Single Cylinder Ignition Timing

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simon.holyfield
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Single Cylinder Ignition Timing

Postby simon.holyfield » Sun Aug 11, 2019 10:28 am

cheers

Simes

'51 Square Four,
'58 Huntmaster,
'42 W/NG,
'78 CX500
http://ariel-square-four.blogspot.com

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chris.shearwood
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Re: Single Cylinder Ignition Timing

Postby chris.shearwood » Sun Aug 11, 2019 12:30 pm

Simon,
I think you've done a very good job detailing all the steps of the timing process. The only thing I would add is that there should be some provision made so that your bamboo stick doesn't disappear down the plug hole if the motor is turned too far. Don't ask how I discovered this to be a good idea. Oh well, it probably needed a decoke anyway, eh?
Chris
1946 4G, 1950 NG and 1951 VH

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simon.holyfield
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Re: Single Cylinder Ignition Timing

Postby simon.holyfield » Sun Aug 11, 2019 5:41 pm

Thanks and good idea Chris, I'll add that in.
cheers

Simes

'51 Square Four,
'58 Huntmaster,
'42 W/NG,
'78 CX500
http://ariel-square-four.blogspot.com

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cmfalco
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Re: Single Cylinder Ignition Timing

Postby cmfalco » Sun Aug 11, 2019 6:09 pm

chris.shearwood wrote: there should be some provision made so that your bamboo stick doesn't disappear down the plug hole if the motor is turned too far.
The first photograph shows the timing stick I made for my 1928 Ariel, with the wire to make sure it doesn't disappear down the plug hole and with two notches corresponding to the two values of inches-before-TDC I found in manuals.

The second photo shows the similar timing stick I made for my 'Competition'-model Gold Star. The reason for the 20-degree notch on it is the hard-stop tool I use stops the piston at ~20-deg. so this notch is useful for the initial approximate setting of the large diameter timing protractor disk I use, shown in the third photo.

After using the timing stick to initially set the protractor at ~20-deg. I then install the hard stop in the spark plug hole and then I can then sneak up on the stop with a series of small movements of the engine, rather than possibly having to turn the engine through nearly 300-degrees before hitting the stop (causing frustration that can result in the piston hitting the stop harder than it should). As can be seen, with this protractor it is easy to resolve better than 1/4-degree.

The fourth photograph shows I have TDC painted on the crankshaft nut of this Gold Star to identify the position of TDC on the compression stroke. Clearly, this is only an approximate setting of the crankshaft, but it is invaluable in avoiding having to peer into the plug hole to be sure I don't carefully set the timing to 39.00-degrees on the exhaust stroke.

Timing sticks and cigarette paper have their uses in emergencies, but this is 2019, not 1950. I only use these timing sticks in "emergencies," such as on the road to reset the timing if it slips, which is precisely what happened on the Ariel one day on the Cannonball Rally last fall. Or, to quickly get the timing close to the required value before doing it carefully. Note that when dealing with an "emergency" on the side of the road it would be particularly easy to lose a timing stick like Simon's down the hole.

The inductance of the primary circuit changes by a large amount when the points open so I use an inductance meter[*] to determine the precise location of the opening which, in combination with the large protractor, lets me reproducibly set the timing on my bikes to no worse than ~0.2 degrees. Further, the inconvenient fact that the timing stick is on one side of the engine but the points are on the other side is irrelevant with an inductance meter and protractor.

[*]Although good ones cost more, LCR meters from China that are perfectly adequate for this are available on eBay for less than $20.
Attachments
TimingStick_Ariel.jpg
TimingStick.jpg
TimingDisc.jpg
TDC.jpg

Mick D
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Re: Single Cylinder Ignition Timing

Postby Mick D » Sun Aug 11, 2019 6:40 pm

Hi

I use this to locate TDC and a timing disc to establish crank position - minimises the 'ineffective crank angle' error
TDC.png
TDC.png (319.1 KiB) Viewed 1037 times

Regards Mick

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Re: Single Cylinder Ignition Timing

Postby cmfalco » Sun Aug 11, 2019 7:02 pm

Mick D wrote:I use this to locate TDC...
The reason why I don't use a dial indicator to determine TDC is movement of the piston is very small there. An error of only 0.001" (0.025mm) in determining TDC on my 1928 Ariel corresponds to a crank angle of 1.7-degrees. Even 0.0001" (0.0025mm) is 0.5-degrees, which is more than 2x worse than I do with a hard stop.

A dial indicator would be useful to accurately determine the 5/8" (or whatever) BTDC position of the piston if it could be inserted vertically in the plug hole, which it can't be due to the lack of clearance. It (aided by trigonometry) could be useful even when at an angle, but only if the piston had a flat top. The problem is that as the piston descends the tip of the dial indicator moves across the top so the dome makes an accurate measurement impossible.

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Re: Single Cylinder Ignition Timing

Postby Mick D » Sun Aug 11, 2019 7:54 pm

Hi

The DI is far more accurate than a 'stick' and to establish TDC my procedure is to determine a point either side of TDC and bisect the angle - this is not subject to the direct measurement errors you correctly identify.

How does the 'hard stop' work?

Regards Mick

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Re: Single Cylinder Ignition Timing

Postby cmfalco » Sun Aug 11, 2019 10:02 pm

Mick D wrote:my procedure is to determine a point either side of TDC and bisect the angle
It appears you have a DTI with 25mm travel that is held off the head by a spacer longer than that so you must have an extension on the DTI. The limitation on the accuracy of doing it this way is still the ever-decreasing movement of a piston near TDC, so the extension must be long enough to contact the top of the piston more than ~1mm BTDC. However, irrespective of the resolution of the DTI, since the long extension is contacting the piston at an angle it must be stiff enough not to bend as it contacts the rough surface of the carbonized piston.

Mick D wrote: How does the 'hard stop' work?
The photograph shows my piston hard stop, which I cross-drilled to let the air out as the engine rotates. Without an escape path it would be an uphill battle to turn the crank.

As I mentioned my stop contacts the piston at ~20 degrees BTDC. This corresponds to the piston being ~3.6 mm below TDC. At this location movement of 0.1 mm (0.004") corresponds to rotation of 0.29 degrees so as long as the piston doesn't contact the stop hard enough to indent by this much it fixes the angle to better than 0.3 degrees.

In operation I use the timing stick to set the protractor to some value (e.g. 20-deg, 39-deg, or whatever), install the hard stop and, since I know the stop will be contacted at ~20-deg., the initial approximate setting of the protractor lets me slowly approach the stop so as not to indent the piston by any amount, let alone as much as 0.004". I note the value on the protractor then turn the engine backwards through ~320 degrees, approaching the stop again slowly. Splitting the difference in readings gives me TDC quite accurately and I then reset the protractor accordingly.
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PistonStop02.jpg

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cmfalco
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Re: Single Cylinder Ignition Timing

Postby cmfalco » Mon Aug 12, 2019 1:45 am

cmfalco wrote:
Mick D wrote:my procedure is to determine a point ...
Oops, I meant to correct a typo in my previous post but screwed up and created a new post that the forum won't let me delete. So, I reduced the size of the quoted text and added this explanation.

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Re: Single Cylinder Ignition Timing

Postby CylvaBirch » Wed Aug 14, 2019 4:35 pm

My timing stick is a plastic drinking straw with the concertina bit bent over so it cannot fall down the hole.


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