[v8volvo]

Steve,

My understanding of the difference between the VE pumps on the D24T vs the 1.6 is a little different. You're right that the D24T setup is under tension where the 1.6 setup is not. However, if I've got it right, that difference is not the result of a big spring applying return force, but rather a function of the location and action of the cold start advance lever.

To my recollection from the last time I had one apart: in the Volvo pump, the lever moves a ball stud on the inside of the pump housing. The ball stud directly contacts one of the "rungs" of the roller cage, moving the cage and rollers however many degrees to effect a timing advance. The Volvo has the CS advance lever mounted on the side of the pump body, and it has minimal mechanical advantage on the roller cage -- that is, for timing advance to take effect the lever moves only a short distance (maybe 15-30 degrees at the most) and with considerable force required. Probably the reason for that short travel range is due to the coinstraints imposed by the limited distance that the wax thermostat is able to move. I believe the high force required to move the Volvo pump's CS lever is a result of the force necessary to move the roller cage w/o much leverage. The external spring is fairly lightweight. (You can remove this spring and you will see that it is still not much easier to actuate the lever.) I think the spring is there mostly for the health and longevity of the CS cable and rest of the mechanism, so that there would be something to pull the lever all the way back against its external sheetmetal stop tab after the lever's internal ball stud backs off from contacting the roller cage.

The VW 1.6 pumps, if my assessment is correct, use quite a different system. The cold start lever is located lower in the body on a Rabbit pump, down in the area of the dynamic advance piston. (In the same location where, on a D24T pump through 1984, there is just a diamond-shaped cover plate, and on 1985+ cars the high altitude compensation advance solenoid is located.) The lever on those pumps moves a much greater distance with much less force -- the difference between advanced and normal positions on a Rabbit, for instance, is almost 90 degrees, and there is a detent at the end of the lever travel that the Volvo pumps don't have. My suspicion is that the advance mechanism in these Rabbit pumps works on a sort of screw principle where the lever's rotational movement horizontally displaces the advance piston in the bottom of the pump, and physically shifts the whole dynamic advance system (and roller cage) that way.

Basically to my understanding it's just two ways of skinning the cat, but with differences -- one which is tailored to operation by human fingers working through a plastic knob and skinny Bowden cable, and the other which is better suited to big mechanical forces applied by fair size springs and a much heftier cable. I believe it would be possible to convert a Volvo pump to use the 4cyl-style manual advance system, but probably the existing advance setup would need to be removed and covered with a side cover plate, and then a manual advance mechanism from a Rabbit or similar would have to be installed in the bottom of the Volvo pump. Or alternatively, a custom pump could simply be built using Volvo internals, aneroid, and head in a Rabbit pump case.

Hope my ramblings are making sense, as I write from Europe with jet lag... I will see if I can find some pictures to demonstrate.

George