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Misc: Ignition Timing of electronic ignition



bodlan

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VOC Member
#1
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
#2
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

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VOC Member
#4
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

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#5
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

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VOC Member
#6
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

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#8
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
 

Attachments

Tom Gaynor

Well Known and Active Website User
VOC Member
#9
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

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#10
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
 

Robert Watson

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VOC Member
#11
Quite a few people here are using H D stuff. The ignition has a hall effect trigger that senses the gap in a rotating cup. On starting it uses the closing of the gap to fire the system and once a few hundred RPM is reached it then uses the opening of the gap, and advances or retards from there depending on engine speed. Obviously the width of the gap must be maintained when a new cup for a 50 deg twin replaces the one for a 45 deg twin. It also uses two different advance curves, triggered by a Vacuum operated electric switch. The switch is adjustable as to when it switches on what vacuum. One can also buy black boxes that are programable on a computer and one can set such things as a certain number of revolutions before it fires (for use with delicate electric starters, or to really annoy those with a kick starter!), at what rpm the nitrous sytem gets armed, and deployed, even vary from one cylinder to another in case your cases are machined at 51 degrees :)-)), and my favourite feature; when an engine accelerates hard there is a small lag as the sensor reads the rpm that has occurred, and not the one that is about to occur, and you can program an slight extra acceleration in the ignition to compensate for this!
When cruising along at 70 mph it runs quite a big advance - depending where the initial setup is made, in the order of 45-50 dgrees. When sufficient throttle is given, the vacuum switch operates and a more conservative curve takes over.
Spare parts in almost every major town in the world, and really bullet proof. I put thi setup in more than 10 years ago, and have not touched it since. I changed plugs before I went to Australia, not because they looked bad but because I couldn't remember (and didn't write in the book) the last time they were even out of the bike.

Robert
 

timetraveller

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VOC Member
#12
A couple of thoughts here guys. Peter's advance and retard curve could probably by approximated by two straight lines. This could be replicated by using two different rate springs in a mechanical ATD and possibly altering the separation for one of the spring mounting supports. A clever fellow might be able to design a multirate spring to do the same. Bob's information looks very interesting. Any chance of photographs, diagrams or part numbers for those of us without H-D bits and pieces to play with?

Cheers chaps :)
 

Robert Watson

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VOC Member
#13
Took a minute to figure out that Bob was me!

These are H D part numbers from 12 years ago - so may have been superseeded by others, but they should be able to track from this

Vacuum switch 26558-84
Spark coil 31614-83
Sensor assembly 32400-80A
Sensor kit 32400-83A
Ignition Module 32421-86
Rotor 32402-83 (need this to measure the gap width)
Plug, body 74521-77

I fitted all this into a Mistral (as in old Lucas Rita) housing. It all fits under the mag cowl but is a little cramped. I have two 3/16" vacuum lines (one from each carb - downstream of the slide) coming to a T and then to the V switch. I also wired in a light that tells me what curve is being used so I could back off the vaccum switch to run more on full advance.

I recall that the wiring plus was very finicky and I replaced it with a more substantial item, however I also recall that this was improved with an update.

I run BPR7ES NGK plugs on this sytem and like I said before change them ever few years. More than 10,000 miles on the current set and doubt I'll pull them out for that many more.

Robert
 

Matty

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VOC Member
#15
Hi
I have had my Comet since 1956 and do around 3000 miles per year.
If one looks a the characteristics for the ATD, with the normal spring arrangement the unit virtually switches at about 2000 engine rpm from no auto advance to about 35 degrees !!
To make it easy to set for many years I just set my ignition with the points just breaking at TDC. with the ATD not advanced.
If I then jam the ATD fully advanced and check the advance, it is as near as I can measure to 35 degrees and the bike runs very well.
With my 8:1 compression ratio, I do not think the setting is very critical and am not trying to achieve optimum performance so my setting method is adequate and simple.
 

Albervin

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VOC Member
#16
Hi
I have had my Comet since 1956 and do around 3000 miles per year.
If one looks a the characteristics for the ATD, with the normal spring arrangement the unit virtually switches at about 2000 engine rpm from no auto advance to about 35 degrees !!
To make it easy to set for many years I just set my ignition with the points just breaking at TDC. with the ATD not advanced.
If I then jam the ATD fully advanced and check the advance, it is as near as I can measure to 35 degrees and the bike runs very well.
With my 8:1 compression ratio, I do not think the setting is very critical and am not trying to achieve optimum performance so my setting method is adequate and simple.
WOW. Talk about restarting a thread. TEN Years!!!
 


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