Author Topic: EW ignition timing  (Read 4964 times)

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Offline patrickhowell

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EW ignition timing
« on: 07 Nov 2015 at 18:39 »
Can someone suggest an easy method of positioning the magneto drive gear, so as to get correct ignition timing, with the cylinders off? Even with cylinders on, how does one measure distance from TDC when the spark plug hole is at the side of the cylinder, thus no direct access to the piston top?

Offline cardan

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Re: EW ignition timing
« Reply #1 on: 07 Nov 2015 at 21:47 »

Hi Patrick,

With an outside flywheel ignition timing should be pretty easy, even on the side of the road. I guess the EW would require something like 35 degrees full advance, so it comes down to locating TDC on the firing stroke than winding the flywheel back 35 degrees with the mag on full advance points just opening. You can use a degree disk, or a dress maker's measuring tape, or...

(Re the dress maker's tape: don't use your wife's good one! Wind it once around the outside of the flywheel and measure the diameter. 36 degrees is one tenth of this.)

Leon

Offline oily bloke

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Re: EW ignition timing
« Reply #2 on: 08 Nov 2015 at 15:32 »
The EW has 50 degrees advance.
according to the book 10 degrees =3/4" around flywheel periphery.
I use a degree wheel on the flywheel and take a valve cap off to see the piston arrive at tdc. Allow it to come to TDC and begin the transition over tdc. Rotate backwards back to tdc to take up the lash in the gears.
Mark the flywheel and away you go.
Hope this helps.
Andy

Offline patrickhowell

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Re: EW ignition timing
« Reply #3 on: 08 Nov 2015 at 16:57 »
Unfortunately, the flywheel is off the engine, and the pistons and cylinders removed. What I am seeking to do is to locate the magneto pinion in the timing chest in the correct position as regards the
 adjacent cam  so I can close up the timing chest. With the slot on the back of the magneto pinion, it should then be a case of bolting on the mag at a later stage - or am I mistaken in this?

Offline cardan

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Re: EW ignition timing
« Reply #4 on: 10 Nov 2015 at 01:44 »

50 degrees advance is quite extraordinary for a vintage bike, but I checked the EW book and that's what it says. For comparison no JAP motorcycle from 175cc to 1000cc uses more than 45, even the racing engines into the 1940s.

Does an EW really go down the road happily at 35mph with 50 degrees of advance? If so, what is is about the design that requires so much advance?

By the way "10 degrees =3/4" around flywheel periphery" is correct provided the circumference of the flywheel is 36 x 3/4 = 27" (8.6" diameter).

Leon

Offline Doug

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Re: EW ignition timing
« Reply #5 on: 10 Nov 2015 at 03:10 »
The anti-oiling pockets that Douglas used on the EW and various other models from c1925 to 1938 tended to slow the flame front down a bit. Hence lighting the mixture a little earlier than typical to get the main charge in the cylinder going at the proper time.

On my 1934 OHV, the timings seems happy at 40 degrees advance, whereas you would think 35 would have been the maximum for a 600cc sport-touring machine. With slower spinning EW, the anti-fouling pockets might equate to eight to ten degrees retardation of the ignition event. 

-Doug

Offline cardan

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Re: EW ignition timing
« Reply #6 on: 10 Nov 2015 at 04:34 »

Wow, interesting. After I posted I studied photos of the cylinders, and noted the slightly unusual plug position, but I'm still surprised it makes so much difference. I don't think I've seen another vintage bike that needs so much advance. 35 degrees seems to work fine for most of the old things I play with, although I'm sure 40 would be fine too.

Leon

Offline oily bloke

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Re: EW ignition timing
« Reply #7 on: 10 Nov 2015 at 06:53 »
My EW is set at 50 degrees and runs best between 45 & 50. Temperature and humidity play a noticeable part in proceedings too.

Offline patrickhowell

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Re: EW ignition timing
« Reply #8 on: 11 Nov 2015 at 09:08 »
Is anyone able to answer my original query, which was how to position the magneto drive pinion, with cylinders and flywheel off?

Offline oily bloke

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Re: EW ignition timing
« Reply #9 on: 11 Nov 2015 at 09:18 »
Hi Patrick,
My personal opinion is to assemble the engine and fit the mag and pinion when assembled.
I see little benefit in fitting the pinion prior.
A degree wheel is the best way to go and can be fitted to the crank either side and will be accurate.
My EW has a pinion fitted to the mag nose and does not have the pinion/dog setup.
Cheers
Andy

Offline Doug

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Re: EW ignition timing
« Reply #10 on: 11 Nov 2015 at 16:01 »
Patrick,

Well, you will have to make some sort of hub for the flywheel end to attache a degree wheel to, in lieu of having the flywheel fitted. The flywheel does make a handy thing to tape the degree wheel to, or for marking out degrees with a felt time marker along the rim. I presume you want to leave the timing side clear to allow arranging of the timing gears. It is easier to determine TDC after the cylinders are fitted. But there are two ways to determine it without. One is to use the keyway on the timing side of the crankshaft. This points to TDC on a cylinder. However it is hardly worth the difficult task of extracting the pinion, if it is still fitted. Nor am I sure how you can utilize it as an accurate reference; it is typically used as a visual reference (which cylinder of to fire). The other is to use machinist combination square off the face of the cylinder base joint, You need to reference the machined slot on the crankshaft throw that is used for the extractor to dismantle the crankshaft. Or off the side of the center web. Both these are parallel to the plane of the crankshaft throws. In theory. Not having tried this, I cannot say there is enough room to pass something into the crankcase alongside the crankshaft.

-Doug