Ignition Timing - Thoughts?

[Myrtles Man]

Of course, I'm well aware of the age-old advice "If it ain't broke, don't fix it" but, being an inveterate fiddler and regarding the Moggie as much as a Meccano set for grown-ups as a means of transport, I've latterly been thinking about ignition timing settings. The car starts immediately, ticks over reliably and drives and accelerates just fine but, purely out of curiosity (watch out, Puss!) I decided to check the static ignition timing and was rather surprised to find that it was set at about 15 degrees BTDC rather than the book figure of 3 degrees BTDC. Looking back through the many ancient threads on the subject reveals pretty wide-ranging opinions on the matter (unsurprisingly) with the 'keep advancing it till it pinks, then back off slightly' school of thought being well represented and it's all left me slightly puzzled. I know that the A-series is a pretty forgiving sort of engine but, presumably, 3 degrees BTDC, although seemingly very retarded in comparison to many (most?) others, was specified for very good reasons. I welcome the thoughts, opinions and perhaps most importantly, experiences of others in my search for true enlightenment in the matter.

[simmitc]

One factor will be how fuel has changed in composition over the years, possibly requiring a different timing. I have always used the static 3 degrees setting and found it to be excellent. However, a few years ago we had one of the Minors checked on a rolling road with all sorts of diagnostics hitched up. The carb needle was adjusted and the ignition timing ended up at 17 degrees BTDC. The HP increased by 2. The tuner said that every engine is different, and I know one of our friends has a Minor running at 23 degrees BTDC. Having said all that, our car still seems happier nearer 3 rather than the recommended 17. I guess that you pays your money and takes your choice.

[philthehill]

The engine ignition timings quoted in the BMC manual were for a petrol that does not now exist.
All you can do is adjust the timing to give the best all round performance and enjoy.
Also no two cars are the same so there will always be a variance in ignition timings to suit the engine and engine spec.
If the engine is going well and yours appears to be doing so I would leave well alone and enjoy.

[svenedin]

I cannot promise any enlightenment but I am also an inveterate tinkerer.....

I assume you are using points as it is tricky to set static timing with electronic ignition and rather easy with points.

I have set up the timing with both points and electronic ignition. My understanding is that the 3 degrees BTDC is indeed conservative but that the fuels we use are rather different to those around when the workshop manual was written. I seem to dimly remember I ran my Morris on "3 Star" petrol a long time ago and that is a lower octane rating than currently available fuels (so more likely to cause "pinking").

With today's higher octane fuels it is possible to advance the timing a bit from 3 BTDC static without causing pinking. I only use the static timing as a starting point to get the engine to run and then once the engine is hot I use a strobe to dynamically time. The worksop manual says 6 degrees BTDC at 600 rpm. It is important that the revs are that low so that the centrifugal advance mechanism in the distributor does not start to advance the timing. Also the vacuum advance is disconnected and the tube blocked at the carb.

I have a strobe that has a tachometer function and also it can be set with the degrees of advance desired. That means that if I set my strobe at 6 degrees advance, the timing mark appears at TDC when the timing is correct (this is easier than guessing with the "finger" markers on the timing chain cover).

My main concern is not to cause damage. I have used the "by ear" method and have achieved ridiculous advance without any pinking that I can detect but an engine that kicks back against the starter which is obviously not good. I have settled at around 8 degrees dynamic advance at 600 rpm. Every engine is a bit different but not wildly different unless somehow modified.

One reason you may want to err towards the workshop figures is if you ever need to start the car with the starting handle. If the ignition is over advanced you will get a nasty kick back on the handle. People have been known to break their wrists that way even with the correct technique of thumbs out of the way.

I was at ESM some time ago and they had a car that the owner had set the timing on "by ear". It was advanced 20 degrees! They told me they use the workshop figures and then a small tweak if necessary.

Stephen

[Myrtles Man]

I was at ESM some time ago and they had a car that the owner had set the timing on "by ear". It was advanced 20 degrees!

Yes, but did they say how well or otherwise it was running? Also, did they alert you to any particular dangers or potential problems as a result of running it at those levels of advance?

[myoldjalopy]

I agree with Phil that if it is running well it is best left alone apart from routine servicing and maintenance. Over the years I have noted many on here ending up with problems after they fiddled with something for no good reason - or worse, fiddled with a number of things and then have no idea which of the things they fiddled with is now causing a problem!

