I've just installed a replacement TW Timer and brush after 7,500 miles excellent service from its predecessor (which developed a bit of arc-pitting at the leading edge of each segment). This is in my '24 Speedster with Z Head, Chaffins 280 cam and Ford Magneto.
I created the following timing diagram showing the points at which the various cylinders fire at Full and Half Advance and also Full Retard.
For this info I marked the crank position on a piece of cardboard then transposed the results onto a protractor diagram — as such there are likely some small errors in my original marking and maybe slight variation in crank position in each of the four possible ways to engage the crank pulley.
The front cover was R&Red last month and am reasonably confident the timer is well centered. The standard alignment tool is not usable if there is an aftermarket seal on the crankshaft end so we made another one that was recessed to clear the seal and fit snugly in the outside ring.
• Is the 2.5-3° range through which each cylinder fires in full or half advance likely to cause a noticeable roughness or lack of power?
• Should the timer rod be tweaked to move all ignition events another 10° counterclockwise? Logic suggests that more available timing advance can only be a good thing, but I know there are timing "steps" that apply when running on mag, so maybe that 10° might not get me into another step, or even if it did, that maybe the last step would not be usable (I seem to recall that a Z Head runs best at a little less advance).
I know there is a printed diagram showing where the steps occur on mag but I can't lay my hands on it.
The most, and maybe only, critical issue is that on full-retard the firing reliably happens a few degrees AFTER TDC. That's what you have. Whether 15 degrees is more than you need, I can't say - although others will have opinions.
If the differences in the degrees experienced by different cylinders is accurate, and all taken at the same setting, that would indicate some inaccuracy in the construction of the timer. However, if they were measured at different times, it is probably indicative of 'slop' in the linkage, which seems to be well within acceptable amounts.
What you show is just one of the advantages of running the ETimer. Yes, I bet even though your varibles are not extreme you would see an improvement.
One thing hat normally happens is the new timer replaces one that is worn out so any new one shows a big improvement.
As Peter has said, you have ATDC firing at full retard.
From checks I have done with Anderson, TW and roller timers, I think the spread you have is about as good as you will get.
You have +/- 2 degrees spread, which is +/- 1 degree in the timer. The track radius is about 1.1", so 1 degree is 0.02" around the track. When you consider that you are working on the edge of a carbon brush moving from insulator to metal, and a timer casing that may be able to move a little radially in its recess, that doesn't seem bad to me. Also, I guess that this new timer is not yet 'run in', and the brush contact won't yet be the full area.
If you are running on magneto, a greater spread between cylinders is tolerable - greater than you have measured. You find the timing 'sweet spot' at about half advance and the sparks are then timed by the magneto, (but influenced by any differences in the coils' set up such as a larger cushion spring travel).
If you are running on 12v DC, a 3-4 degree spread is unlikely to be noticeable in a Model T engine.
Chris : Thanks for posting this as I had no idea of the seemingly excessive advance possibilities. If having an initial setting of 15 deg ATDC you could still achieve almost 45 degrees BTDC of advance at probably less than 2000 RPM. Having anything over around 25-30 degrees seems a waste of travel and setting above 35 degrees would tend to try to run the engine backwards. After reading this post, I'll be a little more careful with the "advance " lever. My experiences with Ford flathead V8 motors is that anything over 22 degrees of advance does more damage than good as the flathead design is "turbulent" and requires a way less advance than say a "hemi" that is a lot less turbulent than the flathead and must have lots of advance. Makes one wonder why Henry would provide such a large range of advance capability. Thanks again : Bruce
Like Chris Barker said, If you are running on magneto, all you have to do is make sure the timer is set at a position that allows all four cylinders to be fired by the magneto's wave. It will take care of the actual timing.
On battery, the timer tells the coil WHEN to fire, ie, it fires when the timer makes contact. On magneto the timer only ALLOWS to coils to fire, which will be the next pulse after the timer makes contact.
Thank you all for your comments, much appreciated. It appears I am within a normal/acceptable range on my timer setup.
Hal, your second paragraph was a very helpful summary.
Hal's description of the timer function is a generalization that completely ignores critical details that differentiates a running engine from an optimally performing engine in my view.
