warm running device thermostat

[dseretakis]

Hi all.  I'm tackling the WRD on my 1971 280SL which I have not been able to get running now for a long time.  See "non-running 280SL" thread for those who are not already familiar.  Anyway, I removed the WRD and all looked OK.  The plunger moves freely.  I immersed the thermostat in  boiling water and the rod traveled by 6mm.  However, when I removed it from the water and let it cool down for 2 hours it had not resumed its original position.  I then pushed the rod back and it insisted on returning to the hot "extended position"  Am I missing something here or is it just defective?

[jacovdw]

The thermostat for the 280SL's is not that expensive to replace. It is the one for the 230SL's that will cost you an arm and a leg.

I would expect at the very least for that pin to return to it's original position once cooled down.

[merrill]

hans at H&R can fix the WRD on the 230 sl's

[dseretakis]

I ordered a new one from www.buymbparts.com.  It was $60.  The local dealership wanted $113.

[ja17]

Hello deseretakis,

Your starting problem lies elsewhere. It sound like your IP thermostat is ok. Once it extends it will resist moving back. It depends on the spring located in the WRD to push it back after installation.

Remember, if you have air, fuel, spark on time and compression it will run. A fresh set of spark plugs is an inexpensive investment.   You can always re-use the removed ones if they are still good. Check the compression while you have the plugs out. If the timing chain has jumped it will show up in your compression readings.
Squirting a bit of starting fluid or hot wiring the intake cold start valve will get fuel into the engine. If fuel will not get it running, check for spark by removing a plug wire and hooking up a loose spark plug to it. Ground it to any point on the engine while someone cranks the starter. You should see spark. If you have spark, it must be on time. Remove the distributor cap and make sure the rotor is pointing to the #1 cylinder when the engine is at TDC #1 compression stroke.

Let us know what you find.

[dseretakis]

I also believe that the problem lies elsewhere, but where?  I have spark, the engine starts and runs smoothly now that I changed to non-resistor plugs.  It will however not continue to run without continuously applied throttle and it puts out much gray/tan smoke. Compression is uniformly good across all cylinders,  cold start valve works well, inside of tank is bright and shiny.
Dimitri

quote:Originally posted by ja17

Hello deseretakis,

Your starting problem lies elsewhere. It sound like your IP thermostat is ok. Once it extends it will resist moving back. It depends on the spring located in the WRD to push it back after installation.

Remember, if you have air, fuel, spark on time and compression it will run. A fresh set of spark plugs is an inexpensive investment.   You can always re-use the removed ones if they are still good. Check the compression while you have the plugs out. If the timing chain has jumped it will show up in your compression readings.
Squirting a bit of starting fluid or hot wiring the intake cold start valve will get fuel into the engine. If fuel will not get it running, check for spark by removing a plug wire and hooking up a loose spark plug to it. Ground it to any point on the engine while someone cranks the starter. You should see spark. If you have spark, it must be on time. Remove the distributor cap and make sure the rotor is pointing to the #1 cylinder when the engine is at TDC #1 compression stroke.

Let us know what you find.

[dseretakis]

Joe, upon reading your post more closely it seems that the spring action in the WRD should push against the thermostat thrust rod.  While the plunger in my WRD moves back and forth freely, there is no spring action.  I can push and pull on the plunger but it is not spring loaded.  It is almost as if the spring is missing.  I want to take it apart but there is a flange on top of the air valve housing that holds the air valve/plunger/spring in place.  The flange appears to be pressed in place.  How do I remove it?
Dimitri

quote:Originally posted by ja17

Hello deseretakis,

 It sound like your IP thermostat is ok. Once it extends it will resist moving back. It depends on the spring located in the WRD to push it back after installation.

[ja17]

Hello,

The spring action comes from within the IP itself. You will feel it push back at the IP thermostat when   you are re-installing it .

[dseretakis]

Thanks, that clarifies it for me.  I wasn't too excited about disassembling it further.
Dimitri

quote:Originally posted by ja17

Hello,

The spring action comes from within the IP itself. You will feel it push back at the IP thermostat when   you are re-installing it .

[mulrik]

I'm pretty much at the end of a total engine restore, and I have a question on the warm running device thermostat.

It's a 250 with the late warn running thermostat device type.

I have two questions.

First of all does there need to be a copper or rubber ring between the thermostat and the housing (at approximately the tip of the pen If you look at the picture I have attached). Does it really hold the water out without a sealing of some sort?

Secondly, how far on the thread does the 2 nuts needs to sit? At least as I understand it the postion of these two nuts is equivalent to adjusting the device by adding or removing shims. Is this correctly understood?

