How the WRD Plunger Works

[alchemist]

I am trying to understand how the WRD plunger works and the purpose of the spring in the plunger. My plunger spring is compressed so tight to a point there is no wiggle room for a spring action. I understand that the air valve pushes on the plunger when the feeler extend, that extends the pin which pushes on pump. If the spring is so compressed, then it has no action in extending the pin. I noticed that my plunger sits at the bottom of the lower WRD’s neck, that made me to increase the round shims considerably for the feeler to works right. This is contrary to the schematic that shows the plunger is seated above the lower neck of the WRD. In the schematic diagram, the lower neck is labeled # 10 and Hynes manual refer to #10 as an adjusting washer. Someone may able to explain my observations. Thank you.

[jeffc280sl]

There is a great write up in the tech manual.  Here is the link.

 http://www.sl113.org/wiki/Engine/WarmRunningDevice

A picture of the components of the WRD is provided.  The order of components is as you see them.  As I recall the plunger spring it pretty stiff I would say.  As the thermostat is heated the air valve is pushed away thereby compressing the plunger spring and closing off air from the filter.  As the thermostat cools the plunger spring presses the air valve away causing the thermostat pin to retract.

The whole operation is a sort of a tug of war between the thermostat pin and plunger spring.  When hot the thermostat pin creates more force compressing the plunger spring.  When cool the plunger spring has enough force to compress the thermostat pin.  This goes back and forth depending on engine coolant temperature.

The components from the WRD can be removed as you can see and cleaned if they are not working properly

[alchemist]

Jeff: You are right, plunger spring it pretty stiff, but I do not think that the plunger spring compression is adequate to push the air valve to reach the closing position. As you said the spring is so stiff, it is only compresses 2 mm, which is not enough to move the air valve from the open to the close position at normal operating temperature. The air valve needs at least 7 mm to go from open to close position. I believe that when the feeler extend, it moves both the air valve and the plunger together and apply a pressure on the injection pump to change the racks. When the engine cools, the injection pump is under spring action pushing the pin up-ward, so, it compresses the feelers’ pin back to 18 mm in length. My feeler is 18 mm when shrinks (not in freezer as some posting suggests, but under pressure), and 24 mm when it extends at normal operating temperature. I hope this helps to understand how the WRD functions. Still, I do not understand why do we need the spring? Perhaps, it acts as some kind of a buffer.

[garymand]

The spring is just a mechanical over-shoot (safety) for the thermostat.  If the FIB stops (freezes) the pin from extending; the spring allows the thermostat to grow, compressing the spring.  Or vise-versa, if the fip pushes back, the spring can keep the thermostate from over compressing.  That is what I see.   It also may be that the spring is there because the pin can possibly go farther than the fip pad can and when the pad stops in its down ward path, the spring allows the wrd to keep moving.

"but I do not think that the plunger spring compression is adequate to push the air valve to reach the closing position"  It sounds like your FIP is not allowing the pin to go far enough down?  Yes, the thermostat moves the air valve and the pin/sp[ring down together.  If you put the wrd in a pan of hot water, the piston should go from open at RT to fully closed at 80C. If not something is jamed.

If it works fine, Try manually pushing the pad that the pin pushes in the fip.  It should move down with little pressure.  I haven't done this for a while, I can't rmember how much pressure is needed to push it down and I don't thnik there is a measurment for that in the manual, but the thermostat can normally easily push it down.

[jeffc280sl]

Makes sense Gary.  Thanks.  It been a while since I dug deeply into this stuff

[wwheeler]

I remember when Jeff went through this in fine detail a few years back. I never knew that the plunger with rising temperature, reaches a certain point where it hits a stop inside the FIP. A real eye opener. At that point the WRD cannot lean the mixture any further. I think that should be around 150*F or so. From there the coolant temperature still rises 30-40*F more. Hence the wax in the WRD bulb wants to continue to expand. Gary is right that the plunger spring is a buffer and allows the wax bulb to expand without affecting the mixture. At some point as Jeff said, the force of the plunger spring equals the force of the expanding wax bulb and the system comes to rest with a stable coolant temperature. I think the spring also acts to remove any slop in the system for consistent mixtures.

Once the coolant begins to cool, the plunger spring and FIP spring overcomes the force of the wax bulb and the whole process repeats itself. What a job to figure out the spring forces required to make this system work!

[glenn]

While we're at it....   Please explain how/what  'air to fuel' ratio the WRD puts out.  Also, the idle air screw provides a lot less air than 1/4 inch air line to the WRD.  The idle air screw/fip is 14.7:1(?) with no WRD compensation.  Seems like the WRD air is overwhelming the idle air screw air.   Inquiring minds want to know.............. 

[garymand]

While we're at it....   Please explain how/what  'air to fuel' ratio the WRD puts out.  Also, the idle air screw provides a lot less air than 1/4 inch air line to the WRD.  The idle air screw/fip is 14.7:1(?) with no WRD compensation.  Seems like the WRD air is overwhelming the idle air screw air.   Inquiring minds want to know.............. 

Wow, let's see.... (1/4 inch air line to the WRD)  My 250/280 diameter of the air passage through the wrd is closer 1/2 inch all the way back to the manifold.  It is a good sized air leak, when fully open, and the little filter is sometimes called an air muffler.  It does a good job of eliminating the sound of all that air entering the WRD as well as filtering. 

