WRD Differences

[Jordan]

So I was going through my parts looking to see what to keep, throw out or sell.  I have a bag with various WRD parts, including what are obviously two different air valve housings.  Below is a pic of the two, obviously having different size connections and the lower part of the housing is different.  Looking at the other side one has some sort of spring loaded arm and the other is blocked off.  You can see this from the inside in the third and fourth pic.  The last pic shows the actual innards look different. 

Is one of these for the short thermostat (280SL) and one for the long (230SL)?  If so which goes with which, and what is the purpose of the spring loaded arm on the side of the housing on the one?  Just trying to educate myself.  Thanks.

[Jordan]

Last picture.

[Benz Dr.]

The cross section that allows air into the slide valve area is much larger on the 230SL unit so the thermostat doesn't have to move very much at 1.1 mm. The cross section on the 280SL is considerably smaller so the thermostat moves about 6mm. Both systems receive roughly the same amount of air but it's done in a different way on the two systems.
The slide valve will move down shutting off both fuel and air at the same time until the limit is reached inside the IP. At that point no further movement is achieved, so the slide valve is provided with a spring which will compress should the thermostat continue to exert any further force on the slide valve.  If the engine were to over heat, the thermostat would try to move the slide valve further and this spring helps to protect the system.

[Jordan]

Thanks Dan.  Good to know.  So the one on the right in the first pic is for a 230SL, which has the longer thermostat.  Are the plunger and slide valve the same (dimension wise) for both WRD's? 

I understand the purpose of the spring that is part of the plunger, but what about the spring loaded arm on the side of the housing as shown in the second pic.  This would appear to only be on the short thermostat WRD used in the 280SL as that part doesn't exist on the earlier WRD.

[Benz Dr.]

That small fitting that extends into the bore on the 230SL unit is so you can turn it to shut the thermostat off by forcing the slide valve to the fully warmed position.  This thing often has a small roll pin through the casting so they really won't turn without breaking something.

The 230 slide valve is probably twice the diameter of the 280 unit.

[Jordan]

That small fitting that extends into the bore on the 230SL unit is so you can turn it to shut the thermostat off by forcing the slide valve to the fully warmed position.  This thing often has a small roll pin through the casting so they really won't turn without breaking something.

The 230 slide valve is probably twice the diameter of the 280 unit.

Thanks again Dan but the slide valve bore for the two WRD's in the pictures are the same.  So is the length of the bore.  The plunger and slide valve fit perfectly in both bodies.  So maybe one of the WRD's is for a different MB vehicle of that era?

[Benz Dr.]

Thanks again Dan but the slide valve bore for the two WRD's in the pictures are the same.  So is the length of the bore.  The plunger and slide valve fit perfectly in both bodies.  So maybe one of the WRD's is for a different MB vehicle of that era?

Then it must be for the same car. Slightly different version.

[BlackForest]

The control valve on the left can be used for an R11 pump (230SL) or R12 pump (300SE 6-plunger).
The spring-loaded arm for the R11/R12 was a side-of-the-road safety device which was carried over from the 2-plunger pumps.
If the t-stat failed, you would be able to move the control valve piston down to the warm running correction end stop.
It looks like the one on your valve is something someone made. The original one had a “0” at the top for normal operation.
When you turned it 180 degrees to full stop the hex flat would show a “1”.
It also looks like the arm is broken at the end and no longer projecting into the slide bore.
In order to remove the control valve piston on this design you had to pull out the roll pin Dan was referring to.
Upon reinstallation you must be careful to not tap the new roll pin in too deep which would incorrectly lock the adjustment.

The control valve on the right would work on all R18 (250SL/SE) and R20 (280SL/SE) iterations (As well as R19 300SE).
They simplified the design by eliminating the spring-loaded arm.

As you correctly observed, the control valve piston is of the same dimension on both control valves.
The R11 pump actually delivered less auxiliary air during warm-up. This makes sense based on its smaller displacement compared to the 250 and 280 motors.
The difference between the 2 t-stats delivering more or less air would be due to 2 factors.
The R11 control valve had a smaller air filter and more restriction on the intake.
But it allowed more air at the very last stages due to a completely open outlet.
The R18/R20 control valves had a stepped down opening at the outlet which meant progressively less auxiliary air was delivered as the piston traveled down.

The other difference is the duration during warm-up that the auxiliary air was delivered.
As Dan noted the R11 t-stat travels much less than the R18/R20.
The actual working travel is 1.8mm from a temp range starting at 20 degrees C to 65 degrees C.
Testing must be done under a load of 7kg.
The duration of auxiliary air for the R11 valve is until a coolant temp of 60 degrees C +/- 2.5 degrees is reached.
The excess pressure spring was designed to absorb the excess travel of the t-stat pin. It has nothing to do with protecting against overheating because it stops moving once at operating temp.
The design criteria for the t-stats were to move a prescribed amount evenly and progressively. After that it just must hold the pressure of the guide plunger spring. If it was designed to have an exact end stop projection as well, that would have made it much more complicated to design. To take up production variances, wear, and simplicity of design it was made to project several mm more than was needed. The excess pressure spring simply absorbs that.

