warm running device thermostat

[awolff280sl]

If I recall correctly, the length of the cylinder that slides within the WRD chamber is nearly identical to the diameter of the air port in the wall of the  chamber. It would thus seem to me that if air is completely shut off at 180 degrees, then any further extension of the thermostat pin (due to higher temps) would reopen the air port as the cylinder slides deeper and begins to open the upper edge of the port.  

[ja17]

Hello Jeff,

I don't think the WRD's main purpose is that of being an engine starting aid.  It does contribute to good cold starts by richening the mixture when cold. However,  the main purpose of the WRD, is as a "cold running device" which allows the engine mixture of air and fuel to be regulated after a cold start.  In this way a richer fuel for cold running is supplied along with more fuel and air for a faster idle when cold. My only area of doubt is exactly at what temperature the WRD stops influencing the rack in the injection pump?  I guess we can set up a test procedure for this.
I will say from experience, removing oval shims will normally lean an injection system even on a fully warmed engine. This indicates to me that the heat feeler had not completely reached the stop pin in the pump. Interesting that the stop pin in the FIP has a jamb nut adjustment. There must be an acutual factory temperature setting that is made on these units new. Someone should have this spec?

You have made a very good discovery on the significance of the stop pin. It appears that it does influence the mixture sooner than I would have expected. It does appear that the stop pin does prevent the heat feeler from changing the mixture shortly after the aux air passage in the WRD is closed.

I will check some other pumps in the morning. Sounds like we can come to some good conclussions soon.

One thing I learned over the years, as long as you keep an open mind to new ideas and observations, there is always something to be learned. I guess you could say "to gain expertise you must become an expert learner first!"

Thanks!

[ja17]

Hello Andy,

I have tested the air passage on this WRD. This one will not allow any aux. air after it closes, no matter how far the piston is pushed down. Eventually it bottoms out, but still no air flow.

It looks like the piston can  travel about a 1/4" more after the air passage is fully closed.

[awolff280sl]

Thanks Joe. (I don't know why I had that impression).
So, if I understand correctly, the hypothesis then is that the WRD may contribute to enriching the air-fuel mixture at higher engine temps?
Then I ask: do air-fuel mixtures need to be richer at higher temps for better efficiency, (and conversely leaner at cooler temps)?

[ja17]

Hello Andy,

I think Jeff has made a good discovery. I think we both agree at this point that the WRD's influence on fuel mixture, is checked at some point by a "stop pin" in injection pump). This seems to happen sometime shortly after full warm up and after the WRD air passage closes.

A richer fuel mixture is needed for a cold engine.

I believe that the WRD constantly adjusts extra fuel and air to the engine during engine warm up and into warm-up. The extra air is regulated through the WRD air passage and the extra fuel is regulated by the WRD changing the IP main rack.  Both  the air and fuel changes occure when the "heat feeler" moves the piston and pin under it. At some point in the warm up cycle after the air passage is closed, the heat feeler is prevented from futher moving the pin, by another pin ( "stop pin")  in the injection pump (thanks Jeff). The exact temperature at which this "stop pin" performes this stop, is yet to be determined, but it seems to be shortly after the air passage in the WRD closes. We know the air slide closes at a certain temperature as described in the BBB. I have never seen any information anywhere on Jeff's "stop pin". It is a very imporstant discovery and should be very helpful for complete understanding of the WRD.

[jeffc280sl]

There are two springs in the overall wrd system.  The upper spring is in the wrd itself and the lower spring is inside the fip under the wrd.  The spring inside the wrd, upper spring, is of higher tension than the lower spring in the fip.  As the thermo buld expands force is exerted on these springs.  The first to compress is the lower spring iside the pump.  Once the thermostat forces the lower spring/pin inside the fip to its stop, no matter how much more expansion of the thermo bulb occurs due to rising temps, this pin can not extend any further to change the rack.   Once the lower spring has been compressed to its stop the higher tension upper spring inside the wrd simply  takes up the difference of  bulb expansion beyond that point. If the spring was not there to do so, the pin would be solid ..and then the thermo bulb "could" create enough force to rupture or pop the heads off the mounting screws. Any length changes inside the wrd after the lower spring/pin has reached the stop is taken up by the upper spring.

