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MG MGA - Static Timing

This question on static timing is not an issue with me as I refine my timing dynamically and by 'feel'.

I am just converting another historic document for the MGCC and came across a paragraph on timing for unleaded fuel. It states to retard the static timing by 3 degrees.

In our advice to 'new' MGA owners we often quote the static timing as 7 degrees BTDC to help them set up the basics. This is the figure quoted in the manual and, of course it is for leaded fuel, being written in the 1950s. Should we not be telling them to set 4 degrees BTDC since we all now seem to be universally converted to unleaded (at least for all the contributors to this forum as far as I know)?

Steve
Steve Gyles

Steve. Unleaded gasoline was available back in the 1950's when it was known as "white gas". The burning characteristics may well have been different from the leaded gasoline of that era, thus requiring a difference in ignition timing.

Modern unleaded gasoline is supposed to have identical, or almost identical, burn characteristics to the previous leaded gasoline. At least that was the claim in the mid 1970's when it was introduced. When the change over (which included aircraft fuels as well as automobile and small boar fuels) was made, none of the various "expert sources" made any comments about the new unleaded fuels having a different burn characteristic than the available leaded fuels--at least nothing which required the older engines to be retimed when switching to the newer fuels.

As to a starting recommendation for initial timing, more than just the lead content has changed in today's available fuels. Thus, a fifty year old comment in the workshop manual or driver's handbook, about the supposed difference between leaded and unleaded fuels is OBE--overcome by events.

It would be wise to note that static timing is a relic of the past--back in the days when a dynamic timing light was part of the test equipment on the Sun Engine Analyzer, something even many of the better quality small repair shops could not afford. Today, we all have a large choice of various models of inexpensive dynamic timing lights.

The information you are transcribing is of historical interest. So, too, is the concept of static timing. Both of useful, but neither may be perfectly accurate today. In fact, it may not have been perfectly accurate even "back in the day". When I have cross checked static timing with a dynamic timing light, I have found more than three degrees (the number under discussion) of variance between the number of degrees I thought I had in static timing and the number of actual degrees of advance as shown with the timing light. Many reasons for this which we do not need to get into here. Bottom line is that static timing will, with an experienced person, get the engine running. Closer timing needs to be set using a dynamic timing light to provide better accuracy and a more consistent setting. There is a reason that the Brits had a vernier timing adjustment as part of their basic distributor until the 1970's. The 1970's were when the personal dynamic timing light began to become an inexpensive and available tool for the hobbyist. That simple fact caused more change in how things are done than a discussion about whether to use four degrees, seven degrees, or ten degrees of static timing to get your engine running.

Les
Les Bengtson

Interesting stuff Les. They say what happens in the USA takes 10 years to materialise in the UK. I seem to recall that unleaded fuel only became generally available over here in the mid 80s. I specifically remember with my brand new Ford Escort GIA in 1986 asking the dealer if it could be converted to unleaded and all he did was to retard the ignition, advising me that the cylinder head was already unleaded compliant.

The historic article I was converting also addressed compliance, since some of the cars being discussed were, at the time, still under warranty and any unauthorised 'messing about' could affect the warranty.

I could publish the full article with the MGCC blessing but would prefer to leave it for them to add it to their website.

I venture to suggest that dynamic timing lights over here have only started to be items of general DIY equipment in the last 10 years at a maximum. They may have been available before, but not in everyone's toolbox by any means.

Steve
Steve Gyles

Steve. Here in the US, AMOCO was selling "white gas", i.e. petrol with no lead in it, back in the 1950's. I remember because my father would only run it in his cars when it was the only fuel available which sometimes happened on trips. The interstate highway system, as we have today in the US, was begun in the mid 1950's and it was common to find only a single gas station in some of the small towns one traveled through in the hinterlands.

