Can a later Warm Running Device replace the one on an earlier style pump?

[scoot]

This is more about injection pumps than about Pagodas, hopefully I can get some answers here...

I have an 6 piston injection pump for a M189 engine (not Pagoda) but it uses the same fuel injection pump thermostat as a very early 230 SL.  I consulting the technical manual I see illustrations of the warm running device and although it looks slightly different, particularly in how the air slide works, it seems that the entire WRD including the later style thermostat could be transplanted on an earlier style injection pump.  They seem functionally to do the same things:   a) close passage for air bypass when warm   and   b) press a piston down in the injection pump to change the enrichment.

The reason I am considering this is because I have a M189 engine car that has a bad injection pump thermostat, and they are expensive to replace - $400+ for used, $1200 for new from dealer, $890 from on-line MB dealers.

Has anyone else had this issue or perhaps can speak to the interchangability of such parts?  The castings look the same.  The rod movement looks the same.  It all looks like the same thing that has been updated and uses a $40 thermostat instead of a $1000 thermostat.

thanks
Scott

[twistedtree]

The short answer is No.  The reason is that the length of the throw of the short and long t-stats is different, so the geometry of the air slide is different, and more importantly the distance that the pin moves the FIP mixture lever is different.  To prevent interchange of the two WRDs, the bore in the FIP body is a different size so the wrong WRD won't even fit in the hole.  I'm bringing two FIPs with WRDs, one of each generation, so anyone who's interested can see them, take them apart, and otherwise inspect how they work.  Are you coming to PUB?

[scoot]

Hi Peter -

I want to be convinced that you are correct so I can move forward with a necessary expensive purchase, but I remain unconvinced.

The short answer is No.  The reason is that the length of the throw of the short and long t-stats is different, so the geometry of the air slide is different,

I would be using the air slide and thermostat from a later car on an earlier FI pump.  So the geometry of the air slide is going to be corresponding to the geometry and throw of the later thermostat and I am reasonably confident that the air bypass will work correctly...

and more importantly the distance that the pin moves the FIP mixture lever is different. 

And this is where I need to do more research (by putting a later thermostat into boiling water and measuring the distance change - I recognize that the amount of push-down on the piston under the WRD should be consistent with what was originally intended.  So that's my homework, or part of my homework...

To prevent interchange of the two WRDs, the bore in the FIP body is a different size so the wrong WRD won't even fit in the hole.  I'm bringing two FIPs with WRDs, one of each generation, so anyone who's interested can see them, take them apart, and otherwise inspect how they work.  Are you coming to PUB?

Unfortunately I'm not coming to PUB, but I think that I may have confused things a bit.  The injection pump that I am experimenting with for a possible donor WRD is from a 250SE, has a separate oil system, etc.  And I have just verified that the M189 injection pump bore is the same as that of the 250SE -- both WRD fit into both injection pumps with no problem.   I'm suspecting that if I took a WRD from a M130 car I would experience exactly what you are describing.  But both mine fit in either injection pump.

[scoot]

In above picture the left WRD is from a 1965 M189 engine injection pump, the right WRD is from a 1967 M129 engine injection pump...

[twistedtree]

I agree that if the correct thermostat (heat feeler) is matched with the corresponding air valve assembly, the air mixture will be correct.  But I'm pretty sure the pin throw is different.  Let me go find the source of that info, assuming I'm remembering it correctly.

BTW, what FIP pumps are we talking about?  I've compared an R11 which is a 230SL FIP, with an R20 which is an early 280SL FIP.  I think the 250SL pump (R18) uses the short thermostate variant, but I'm not certain.  Don't have a 250 anymore.

[scoot]

BTW, what FIP pumps are we talking about?  I've compared an R11 which is a 230SL FIP, with an R20 which is an early 280SL FIP.  I think the 250SL pump (R18) uses the short thermostate variant, but I'm not certain.  Don't have a 250 anymore.

The donor pump says R18Z

[ctaylor738]

Even if it's not an exact match, wouldn't you have some flexibility through the use of shims?  The important thing is that it fully close off enrichment by pushing the lever in the pump all the way down and closing off the extra air at operating temperature.  So you might be able to accomplish that by shimming the top of the air slide.  The enrichment and extra air when cold and warming up might not be quite right, but that that wouldn't be the end of the world.

[twistedtree]

Being correct and being serviceable are two different things, and it might work well enough.  I think Scoot is correct that a tall heat feeeler paired with the corresponding air valve should provide correct supplemental air from cold to fully warm.  The issue is how far off the mixture range will be.  Of course you would want to adjust/shim it for correct mixture at normal operating temp.  The question then becomes how far off the mixture will be on a cold start.

