Author Topic: Douglas Aero 1937  (Read 73853 times)

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Offline cardan

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Re: Douglas Aero 1937
« Reply #350 on: 06 Apr 2020 at 05:34 »
1. Are the ring grooves clean enough?
2. piston condition remain still usable? I hope so as I don't plan to change them and in any case the engine was running fine with them in.
3. Any order/matching in ring gap dimension or we just don't care?
4. I cleaned and removed any gasket compound (used on top of paper) surplus and removed everything I can see. Is it quite critical given the oiling system to have a real clean engine interior or is it tolerant. I mean do I need to make 200% sure nothing is left behind that may plug the oiling system. Not sure of the pression and size of ports in this system.
5. any comment?

Hi Eric,

1. Probably
2. They look OK, but the critical issue is the fit of each piston to its cylinder. Check there is more than 6 and less than 10 thou between the skirt of the piston and the cylinder wall at the bottom of the stroke. I assume the bores are ok - not too badly worn at the top. If there are any scuff marks on the pistons, smooth them off with a "flat" file - preferably a brand new one that has never been used on steel.
3. Personally, I think 4 rings per piston is way too many in a bike like this. I'd use plain rings in the top two grooves and leave the others empty. Not everyone will agree, so if you want to fit more use the order proposed above. Use the smaller gaps on the top rings, and the shockers on the skirt. The ring gaps should be set by filing, rather than cutting. Make sure - with a file - the ends of the rings are square and free from burrs.
4. Clean is good. If you have sand/glass/abrasive blasted anything internal you will need to clean, clean and clean again. A few tiny floaties of gasket material won't hurt, but if you wash thoroughly most should be gone.
5. Comment: If you don't have a copy of Radco's "Vintage Motorcyclist's Workshop" get one. It has most of the answers to our questions, and contains almost nothing that is "wrong". I like the way Radco recognises that we're not trying to build MotoGP racers, and cuts some slack to the home mechanic!

Cheers

Leon

Offline Red

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Re: Douglas Aero 1937
« Reply #351 on: 16 Apr 2020 at 08:04 »
I didn’t want to start a new topic as the subject is briefly mentioned within the pages of this exchange. I have an Aero 6oo and my son has an Aero 500 but on both engines the ball and spring in the oil sight drip feed on the timing cover is missing. Doesn’t affect the running of the engines but as soon as we switch off, we have to remember to turn off the oil supply as the window will quickly fill up with oil. Both engines have a tap in the oil supply line. I believe the ball bearing is a ¼ inch, but can anyone give any dimensions for the spring – length, number of coils and wire diameter. I assume it is a very light spring, possibly something like a magneto brush pick up spring. Any help/guidance will be very much appreciated. Thanks.
Roy

Offline Eric S

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Re: Douglas Aero 1937
« Reply #352 on: 16 Apr 2020 at 08:25 »
Interesting, I never notice any spring and ball and did not know it was supposed to be there !

Offline eddie

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Re: Douglas Aero 1937
« Reply #353 on: 16 Apr 2020 at 08:35 »
Roy,
        It could possibly be the same spring and ball as used for the engine breather in the timing end of the crankshaft on the 2¾ models - Douglas were good at making use of existing parts from earlier models!

  Regards,
                 Eddie.

Offline Red

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Re: Douglas Aero 1937
« Reply #354 on: 16 Apr 2020 at 08:49 »
Hi Eddie
Thanks for that. In which case I suppose there is a possibility that pre war spares may have some parts, but I will have to wait until the current crisis is over and the spares service is up and running again. As I say it doesn’t affect the running of the engine, we just have to remember to turn off the oil supply when we park up.

Roy

Offline eddie

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Re: Douglas Aero 1937
« Reply #355 on: 16 Apr 2020 at 09:13 »
More important - turn it back on when you resume your run!!!

  Eddie.

Offline Aero

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Re: Douglas Aero 1937
« Reply #356 on: 16 Apr 2020 at 10:26 »
Hi Roy,
my 600 luckily had the spring fitted.
It was broken in two but at least it meant I had something to measure up, and it turned out to be the same gauge as a B string on an old electric guitar that was knocking around.
Just checked the workshop & I still have my first attempt at winding one. As luck would have it my later attempts were no better!
Its yours if you can make use of it.
Mark

Offline Red

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Re: Douglas Aero 1937
« Reply #357 on: 16 Apr 2020 at 16:07 »
Hi Mark

That's very kind of you. If you could post it to me I will be happy to refund the postage. I assume you are a club member and my address is on the inside cover of the Conrod under  Secretary. Many thanks.
Roy (Staunton)

and yes Eddie - that is my biggest worry. I am parnoid about checking that the oil supply is turned back on before I ride off. A club member well known to both you and I (DR) did exactly that and he tells me he covered 20 miles before the engine seized!

All the best .


Offline Eric S

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Re: Douglas Aero 1937
« Reply #358 on: 16 Apr 2020 at 17:21 »
I would be interested to see where this spring fits and how it works. My bike do not have it and I get used to open and close the oil tap since I had it as I was told to do so.

Offline Red

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Re: Douglas Aero 1937
« Reply #359 on: 17 Apr 2020 at 08:38 »
Hi Eric

Perhaps Aero (Mark) can give us his advice as to how this is actually fitted as like you I don't have these parts fitted to my bike. My understanding is that with the engine running the ball is lifted of it's seat and allows oil to be pumped to the drip feed tube. When the engine is stopped the spring pushes the ball valve back on to its seat and stops the oil flowing otherwise the oil sight window quickly fills up with oil and eventually drains down in to the sump. Even with these parts fitted I am told by those far more expert than me that it is recommended that you still have a tap fitted in the oil feed line from the oil tank otherwise if left overnight some oil will still seep through.

