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Misc: Ignition Timing of electronic ignition

bodlan

Well Known and Active Website User
VOC Member
Hi

I have just become the owner of a 52 Comet that is fitted with a Boyer electronic ignition unit. It runs OK but I would like to check the timing using a strobe light anyway. Can anyone advise me on the method since I do not have any other information from the previous owner on the unit.

Thanks

Dave
 

bmetcalf

Well Known and Active Website User
VOC Member
Timing

Francois Grosset advertised a timing device a few years ago in MPH. It was a presumably safe substitute for the quill. Maybe he or Trevor can comment.
 

timetraveller

Well Known and Active Website User
VOC Member
I checked out the site refered to but can find no reference to Vincents, although they have been providing ignition systems for Vincents for years. Possibly finger trouble on my part but 'New Boy' Dave might need more help. Without wishing to scare him to death he should be aware that modern fuels burn faster than old style petrol and therefor less ignition advance is required. About 34º instead of the original 38/39º. That assumes no squish bands and only one plug in the head. The problem with just retarding the ignition system with, say, a magneto, is that the system is then so retarded that starting is difficult/impossible. Boyer Bransden, and others are aware of this problem and provide systems with a reduced advance and retard range. So Dave needs to look for a serial number on his system and then contact Boyer Bransden to find out what it was supplied for. The timing disc kit available from CLEVTREV works well but it is easy to break the CD which is supplied as a timing disc.

Good luck :)
 

Pete Appleton

VOC Hon. Social Secretary
VOC Member
VOC Forum Administrator
Timing

You can get a pretty good idea of the timing by removing the advance/retard cover from the timing case, finding TDC through the plug hole with a screwdriver and then scribing a mark on a fibre gear tooth that lines up with a corresponding mark on the inside of the timing cover.

To work out the advance you need to divide 720 degrees by the number of teeth on the fibre gear (720 because it turns at half engine speed). This tells you how many degrees advance per gear tooth you are getting. This method is a bit rough and ready but seems quite accurate.

It is fashionable to keep retarding the ignition to allow for unleaded petrol e.t.c. If you look at the octane rating of the 'pool petrol' that the bike was using when new you could think that unleaded, with its higher octane rating and no need for compression plates, will need even more advance. Most of the 'pinking' problems occur when the Boyer unit (and to an extent the old ATD) advances to full advance too early. I run my Comet & Rapide at 8:1 and 40 degrees of advance at 3000 Rpm with a digital ignition system. I get no 'pinking' and no signs of melted spark plugs or pistons.

It is worth checking, with the strobe, when the advance takes place. If you are at full advance by 2000 RPM then 35 ish degrees advance is the best that you should use. If the timing curve keeps going beyond 2500 RPM then you should be able to give it a few degrees more.

Sorry to go on a bit but this is a pet project of mine

Pete
 

timetraveller

Well Known and Active Website User
VOC Member
Thanks for that information Pete. This is just what we need, ie some facts. However, how much retard does your electronic advance and retard system give and what are its characteristics? Certainly my bike on 9:1 pinks at mid range revs if I open it up suddenly but I have not checked at what revs it achieves full advance. I better do that once it is back together. That is timed at 38/39º and run on unleaded plus Millers octane booster and lead replacement. Roy Robertson's racer with twin plugs and squish bands seems to work well with full advance in the 18º to 24º range. That is on super unleaded and Avgas with a 50/50 mix. Is there anyone on this forum who has done proper tests on a rolling road or similar bit of kit who is prepared to pass on their results? :)
 

Pete Appleton

VOC Hon. Social Secretary
VOC Member
VOC Forum Administrator
Advance curve

how much retard does your electronic advance and retard system give and what are its characteristics? Certainly my bike on 9:1 pinks at mid range revs if I open it up suddenly but I have not checked at what revs it achieves full advance.

It certainly sounds like your advance is coming in too early. It will be interesting to hear what you find. I am running a homemade digital system with a programmable curve capable of 20 degrees retard to 60 degrees advance. As you will see from the picture below I have reached full advance by 3000 RPM. As it is the time before TDC in, milliseconds, rather than angle that is important you should be able to continue the advance upwards beyond 3000 RPM(in fact some cars run to 60 degrees at full speed). I have never been brave enough to try more than 40 degrees of advance as I suspect that it could end up with Mr Vinparts reaching for his order pad.

Pete
 

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Tom Gaynor

Well Known and Active Website User
VOC Member
Ignition advance

I took the Rudge out yesterday, having restored the cr to about 7.1:1. It was about 6.8 before. While it is timed by piston drop, I know it's about 40 to 45 fully advanced. It has a manual retard. What was interesting, and what bears out points made below, is that while it ran easily at full advance at 80 mph, when accelerating from about 50 to 80 it was clearly happier with quite a lot of retard. Once a speed had been set the ignition could be fully advanced and it was happy. Putting numbers to it is difficult, but I'd guess from the lever movement that it accelerated better retarded 15 to 20 degrees. Presumably the more sophisticated car systems (of the 1970's - I've no idea how they work now) with a vacuum input in addition to the centrifugal input would cope better delaying the advance while the throttle was wide open.
What I've also read is that while a Lucas ATD in good condition will steadily advance the ignition over the first few thousand revs, what is likely to happen on older units is that it stays retarded while the revs build, then lets go. They're sticky, in other words. I believe this is what prompted Francois Grosset to design his distributor, since if an ATD sticks fully advances, a starter motor transmission will have a life nasty, brutal and short.
All of that said, my feel is that you're getting full advance too early, either before the design speed, or before the speed it should have been designed for, and if the ATD is in good nick, moderating the right wrist is the answer. One famous Manx Norton (fixed 34 degrees advance, 11:1 cr) tuner insisted that his bikes were raced with a slow-action twistgrip - infuriating his riders - because "they meter the fuel better". Hmmm.....
 

Pete Appleton

VOC Hon. Social Secretary
VOC Member
VOC Forum Administrator
Breaking starter clutches

I believe this is what prompted Francois Grosset to design his distributor, since if an ATD sticks fully advances, a starter motor transmission will have a life nasty, brutal and short.

I believe that the thing that is breaking starter clutches with electronic ignition systems is an effect that I first noticed when I fitted a Boyer system to my Triton. High compression pistons, Wide-line frame, Clip-ons and no decompressor does not lead to a comfortable starting position. When you try to ease the engine up to & over compression, in order to be ready for a full kick, it will suddenly fire just before TDC and launch you out of the saddle.
This is due to the inability of most electronic systems to advance! They can only retard. When setting up the Boyer (and many others) you set the pickup pulse to occur at the point where you want maximum advance to be, in the case ot the Triton 40 degrees BTDC. At intermediate engine speeds the unit waits for the pickup pulse and then calculates the delay time to wait before sparking, based on engine speed. e.g. at 1000 RPM if you want 15 degrees advance you must wait 25 degrees worth of time from the pickup point.
With the engine being turned over at an irregular speed, either by me on a kickstart or by an electric motor, then this delay time cannot be accurate. Hence if you ease the engine past the pickup point then stop you get an enormous kickback and I suspect the same thing wrecks the starter. The answer to this is to either mechanically retard the pickup point as M Grosset has done or use a second pickup at TDC for starting purposes.

I hope this all means something
Pete
 

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