So far I have not been able to find the reference material on how far the two heat feelers move per 10 deg C.  The Wiki says 0.5mm/10C, and I assume that's for the small heat feeler, but I'm not sure.  When I was trying to get mine working I remember that the two heat feelers had significantly different movement over the temp range, but you know how memories work as you get older... :-)  This difference is what I attributed the incompatible bore sizes and physical un-interchangeability (is that a word?) of the WRD assemblies.  I re-checked this when I was packing up the gear for the WRD hands-on-display, but frankly can't say whether the bore size difference prevents interchange in both directions, or only in one.  We can explore this later in the week if you will be at PUB.

Scoots FIP is an R18, and I no longer have one of those to inspect.  As best I know, there are only two forms of the WRD, but that might not be true.  It's possible the R18 FIP has yet a third variation.

Let's try to sort this out at PUB.  It's high time the wiki got updated to reflect all this.  My draft article has all the questions, but is currently short on answers :-)

[scoot]

So far I have not been able to find the reference material on how far the two heat feelers move per 10 deg C.  The Wiki says 0.5mm/10C, and I assume that's for the small heat feeler, but I'm not sure.  When I was trying to get mine working I remember that the two heat feelers had significantly different movement over the temp range, but you know how memories work as you get older... :-)  This difference is what I attributed the incompatible bore sizes and physical un-interchangeability (is that a word?) of the WRD assemblies.  I re-checked this when I was packing up the gear for the WRD hands-on-display, but frankly can't say whether the bore size difference prevents interchange in both directions, or only in one.  We can explore this later in the week if you will be at PUB.

That's interesting.  I _was_ able to find the specs in the 1959 BBB indicating .5mm/10C for the long thermostat.  I haven't checked the later BBB to check specs for the shorter one yet.  I can also say from trying it that the R18 air valve setup will interchange with the injection pump on an M189 engine, although the shims may need some adjustment.  But either will fit into either bore - those are the same size.

Scoots FIP is an R18, and I no longer have one of those to inspect.  As best I know, there are only two forms of the WRD, but that might not be true.  It's possible the R18 FIP has yet a third variation.

Let's try to sort this out at PUB.  It's high time the wiki got updated to reflect all this.  My draft article has all the questions, but is currently short on answers :-)

It would be great if this got sorted at PUB, I wish I could be there.  I appreciate the comments and feedback.

Scott

[twistedtree]

What FIP is in the M189 engine?  That might help sort this out.

[scoot]

What FIP is in the M189 engine?  That might help sort this out.

Will check when I get home.  Looks very much like the one from the 250SE/SL.

[twistedtree]

And just to be clear, the R18 from the 250SL has a tall or short WRD thermostat?

[scoot]

The thermostat in the R18z is short, but a taller housing.  I haven't checked to see what is in the R18 that is in my 250 SL

I did as much research as I can tonight and here's what I can report:
1)  The BBB 1959 -   makes reference to the thermostat rod length as follows:  "Another check can be made on the thermostat itself.  Measure the dimension “a” with a load of 3 kg on the working pin (2) at a temperature of 20C; “a” should be 6 +/- 0.08 mm
For every increase in temperature of 10C the working pan travels 0.5 mm so that at 80C it projects 9 mm."   So here's a source for the .5 mm / 10 degrees C
2) The BBB 1959 -  makes very little reference to the 6 plunger injection pumps but does mention them.  It is way more focused on the 2 plunger pumps in the 111 fintails.  It makes no mention of the injection pump in a 250SL anywhere that I can find.   (and for purposes of this discussion I was using a BBB printed way later than 1968)
3)  The BBB 1968-1973 makes no mention whatsoever of either the 230 SL pump or the 280 SL pump, as expected.
4)  The BBB 1968-1973 makes no mention as to the specifications of the thermostat rod.

Pics attached on this post of the BBB reference on page 00-15/2, a picture of the thermostat and housing from the 18Z pump, and a picture of the Air Valve that was lifted from the Technical Manual pages.  In my 18Z pump I am missing the air valve part between the thermostat and the plunger in the photograph - I hope it is the same as on a later pump.

The next post will have pics of the pumps.

[scoot]

And here are my pumps - the R18Z is on the patio table and is the donor injection pump.  The R12 is in the 300SE and looks very much like the R18 pump, and the other R18 pump is in my 67 250SL.