[svenedin]

I was at ESM some time ago and they had a car that the owner had set the timing on "by ear". It was advanced 20 degrees!

Yes, but did they say how well or otherwise it was running? Also, did they alert you to any particular dangers or potential problems as a result of running it at those levels of advance?

Yes they said it was pinking but the owner could not hear it.

[Chipper]

A good many 'classic' petrol engines seem to like a base setting of 10 degrees of advance or so.

I once bought from E-bay, an 'abandoned project' Fiat 2.0-litre twin-cam Minor that had allegedly been 'rebuilt', however, when I tried to get it to run, it initially overheated badly; I discovered (in addition to other faults) the timing had been set to TDC, and by tweaking it to 10 degrees BTDC as per the manual, it ran thereafter pretty well.

My 1275 Midget-engined Traveller has the Accuspark electronic ignition, and when I first fitted it, it wouldn't run at all; I had to rotate the distributor quite a way to even get it to fire up, then adjusted it until it just didn't pink when under load. I still have no actual idea of what the exact advance setting is, but it runs well enough.

[oliver90owner]

Static timing, in my book, is just a means of starting and warming the engine. No point, whatsoever, leaving it at factory settings if they prove to be inadequate in practice.

The advance-retard curve will be different, for optimal performance, for any modified engine. The factory settings for an old vehicle, such as the Minor, were simply based on being safe for the variations between engines, plus a bit.

Any tuned engine would only run at optimum if set up on a dynamometer - unless extreeemly lucky!

[kevin s]

This is the map we are running on our mildly tuned 1098 with a mapable ignition and std carb.

rps20210808_204723.jpg (54.26 KiB) Viewed 6836 times

Drives really well no pinking etc.

[svenedin]

This is the map we are running on our mildly tuned 1098 with a mapable ignition and std carb.

rps20210808_204723.jpg

Drives really well no pinking etc.

Yes but what do any of the numbers mean? I can make head nor tail of this.

[simmitc]

Ditto. How can it be applied to a standard distributor?

[svenedin]

Ditto. How can it be applied to a standard distributor?

Exactly Simon. What is the advance at how many degrees at what rpm? I cannot understand that screen grab.,

[myoldjalopy]

But Stephen, being a clock and watch maker I thought you'd be an expert on 'timing'!

[svenedin]

Haha and yes. Since the earliest electronics some kind of print out has been used of rate and rhythm. I’m a doctor actually. I just don’t understand the data presented. “Xavier” has always been my elderly patient but there’s never been much difference in age between me and my car. He’s a little older than me. I expect Xavier to behave with the precision of a decent Smiths watch. He never has, he’s too worn. I do have his mileage figures somewhere but now with 2 different “clocks” (speedos) it’s hard to say. He’d done 55,000 by 1975. I’ve taken him twice round the clock and it’s the original engine, never rebuilt. Minimum 300,000

[myoldjalopy]

Yes, my car is about four years older than I am. Its funny to think someone was driving it around in 50's attire before I was even born!

[svenedin]

Yes, my car is about four years older than I am. Its funny to think someone was driving it around in 50's attire before I was even born!

Marvellous. My hood leaks badly so I hardly ever use it. I just get wet. Full outdoor clothing in Xavier. I drive him almost every day. Sun, rain, extreme cold, dark, whatever. I learnt to drive in Xavier at 17. My mum and dad now sadly gone bought Xavier for me and probably loved that car even more than I do. If that’s possible!

[liammonty]

Surely the numbers are degrees of advance at a given rpm (mechanical advance) and load (vacuum advance)?! RPM on the x axis, load on the y axis. There is essentially a max of 32 degrees of MECHANICAL advance at full revs and full load (with no vacuum advance of course), but under lighter load conditions, the vacuum advance allows greater advance than this.

ON aircooled VWs, which are very sensitive to timing, 32 degrees of max centrifugal or mechanical advance was what I used to work to as the maximum safe level.

[kevin s]

Apologies I should have added an explanation.

Yes that's it the table is constructed from the data I could find for the standard distributor. There is a seperate function which drops it to 0 when cranking.

Once we have fitted the twin carbs and free flowing exhaust I might get it put on a dyno to find the ideal settings.