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MG MG Y Type - Timing advance

As a newcomer to care and feeding of the Y and its XPAG motor, I am somewhat amazed at the factory static timing setting of TDC. The enginf seems to run alright, but I am going to experiment with a bit more advance. A quick look at the archives seems to indicate that the consensus is roughly 5+ degrees static. I went out and reset my YA but it's raining so I can't road test the change. Any comments from you longer term owners?
Paul Briggs

I have asked myself the same question for a while. But somewhere I read that at idle (800~1000 rpm) this type of distributor already has an advance of around 10 deg. Setting at TDC static will be very beneficial for hand-starting, as there is less danger that the starting handle hits back, breaking your wrist. But I would also like to hear from others who may have experimented with greater advance (I haven't done so yet).
Remo Peter

Paul: some thoughts on your question.

I guess we need to remember that the fuel available in 1947 Britain was somewhat inferior to that of today: the Y-type owners' handbook I think refers to 70 or 75-octane (!) "pool" petrol. Pre-ignition was a fact of life in any engine in a relatively high state of tune then - it was rare to find an engine of around 1200cc making 40bhp. Nowadays, even regular unleaded in Europe is 91-octane, though I know that in the US the equivalent grade is 87 or 88-octane.

So there might be the potential to advance the ignition somewhat. And to address Remo's point, from my recollections of setting the timing on my XPAG, using a strobe light, the centrifugal advance has no effect until about 1200-1500 rpm, so you can reliably set the idling (TDC) firing point statically and then check it with a strobe. It will be interesting to hear your impressions of performance improvement!
Tim Griggs

Paul

What has worked for me over the past 40 years of Y ownership is to find a reasonable hill and climb it (as many times as necessary) in 3rd or 4th. If it pings then I back off the timing a bit. If it doesn't then I advance the timing a little until it starts to ping. Then I back it off slightly and secure the distributor setting. This purely experimental (trial and error) approach has the advantage of matching the condition of the engine and the characteristics of the fuel. As the seasons change and the fuel characteristics are changed (at least here in California) you may want to reset the timing if you start to hear a ping under load.

FWIW

Larry
49 YT

Lawrence Hallanger

Well, the rain finally stopped so I could do some testing. I dialed in approx. 5 degrees of advance and tested.( I had to guess at 5 until I can mark up a degree wheel of some sort to get some accurate marks) I noticed some smoothing but still harsh sounding. Then I did a little carb setting per the book, and found it to be running rich. Wow did it smooth out now! Much more pleasant to drive and she lost a vibration period that had been apparent at 40 mph. Lawrence, excellent advice, as I have found that each car wants a little different timing setting to be really happy. More play to follow.
Paul Briggs

the TDC ignition timing of the engine is for idle rpm only. Once the engine speeds up the advance weights move the timing forward. If you advance your idle timing by 5 degees, then you advance the whole range by 5 degree. This may well put the flame front of the ignition too far advanced. With the older fuels of the 1950's this may not be a problem, but with modern fuels you will probably get a lot of pinking, but at an engine speed you will not hear it at. This can melt pistons, be warned.

The actual timing curve of the engine ABOVE idle rpm is almost identical to that of the standard 1990's 1275cc Mini, and that has a 10 to 1 compression ratio and runs on modern fuel. The TDC timing was to give the engine a 'soft' and regular tick-over on its very solt camshaft timing. Advance it at your peril. Too much advance can also knock out crankshaft bearings.

Neil.
Neil Cairns

Neil, warnings duly noted and I will certainly not get carried away with too much advance, but this is the sort of discussion I wanted to inspire. I will note that the engine has lost much of its "harshness" at speed, whereas before it was not very pleasant to drive at anything above 35 mph and it had a couple of vibration periods that were worrying. Now, the vibration periods have disappeared and the engine revs relatively smoothly through its range. I don't press it, I don't think I have exceeded 60 at all, Usually cruising about 50 or so.
Paul Briggs

Hi all

A couple of issues here and one is to do with octane rating. As octane increases, burning is slower and easier to predict, and so prevent pinging, or the noise evident from early combustion. Hence the tradition of retarding engines when going from Super (98) to Regular (91).
Engines are usually tuned to provide maximum downward gas pressure on the piston crown at round 40 degrees or so of rotation After Top Dead Centre or ATDC.
The need for ignition advance relates to the basically fixed burn time requirement of a given fuel, compared to the decrease in time available for the process as engine revs increase.
At idle, the time taken for combustion means we can have static timing about TDC or just before.
As engine speed increases, there is less time for the combustion process to take place, so the timing needs to be advanced.
Over 15 years or so I have recalibrated many hundreds of distributors using a Vane distributorscope, many Lucas units have weak springs and so advance too rapidly. Too much advance for the fuel (type and quantity) and engine revs gives high piston crown and combustion chamber temperatures.
I feel that with common fuels, an advance curve similar to Mini 1275, or Ford escort (pushrod 1300 or 1500) would compliment a single carb Y. If you run a YT (two carbs) or have updated the cam, compression or breathing, the engine may benefit from a variation from those base figures.
Most competent engine tuners, or anyone fitting LPG fuel systems, should be able to steer you to a workshop with a distributorscope.
bye for Now, Geoff, YT3477
geoff meller

This thread was discussed between 05/06/2002 and 23/06/2002

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