The aux air and fuel enrichment terminate at different temps depending on the model pump.
As stated above on the R11 pump the aux air termination is once 60 degrees is reached.
The fuel enrichment termination is at 50 degrees C +/- 2.5 degrees.

The design of the R18/R20 control valve allowed for a longer control valve piston travel, as well as a longer duration.
The aux air stepped down outlet hole also kept the air fuel ratio more closely in balance as the motor was getting closer to operating temp. Keep in mind that the fuel enrichment was progressively leaner as the control piston moved down. The stepped down outlet provided a much better transition.
Using an R20/R20Y pump as an example the aux air termination was at 67.5 degrees C +/- 2.5 degrees.
The fuel enrichment termination was at 62.5 degrees C +/- 2.5 degrees.
The difference of movement in the control piston between these 2 temps is 0.45mm +/- 0.05mm.
The working travel of the t-stat pin is approximately 7.85mm from -20 degrees to 67.5 degrees.

[Benz Dr.]

The control valve on the left can be used for an R11 pump (230SL) or R12 pump (300SE 6-plunger).
The spring-loaded arm for the R11/R12 was a side-of-the-road safety device which was carried over from the 2-plunger pumps.
If the t-stat failed, you would be able to move the control valve piston down to the warm running correction end stop.
It looks like the one on your valve is something someone made. The original one had a “0” at the top for normal operation.
When you turned it 180 degrees to full stop the hex flat would show a “1”.
It also looks like the arm is broken at the end and no longer projecting into the slide bore.
In order to remove the control valve piston on this design you had to pull out the roll pin Dan was referring to.
Upon reinstallation you must be careful to not tap the new roll pin in too deep which would incorrectly lock the adjustment.

The control valve on the right would work on all R18 (250SL/SE) and R20 (280SL/SE) iterations (As well as R19 300SE).
They simplified the design by eliminating the spring-loaded arm.

As you correctly observed, the control valve piston is of the same dimension on both control valves.
The R11 pump actually delivered less auxiliary air during warm-up. This makes sense based on its smaller displacement compared to the 250 and 280 motors.
The difference between the 2 t-stats delivering more or less air would be due to 2 factors.
The R11 control valve had a smaller air filter and more restriction on the intake.
But it allowed more air at the very last stages due to a completely open outlet.
The R18/R20 control valves had a stepped down opening at the outlet which meant progressively less auxiliary air was delivered as the piston traveled down.

The other difference is the duration during warm-up that the auxiliary air was delivered.
As Dan noted the R11 t-stat travels much less than the R18/R20.
The actual working travel is 1.8mm from a temp range starting at 20 degrees C to 65 degrees C.
Testing must be done under a load of 7kg.
The duration of auxiliary air for the R11 valve is until a coolant temp of 60 degrees C +/- 2.5 degrees is reached.
The excess pressure spring was designed to absorb the excess travel of the t-stat pin. It has nothing to do with protecting against overheating because it stops moving once at operating temp.
The design criteria for the t-stats were to move a prescribed amount evenly and progressively. After that it just must hold the pressure of the guide plunger spring. If it was designed to have an exact end stop projection as well, that would have made it much more complicated to design. To take up production variances, wear, and simplicity of design it was made to project several mm more than was needed. The excess pressure spring simply absorbs that.

The aux air and fuel enrichment terminate at different temps depending on the model pump.
As stated above on the R11 pump the aux air termination is once 60 degrees is reached.
The fuel enrichment termination is at 50 degrees C +/- 2.5 degrees.

The design of the R18/R20 control valve allowed for a longer control valve piston travel, as well as a longer duration.
The aux air stepped down outlet hole also kept the air fuel ratio more closely in balance as the motor was getting closer to operating temp. Keep in mind that the fuel enrichment was progressively leaner as the control piston moved down. The stepped down outlet provided a much better transition.
Using an R20/R20Y pump as an example the aux air termination was at 67.5 degrees C +/- 2.5 degrees.
The fuel enrichment termination was at 62.5 degrees C +/- 2.5 degrees.
The difference of movement in the control piston between these 2 temps is 0.45mm +/- 0.05mm.
The working travel of the t-stat pin is approximately 7.85mm from -20 degrees to 67.5 degrees.

Your explanation is more precise but I didn't say anything about protection against over heating. I said, " IF the engine overheats the spring loaded  slide valve will compress ". We are both saying the same thing - just in different ways. 

