Learning to Tune

OK - now setting the octane selector.....I have these instructions.....

"In addition to automatic timing advance and retard mechanism, the distributor incorporates a hand setting control, known as the octane selector. This is a vernier adjustment attached to the distributor, fitted with a sliding portion controlled by an adjusting screw and a calibrated scale marked R (retard) and A (advance) with a number of divisions between. The standard setting for the ignition is with the long line of the scale on the sliding portion against the mark on the selector body, thus leaving one division further possible advance and four divisions retard."

Makes absolutely no sense whatsoever.

1. Where is this "long line of the scale" - I have a double ended arrow with A and R each end.
2. Mark on selector body? It's a wheel - there is no mark on it. What does this mean?

You'd think across the entirety of the internet, there would be some simple diagram explaining this....but I can't find one!

Well, hats off to my mate Killer.....tap a tap tap on the door, 30 seconds before my final grille badge auction was to expire on eBay (!) mind ......with an explanation....

https://www.aulro.com/afvb/images/im...014/02/404.jpg

The graduated lines are in the middle of my pic.....between the vacuum advance and the AR arrow. I can see them now with a bit of a clean up! How good is that Mick? The lines appear!

Thanks mate! I guess the rest of the Landy Universe already knew this but it's a revelation to me.

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Originally Posted by Scallops

OK - now setting the octane selector.....I have these instructions.....

"In addition to automatic timing advance and retard mechanism, the distributor incorporates a hand setting control, known as the octane selector. This is a vernier adjustment attached to the distributor, fitted with a sliding portion controlled by an adjusting screw and a calibrated scale marked R (retard) and A (advance) with a number of divisions between. The standard setting for the ignition is with the long line of the scale on the sliding portion against the mark on the selector body, thus leaving one division further possible advance and four divisions retard."
1. Where is this "long line of the scale" - I have a double ended arrow with A and R each end.
2. Mark on selector body? It's a wheel - there is no mark on it. What does this mean?

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If you find yourself a older distributor as I don't know if a new one has the marks ( I don't have access to a new one to check and see if those marks are there), you will see on a old distributor that the vernier adjustment is on the sliding potion where it passes through the body of the distributor with the thumb screw adjuster at the end of that slide.

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You'd think across the entirety of the internet, there would be some simple diagram explaining this....but I can't find one!

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I sympathise with you on this, as I haven't found any info on any sites for Land Rover engines either and now the good news, have a look for information for the same style Rover car engine.
I think it's on a Rover car restoration site and it's part of the owners handbook.

Still takes a bit to get your head around because of the shift of the refining of petrol over time, I believe the octane rating is offset by other additives now days, I wish there was some easy explanation about this.
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With the quality of the petrol that we have today I don't think there is a lot of use for this. It was designed so that if you were in an area that had poor quality petrol you could retard the timing without needing to change the position of the distributor and therefore mess up the overall tune. The same thing could be done by putting marks on the base of the distributor that would allow you to move it a set amount and put it back again but it would be difficult to get a fine adjustment that way.

If you are running a lower octane fuel (than that at which you have already tuned your engine) you may need to retard the timing to stop pinging and if you are running higher octane you can advance (though this is not as critical as the vehicle will run fine without). Please note that if you have set your timing to the book then advanced it until you get pinging then bought it back until you don't you will be pretty much set up for the quality of petrol you tuned with. Any adjustments are then made from the known quality of petrol which is very much standard across Australia. Ethanol may vary this slightly but you should be avoiding ethanol anyway if you can.

Cheers,

Tim.

My nephew has a 1928 Chev which he has fully restored. He told me recently that he, and most members of the club have discovered over the years that Shell V power (98 Oct) works best in their engines. It provides a very stable burn and performs better in the low compression motors than other brands/octane ratings. Some of these vehicles have manual advance/retard levers behind the steering wheel for controlling the spark.

A vernier was standard fitment on the Lucas distributor fitted to millions of engines of British origin in the 50s and 60s especially. Once the point gap was correctly set, you loosened the clamp holding the distributor, rotated the distributor body to get the timing as close as possible, tightened the clamp, then used the vernier as a micro adjustment in conjunction with a timing light to get the "dynamic" timing spot on. As mentioned, you could later retard /advance the ignition a couple of degrees depending on whether you filled up with "standard" or "super" grade petrol.