As always 250 times thanks!!
Ulrik

[ja17]

Hello Dimitri,

Sounds like the rack in the injection pump is stuck.  If this is the case the spring action under the heat feeler is canceled out. This will also cause the symptoms you descrbe.  Check the rack for movement.  There is an opening on the front end of the IP where you can check the rack movement with a screw. If you need more guidance to find it let us know.

[ja17]

Hello Ulrik,

The two nuts on the heat feeler are factory set and not usually changed. In fact with the latest version of the heat feeler, the setting is not adjustable.  Changing the adjustment does change fuel mixture at cold idle and everthing else also! It also changes how soon the cold start air supply shuts down. So this is not something that is usually tampered with. Adjusting the length of the heat feeler will change fuel mixture all speed ranges, and will change the  shut of temperature of cold air supply.

Oval shim change, barometric compensator shim change, or rack adjustment will change fuel mixture at all speed ranges and temperatures. I like to do the oval shims since it is easy and things are easily put back to the way they were if needed. A rack adjustment is preferred by some but more work and more difficult to put back.

Idle thumbscrew change will change idle fuel mixture only.

Internal centrifugal governor paired screw adjustments, adjust mid and high speed range fuel mixture. Lots of work and normally not for the amateur.

Make sure linkages are correct, basic engine tuning is good, and fuel volume and pressure are correct or you will be wasting your time.

What are your issues at this time?


Yes there is no additional seal at the connection of the WRD heat feeler and the special tapered spacer. It is a compression seal.

[mulrik]

Thanks Joe!!

OK I guess it was stupid of me to play with those two nuts then!!! I seem to remember that they were ~2/3 to 3/4 towards the end of the pin when I removed it, but I don't remember exactly. When I read on the forum about this WRD nobody ever mentioned these nuts, all the talk here was about the shims, so I didn't know the implications of playing with it. Well don't play with things you don't understand I guess is the lesson...

Well then, can you or anybody else measure the distance from the end of the tip to the nut (and maybe also the distance from the other side for quality control...). That at least will give me a starting point. Knowing how sensitive it is since a single shim can alter things a great deal, I guess I can expect some time fine tuning this thing....

I really do not have that many other issues, everything has been running pretty smoothly uptil now, so I'm optimistic and confident...

Best wishes,
Ulrik

[Raymond]

Hi Mulrik,

You're chasing a problem that bugged me for a long time.  I had the same WRD thermostat as you with the adjusting nuts.  I think it was a much better system than the shims, but there is no longer a choice.  It sounds as if your's is still working, so you can do with the nuts, the same as the rest of us do with the shims: trial and error.  You can write down the amount or turn you give the adjustment nuts and see what happens.  If the mixture is worse, go back.  If it's better but not good enough, go forward.  Just keep notes on which way you adjust and what happens.  If you suspect it may be weak, get a new one and a few shims.   To adjust the mixture with shims; add or remove them.   

Be aware that the seat washer that the thermostat sits in may need to be drilled out to 13mm to accommodate the newer thermostat because the bottom from where the rod protrudes is different.  Good luck.

[Dave Gallon]

Just for reference, the thermostat is part number 001 203 95 75. MB USA list $100 (whoever was quoted $113 was being ripped off), my price $73.83 from Mercedes. However, you can get one from AutoHAusAZ.com made by the original vendor (Behr) for $19.18.

[mulrik]

Joe Alexander wrote earlier in this post that "Oval shim change, barometric compensator shim change, or rack adjustment will change fuel mixture at all speed ranges and temperatures."

So let me try to understand this. If you add shims under the WRD (or adjust the two nuts) this will change the fuel mixture at all RPM ranges, that is if the engine is cold. I understand that much!!

So here's my question. If you adjust the WRD (shims or nuts) will it also affect the fuel mixture when the engine is warm? If so please explain. In my view the WRD shuts of completely when warm and that's the business of it, but does it also affects fuel mixture when warm?

The reason for asking is that I have just started my engine after a complete rebuild (which included playing with the WRD...), and now I'm in the proces of making it run nicely.

As always, thanks,
Ulrik

[ja17]

Hello Ulrik,

Here is my take on the WRD....

First of all with all adjustments of the IP system, the engine must be in good tune, with a clean fuel supply with proper volume and pressure. Engine linkages should be set correctly. A leak free intake starting solenoid is important. The engine should have no vacuum leaks. The small round air filter on the injection pump WRD should be checked to make sure it is not clogged. The WRD heat feeler should be functioning correctly.