[Jordan]

It looks like the one on your valve is something someone made. The original one had a “0” at the top for normal operation.
When you turned it 180 degrees to full stop the hex flat would show a “1”.
It also looks like the arm is broken at the end and no longer projecting into the slide bore.
In order to remove the control valve piston on this design you had to pull out the roll pin Dan was referring to.
Upon reinstallation you must be careful to not tap the new roll pin in too deep which would incorrectly lock the adjustment.

Thanks for the great and precise explanation.  I'm not sure where I got the one on the left with the arm that projects into the bore.  Something you can't see in the second picture is that the knob that controls that arm rotates 90 degrees and can be pushed in.  There is a spring between the knob you see in the pic and the valve body so you can not only rotate the arm but push it in so the arm extends past the bore boundary.  The end of the arm that extends past the bore boundary is also in the shape of an L.  So its like you can push it in, rotate it and then it perhaps locks onto the slide valve, holding it in place.

[ja17]

Black Forest, thanks for the informative contribution.

[stickandrudderman]

Great post Blackforest!

[BlackForest]

"If the engine were to over heat, the thermostat would try to move the slide valve further and this spring helps to protect the system."

The t-stat pin stops moving well before the engine reaches operating temperature.
So, it is an incorrect statement to say it has anything to do with protecting the system in the event the engine overheats.

In the interest of being precise, and more importantly correct, we are most certainly not saying the same thing.

[Benz Dr.]

"If the engine were to over heat, the thermostat would try to move the slide valve further and this spring helps to protect the system."

The t-stat pin stops moving well before the engine reaches operating temperature.
So, it is an incorrect statement to say it has anything to do with protecting the system in the event the engine overheats.

In the interest of being precise, and more importantly correct, we are most certainly not saying the same thing.

The lever inside of the pump will eventually move to the warm running position and no further. If the engine runs above normal operating temperatures and the thermostat tries to extend any further the spring will compress but the rack inside the pump won't move beyond its preset limit.

How are we saying anything different? 

[rwmastel]

Black Forest,
I see these are your first posts - welcome to the Group!  Here's the thread, inside the General Discussion board, where you can introduce yourself, share pics, or whatever.  https://www.sl113.org/forums/index.php?topic=529.0

[BlackForest]

The question you are asking me is a lot more complicated than you might think, based on how you are asking it.
When you first said we are saying the same thing I responded by clearly stating the t-stat pin stops moving well before operating temperature.
You have now rephrased the statement saying if the engine runs above normal operating temperatures (overheating) and the t-stat “tries” (I do not understand this) to extend further the spring will compress…
The t-stat does not move an infinite amount progressively as the coolant temp increases.
I’m trying to help in the understanding of its function in stating this.
To discuss it doing something it cannot do on the guide plunger after the warm-up function of the control valve has reached its limit is pointless.

And as far as t-stats are concerned, don’t get me started on the nonsense of heating them in water.

Back to the complication of your question:
There is no single lever that moves eventually to the warm running position.
Eventually is a vague term that in the discussion of how this device works and is tested is not useful.
In the case of the R11 pump we would be testing this “eventuality” as a travel of precisely 0.4mm per 10 degrees C under the load of 7kg as I had previously stated.
I hope I have made it clear that the t-stat has no idea if the engine is overheating, so I will clarify the last part of your statement regarding the rack.

The rack does not have a preset limit. It floats silky smooth within a range of 18-18.5mm.
It is the last messenger after a series of commands have been sent from the governor.
Where it happens to float at any throttle (load) or speed (RPM) is precisely calibrated on the test bench.

Whether it happens to be too rich or too lean during the warm-up stage is a complicated function that could not be solved by a fuel injection pump interactive toy.

Dan, feel free to call me tomorrow to discuss in more detail if you have time.

[Benz Dr.]

Fuel injection pumps are a technical marvel of their time. I'm not a pump rebuilder but I think I have a basic understanding of how they work. You appear to be a pump rebuilder so I would expect that you would have a greater knowledge of the various systems and components of said pumps than I do. Everyone here understands this, as do I.  Since I have no intention of ever becoming an IP rebuilder, I'll leave that up to the experts.
 However, in order to correctly diagnose a defective IP, one needs to know enough about how they work in order to not send a perfectly working pump off to be rebuilt. In the event that the said pump gets rebuilt, and the engine still runs terribly afterwards, I've just spent the customers money and perhaps a large part of their budget as well. I have a number of tests and adjustments I make before I send a pump off to be rebuilt, so a fairly high understanding of all of the working components of the engine ( which includes the IP ) becomes key to any sort of success.

I often tell customers that they probably don't need to know how to rebuild an engine; they need to know how to properly maintain one after its been rebuilt.  The same goes for injection pumps - I need to know if one isn't working, not how to rebuild it.  Send me a PM with your phone number if you like.