The air slit opening in the wrd is small enough to be covered by the air slide valve as it to is compressed downward up the upper spring.

Joe,  I agree with you about the learning part.  If I weren't able to absorb and build on the knowledge you have generously shared I would never have gained this level of understanding about the wrd and other pieces of the 113.

[jeffc280sl]

I'm pleased we now have a complete understanding of the WRD.  Joe, thanks again for generously sharing your knowledge.  I'll add your description to the tech manual.

[awolff280sl]

Thanks Joe and Jeff, I get it! Especially now I understand the purpose of the spring inside of the WRD which acts as a safety buffer against excessive pin pressure. Makes sense.
One question remains unanswered in my mind. Is the WRD designed to further lean the mixture above "normal" operating temps (as Joe suggested), or should the fip lever hit its stop simultaneously with closure of air intake?

[ja17]

Hello Andy,

I think we are all in agreement at this point, that the WRD hits it's stop shortly after the air passage closes. The question of the hour is "exactly at what engine temperature is it supposed to happen?". The "stop pin" in the injection pump has an adjustment feature.  I suspect that it is set to happen at an exact engine coolant temperature when the pumps are built. It appears that the influence of the WRD after engine warm up is slight or short-lived.

[ja17]

Hello,

I guess some good photos are next on the agenda !

[jeffc280sl]

I ran some tests that indicate the thermo bulb deployment at 130 to 140 degrees F is sufficient to close the air slide and cause the pin inside the pump to rest on its stop.  No leaning or enrichment of the rack is possible at temps over this range because of the stop.  Any additional thermo bulb deployment is absorbed by the spring inside the wrd and below the air slide.  The spring tension inside the wrd is sufficient keep this side on its stop no matter what happens on the BC side.

I will take some pics and post them later today.

[jeffc280sl]

The first pic is the air slide valve and wrd pin/spring.

Here are some other pics of the WRD operation inside the fip.

The second picture shows the position of the pin/spring/stop, rack and levers when the engine is cold.  Notice the position of the lower right side of the rack lever.

The third pic is a closeup of the pin/spring/stop.  There is an outer sleeve which is forced by the thermo bulb to compress the spring to a stop on top of the adjuster nut. 

The forth pics shows the position of the pin/spring/stop, rack and levers when the engine is warm. Notice the compressed spring/sleeve resting on the stop and the position of the lower right side of the rack lever.


 

[wwheeler]

WOW, great work on this. I have been reading this with great interest as it has evolved. I have noticed the upper spring on the rod/pin and have wondered what was it's purpose. It makes sense that it prevents the bulb from binding the levers when the pin is on the stop. Given the bulb is some waxy material, it will continue to expand as the temperature increases beyond 140*F. I guess the upper spring keeps that expansion in check without creating excessive stress as Jeff says.

If I understand correctly, are we saying that once the engine temp is 130-140*F, you CANNOT change the mixture at all ranges with the oval shims? If this is true, then what is the best way to do so (BC, full rack screw...)? Then are the oval shims just for changing the fuel mixture with the WRD when the engine is below 140*F?

If the pin is on it's stop, the BC can no longer effect it? If you went up in elevation, you would need to further lean the mixture. How does the BC accomplish this?

One last question. If you removed enough round shims so that the air valve no longer closes when above 140*F, would the pin still be able to close on the stop?

That is one complicated device! I wonder if the guys who rebuild these injection pumps, could confirm some of these findings?

 

[jeffc280sl]

Wallace,

This stuff is pretty hard to describe so let's use the second picture in my last post.  Notice the wrd pin in the upper left side of the fip.  There is a preload of this pin on the spring/sleeve/stop and the horizontal control lever at the top of the spring.  If you remove oval shims this preload will be lower and the rack will start at a leaner afr.  If you add shims the preload will be higher as will the horizontal control lever and the rack will start in at a richer afr.  Please understand these are both rich conditions to aid in start and warmup of your engine.  The oval shims make this rich condition leaner or richer.

