21-07-2019, 08:40 PM
(This post was last modified: 21-07-2019, 11:11 PM by Bob Culver.)
This topic has been exhaustively covered before but it is easier to redo from scratch.
Those very familiar with Sevens can adjust by ear. It is vital that no more advance than necessary is applied as crank stresses rise very significantly with advance. An engine with generous advance sounds stroppy and has a sharp exhaust but may not be better. Don’t judge by stroppy sound.
The following applies to normal Sevens driven as intended to about 3,500 rpm (30 in 3rd/2nd). Not the high revving sports and racers. The original handbooks for manual advance cars suggested 1 ¼ to 2 inch (14 to 22 deg) full advance on the crank as an initial setting. Most will run merrily with considerably less than 2 inches (the Williams book adopts only 1 7/8 for specials.). An ongoing source of confusion is that the early Ruby book and many others repeated the manual recommendation. But when hand cranking the auto advance ignition is retarded not fully advanced. This has led to myriad problems over the decades and a lot of unnecessary crank stress. To further complicate matters there are two original auto advance distributors. Whatever the markings on the body just what springs and innards are fitted and the degree of wear and effect is often a puzzle. The eary Ruby distributor with 3 dist/6 crank deg of advance should be set about 7/8” btdc on crank or a bit more and the later 8/16 deg Ruby distributor, at tdc or somewhat more.
In general, as distributors wear, advance increases. If you can find a suitable long screw to fit down the middle advance can be twisted to full advance and locked in place with a washer. Can then find where full advance takes you.
15 deg btdc is piston 1/16 from top of stroke, on later heads can be found with a vernier depth gauge etc.
Those very familiar with Sevens can adjust by ear. It is vital that no more advance than necessary is applied as crank stresses rise very significantly with advance. An engine with generous advance sounds stroppy and has a sharp exhaust but may not be better. Don’t judge by stroppy sound.
The following applies to normal Sevens driven as intended to about 3,500 rpm (30 in 3rd/2nd). Not the high revving sports and racers. The original handbooks for manual advance cars suggested 1 ¼ to 2 inch (14 to 22 deg) full advance on the crank as an initial setting. Most will run merrily with considerably less than 2 inches (the Williams book adopts only 1 7/8 for specials.). An ongoing source of confusion is that the early Ruby book and many others repeated the manual recommendation. But when hand cranking the auto advance ignition is retarded not fully advanced. This has led to myriad problems over the decades and a lot of unnecessary crank stress. To further complicate matters there are two original auto advance distributors. Whatever the markings on the body just what springs and innards are fitted and the degree of wear and effect is often a puzzle. The eary Ruby distributor with 3 dist/6 crank deg of advance should be set about 7/8” btdc on crank or a bit more and the later 8/16 deg Ruby distributor, at tdc or somewhat more.
In general, as distributors wear, advance increases. If you can find a suitable long screw to fit down the middle advance can be twisted to full advance and locked in place with a washer. Can then find where full advance takes you.
15 deg btdc is piston 1/16 from top of stroke, on later heads can be found with a vernier depth gauge etc.