E: Engine Ignition Advance

Chris Launders

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Martyn.
A little trick I have learnt with Lucas magneto's when timing them on your own.

Remove the earth brush and clean out the threads in the body (5/16 BSF on K type), get a 5/16 BSF bolt with about 1" of thread, put a smooth radius on the end and holding the magneto in the advanced position screw the bolt in FINGER TIGHT ONLY. Any tighter and you will risk damaging the armature.

This will lock the armature enough for you to be able to tap the ATD on and start the nut without needing 3 hands.

Do NOT use this to hold the armature while you tighten the nut and remember to remove the bolt and fit the earth brush after.
 

greg brillus

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Oh don't worry the newer BTH mag installation is not always spot on. Ok, not necessarily a fault of the mag more the pinion nut not machined quite correct.......In short, they become shank bound before the taper pulls up tight........This causes the timing to shift either sooner or later causing starting problems and so on. So it's not always the main item that's the culprit more some other part of the puzzle.
 

BigEd

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Once I get the tacho all should be revealed regarding the action of my atd.

Martyn

PS my 'revised' signature says it all.
When we talk about the advance/retard range it depends on what rpm we start our calculation from. I remember some years ago doing some test on one of the late Don Alexander's twins that had an electric start fitted. I think that the figures were around 280 - 300 rpm mark. I will check mine next time I'm in the garage. I don't remember what the kick starting speed was.
 

Monkeypants

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This is the Pazon Smartfire ignition curve for 2 plug head high compression Vincent twins.
The curve made up for the 1360 is similar but only goes to 26 degrees total advance. With the big squish areas on the TP heads, it would probably work at 31 but 26 is a lot safer. From Roy Robertson's dyno findings, on that type of engine there is no power loss by dropping back to 26.
 

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Martyn Goodwin

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Does Martyn use Mk2 Amal ??, If He is some people use a 105 needle jet, I have found 106 for me, U.K.
I know He says use a bigger main jet, But the petrol still has to go though the needle jet.
And being hotter out there, I would have thought it needs to be rich.
Pulled the jet block today. Main jet is 220 and needle jet is 106. Needle positioned midway between middle and bottom groove.

Amal Mk1 Concentric Premier 30mm
 

Bill Thomas

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All you need now is to use the best, Highest cost petrol you can buy, Can't see the point in you
using 91 octane.
All my Bikes are race spec' I don't have pinking, But it's not so hot over here !.
Also use a single grade oil 40.
Cheers Bill.
 

MarBl

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on that type of engine there is no power loss by dropping back to 26
It should be pointed out, that on most engines advancing the ignition is done not only because of power gain, but of heat reduction. In general, the more the ignition is retarded the hotter the engine runs.
If you have an ignition time intervall that delivers more or less constant power, you choose the most advanved ignition point to get the thermal optimum.
Now of course high speed pinging/knocking has to be avoided at all cost, so that sets an upper limit. But you want to run the engine close to that point.
That effect has not to be confused with the retarding of the ignition in a twin spark system. Because of the two ignitions on opposite sides of the combustion chamber the mixture is burnt much faster overall (but still in a controlled way).
One other advantage of a twin spark system is the elimination of ignition induced pinging. A weak spark (and/or slow burning mixture) in a big chamber (500cc and above) can lead to the effect, that the (pressure) shock wave of the ignition starts an uncontrolled, compression induced detonation somewhere else. You dont want that. You want the whole mixture being ignited by the flame front, not by pressure increase.
 

Marcus Bowden

VOC Hon. Overseas Representative
VOC Member
I've been twin sparked since 1990, retarding ignition to 24 / 25 degrees with the addition of a manual advance/retard as conditions do vairy with fuel and terrain, giving less negative power as pressure build-up comes later. It also reduces the blueing of exhaust pipes, a start-up with pipes off the blue fame is much shorter on two plugs than a single plug firing. I have switches to isolate each double coil so periodically I can check that each coil is working. 2010 a coil failed, dropping an exhaust seat in front and hole in the rear piston, the reason for installing switches. (All the time modifying.)
Question:-
Careful inspection of a head I think it possible to fit smaller spark plugs either side of the valves, if the addition of one plug retards ten degrees what would another four do??? Oh, also a central plug as that's been done too.
1990 I stayed with Herve' Hammond for a month doing an engine strip for him to sleave my main bearing housings and saw an engine he had made for record-breaking attempts on low profile three-wheelers for fuel economy, cylinder head consisted of four inlets & four exhausts also four plugs the engine size was 33cc valves operated by solenoids. I think it was shelved because the electrics had to be made by the fuel a not a battery sauce. But it was a magnificent bit of engineering machining.
going bananas !
 

Monkeypants

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Roy's bike, with ignition set up with timing as late as possible,
It should be pointed out, that on most engines advancing the ignition is done not only because of power gain, but of heat reduction. In general, the more the ignition is retarded the hotter the engine runs.
If you have an ignition time intervall that delivers more or less constant power, you choose the most advanved ignition point to get the thermal optimum.
Now of course high speed pinging/knocking has to be avoided at all cost, so that sets an upper limit. But you want to run the engine close to that point.
That effect has not to be confused with the retarding of the ignition in a twin spark system. Because of the two ignitions on opposite sides of the combustion chamber the mixture is burnt much faster overall (but still in a controlled way).
One other advantage of a twin spark system is the elimination of ignition induced pinging. A weak spark (and/or slow burning mixture) in a big chamber (500cc and above) can lead to the effect, that the (pressure) shock wave of the ignition starts an uncontrolled, compression induced detonation somewhere else. You dont want that. You want the whole mixture being ignited by the flame front, not by pressure increase.
In the past, this was always my method too, advance as much as possible but stop just short of the pre-ignition point. Back in the 1960s, Popular Mechanic's Smokey Yunick referred to this method as " Power Timing."

Roy set his racer's timing in just the opposite manner, retard as far as possible without power loss. Knowing how successful and reliable that engine has been when used for years of Sprinting, Road racing and Land speed racing ( holds a UK record), I followed his advice on the ignition timing.
So far its been fine for about 5 k road miles with occasional abuse, although nothing like the beating his 1272 will have endured.

Glen
 
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van drenth

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On advice of the late Big Sid I had been using Nippon Denso W22EP-U plugs for years - and have plenty of new old stock on hand.

Just lately I switched to NGK BPR7EIX iridium, gaped to 0.018" as a trial, mainly to avoid plug fouling.

Here is a photo of the NGK plug after a 10 km run yesterday - no extended idling. Would rather run rich than lean!

View attachment 37877
View attachment 37879
Check your choke valve.
Got the same problem with my Dellorto carbs due to ethanol.
Jan van Drenth
 
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