The round shims affect when the thermo bulb starts to lean the rich starting condition.  Raise the thermo bulb higher and it will take a little longer to start leaning the mixture.  Lower the thermo and it will start to lean the mixture earlier.

Round shims affect when leaning of the mixture begins.  Oval shims set the richness of the cold starting mixture.

I hope this helps.  It is explained in the BBB if you have a copy.

The BC operates on the right side and tranfers it force via the diagonal fulcrum to the rack.  It operates independantly from the wrd.  The thermostst pin moves almost 8 mm when heated.  It onlt takes 3.5 mm to close the air slide valve and put the spring/pin on its stop.

[ja17]

Yes, I agree for the most part. 
I think the BC works in conjunction with the WRD to change the mixture. The BC is not restricted by the "stop pin" at all, but it does manipulate the same lever that the WRD changes. The fulcrom blends  the inputs from the two devices. Also since the pin from the WRD stays in contact with the linkage levers in the pump, It looks like adding or subtracting small round shims directly changes the fuel mixture by moving the rack and also change the amount of air flow in the WRD by moviing the piston over the aux air passage. These changes occure only during wrm up.

Theoretically, removing oval shims should also lean the mixture during warm up  without  changing the postition of the air piston in the WRD.

Wallace, the heat feeler will continue to move the piston in the WRD even if the pin under the WRD reaches the stop limit. So oval shim removal should not create a problem of with the WRD air supply cut off. Understand that the air piston in the WRD can still be moved by the heat feeler, even if the pin coming out of the bottom of the WRD is stopped by the stop pin in the IP.

I have a good factory diagram of all these relationships, but my scanner is not working at the moment

[mulrik]

Andy and Joe
Thanks a million for this! I think the WRD has been nailed in this thread! So I guess the WRD should complete it's "warm up" function at ~55 degrees C (130-140 F), at least with regards to the extra air it allows into the intake manifold, i.e. when it has travelled ~3,5mm. Whether it then subsequently also affects the fuel amounts thereafter i.e. acting on the lower spring any further remains to be solved.
BR,
Ulrik

[awolff280sl]

Ulrik, thank Jeff and Joe. I'm just tagging along.

[mulrik]

Sorry Jeff, My confussion!! Thanks!! I don't think (hope) nothing else needs to be written on the WRD in the future after this...
Ulrik

[Dash808]

Good stuff.

I hereby nominate Jeff & Joe for the WRD tech session, PUB '11 

[wwheeler]

I hereby second the nomination for Jeff & Joe!

I am sorry to run this one point into the ground concerning the oval shims. I understand that adding or removing the oval shims can change the mixture during cold operation. But do the oval shims affect the mixture for a fully warmed up engine? If not, what is the best way to adjust the mixture at all speed ranges?

Thank you for your patience!

[ja17]

Hello Wallace,

Don't be afraid to ask for more details or clarification. This is basically a brain storming session.

Jeff and others here are some of my thoughts from this information comments welcome....

For most of us, rich running at all speed ranges during the cold engine warm-up cylcle of the engine,  is the most common problem. The removal of the oval shims is the best cure for this situation assuming other factors are not causing the problem. This may be as far as you need to go. This is quick and easy and you may  not need to go any further, if rich cold running is your problem.

Assuming the pin under the WRD reaches the full stop after warm up,  the WRD will not normally change mixture at all speed ranges after the warm up cycle. It will change mixture during the warm up cylcle. "jeffc280sl " discovered this bit of enlightening inflormation. Thanks Jeff !

The internal single screw on the injection pump rack will adjust injection mixture at all speed ranges and all temperatures uniformly.  The BC (Barometric Compensator)  shim changing will also do this. Adding or replacing the small round shims in the WRD can be used  to set  the engine temperature at which the air passage in the WRD completely  closes.  This is a basic factory adjustment and normally does not change much. A secondary effect of changing these shims is a mixture change from the pin going down into the IP also changing length. I suspect that the closure of the air valve should be looked at first, then the oval shim adjustment to tweek cold engine mxture next.

