13-11-2017, 08:41 PM
(This post was last modified: 13-11-2017, 08:44 PM by Bob Culver.)
Spark timing was another recurrent question on the old site and all aspects were covered using Search. But seems will need to start again.
Setting by ear is fine for experienced Seven hands familiar with the normal “performance” and the characteristic degrees of mechanical harshness of Seven engines in various states, but it is a mystery to those mainly familiar with more conventional engines. Performance must not be judged by noise.
Manual advance is a blessing in that many variables are eliminated and can experiment and immediately observe the result. Check that it is not a manual override of an auto distributor! (Convenient but confuses advice)
Unnecessary advance severely stresses the crank so should trend on the side of caution, as did Austins originally.
The original manual recommendation was 1 ¼ to 2 inches BTDC full advance but, at least for non racers, 2” is generally excessive. Even the Williams book only goes to 1 7/8 and that for revving Specials. Of course with manual advance you have the option of seldom using full advance. The manual advance range is considerable and full retard not normally used. Once underway at normal revs the range used is very small.
There were two auto distributors; both set to give about the advance above when fully advanced. Unfortunately this is not easily established. The early Ruby manual repeats the advice for previous manual distributors with the effect that myriads of auto advance engines have been set to this at normal static retard and operated or at least started with gross over advance.
The early auto is 3 dist/6 crank degree, for which ¾ to 7/8 inch static advance was recommneded, and the later for smooth 3 bearing engine was 8/16 with 0 to ½ inch static advance
One inch on the flywheel is about 11 crank degrees
For all settings final refinement on the road was suggested, but it is not easy to compare small auto adjustments. Must not judge performance from din.
Just what the actual characteristics of many worn, meddled, interchanged, auto distributors is now is anybody’s guess
Setting by ear is fine for experienced Seven hands familiar with the normal “performance” and the characteristic degrees of mechanical harshness of Seven engines in various states, but it is a mystery to those mainly familiar with more conventional engines. Performance must not be judged by noise.
Manual advance is a blessing in that many variables are eliminated and can experiment and immediately observe the result. Check that it is not a manual override of an auto distributor! (Convenient but confuses advice)
Unnecessary advance severely stresses the crank so should trend on the side of caution, as did Austins originally.
The original manual recommendation was 1 ¼ to 2 inches BTDC full advance but, at least for non racers, 2” is generally excessive. Even the Williams book only goes to 1 7/8 and that for revving Specials. Of course with manual advance you have the option of seldom using full advance. The manual advance range is considerable and full retard not normally used. Once underway at normal revs the range used is very small.
There were two auto distributors; both set to give about the advance above when fully advanced. Unfortunately this is not easily established. The early Ruby manual repeats the advice for previous manual distributors with the effect that myriads of auto advance engines have been set to this at normal static retard and operated or at least started with gross over advance.
The early auto is 3 dist/6 crank degree, for which ¾ to 7/8 inch static advance was recommneded, and the later for smooth 3 bearing engine was 8/16 with 0 to ½ inch static advance
One inch on the flywheel is about 11 crank degrees
For all settings final refinement on the road was suggested, but it is not easy to compare small auto adjustments. Must not judge performance from din.
Just what the actual characteristics of many worn, meddled, interchanged, auto distributors is now is anybody’s guess