Author Topic: Idiots guide  (Read 420 times)

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Offline Sgtbiro

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Idiots guide
« on: 02 Mar 2020 at 17:42 »
Hi
As mentioned in a previous post i am trying with my very limited experience of restoration to restore a Dragonfly,so i was wondering if someone could please wright out a step by step idiots guide on how to set up the timing on a Fly, i have checked previous posts for this information but cant seem to find what i am looking for, so if someone could do this for me it would be much appreciated.

Cheers Kevin...     

Offline EW-Ron

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Re: Idiots guide
« Reply #1 on: 03 Mar 2020 at 00:38 »
What does the Owners Handbook have to say about this ?

And if you say you don't have one....  !!! ?
We'd then say thats a VERY good starting place.

Most timing of these old bangers involves a pencil down the plughole,
and a cigarette paper in the points. And knowing what that timing number
(degrres/inches) is thats mentioned in the Owners Manual.

And, ALWAYS rotate the engine forwards when doing any timing,
or all your backlashes may accumulate.
And watch that the correct wire goes to the correct spark plug !
Thats about all there is to know really.

Offline Sgtbiro

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Re: Idiots guide
« Reply #2 on: 03 Mar 2020 at 17:02 »
What does the Owners Handbook have to say about this ?

And if you say you don't have one....  !!! ?
We'd then say thats a VERY good starting place.

Most timing of these old bangers involves a pencil down the plughole,
and a cigarette paper in the points. And knowing what that timing number
(degrres/inches) is thats mentioned in the Owners Manual.

And, ALWAYS rotate the engine forwards when doing any timing,


or all your backlashes may accumulate.
And watch that the correct wire goes to the correct spark plug !
Thats about all there is to know really.

Hi Ron thanks for your reply, yes i do have a owners handbook but as the title of my post says i need a idiots guide.
In the handbook it says to rotate the engine to TDC in the left hand cylinder then rotate two full revolutions forward to 5 degrees before TDC.
Q1   How do i find TDC
Q2   Is the left hand cylinder as you look at the bike from the back or the front
Q3   How to i find 5 degrees before TDC.
I am doing a lot of these things for the first time and unfortunately my good friend that was advising me is no longer able to do so, so i need all the help i can get so any help answering these questions would be very much appreciated.
Cheers Kevin..     



Offline tck

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Re: Idiots guide
« Reply #3 on: 03 Mar 2020 at 18:38 »
regarding TDC this does not just mean when the piston is at the top of its stroke because there are two occasions when that happens 1 when the bang occurs and one when both valves are open we need the piston at the top when the valves are closed a rocker box off may help you to see this.
you can get surprisingly close to finding the very top of the stroke by feeling the last moments of movement with the bike back wheel off the ground in gear and pulling the wheel backwards and forwards and with a screwdriver on the piston you will feel it rock over the top.
as to your question of five degrees I think what you need is a measurement in fractions of an inch i am a lonf way from my books but I am sure someone here will give you the measurment and how to measure it (its not much before TDC) it may be that someone has already marked it on the flywheel visible under that little cover on what looking from the back we call the LH side

Offline Eric S

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Re: Idiots guide
« Reply #4 on: 03 Mar 2020 at 20:34 »
Hi Kevin
I am looking for kind of same information for my 600 Aero. I have to rebuild the engine and I need to know how to check for the timing. I made marks on the wheels when I disassembled the engine but want to make sure I put them back correctly.
My thread is here https://www.douglasmotorcycles.net/index.php?topic=6434.300 but so far I did not get any reply to my last bunch of questions.

I am not sure your engione is built the same as mine but we might be on the same boat here.

Offline Roys rider

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Re: Idiots guide
« Reply #5 on: 03 Mar 2020 at 21:25 »
Old Pythagoras might help:  2 pye r gives the circumference of the rear tyre where pye is 3.142 and r is the distance from the tyre side wall to the centre of the axle (6.284 x r). A circle has 360 degrees so divide the circumference by 360 degrees then multiply that answer by 5 degrees (before TDC).
Mark TDC on the tyre, measure back the 5 degrees distance. Turn the wheel back further and then forward to the mark.
I haven't tried this but the theory has a lot of history behind it. There must be something wrong because it is too easy. I'll have to try tomorrow it is too late now.
Peter

Offline EW-Ron

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Re: Idiots guide
« Reply #6 on: 03 Mar 2020 at 21:54 »
There is a problem there - the back wheel doesn't spin the same rpm as the engine,
since the primary drive gears it down, probably to a quarter to a fifth the speed.
So 5 degrees on the back wheel is 4 or 5 times that approx in the engine.
And thats ONLY in top gear (1:1 ratio)

You do have an external flywheel, so by careful measuring and feeling should be able to mark tdc on it,
and use a protractor to get the 5 degrees marked (which doesn't sound much for full advance ?)
You'll need a pointer aimed quite nearish the flywheel, no big air gaps. Bolt something suitable to something (!).

You can feel for TDC by placing a thumb over the spark plug hole, and feel when the pressure reverses
when you rotate the engine (always rotate it forward). This may be a little approximate, but if you can get
a soap bubble over the plughole (not so easy without getting messy) is surprisingly accurate.
Mark the flywheel, with something like a pencil mark - or punch a dot if you are really confident !
Use that school protractor to mark the 5 degrees - don't forget to make it BEFORE TDC.

