936-37 Aero spares book, though I do not have a copy. That would suggest that the 1936-37 models were essentially the same (but no guarantee without seeing the contents). If so, then the change to the oil pump drive must have happened in 1938. Perhaps someone replaced a bad 1936 crank with a good used 1938 unit. No reason I can think of the entire assembly would not interchange. They would need the 1938 timing cover as well, though. Yet I think it was determined from Eric's machine that the change did happen in '37. Not very conclusive, but the moral is there is a high degree of parts interchangeability and you don't know how many times it has been apart and rebuilt in the last eighty plus years.

Douglas popularity was falling off rapidly in the mid- to late thirties. There are far less 1937 Aero 600s than there are '36; and the '38 model is downright rare.

-Doug

[fix typos. 02May19 Doug]

Aero · « **Reply #19 on:** 02 May 2019 at 21:32 »

Couldn't quite tap the top guide out, as the edge of the barrel was just covering it by a gnats whisker, so took the opportunity to whip the barrels off as I was unsure of the condition anyway.
Inside were fresh +60 pistons, but the rear one had a stuck top ring in it. Pretty certain it was due to slight water ingress as I know the bike had previously stood outside under a tarp for a while & the inside of the cylinderhead was a bit rusty on that pot too.
I can see a weld repair to the crankcases but it looks decent quality. The crank must have been out for that & who knows what catastrophe caused that to crack in the first place so I'm going with Dougs hunch that a later crank was likely substituted in the past.

Eric S · « **Reply #20 on:** 03 May 2019 at 08:39 »

Hello
Glad if I can help.
As for the tappets, when I disassembled the engine, I was not sure the way the tappets were going but I found out they can fit only one way. (everything being removed from the engine). I tried them both ways and there is a way where they can not slide freely. From what I remember one side is flat and one is round so it can fit just one way.

Let me know if you need anything help. My engine is unfortunately for me still open so I can fortunately for you still make pictures.

Aero · « **Reply #21 on:** 03 May 2019 at 18:52 »

Eric, is there any chance of showing me a pic of what the assembly looks like in front of your timing pinion gear on your crankshaft please?
It seems there should be a spring that loads the generator pinion gear which is missing on my engine & I have no idea what it should look like.

The tappets on mine were definitely the wrong way around & fit just fine in their wrong positions.
This is a pic of the correct orientation, followed by incorrect

Eric S · « **Reply #22 on:** 05 May 2019 at 17:56 »

Hello
I only have this picture. Is it what you asked for?
I did not had a spring in there.

Aero · « **Reply #23 on:** 05 May 2019 at 21:51 »

Hi Eric,
it is what is behind "C" that is of interest to me. According to the parts list behind there should be a spacer, *Spring*, washer, then the timing pinion. The spring is necessary to apply pressure to the generator pinion gear so that it "grips" to its cone to provide drive from the crank. Without the spring the generator pinion gear spins freely on the crank.

Aero · « **Reply #24 on:** 07 May 2019 at 16:37 »

After giving it some thought over the bank holiday I think this spring design will do the job.
I've just adapted an old spring from inside an oil filter & its not very tough so will need to be remade in a better material before I can use it.

Aero · « **Reply #25 on:** 09 May 2019 at 20:33 »

This is a pic of the assembly order just in case anyone ever needs it for future reference.
I'm just waiting on the one main bearing to be delivered before I can reassemble the engine. Is there any interest in documenting the rebuild on here?

Jonathan Hewitt · « **Reply #26 on:** 10 May 2019 at 18:50 »

Good evening
' All information is good '
Have fun in the rebuilding
Jonathan

Eric S · « **Reply #27 on:** 12 May 2019 at 16:50 »

Sorry or delay.
Here are the pictures of the parts. In no particular order.
No spring here.

Aero · « **Reply #28 on:** 13 May 2019 at 17:52 »

Eric,
thanks for the pic. I see your generator drive gear is solid. You don't have a bronze cone inside as on mine, so you don't need a spring.
So now we have 3 types of generator drives on our Aeros, short shaft with combined dog drive, long shaft with straight gear, and long shaft with cone gear driven!