Double checking my timing methodology

Hey there,

My strobe light and kickstart lever arrived within the last 48 hours or so. I've finally been able to have a go at trying to start the machine for the first time since I did a bunch of work on her over the winter. I'm pleased to report that she started up, and sounds much better than last year, now that she has proper pipes and mufflers . Still pretty loud though, and she is still running a little rich, according to the sooty look of the plugs.

I had static timed the bike and used a degree wheel and piston stop to check my timing marks - one of them seems to be spot on, so I colored it to make it extra visible with the strobe light. I've really just used the strobe light once so far, and I'm trying to time the bike at lower RPMs as per these instructions:

http://www.nocnsw.org.au/technical/ignition-timing-for-commando-boyer

I was getting what looked to be about 18 degrees at 1500 RPMs, and according to the instructions just mentioned, it should be only at about 11 or 12 degrees at that point. So I figure I need to retard the timing about 6 degrees, and I've attempted to do this by moving the Boyer stator plate counter clockwise just a hair so far. Before doing so I made a few marks so I know where the plate sat before I messed with it.

I just want to make sure that this approach sounds ok before I try to fire her up again. I imagine that retarding the timing should come with the added bonus of reducing my chances of kickback too eh?

Thanks!!

J

Personally, I would take it up to 5,000 rpm and time it there. You really only need to blip it up there a few times. It won’t break. I also would not time at 31 degrees but something a bit closer to 28 degrees per the factory.

If your timing was 6 degrees advanced it would kick back all the time.. If its running without kicking back on start up, advance until it does very occaisonally and then pull it back half a degree , that is how I have timed my original Analague Boyer and a Mk4 Digital . You can always carry out a 5000 rpm blip with a strobe as a final precaution. Personally I have never found strobing very easy or reliable. You take a flash read and then adjust the stator plate , I think its about 1/00 of an inch movement for a degree, but its not too difficult to work out.

Time it with a strobe at the rpm advised by Boyer.

Otherwise you’re just messing about and you don’t even know what your fully advanced timing is.

Triton Thrasher said:

Time it with a strobe at the rpm advised by Boyer.

Otherwise you’re just messing about and you don’t even know what your fully advanced timing is.

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Well my method has worked very well since my first Boyer was fitted in December 1972.If it kicks back most of the time then the timing is at 36degrees .
and Dances , Norton themselves in one of their tuning manuals state 31 for Boyer.

I thought it was common knowledge that the Norton big twins actually performed better at high speed with a little less advance than the factory recommended 28 degrees at high speed. Perhaps even Norton learned something from their earlier days as they changed it to 28 degrees.

Have to agree with Triton Thrasher that unless you check the advance at higher rpm, you really do not know what your full advance is, especially since the ignition gain is so much greater at lower rpm. I also have to ask if all Boyer ignition curves are identical, especially from model to model?

Thanks guys! So moving the stator plate counter-clockwise to retard the timing is the way to do it right?

It might have been more like 4 degrees off, rather than 6. I was doing this alone and with only a few minutes, and the mark was moving around a bit. It wasn't kicking back all the time, only occasionally, so I'm hoping that what I've done thus far fits with your way of doing thinks Oldmikew. I will blip it up to 5000 to check as well if she starts now that I've made this minor adjustment, as all three of you have recommended.

Supercat said:

Thanks guys! So moving the stator plate counter-clockwise to retard the timing is the way to do it right?

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If your ignition stator plate is located at the end of the cam (typical of later model Commandos), yes, rotating the stator plate counter clockwise (as you face it) will retard the ignition.

Dances with Shrapnel said:

I thought it was common knowledge that the Norton big twins actually performed better at high speed with a little less advance than the factory recommended 28 degrees at high speed. Perhaps even Norton learned something from their earlier days as they changed it to 28 degrees.

Have to agree with Triton Thrasher that unless you check the advance at higher rpm, you really do not know what your full advance is, especially since the ignition gain is so much greater at lower rpm. I also have to ask if all Boyer ignition curves are identical, especially from model to model?

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Surely the 28degrees figure was for points ? The Atlas was timed at 32 but that had a significantly lower compression. The 31degrees was in a service release for the production racer and tuning. It gave 28degrees for points and 31 for the Boyer.