As to the dynamic timing lights, they were coming into common usage, here in the US, by the mid 1970's. My first was hooked in series with the spark plug and the firing of the spark plug also caused the light to flash a rather dim strobe. By the late 1970's, the lights had connections to the battery and a connector which hooked onto the spark plug with the lead connected to the other end of the connector. These provided a much brighter flash and are the basis of the current timing light having either a physical connection or an inductive connection (clamps around the spark plug wire). My latest has the dial back feature and was purchased about ten years ago. More recently, models having both a digital dial back feature and a built in tachometer have become relatively inexpensive and have moved into general use.

As a general thing, unleaded fuel was mandated to be available in the US for the 1975 model year cars which were the first ones to have catalytic converters installed by government requirement. At the same time, aviation fuel began to be available in the low lead versions with the 80/87 octane fuel being replaced by the 80/87LL fuel. The 100/130 octane fuel was, slightly later, replaced by 100/130LL and I used to run it in one of my cars because it was all that was available that would perform as the old leaded, premium fuels used to in that car.

Les
Les Bengtson

Les

I should have been more specific about the timing lights. I was specifically referring to the type with the dial in advance that you mention.

I honestly do not remember unleaded here in the UK until the 80s. I am sure others will say if it was here.

The article I was converting was making repeated references to MG and BL work (and lack of it on some engines) on the unleaded fuel impact on engines in the 80s and 90s. I would bet on the company having not even thought about unleaded implications for the B series back in the 50s.

Steve
Steve Gyles

Steve just to add to memories. In the late fifties ? ? when BMC were selling Morris Minors and also Austin A 30s with the same engine, Morris specs said 5% BTDC and Austin said 10% BTDC. At dealer level there was an avalanche of complaints about the Minor. Cure was to set the timing as the A30s and ignore the factory specs. By then a higher octane petrol was available Sean
S Sherry

Steve
Firstly ignition should never be set by feel, inevitably this will lead to the timing being set too far advanced and if the CR is on the edge then pinking will definately occur and damage accordingly

Static timing is a figure calculated by the factory to achieve dynamic timing at full revs at about 34 degree BTDC.

Because different distributors used differing amounts of mech advance thus each dissy required a different static figure to achieve the desired high rev advance which is the IMPORTANT figure.

When unleaded fuel came onto the market it was the lower octane rating that caused the ignition timing to be retarded. This was simply to ensure that with lower octane fuel the pre ignition value reduces and with CR remaining constant ignition timing reduced to 32 degrees BTDC would ensure pre ignition did not occur

I seem to recall at the time that retarding the timing was only necessary on certain engines, obviously the ones that were on the limit.
Robert (Bob) Midget Turbo

Robert, you make a good case for setting the max advance only and all things being equal ,the static is what it is. Thats what I do on my 1500 and for the record my static ends up at 15/16% at 800 RPM. Checking the engine vacuum this is spot on. Pulls like a cart horse. Sean
S Sherry

Bob

I hope you did not misunderstand me with my throw away word 'feel'. I tune my engine just as you do. I just added the word to denote that the ignition can then always be backed off a smidge if the engine then pinks under load. That said, I do not recall having to do that as the dynamic timing has always worked spot on for me. I also usually fill up with 98 RON rather than the standard 95. It makes a lot of difference, both to overall performance and reducing pinking. I have no idea what my resultant static setting is. If I have pulled the dizzy I normally reset it at about about 5 degrees just to get the motor fired up.

And this was the sole purpose of the thread - to query the static timing figure that was was written at Abingdon in the days of leaded 98 (or greater?) RON fuel. If we are going to give advice on settings to newcomers should we not amend the official figures to reflect the standard unleaded 95 RON fuel used by the vast majority? After all, I bet that less than half of us on this forum own or have use of dial-in advance timing lights.

Remember, the book also gives tyre pressures for cross ply tyres. We always tell new comers the revised figures for radials!

Steve
Steve Gyles

This thread was discussed between 28/12/2010 and 29/12/2010

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