And use that cigarette paper in the points to get the magneto just on the verge of the points opening.
Make sure you have it spinning in the usual direction of rotation.

Tapping the gear onto the magneto shaft with a LIGHT hammer tap should lock it sufficiently to enable
the magneto shaft nut to be tightened up without it moving while you do this.

If this is too brief or rudimentary a description, ask further questions.
Having a clear visualization of all that is happening, in all the correct directions of rotations is rather important.
Hopethishelps.

Offline eddie

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Re: Idiots guide
« Reply #7 on: 04 Mar 2020 at 07:21 »
The original posting above talks about 'timing' - it doesn't say whether that is 'valve timing' or 'ignition timing'.
  From Kevin's previous postings, I understand he has had his engine rebuilt, so assume the valve timing has been attended to, and he has been trying to rig up an ignition circuit to test run the engine. With this in mind, the only thing left to get correct is the ignition timing.
  Start by removing both spark plugs and one rocker cover (doesn't matter which one), and the clutch inspection plate - select top gear so that you can turn the crank by inching the back wheel round (in the forward direction). Turn the crank until the exposed valves are just 'rocking' (exhaust closing and inlet opening) and the piston is at Top Dead Centre. With TDC established, use a marker pen to put reference marks on the clutch spring plate and crankcase - put a second mark on the crankcase " above the first one. Turn the engine backwards a little, then bring it forward until the mark on the spring plate aligns with the upper mark on the crankcase. (the engine is now at 5 degrees before TDC). At this point, turn the distributor body in the OPPOSITE direction to the crank, until the points just start to open (check with a cigarette paper between the points) - tighten the distributor clamp. The engine is now timed to fire on the OTHER cylinder, so make sure the distributor rotor arm is pointing to the correct HT lead. With the plugs and rocker cover replaced, your engine should now run, but be aware that there are other factors that now influence the running of our engines (unleaded fuel, etc.), so some fine adjustments will still be needed when the bike is on the road.

  Hope this helps,
                             Regards,
                                            Eddie.

Offline tck

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Re: Idiots guide
« Reply #8 on: 04 Mar 2020 at 07:41 »
I did not want to get technical about finding TDC but although I think the feel method I outlined above is OK for a road going Douglas the best method is with a timing disc on the crankshaft with a pointer approximately on TDC then TDC is found with a modified sparking plug ( knock out the insulator and add a long 1/4 screw and nuts take away a side of the spark plug thread to let the air in and out) this is screwed in about 10 turns into the plug hole with the piston halfway up the bore on the compression stroke and the piston is advanced till it touches the sparkplug screw. the reading is taken (Lets say its 25 degrees before TDC) the plug is removed the piston is sent over tdc  to halfway or so down, the plug is reinserted (count the turns) the crank is reversed till the plug is contacted the reading taken (say30 degrees ) after TDC, then you add the two figures 25+30=55 and divide by 2 =27.5 you then adjust the disc to read 27.5 degrees after TDC remove the sparkplug tool and you have a spot on timing disc ready to read 5 degrees or to mark your flywheel.
Although I use this method on more conventional arranged machines I have never affixed a disc on a post war douglas I guess it would mean removing the timing cover but given access to the flywheel edge for marking  via the cover on the LH side I guess it would only need to be done once

Offline eddie

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Re: Idiots guide
« Reply #9 on: 04 Mar 2020 at 08:05 »
In my above post, I have assumed that the engine still has the original ignition system. If it has been modified by fitting a 'modern?' twin spark coil, the HT side of the distributor will have been bypassed, and the engine will be running a 'wasted spark' system where both cylinders fire together at each TDC, so it doesn't matter which lead goes to which cylinder. With this system, it is still necessary to keep the distributor cap and rotor arm in place to prevent the points cam lifting off it's driving pins. Also, when testing for a spark with this system, it is necessary to have the whole system in place in order to get any sparks. With 'twin spark' coils there is no internal connection to earth for the secondary winding, so the HT circuit is - cylinder head, spark plug, HT lead, coil, 2nd HT lead, 2nd spark plug, other head. Leaving one HT lead dangling will result in no sparks at either lead.

  Regards,
                 Eddie.

P.S. Whilst tck makes valid points, the Miller ignition system fitted to Dragonflies is not the most robust, and therefore subject to wear, making the fully advanced timing more important than the 'static' timing - hence, my previous comment regarding fine tuning once the bike is mobile.

Offline Sgtbiro

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Re: Idiots guide
« Reply #10 on: 04 Mar 2020 at 15:33 »
Wow thanks guys i knew you would come through for me, the amount of information is great it really helps me understand and theirs an awful lot to digest, i will study the posts and try to take in all the information you have all given me, wish one of you lived on my door step,i will probably get time at the weekend to have a go and i will let you all know how i get on once again thank you very much for all your help.

Regards Kevin..         

Offline tck

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Re: Idiots guide
« Reply #11 on: 04 Mar 2020 at 15:48 »
I would take Eddies advice