It looks like all the warm engine adjustments should be carried our first if you have both warm and cold engine adjustments to make. If the warmed up engine needs an adjustment at all speed ranges, then the BC or the single internal main rack adjustment screw (not the idle thumb screw) can be used to adjust the warm engine mixture at all speed ranges. If the mixture needs an adjustment at mid or high range on a warm engine, then the two pair of internal governor screws can  be used  or (see option below). If the warmed up engine is in need of mixture adjustment only at low rpms and idle, the idle thumb screw  on the IP or the intake air screw may be the only adjustment needed.

The option....Here is a situation, say you determine that your warmed up engine is fine at idle but rich at mid and high rpm ranges.....   The best solution I see would be to do a total mixture adjustment at the BC or the single internal rack screw.  This would cure the mid and high rpm issue but  cause the idle mxture to become too lean.  Next I would adjust the idle thumb screw to bring the idle into correct mixture. This sequence would avoid the need to do internal governor adjustment on the two pairs of range screws.

After  warm engine adjustments have been made. The WRD air valve should  be checked to make sure it closes at the correct temperature (small round shims).  The mixture at cold idle can be adjusted by adding or subtracting oval shims.

I stress the importance of checking first, things like correct linkage adjustments, plugged WRD air filters, stuck WRD pistons, engine vacuum leaks, bad Baro. Compensator units (BC), bad heat feelers in the WRD, leaking intake starting valves, poor engine tuning, and bad fuel pressure or fuel volume. These other faults may just cause you to make uneeded changes on your complicated injection systems if you do not fix them first !

[jeffc280sl]

I agree with Joe especially the part about checking everything else first.  I think everything else includes checking the thermo bulb and slide valve in the WRD.  This is just like making sure you have a good bc.  After everything else is checked and fixed then you can begin to think about changing shims and other fip adjustments.

If you choose not to check and repair everything else first you will be chasing your tail with fip adjustments.

[twistedtree]

Adding or replacing the small round shims in the WRD can be used  to set  the engine temperature at which the air passage in the WRD completely  closes.  This is a basic factory adjustment and normally does not change much. A secondary effect of changing these shims is a mixture change from the pin going down into the IP also changing length.

Sorry to be late to the party, but I'm working on a WRD that doesn't close all the way despite being clean and having an operative heat feeler.  My conclusion is that I need to add some shims between the heat feeler and plunger assembly.

When first thinking about it, I was thinking the same as Joe in the above quote, namely that adding or removing round shims would change BOTH the temperature at which the air valve closes completely AND the mixture during warm up.  But the more I think about it, I don't think that's true.  Changing the round shims moves the whole plunger assembly in tandem. The point where the air valve closes is exactly the same as the plunger protrusion that affects fuel.  Adding shims moves the air valve a little bit further closed, but it also moves the fuel plunger to a commensurately leaner position - exactly the same as without the shims, just at a lower temperature.  It's the relative distance between the air valve and the pin that determines mixture, and that distance is changed only by the oval spacers.

Does that sound right?  I'm thinking I can add round spacers and not screw up my warm-up mixture.

[wwheeler]

I removed round shims until my WRD air suction would not shut off. That ended up being .025" on my car. I suspect it is similar for most. What thickness of shims do you have?

Adding round shims does reduce both the air and fuel although I am not so sure it is 1 to 1. If you look closely at the orifaces in the WRD where the air comes in from the filter, there are three rectangular grooves that resemble an upside-down pyramid. The smallest groove is for higher starting tempertaures, the middle groove (including the small groove) is for cooler starting tempertaures and the largest groove (all three combined) is for very cold starting temps. And changing the round shims does affect the temperature when the WRD shuts off.

Because I am not 100% sure the air and fuel change at the same rate ( I doubt they do) when adding shims, you may have to adjust the lower oval shims to compensate. But that is no big deal. The round shims are harder to change.

[Benz Dr.]

There is a difference between the 230Sl system and the later 250/280SL system. They do the same functions but the parts are not the same nor do they work in the same ways.
The 230SL thermostat has a very short travel at about 1.5 mm while the 280SL has about 7 or 8 mm of travel. If the late system won't shut off at a fully warmed engine, you can add  round shims at the top of the slide valve until there is no longer any vacuum with the air filter removed.