Timing

[Dave Mann]

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[Brettfcars]

Hi,
I have a similar pointer On my car indicating exact top dead centre. It aligns with a notch, not shown.

     

And I am using a Gunson’s superstrobe to set up the timing.
As the pulley is smaller and rotating at a different speed to the flywheel how much advance at 3000 rpm ?

As can be seen below the advance can be dialled in.

   

Been pondering this for a while....

Thanks

Brett

[Steve Jones]

Exactly the same as on my engines even to the socket heads. Try 28 degrees.

Steve

[Bob Culver]

The very simple direct powered lights are fine for a Seven but care necessary, esp if you have a Pacemaker.
Timing lights are useful for determining actua total range and observing auto advance operation but otherwise unnecessary. A rough indication of total range can be obtained by twisting the mechanism and locling in place with a long screw of the correct thread with washer.
With all the tinkeringit is probably just as easy to arrange a choke control or motor mower throttle control as a manual override and establsih exactly if timing is ideal or not.

[John Cornforth]

For those placing timing marks on the Austin camshaft pulley, the diameter of the outside of the flange is 4.25 inches, so the circumference is 13.35 inches which represents 720 crank degrees.  This gives a distance of 0.0185 inch (0.47 mm) per crank degree.

So 10 crank degrees is 0.185 inch (4.7 mm), 20 degrees is 0.37 inch (9.4 mm) and 28 degrees is 0.52 inch (13.2 mm)

[Howard Wright]

Hi John

That info is very useful.  I have an almost identical marking system and am about to run a strobe on my engine.

Thanks

Howard

[Zetomagneto]

Hi Steve, I can nip over and time it up if you like.
Best Wishes Gene

[Tony Press]

For those placing timing marks on the Austin camshaft pulley, the diameter of the outside of the flange is 4.25 inches, so the circumference is 13.35 inches which represents 720 crank degrees.  This gives a distance of 0.0185 inch (0.47 mm) per crank degree.

So 10 crank degrees is 0.185 inch (4.7 mm), 20 degrees is 0.37 inch (9.4 mm) and 28 degrees is 0.52 inch (13.2 mm)

And don't forget as mentioned the fan pulley is not keyed so can be all over thevplace if taken off 

[Oxford Jack]

I have written elsewhere about the issues I had with the rebuilt engine, which stood for 15+ years.
Now running and having done about 250 miles it seems to have plenty of urge and is freeing up as the miles add on.
The engine has a 1 ⅛" SU carb, from the last engine, with an AN needle, it has an HC head from the last engine, which is flat, it is fitted with a new Phoenix crank, the dynamo and gear are also from the last engine, as is the Accuspark dizzy. I have listed the pre used parts to indicate that they are known and were previously working satisfactorily. The A - R lever is connected and works. 
I got the engine running, at first it was much retarded, I got it into what I would consider the best running position but it is noisy, it has a harsh sound and is a little rough until I reach upper 30's mph when it smooths out and seems quieter. I should add that I have in 55 year of A7 ownership always got the timing to my satisfaction by ear (which of course may have been incorrect, but I have done 20,000 miles in this car in the last 10 years)
Yes, I imagine the common thought will be its too far advanced, this is where I need your guidance please. If you look at Brett's photo in a previous post, I have fitted a similar pointer and have a Gunson strobe which I purchased recently. I also have a notch filed on the pulley at TDC number 1, which I established when the head was off, so I am confident it is in the correct place. I decided I would check the calibration of my ear with the strobe, which is where not having used one before showed up the weakness in my cunning plan. I read all I could on the Forum, but I dont think anyone has done Strobe Timing 101.
Looking from the front of the engine the cam pulley rotates anti-clock. My understanding of the terms for firing, ie TDC, degrees advanced etc have been challenged by what I found. Bear in mind that the dizzy is electronic. I warmed the engine and tried the strobe, set to 0 deg advance on a fast tick over, probably 1,000RPM. I eventually found the pulley mark not by the pointer but about 1 ½" forward of it, ie counter clockwise 1 ½" forward of the pointer (white arrow points TDC mark on pulley), as you will see in the attached photo. At about 2,500 RPM the pulley mark moves back towards the pointer about 1/8". 
It looks to me as if the spark is occurring after the piston reaches TDC, is that correct? This was my thought, so I turned the dizzy to try and make the spark occur in advance of TDC, before the timing mark reaches the pointer the engine stops. As the Gumbies used to say"My brain aches!" help please I are confused of Oxford.


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[John Cornforth]

Hi Oxford Jack

A discrepancy of 1 1/2 inches on the cam pulley corresponds to 81 crank degrees which is absolutely miles off, so something aint right.

I'm just wondering if the strobe is being triggered correctly from the plug lead ? If it has the "clothes peg" style inductive pickup then this senses the spark current and is polarity sensitive. If the polarity is wrong then it could be that it is triggering when the "points" close rather than when they open which would give the sort of offset you are seeing. It might therefore be worth trying it in the other direction (it has an arrow on) and see if that is better.

Fot a standard DK4 i'd expect the auto advance to increase about 10 crank degrees between 1000 and 2500 RPM, which will be about 5mm at the pulley rim so 1/8 inch (3 mm) is believable, but check again once you have a proper trigger.

I use an inductive triggered xenon strobe (with its own 12v battery) and a pointer on the cam pulley and it works fine. It's a little sobering to see how much timing scatter is introduced by all those meshing gears between crank and distributor ! Interestingly I find that scatter is a tiny bit less when the dynamo is set to winter charge, maybe the mechanical load damps things out a bit ?