1950 nh - advance and retard lever

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BrianSteytler
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1950 nh - advance and retard lever

Postby BrianSteytler » Wed Mar 06, 2013 4:24 pm

ok, this is almost the last 'stupid' question....hopefully.

its been many years since i used a manual advance/retard level on anything and im puzzled by something so im having to ask - in the ariel owners guide for the bike it clearly shown the 'twin' (a/r and exhaust lifter) levers and the a/r is shown as advanced when pushed forward (cable stretched). this seems a bit odd as i have what i believe is an origional twin lever (similar to the one below with the two cables comming into it nearest me - and not to the front of the unit) and yet when im say riding along at 40mph and i push the lever forward (cable stretched) to advance it the bike looses power and when i pull it back so the cable is 'at rest' so presumably retarded the bike surges ahead.

i have a mo magdyno with the cable entering on the left.

i know it makes little difference as all i have to do is adjust the lever to whatever position the bike runs best - but id just like to get it right in my head!!

0003509_magair-lever-78-rh-dual_480.jpg
0003509_magair-lever-78-rh-dual_480.jpg (52.63 KiB) Viewed 1513 times

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PeterW
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Postby PeterW » Wed Mar 06, 2013 7:01 pm

They are usually set at full advance with the cable slack so that pulling the cable retards the ignition. Having said that some mags may be wrong handed or a previous owner may have timed it with the cable tight so pulling it over advances the timing.
Best to check it is set correct, doesn't take long.

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john.nash
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Re: 1950 nh - advance and retard lever

Postby john.nash » Wed Mar 06, 2013 7:14 pm

Depends where the take off is on your mag.
If it's on the left (on an Ariel) then it's a slack wire for advance.
If it's on the right, like mine, then it's a tight wire advance

points open.jpg
Note position of magcable take off


It looks like left hand "double levers" were the wrong way around.
This means that you would be moving the lever clockwise (pushing forward) for a tight wire advance and anti-clockwise for slack-wire

wng controls.jpg
note the lever is the "wrongway around"


So if your mag has the cable on the left and you have a double lever control then I'd expect the lever to be pulled towards you (at rest- slack-wire) for full advance
John "Josh" Nash
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2009 royal Enfield,1978 t140 bonneville, '67 CJ750, 196-ish Ural M62 outfit, 1960 k750, ''51 kH500, ''49 soon to be Ariel bobber, 47 VH twinport, '44 Ariel WNG, '43 Ariel WNG, ' and piles of rusty scrap ....

BrianSteytler
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Re: 1950 nh - advance and retard lever

Postby BrianSteytler » Wed Mar 06, 2013 9:07 pm

yes, i think i will check just in case and

"So if your mag has the cable on the left and you have a double lever control then I'd expect the lever to be pulled towards you (at rest- slack-wire) for full advance" - just as mine is, presumably the points plate is spring loaded and by bringing the level towards me (slack wire) the spring is relied upon to push the plate to the full advanced position.

thanks.

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john.nash
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Re: 1950 nh - advance and retard lever

Postby john.nash » Thu Mar 07, 2013 9:15 am

BrianSteytler wrote: presumably the points plate is spring loaded and by bringing the level towards me (slack wire) the spring is relied upon to push the plate to the full advanced position.

thanks.


Go out to your bike and take off the points cover and work the advance/retard lever.
You'll see the cable operates a little plunger that moves a cam plate (there is actually a spring in the end of the cable that pushes the plunger back down, when the cable is "slack" and hence the cam plate )


2013-02-12 18.39.10.jpg
Not the right camplate on this one - the indented bit should be around the other side. I changed it.


The cam plate just has an ident that allows the points to open/close. By moving the camplate, you move that indent around.
So a "tightwire" advance, like in the picture, pulls the cam plate anti-clockwise when the cable is pulled.
To do the same thing the "slackwire", with a cable take-off on the left of the points, the cable needs to be loose so that the spring pushes the camplate anti-clockwise.
John "Josh" Nash
webmaster@arielownersmcc.co.uk
AOMCC No.4119
2009 royal Enfield,1978 t140 bonneville, '67 CJ750, 196-ish Ural M62 outfit, 1960 k750, ''51 kH500, ''49 soon to be Ariel bobber, 47 VH twinport, '44 Ariel WNG, '43 Ariel WNG, ' and piles of rusty scrap ....

BrianSteytler
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Re: 1950 nh - advance and retard lever

Postby BrianSteytler » Fri Mar 08, 2013 9:53 pm

i will check it out, still, its a bit strange the 'owners guide' would show an illustration not used on the bike the guide is made for.

incidentially, as i understand it the 1950 nh is fitted with a 6.2:1 compression piston as standard and (again) the guide says the ignition timing is 1/2" btdc for low compression engines and 5/8" btdc for high compression. from what i can glean 6.2 is considered high compression........is that right????


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