A more accurate summary of battery operation; the timer tells the coil when to begin charging the coil. The coil point adjustment determines when the coil will fire spark with respect to timer activation. Advancing or retarding the timer directly effects the coil spark timing. On magneto, the timer position determines which magneto pulse and its associated relationship to piston position is used to charge the coil to fire spark. Minor misalignment between magneto voltage pulse and timer position has minimal impact on engine performance because the magneto voltage increases with time. So even if the timer is not set to begin charging the coil exactly at the very beginning of the magneto voltage pulse(0 volts), this delay in charging the coil is compensated for by the fact the magneto voltage will be higher than 0 volts when the timer does make contact and begins charging the coil; the dwell time to fire spark will be faster due to the higher magneto voltage.
Cylinder to cylinder timing variation will impact overall engine performance; how smooth the engine runs and the top speed it can achieve. Minimizing cylinder to cylinder timing variation will provide the best engine performance but you have to consider all the variables that contribute to this variation. The cylinder to cylinder timing variation Chris measured on the timer can be compensated for by mis-adjusted coils for example such that it minimizes cylinder to cylinder ignition timing and the engine runs exceptionally smooth. The more likely scenario, however, is differences in coil to coil dwell time to fire broaden cylinder to cylinder timing variation degrading engine performance. Setting all 4 coils for equal dwell time to fire spark helps minimize the cylinder to cylinder timing variation. Folks who adjust their coils this way consistently report remarkably smooth engine performance.
You know, Mike? When I was writing that, I wondered if you were going to come on here and take exception to what I said. But I told myself, "This is not an E-Timer or ECCT discussion, and I've not done anything to piss him off, so maybe he won't." I should have known better.
I am fully aware that there are some other factors in play, but for a two sentence statement, I think I did a pretty good job of summing up how the thing operates in a way that most anyone could understand. I'd like to think my generalization was helpful to some, and since I'm not trying to market any product here, I thought my explanation was good enough.
Now, time to break out the charts and graphs and oscilloscope screenshots dazzle them with your brilliance.
Hal, Nothing wrong with your generalization for some but thought it seriously lacking in detail for the OP seeking advice on ignition timing variation. Especially considering the meticulous detail and initiative they took to characterize their timer variation. I thought the added detail I shared would be of interest to the OP and aid them in attaining their desired level of ignition performance so I offered it.
I do have to commend you for providing such an excellent example why many knowledgeable Model T enthusiasts strictly lurk on this forum but Never participate in sharing their considerable knowledge and experience here.
Then perhaps you should have skipped your first sentence in your 12:14 post. Re-read it and tell me you weren't getting personal. As for your last sentence in your 4:41 post, I know a few who think the same of you.
Sorry I do not see his first line being that way.
For what it's worth (probably nothing - but that's me) - there is, has been, and no doubt will continue to be a great amount of information disseminated on this Forum - and it truly pains me greatly when squabbles erupt.
There will ALWAYS be a difference of opinion - how boring things would be if there were only black tudor Fords on the roads today....how many folks look down upon anything that looks "cookie-cutter".
Please - Please - for the good of the hobby - for the benefit of all - please play nice.
It is true - I personally know several very knowledgeable folks who refrain from posting on this Forum because of personal attacks after a post.
Can't we be nice here? - There is just too much grief, aggravation, suffering and discontent in too many other places these days.
How about a "time out" and watch this...
Sorry Hal, I don't see my first line being that way either; nor was it meant to be. Perhaps if I stated:
Hal's description of the timer function is a good generalization but completely ignores critical details that differentiates a running engine from an optimally performing engine in my view.
It may have averted your terse verbal lashing. I know better now for next time; should I dare to participate in the dialog.
Thanks Mike for taking the time here to explain more about what is Chris's concern.
Hal I wasted part of my day going back and rereading what Mike said that so terribly offended you and will have to say Man, you must have some very thin skin or something. I also didn't see where Mike tried to sell anything?
One could easily see that Chris spent considerable amount time of time and detail and while your explanation was good there was nothing wrong with Mike adding more detailed content.
You must be related to that new Hot Head guy trying to sell his '13 touring and got so offended by blah blah blah.
Thanks Dave you are Certainly RIGHT
As an experienced battery only coil user, I found that by setting the dwell time on each coil to be the same, there was a noticeable improvement to the performance.
If one coil fires at, say, 2ms after timer contact is made, and the next coil fires at 4ms, and so on, this is not going to allow the engine to perform optimally, with the coils firing advanced or retarded relative to each other.
The difference in dwell time across a random selection of coils is clearly measurable, and it stands to reason that if they are all made the same, then timing variation is only limited by the timer itself.
I'm curious why anyone would assume Mike is trying to sell something here, because coil dwell time can be measured using common laboratory instruments.