I would imagine that you were running significantly higher compressions than the stock 8.9 to 1 which would require less advance.

Yes you are probably right , I doubt that all Boyer curves are identical and certainly the analogue one would go on advancing beyond 5,000 rpm. My first assumption with Boyer was that if you timed it to 28degree at 5000 you would get 31 at 7000 Whether this is so I do not know and with the digital ones may well be different. the other thing is the cam chain will affect accuracy by as much as 2-3 degrees and if you have a strobe that plugs into the ht lead there goes a sharp image once your blip goes over a few thousand rpm.

As a final check and precautionary measure a quick blip upto 5000 rpm with a strobe is a good idea
but crude though it sounds my method will not hole a piston and gives a good approximation which is all you are going to get with a strobe anyway.

oldmikew said:

Surely the 28degrees figure was for points ? The Atlas was timed at 32 but that had a significantly lower compression. The 31degrees was in a service release for the production racer and tuning. It gave 28degrees for points and 31 for the Boyer.

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Yes, 28 degrees was for points and 31 degrees is a peculiarity (compromise) associated with the Boyer. Lower compression (ala Atlas) seems to infer less efficient combustion chamber thus less efficient combustion thus a need for more advance (apparently 32 degrees) but we are discussing the Commando application on a Commando forum, correct? After all, vintage Triumphs specify somewhere in the mid 30 degrees but that's not relevant here other than a somewhat irrelevant reference.

I am pretty sure the 31 degrees for a Boyer has more to do with Boyer's recommendation which the service release had to parrot or think about and demonstrate otherwise. As far as I am concerned, the 31 degree target for a Boyer is a deficiency (and compromise) as they are probably trying to get the curve to where the engine wants it at for the lower rpm. I seem to recall a properly operating OEM AAU more or less slams to full advance (to 28 degrees) somewhere around 1,500 to 3,000 rpm and the motor runs happily along from there on so what is the point of an additional 1, 2 or 3 degrees for beyond that? I think Jim Comstock found the Commando motor at speed is happier with a little less than 28 degrees advance at high speed but I cannot recall if that is a general application or for some highly refined Commando race engine. From dyno results I have found the race motors are happier with a little less advance for whatever reason.

Dances with Shrapnel said:

As far as I am concerned, the 31 degree target for a Boyer is a deficiency (and compromise) as they are probably trying to get the curve to where the engine wants it at for the lower rpm......

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My first Boyer , the analogue one with a large brown slab was also intended for BSA and Triumph
as well as Norton , so yes you are right the 31degree timing is a compromise. And yes would put my hand up to confusing CR with combustion efficiency in my rule of thumb thinking.

However there is another factor ... the time available for combustion decreases quite dramatically as revs rise so other things being equal one might expect to need a stronger spark . Magnetos were always held to be superior to coil ignition at high revs , I had assumed the advance was to compensate for this by allowing more time for combustion in conjunction with a progressive advance curve. 31 degrees or more advance at say 2000 rpm , which used to happen with the OEM AAP once the slots elongated was a receipe for mechanical disaster, one at least the boyer avoids. Of course the factory knew about this and welded their ARs up on test bikes but never said.

Dances with Shrapnel said:

From dyno results I have found the race motors are happier with a little less advance for whatever reason.

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But with stock engines the opposite seems to be the case.. If I want a sweet running engine with loads of torque that responds well to small amounts of throttle then I pull it back to around 26or 27 at 5000rpm .If I want max power and top speed then around 28 or 9 but it feels slightly harsh.

Instead of a dyno I used to fine tune my ignition by wto runs on the Motorway and incrementally adjusting the Boyer stator..at a service station ..and then blasting off to the next one. Unfortunately there are now too many speed cameras to risk 120mph on a British Motorway. But these were very fine tuning exercises .Now adays I do not bother and just set up as suggested to the OP

Clearly ,whoever flowed your heads knew what they were doing.

I did not take it that you confused anything. There is a general well known and over simplified correlation between CR, combustion efficiency, and time to burn. Time to burn has always been an interesting one for me as one would simply think more speed - less time - more advance but it is not that simple and ignition mapping can get real wonky looking. I've read that with higher port velocities you get greater in cylinder/combustion chamber turbulence which reduces time necessary to burn. I suppose (speculate) that the air/fuel is better mixed at higher speed lending itself to requiring less time to burn. You are really dealing with a whole slew of related rates and changing conditions so engine speed alone is obviously not the whole picture.

