ATD Advance Timing Curve?

Pete Appleton

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When using the rear wheel with top gear engaged, I was told to bump the engine forward slightly past your chosen full advance position, then bump backwards towards your desired setting, to put the lash in the state it would be when the engine is pushing the drive train, then tighten up the ATD on the magneto taper. Is that correct?

Sorry Steve, that is not the way. You are quite right to worry about backlash but the backlash that we are interested in is that between the crankshaft and the magneto. For that reason you turn the crank forwards up to your timing point. The method of turning the crank is unimportant so backlash in the primary/gearbox being in the wrong direction doesn't matter.

I seem to spend most of my life shouting at apprentices "Don't turn the ####### thing backwards " when setting timing.

Cheers

Peter
 

cinquecento

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update; openining points by 2K makes it a b*gger to start, settle at a slack 12K on the points and things seem a little crisper; surely that's got to be placebo effect?.

Whatever, the next step would be to file a little off the retard ear stops but i think i shall just enjoya releable ride for the immediate future.
 

vibrac

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Thought this would be a good place to raise the question:
I have just finished timing my Grey Flash Replica with a BTH (no - an Original one ) with manual control
It took me back to all my days on a 350 G3LS with manual advance lever all without trouble. I would have thought it a joy for a Comet plenty of retard for starting then wack it on for running.
For me if I go back to Mag for my road Comet I would love to ditch that ATD ,so what manual ends fit the standard Lucas Comet mag? tight or slack wire advance ,experiences?
 

timetraveller

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Definitely go for the slack wire advance. At one stage I used a tight wire advance on my production class sprinter. Half way down the front at Brighton, which used to be either a half mile or kilometre, it slackened off and retarded the ignition. I had to take my hand off the left hand grip at over 100 mph and move the advance/retard lever on what was then, and still is, a very bumpy course. The fact that I can still remember it show that it was a 'stimulating' experience.
 

Kansas Bad Man

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I don't know the part number for the mag end, probably magnitoman does. I humbly disagree with timetraveller . The cable should be made up with zero slack, the reason is for positive response to advance and retard choice. You are in constant play with the opposing force of the mag end clockwise and counter clockwise positioning spring. The friction spring or springs on the advance/retard lever is the positioning force. this must be in good nick and have enough friction coefficient to insulate it against any adverse vibration input causing unwanted movement .
 

TouringGodet

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Max, there are two directions of rotation. Tight vs slack in this context refers to whether pulling the cable rotates things from full retard towards full advance, or pulling the cable rotates things from full advance towards full retard. I believe tight means the former, and slack means the latter, ie, do you need to maintain tension to keep the timing advanced, or maintain tension to keep the timing retarded. If the friction at the lever fails and the lever closes, the cable goes 'slack', are you now running at a retarded timing position, or an advanced timing position?
 
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greg brillus

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Look at it this way.....if the cable breaks, which way do you want it to go......full advance me thinks, otherwise you will loose all power. What type of mag was a KVF-TT you need to copy that. Thy had the same end housing as a twin mag off a Constellation, same rotation as a Vin...cheers.....Greg.
 

vincenttwin

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Just put the newer BTH mag on my A comet set it up for 36 BTDC running about a 9-1 piston , our fuel over in colorado is crap 10% ethanol, I will see how this works out.
 

greg brillus

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On 9:1 pistons 36 degrees may be too high.....listen carefully for any detonation, no one likes pulling these things apart again so soon........Just ask MartynG.
 

Kansas Bad Man

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If you use the procedures I suggested , it makes no difference if the retard is a full open lever or a full closed position , assuming the ratio of the mechanics
provides the desired advances and retards. If the lever has a over amount of degree of travel you will find where the engine is happy after all that is the main reason to have a manual advance so you can tune for best performance under various conditions.
 
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