The WRD is designed to change the fuel and air supply to the engine during the warm up period when additional fuel and air is required. The WRD perform the same purpose that a manual or automatic choke preforms on a carbureted engine.  The rate of this mixture change in the WRD, is constant and not adjustable being that it is regulated by the heat feeler which is constant. The temperature that the extra air supply is closed off is set by the Bosch factory when the pumps are being manufactured. This closing of the air passage is accomplished by the addition or subtraction of the small round washers or the two adjuster nuts (earlier heat feelers).
Any change in the length of the " rod"  from the WRD, extending down into the IP, will change the main rack position and consequently the fuel mixture. Changes in the quantity of oval shims, small round heat feeler shims, or the two adjustment nuts (early heat feelers) will change the length of this WRD "rod" and consequently the fuel mixture by moving the main rack in the IP. Here again, rate of change is constant  depending on engine coolant temperature and the heat feeler.
Removing or adding of any oval shims will change the mixture of the IP at all speed ranges. It will not alter any function of the WRD. Removing or adding small round shims or the changing the adjustment nuts on early units, will also change the fuel mixture in all speed ranges. In addition adding or subtracting any small round shims will change the function of the WRD (the temperature that the extra cold air supply is shut off).

These WRD units are factory set and are not a normally meant to be tampered with. The adjustment that can be made is the actual temperature at which the extra air passage is closed off. This accomplished by changing the small round shims. Remember any changing of the small round shims also changes the length of the WRD "rod" and thus the IP mixture at all speed ranges.

You can add shims one place and subtract at another to keep mixture the same and theoretically accomplish a change in the shut down temperature of the air passage without changing the mixture.

Engines and IPs wear with age, things change and engines are different. Certain adjustments compensate for wear and differences in engines.  You can remove small round shims and add the same thickness large oval shims to make the extra air supply stay open a little longer ( later temperature) to create a "leaner " cold running mixture, but you are deviating from the factory settings. I suspect the range of adjustment in this process is quite small before the WRD air supply fails to shut off completely.

[jeffc280sl]

Here is my understanding of the WRD adjustments.

The top round washers are used to adjust timing of the heat feeler impact on the fip.  Fewer washers means the heat feeler will impact the rack earlier.  More round washers means the heat feeler will impact the rack later.  Example:  Let's say the heat feeler fully extends in 180 seconds.  If you move the feeler closer to the rack by removing washers it will effect a change earlier.  If you move the heat feeler farther away from the rack adjuster it will effect a change later in the heat cycle.

The lower oval washers act differently.  When the engine is cold the heat feeler is retracted.  In this position the fip is at the rich setting as a warmup aid.  If you want the mixture to be richer (higher rpm)  during the warm up add washers.  If you want to lower rpms during warmup remove washers.  Explanation.  The wrd pin has a fixed minimum position.  If you move the pin farther away from the rack lever the cold starting position will be richer (higher rpms).  If you move the fixed starting position of the pin lower, remove washers, the initial or cold setting of the rack will be leaner.

I don't think the wrd affects the rack in any way after warm up.  Inside the fip the wrd exerts force on a spring loaded limit pin.  Once the limit is reached the effect of the wrd on the fip is zero.  It reaches the same stop pin no matter what you do with the round or oval washers.  These washers just determine how rich or lean the mixture will be and when the wrd reaches this stop limit.  After the stop limit is reached the wrd is has no continuing effect on the fip.

Joe, Maybe you can check my understanding and the function of the spring loaded stop pin.

[ja17]

Hello Jeff,

I am sitting here with an injection pump on my lap, working all the levers, pins and rods.  I know you have a parts injection pump you are learning from also. There is very little information available on these WRDs.  I have just searched my early and late BBBs and found them of little help. Other injection pump information I have also is of little use.

So we rely on our own observations and experience for our conclusions.

First of all the BBB uses the shut off temperature as the only basis of the small round shim adjustment. Having to deviate from this seems to indicate that a problem may lie elsewhere. However I do understand that at times deviation may be necessary.

From my observations the heat feeler is in constant contact with the injection pump rack through a series of levers, and cams etc. Yes there probably is a min. length of the feeler but probably a much lower ambient temperature than we will ever see in our climates. Yes there is a max. length the heat feeler can reach, since the spring pin in the WRD will no longer lean the mixture at some temperature. I seems to me to be considerably higher than 180 degrees F. If so, the WRD or the length of the plunger rod and heat feeler of the WRD will effect the main rack and fuel mixture at cold temperatures and normal running temperatures. I base my opinion here on the fact that removal of oval shims always leans the mixture of an engine during warm up and during normal running temperature. I do see that the mechanical movement on one lever is reached at some point above 180 degrees. So at this point, the spring pin in the WRD will no longer allow a leaning of the mixture. If this happens after 180 degree F. (as it seems),  then I must still conclude that the WRD is not designed to be able to adjust cold mixture only. Small round shims will adjust IP mixture during warm up and normal running temperatures. Removal or addition of the  small round shims or jamb nut adjustment (earlier heat feelers) will change at what temperature the air supply  in the WRD will shut down. As mentioned previously deviating from the specified "shut down" temperature may create a leaner or richer mixture during warm up by allowing the extra air supply to stay open wider and longer. This adjustment can only work if round shims are removed and oval shims of the same thickness are added. This basically achieves a leaner mixture during warm up by allowing the extra air supply to the WRD to stay open longer. Hmmm... seems to me you could do the same thing easier by just turning the air idle screw open more, on the intake  and leave the WRD alone? Anyway, removing too many  round shims, will at some point,  cause the extra air supply to never close completely.