Yes, the wrd overwhelms the screw when the engine starts cold.  On a carb its called choked: the choke butterfly overwhelms the throttle valve.  The wrd is a much more eligant solution in that it allows both more air and fuel to feed the engine moving the A/F ratio to very rich (to the 10's on my meter, but I haven't gotten too far in optimizing that yet.)  So, the wrd allows us to shim the piston and the pin orientation for the A/F ration (as the two will then move together based on the little washers on top the piston, and shim the reach of the pin the adjust how much overall rod enrichment there is on the fip.   I've seen the enrichment null out at about 150F 180F.  But it is scarry that shimming the wrd has a significant effect on the normal running A/F ratio.  I was expecting the wrd effect would be stopped below 100F, but aparently the designers knew there was a benefit to allow its influence on the fip all the way to about 80C.  I can see it on the warmup A/F that it takes a while for the temp of the wrd to catch up to the engine temp, not surprising due to its remoteness.  But it is not insulated, so I suspect that is intended to allow it to help out when the ambient is -30F in Canada.  I started mine once a long time ago at -10F and it was not adjusted OK for San Fransisco, but could barely maintain 300 rpm in Tahoe.  I digress.

Yes the WRD is the dominant contributor to 80C and a significant player just below that.  I ran into a lot of trouble plying with it before I got the FIP regulator and rod in about the right harmony.  I'm experimenting now with that relationship by getting the cold A/F right for great cold idle/startup and what it does to the rod, so the rod is still well adjusted at 80C and above.  And, you can't just do it all at once!  The fip delays its response, so you have to make an adjustment and drive it awhile for the fip or combustion to settle in.  Some times its significant and further tweeks without a long drive is a waisted effort. 

[wwheeler]

If you add more round shims on the piston, it will shut off the WRD mechanism earlier (@ a lower temperature). My particular set up requires a minimum of .032" worth of round shims in order to just barely shut off at operating temperature. I have .052" now and works well. Every engine will have different requirements.

[garymand]

That is pretty close to where mine is.  You got me thinking.  There are 4 things going on with the WRD
1) fully closed at ~80C
2) fully open at some temp, not sure what that is
3) the amount of air in the A/F ratio cold start and during warm up
4) the amount of fuel in the A/F ratio cold start and during warm up
So I just made my first attempt at the A/F ratio between the air piston and fuel set by the pin.  I added 2 washers ~ .040" and 2 shims ~.030, it is too lean during warm up, and too lean after.  Makes sense to me now.  I hadn't thought about keeping the spacing equal for the added washer and added spacer.  I'll give that a try tonight and see how the fip responds.  Seems reasonable the two would be correlated.
The .010” extra shimmed pin made the rod leaner by 3 to 4 clicks.  Perhaps, if I had applied equal spacer and shim the rack would not have changed. 

[alchemist]

Thank you Gary, Jeff, Wallace and Glenn for a great discussion of WRD function. I am struggling with making the air valve closes; it reaches the middle point and won’t go further, even by adding round shims and even spacers on top of the air valve. The engine runs good when the air values reaches to the middle point, but I would like to see the valve completely, or at least 80% closed. A bit of a background on my 67 230SL, the previous owner changed the engine to M130 along with FIP R20Y. However, I feel that they might used the older WRD which may not be compatible with R20Y. I came to this conclusion because I did several experiments and measurements of how many mms would the air valve need to reach the closing point. I also watched the feeler works in action by inserting an endoscope attached to a laptop into the WRD while the engine is running. My measurements suggest that the feeler must extend 34 mm from its compressed position to close the valve completely. I have 2 feelers (one old and the other is new); both extend in hot water to a length of 23 mm, not enough to move the valve to the closing positing. I added more round shims and that was not enough, then added spacers on top of the air valve, that moved it to half way to close. As I read in the Forum, some postings suggest that there are pre 67 fellers with a pin extend to 60 mm. That makes me think that my WRD may be a pre-67 models and I am using the wrong feeler. Here are my questions:
1.   Can an older WRD be compatible with FIP R20Y?
2.   If so, then I need to purchase the pre-67 feelers. I searched on line and all what I found is one kind, the one I am using. Do you guys have any resource for an older feeler?
3.   Reading my description above and taking your experience into consideration, what do you think is going wrong?
I value and appreciate your expertise and I hope your responses will direct me to the right path. Thank you again.

[ctaylor738]

I'm not sure what WRD you are working with, but here is a post that I did a while ago while working on a 230SL with the correct R11 pump.  The pictures may help you figure out what is going on and what parts you have.

http://www.sl113.org/forums/index.php?topic=14677.0

FWIW, I don't remember the spring being super-tight.

Cheers,

CT

[alchemist]

Thank you C. Taylor for the wonderful WRD pictures that you provided. Your WRD is an earlier model, mine is completely different. However, you may help me understand the assembly of the air valve and the plunger. I know that the air valve sits on top of the plunger; my question is how far the plunger and its pin go into the air valve? I mean when the air valves pushes on the plunger, would the C-clip that retain the plunger on the pin stands in the way? Or are the C-clip and the pin both go inside the middle hole of the air valve. The reason I am asking that my air valve was stuck and it took me 3 weeks of PB blaster, sonication, and mechanical extraction to pull the air valve out. However, the plunger came out dis-assembled. I found only one C-clip (thin wire looking) which goes at the bottom of the spring to hold it in place. Then I found that I am missing a C-clip that has to goes on top of the spring to keep it compressed. So, I put a conventional C-clip that does not like the original, wire looking. This C-clip is currently standing between the air valve and the plunger and won’t go into the air valve. Would the upper C-clip go into the air valve? This information is important to figure out how far it would take for the valve to close completely. Thanks.

[ctaylor738]

I am still having a hard time figuring out what you are asking.  A picture of the WRD that you are working with would be a big help.

The only spare pump that I have at the moment is an R!8.  I removed the WRD and took it apart, and took a picture.  Does it help you?

As to your specific question, the upper end of the pin fits into a recess in the bottom of the valve.  The recess is about 2 mm deep.  The recess in the top of the valve, where the rod from the thermostat fits is deeper, about 6 mm. 

Hope this helps,

CT