Your topspeed/ max power setting experience of 28 or 9 degrees seems closer to 28 degrees than it does to 31 degrees. Do you (did you) have dyno results to support your experience?

Unless you get it on a dyno, you really don't know what the ignition timing is doing throughout the rev range. WOT timed tests are great and seem to be acceptable for timed WOT conditions but I ask rhetorically only; what about the rest of the engine's performance range. In other words, where most of us mortal reside and play on our Nortons?

There are three things which must be balanced to achieve optimum combustion conditions - comp. ratio, fuel mixture and ignition timing. As your revs increase the rock-over time becomes less depending on the internal geometry of the motor - rod and stroke lengths, so in trick ignition systems there is a curve which advances the timing so that the combustion event always begins and ends at the same piston positions. Changing the static advance moves the whole curve forwards and backwards. When I set my motor up, I choose a static ignition advance to suit the fuel I am using, then I change the jetting of the carburation to suit it.

Dances with Shrapnel said:

I've read that with higher port velocities you get greater in cylinder/combustion chamber turbulence which reduces time necessary to burn. I suppose (speculate) that the air/fuel is better mixed at higher speed lending itself to requiring less time to burn. You are really dealing with a whole slew of related rates and changing conditions so engine speed alone is obviously not the whole picture

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Absolutely and I think I remember reading in a Cycle World no less a personage than Dick O'Brian sayin g that a batch of heads that came back from the foundry with undersized ports actually gave the best power..

The bike has never been put on a dyno , so nothing to show but I take your point . I am also building a Steve Maney engine ie have the cases crank stage 2 head cam , cylinder and pistons. That I definately will set up on a dyno.

Glad that's all cleared up. Did we time the motorcycle?

acotrel said:

in trick ignition systems there is a curve which advances the timing so that the combustion event always begins and ends at the same piston positions. Changing the static advance moves the whole curve forwards and backwards.

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interesting point .

This forum is amazing. Every time I post a question I learn an awful lot. Thanks for all the responses folks.

I had a chance to get back to the bike this evening, so I've got an update. I tried starting the bike with the new setting I mentioned in the first post, and I could not get her running - just an occasional backfire. So I adjusted the stator plate a half a hair back towards where it was originally. That worked and the bike fired up pretty easily with that setting, and she sounds a hundred percent better than the last time I had her going. My neighbors came over for a look and it was possible to talk to them over the running engine with no trouble, and they said nice things about the sound. She sounds like the Commandos on YouTube now, rather than overly obnoxious. Things looked closer with the strobe light according to the low RPM instructions I was going by before. I think I've got to be very close, since I'm half way between what seemed to be too advanced, and being too retarded to start - and the entire adjustment was extremely tiny. I'm probably ready for the 5000 RPM blip, and maybe a test drive. I'll have to wait till tomorrow for the blip as it's getting late and I don't want to disturb the peace .

The richness is looking like the biggest issue now. The plugs are coming out coated in soot after running for just a few minutes. It doesn't seem to be affecting combustion so far, but I pull them and wipe them off each time I turn the bike off. It would be nice to not have to do that.

Movements of the stator plate are very small... be careful when you tighten the two screws it does not move back toits original position... btw I always use a magnifying glass to look at the stator plate marks I made when making adjustments

It's really a 2 man job - one to hold the throttle and another to read the timing marks. With a Boyer it's 31 degrees at 5000 or 29 degrees at 4000 rpm.

Yes, strobe timing is ideally a two person excercise; most efficient. Three people is even better where the throttle person can sit on the bike with the main benefit being revving the bike off the center. On the center stand on a hard surface the bike tends to buzz along the floor a bit.

As for blip, take your time and don’t be timid about revving the engine to 5,000 or maybe even target something above 5,000 rpm to assure you have reached the plateau range of the Boyer advance curve.

Hearing protection also helps, mainly to calm the nerves a bit while doing this.

Suggest a fan on the engine to keep heat in check or campaign the work and let the engine cool off in between attempts. Usually it only takes about 1 minute or less to do this if you have the help and a plan in place.

Let us know how it goes.