Thanks for your input..comments?

[bpossel]

Hello Joe & Jeff,

I find this very topic very interesting, but still a bit confusing.

As I look through the Tech Manual and earlier posts, we dont really have pics showing all of the details you discuss (at least I cant find them).

If possible, could you post pics of:
1. Early & late style heat feelers (i thought the later style has the nuts & earlier w/o the nuts?). My current setup has the heat feeler w/nuts.
2. Clear pics of the round shims for the upper section (heat feeler). I only see pics of the lower section with oval shims currently posted.

Maybe we can then update the Tech Manual with the add'l pictures and description of exactly what the top section (with shims or nuts) and the lower section with oval shims actually does.  It would be nice to include in the manual, along with pics, and clear description of:
1. Removal of oval shim from upper section (heat feeler) - leans, or enriches fuel when cold ...  or if later style w/nuts, turning nuts towards top body of heat feeler lengthens the rod of the feeler which - leans or enriches the fuel?
2. Removal of oval shims from lower section of the WRD - leans or enriches fuel when cold ..?  etc...
3. Specific conditions that apply to removing, adding round shims (or adjusting nuts) on the top section of the WRD, vs. when to add, remove oval shims from the lower section, etc..

I would be happy to help.

Thanks!
Bob  

[jeffc280sl]

Hey Joe,   

I have taken some measurements and can say the air valve closes and pin inside the fip reaches its stop when the thermostat rod moves outward about 3.5 mm.  I find this interesting.  In a pan of boiling water the thermostat pin will extend 7.8 mm. I think we all agree the air slide valve closes during warmup.  It follows that the leaning of the pump also ceases at the same or near the same temperature.

Since the air slide valve and leaning pin in the wrd are part of the same mechanism I think we can conclude that if the air valve closes the pin inside the pump is on it's stop and no further air or fuel adjustments take place until the thermostat cools. 

If I get some time I'll cycle water through the wrd mounted on my pump to see if I can determine the approx temperature the pin inside the pump reaches its stop.

[jeffc280sl]

Using a hand pump and 140 degree F temperature water I cycled water through the WRD while mounted to the fip.  After a minute or so the air shut off valve closed and the fip pin reached its stop.  By the end of the test the water had cooled to approx 130 degrees F.  The BBB tells us the heat feeler switches off at 50 to 55 degrees C.  I now understand this to also mean the air slide valve will close and the fip pin will rest on its stop.

What do you think Joe?

[awolff280sl]

Like Jeff, I assumed that complete shut-off of air intake into the WRD should occur simultaneously with the maximum thermostat pin extension once the engine is fully warmed. During my trials and tribulations with the WRD, I discovered that it is possible, depending upon the number of round and/or oval shims, to disassociate these from one another. In such a situation, air may still be sucking into the WRD even though the thermostat pin is at full extension. I eventually came to the conclusion that, at the very least, one must use the correct number of the appropriate shims that ensures that the sliding cylinder completely blocks the air intake port at full warm-up. I identified that it is not only possible for the cylinder to either come to rest just short of fully covering the air intake port, but also possible for the cylinder to slightly overshoot the port and thus cause an air leak.
Once I had determined that I had the correct number of shims to fully shut off air at full warm up, I was then able to use the appropriate other shims to make sure that my AFR, CO, RPM etc was correct at idle. 

[ja17]

Hello Andy and Jeff,

Jeff, ponder this question a bit..... At 180 degrees F. the IP WRD has regulated air and fuel to allow the injection pump to inject the correct fuel mixture, as we understand.  Now what happens at 200 degrees or 220 degrees? Are you saying that the WRD just shuts down at higher temperatures and allows the entire mixture to go out of adjustment?  I don't think so. I have to believe the heat feeler still regulates the fuel mixture even though the air slide has completely closed, now that a high rpm cold idle is no longer needed.

[jeffc280sl]

Let's say the air slide just closes and the wrd pushes the pin and lever in the fip to its stop when the temp is 130 degrees.  At 140 and above the thermostat pin continues to extend compressing the slide valve against the spring/pin just under the slide valve inside the wrd.  This compression just adds tension on the wrd pin which is perched on its stop.  

At 130 degrees and above the wrd causes the pin inside the fip to sit on its stop. The WRD is simply a starting aid and does not change the rack as the engine warms above 130 de.grees