Roy

Offline Aero

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Re: Douglas Aero 1937
« Reply #360 on: 17 Apr 2020 at 12:44 »
Thats a good description of how it works. However I have not found the need to turn the oil tap off. Even if not using the bike for a few weeks the most I have seen the sight glass is half full.
To save me stripping it down to show the gubbins I've marked the spring position in red & the ball bearing sits underneath marked in black.

Offline Red

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Re: Douglas Aero 1937
« Reply #361 on: 17 Apr 2020 at 13:25 »
Thanks Mark

It was interesting to hear you say that even when left for a few weeks the oil sight glass was only half full. As I mentioned to Eddie I am paranoid about making sure I've turned the oil tap on before moving off. The last thing I need is a seized engine. Once I get these parts fitted I will experiment with the need for the tap in the oil feed line. If I can leave it on all the time I think I will be alot happier.

Roy

Offline Eric S

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Re: Douglas Aero 1937
« Reply #362 on: 17 Apr 2020 at 20:26 »
My memory is really bad. A few months back I removed the assembly and I remember this spring and ball. As for the tap, I am using the wheel on top. I close it and open about 1/2 turn I guess.

Offline Aero

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Re: Douglas Aero 1937
« Reply #363 on: 18 Apr 2020 at 09:57 »
Roy, the spring is on its way.
If you tap the ball bearing into its seat sharply using a brass or alloy drift it should seal nicely.
This is how much oil is in my sight glass after the bike standing for the last 2 weeks.

Offline Red

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Re: Douglas Aero 1937
« Reply #364 on: 18 Apr 2020 at 14:02 »
Hi Mark

Thanks once again. If I can achieve the same result I will be happy to leave the in line tap on all the time. Without the ball and spring the sight window fills up very quickly - matter of minutes so I need to shut off the tap even if I'm just stopping for petrol. My son has the same problem with the 500 version he has just finished restoring - see photo attached. He was hoping to take it to this years Annual Rally but sadly as you know this has been cancelled. Never mind there is aways next year so I will keep working on my Aero 600 so I don't show him up! Mind you I've got the bigger engine although frankly there doesn't seem to be any difference in performance.

Best wishes

Roy 

Offline Eric S

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Re: Douglas Aero 1937
« Reply #365 on: 01 May 2020 at 13:32 »
I am now ready to re-install the cylinders.
What is the best, slide the piston and top rings in the cylinder, then drive the piston's axis on the conrod and then drive the bottom ring in the cylinder
Or
Install the piston on the conrod and then drive the piston in the cylinder?

I got a tool to compress the rings but it can't be used as it does not fully open and is too wide.

Also am I happy with a 2.5 grams difference in piston weight?
Any tip welcome one more time.
« Last Edit: 01 May 2020 at 17:59 by Eric S »

Offline Eric S

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Re: Douglas Aero 1937
« Reply #366 on: 10 May 2020 at 11:11 »
Making slow progress on engine assembly.
Still have to adjust for timing where a friend should be able to help me.
As for the tappet adjustment, the book of jhe Douglas ask for .006". Is that still correct although I don't see ay reason to have it changed over the years?

Offline Red

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Re: Douglas Aero 1937
« Reply #367 on: 10 May 2020 at 12:43 »
Hi Eric

I was told .006" exhaust and .004" inlet

Roy

Offline Eric S

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Re: Douglas Aero 1937
« Reply #368 on: 10 May 2020 at 13:26 »
Anybody knows the wrench size normally required to adjust the tappets? I did not unlocked them while the cylinders were out. Too bad and the nuts are damaged so wrenches fits oddly. Seems to be 3/8 and 7/16...
Adjustments are all over the place.

Edit : it's well 3/8 and 7/16.
« Last Edit: 10 May 2020 at 16:28 by Eric S »

Offline Doug

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Re: Douglas Aero 1937
« Reply #369 on: 11 May 2020 at 17:01 »
I have a factory supplied service sheet for the Aero models and it mentions 0.006" for the tappets. No distinction for either inlet or exhaust. Nor if the setting was done hot or cold.

By the mid-thirties Douglas were using a lot of Whitworth wrench sizes. So 0.340, 0.4245, 0.520", etc. Earlier you do find imperial fraction sizes. The tappet jam nut us part number 8376, so predates the Aero era quite a bit. That number dates back to the time of the 350EW.

-Doug

Offline Red

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Re: Douglas Aero 1937
« Reply #370 on: 11 May 2020 at 17:12 »
Hi Doug

Is it possoble to post a PDF copy of the service sheet you have for the Aero. The only information I have when servicing my Aero is what other people tell me. Hope you can help. Thanks

Roy

Offline Doug

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Re: Douglas Aero 1937
« Reply #371 on: 11 May 2020 at 18:09 »
Roy,

Much of it is the usual palaver about running in and adjustments. Only a little really useful info. I have uploaded it here in the Technical Articles board:

https://www.douglasmotorcycles.net/index.php?topic=8098.msg31144#msg31144

-Doug

Offline Eric S

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Re: Douglas Aero 1937
« Reply #372 on: 11 May 2020 at 19:06 »
Tappet adjustments made a .006".
Cams measured and all are equals.
When I check or valves opening (I am not sure of english term for that, balance maybe?) the valves on 1 cylinder are closing and opening when piston is up for less than 1mm
On second cylinder in same conditions, valVes open for 3mm+
I can't understand why with same cams and same tappet adjustments I come with different valve openings?

PS Doug I sent you an E mail
Eddie I sent you a PM
« Last Edit: 12 May 2020 at 08:10 by Eric S »

Offline Red

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Re: Douglas Aero 1937
« Reply #373 on: 12 May 2020 at 08:41 »
Thanks Doug - much appreciated

Roy