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MG MGA - Timing & unleaded fuel

Reading this months Practical Classics (p78) it says ignitions needs to be retarded to run on unleaded petrol. I have a 1622cc with "unleaded head". Can anyone advise what the correct setting should be please?
Graham M V

Graham,
Truthfully, if your engine is not experiencing predetonation (pinking,I think you Brits say)I would not worry about this. Lead was originally used to help control detonation (way back in the 20's) but when it was removed other additives were used to replace it. Octane is what really controls pre-ignition.
Cheers,
Gerry
G T Foster

When unleaded was introduced it was widely commented that timing needed to be retarded in comparison to the settings used for leaded fuel for the same engine setup.

Getting an engine properly set up and running sweetly is a combination of octane, mixture setting, compression ratio and timing / advance curve. For instance my supercharged engine suffers from detonation if I use 95 octane but behaves if I use 98. The Shell 100 octane stuff is wonderful, but far too expensive to make sense for regular use.

If a car is standard and unmodified in any way from factory specs, then the book settings can be used, no problem, with a minor correction for unleaded - I used to use 2 degrees of retard for unleaded I think before I started "doing stuff".

The ultimate way to set a car up is on a rolling road, you have to check that CR is in the desired range (head off, and measure the head chambers and bores and get the calculator out), then to set the carbs right so that the mixture is not too lean (kills high performance engines very quickly), or too rich (just buries the performance under a fuel soaked blanket), then set the timing so that power is delivered when you want it without any unwanted hiccoughs or expensive noises. Timing has to be set to suit the compression ratio - the higher the CR the more likely detonation is to occur, so timing may have to be retarded a bit to take account of higher than standard compression (e.g. having had the head skimmed).

The advance mechanism of the distributor has to be correct for the engine, cam and CR, and all in working order (that's why a new distributor can make such a difference to even a fairly worn engine). If the distributor has too much, too little or just inappropriate advance, then all the other careful checking is a waste of time.

So unless all the other things are on song, retarding the ignition on its own is not going to make much difference.
dominic clancy

The sure fire way to set timing and the way it is done by many is to set the maximum advance at 32 degrees. It helps if you use a programable timing lamp Then with the engine revving at 4000 rpm and the vacuum DISCONNECTED set the timing at 32 degrees BTDC

As stated above distributors may be all over the place so setting the timing to a book figure is hopeless unless you can guarentee the dissy is the perfect one. The original spec was the timing at static or idle that when the engine is revved would have the 4000RPM figure at about 32 degrees.

Also as stated above if the car does not pink you do not need to worry too much.
Robert (Bob) Midget Turbo

I've been running my MGA 1500 for years on 87 Octane unleaded petrol with ignition timing set at 20º BTDC dynamic at 1100 r/min. Cranking compression is around 155 lb/sq in.
Seems to run just fine: no pinking; a little run-on when hot.
Fraser Cooper

Went to Argentina for a vacation last year. The top grade of gas available was called "Fangio"
Art Pearse

Speaking of Fangio. If anyone here gets a chance to visit Argentina I highly recommend visiting the Fangio Auto Racing Museum in Balcarce, just west of Mar Del Plata Argentina. It is one of most amazing auto museums in the world, full of old Ferraris, Alfas, Mercedes, etc. all raced by Fangio and other famous drivers. I was there two years ago and it's a great place to spend winter (in their summer). There is also a cafe next door to the museum that has four stories of formula one cars wraping around the inside! I know this is not about MG's but if you appreciate fine cars... check it out at www.museofangio.com
MG Grover

I set my timing as Bob describes above. I tend to alternate refuels between standard unleaded (85 octane) and super unleaded (98) purely on a cost basis. The engine sings like a bird on the predominantly 98 octane in the tank. If the 85 is the greater volume the difference in performance is noticeable and the tendency to pink. Now that I am not commuting any more and mileage has decreased accordingly I intend to stick with the higher priced 98 octane. The B-Series loves it. That was the standard fuel when the engine was designed.

Steve
Steve Gyles

Thanks - all very helpful. I do experience a little pinking sometimes, but overall it runs quite well.
I do find it quite difficult to use my timing light as the timing marks on the crankshaft pulley are partly damaged/broken off.
So probably a stupid question but if I use a programmable timing light like Rob has, does this work without having to refer to these timing marks?
Many thanks
Graham M V

Graham

No. You still need a timing mark on the pulley. I highlighted mine with a spot of white paint (Tippex - typists correction fluid). I guess you just need to find your TDC amongst all the broken bits and mark it!

Steve
Steve Gyles

Graham

Basically, with the progammable timing light you dial in the advance (32 degrees), run the engine up to the desired RPM (4000), and point the the timing light at the pulley. You then rotate the distributor until the timing mark on the pulley is stationary against the TDC mark on the timing chain cover.

It's all done by bright flashing lights!!

Steve
Steve Gyles

Steve,
Thats very helpful, thanks. So as I understand it fully does that mean
(1) I just need to make sure I have the TDC mark, and the other marks I can ignore as they wont be used
(2) and that the real advantage comes as I can accurately find 32 degrees BTDC at high revs?
Graham M V

Graham

That's about it. When setting up a new engine or after distributor replacement you need the other timing cover marks to get the static advance about right so you can start the engine. But after that it's all about the TDC pointer on the cover and the TDC mark on the pulley - vacuum disconnected. You will pay around £50 or more for one of these timing lights from Halfords etc.

I replaced my cover for one with timing marks on the top. Makes the job easier looking down into the engine than lying underneath!

Steve
Steve Gyles

Nobody has mentioned spark plugs. Does the type of fuel influence the plugs? i.e. Hotter or colder plugs for higher or lower octane?
Neil McGurk

The original recommended grades for MGAs were as follows-

1500: First Grade
Twin cam: Super Premium
1600: Premium

As given in Autocar Road Tests 1955, 1958, 1959

midget: Super Premium
MGB: Premium (97)
MGC: Premium (97 ****)

Autocar 1961, 1962, 1967
Geoff Everitt

NGK BP6ES plugs are what I use. A hotter plug can contribute to pinging. A hotter plug can stay cleaner in an oil burning engine.
R J Brown

This thread was discussed between 19/10/2009 and 20/10/2009

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