Knob on older WRD?

[twistedtree]

On the body of the WRD from an early 230SL (R11 Injection pump), there is a spring-loaded hex knob just below the heat feeler housing.  This knob doesn't exist on later WRDs.  As best I can tell, the knob enables/disables the WRD.  Can anyone confirm this or correct if it does something else?  The knob protrudes into the valve body and has an eccentric pin on the end sticking into the valve throat.  The knob locks in two positions, each 180 deg apart.  In one position it appears to hold the WRD valve plunger in the Warm position, and the other setting allows the plunger to retract and be controlled by the heat feeler.

At first I though it was just a retaining plug to hold the plunger in place, but I finally got it freed up and working and think it actually has this enable/disable function, presumably for summer/winter operation.  I've read tons about the WRD, but never seen this discussed, or missed it if it has been.

Just curious...

[pagoden]

Now that is cool; a sort of miniature barn find, all by itself.  Very neat car - - and experience, it seems.       Kudos,  Denny

[twistedtree]

I found some info on the knob in the older '59-'66 BBB which confirms its WRD enable/disable function.  It's from the section on the old ZEA 2-pump injectors, and appears to have carried forward to the first generation of WRDs used on the PEK 6-pump injectors on our cars.  Here's the section from the BBB:

"A defective cooling water thermostat can be fixed in the switched-off position corresponding to a cooling water temperature above 60 deg C or 68 deg C respectively by pressing the stop bolt (59) in and giving it a half turn to the right until it engages again (Fig 07-10/15).  The whole warming-up mechanism is then inoperative".

I like the Barn Find analogy.  Maybe we can call this a Knob Find?

For anyone with this older style WRD, it's entirely possible that it is interfering with proper operation of the WRD.  Mine was seized in a not-on-and-not-off position.  If you want to free yours up, do it very carefully - I broke the first one I tried to free.  The trick (after the WRD is disassembled) is to soak the knob in PB-blaster for a while, then gently tap the knob head inward against the spring.  You may then need a punch to tap it back out until it frees up.  Then you can rotate it until it completely frees up.  Be very very careful attempting to turn the knob when it's not free.  There is very little meat between the knob and its inner half, and it's easily broken if forced.  I found out the hard way.