Fuel damper rebuild

[wwheeler]

I just rebuilt the fuel damper on the 220SE. Yes this is a Ponton car and a little different from the later engines, but the basics are the same. If there is interest, I could post the pictures with an explanation attached on this thread. I don't see anything in the tech manual covering that.

Attached is the finished item.

[ja17]

Hello Wallace,

Yes would like to see the process. 

[Tyler S]

Yes I think that would be a good addition to the tech manual. Where did you find the diaphragm?

[Bill Sgro]

I am interested.  I have mine apart now and would like to see and hear what you have done.

[wwheeler]

I'll have to this in a few parts because of time constraints. And if I miss something, please add or correct.

This damper is for a 1960 220SE Ponton M127 engine. There are a few differences between this and the W111 and W113 damper that I will point out, but basically are the same. The fuel damper is comprised of (5) main parts. 1) the main body with mounting studs 2) back cover 3) diaphragm 4) diaphragm spring 5) fuel line fittings. The wearable parts are #3, #4 and seal rings for #5. For both the 220SE Ponton (W128) and the W111 damper, The Classic Center sent the following parts:
Diaphragm #127 070 00 52
Spring # 127 993 00 01
(2) 14mm x 18mm aluminum seal rings - may need more depending on the fuel line fittings required
As of 2014, the parts were available. Might need to check current status. I am sure these parts are the same for the W113, but please let me know if not.

This is a simple device and would normally not require any repair unless it is leaking. Over time though, the diaphragm becomes hard and will no longer function. I am not sure how vital this damper is to the operation of the injection system, and could use some input on that here. The diaphragm element on this 56 year old part was intact but was as hard as a rock. So it was in need of replacement.

So to start, It is helpful to place the damper unit in a vice. See pic 0620. You will need "soft" jaws on the vice so the threads on the studs are not damaged. If you don't have any, soft jaws are a nice thing to have and can get from places like McMaster Carr. You will also need to document what came off where. For instance fuel fittings can be switched and also note what attaching pieces are used.

Begin by removing the fuel fittings. See pic 0619. The W128 has different fittings than the W111 and I am sure the W113. No matter, but just make sure you put them back in the same place. It should now look like pic 0630. Next remove the (6) hex bolts that have a 10mm head. These should use steel wave washers which work well as a lock washer for aluminum surfaces. Replacement metric wave washers can be bought at McMaster Carr. Just don't use split lock washers as it will gouge the aluminum or (bakelite) surface below the bolt head. The biggest difference between the old and newer dampers is the back plate. The old Ponton unit is aluminum as seen here and the later W111/W113 units are a bakelite (phenolic) material. Another minor difference is the color of plating for the hardware. Pontons never used yellow CAD and was either black oxide or silver CAD. Later W111 and W113 cars used yellow CAD (or zinc) finishes on the bolts and fuel fittings.

Once the screws are out, the spring and diaphragm are visible. Be sure to note the position of the spring and orientation of the diaphragm center boss. This is a good place to stop for now. I'll keep chugging ahead.     

[Tyler S]

Great write up so far! As of 08/1967 (my W113) still used the older style with the aluminum housing plate. Don't know when the switch was made to the Bakelite housing but was sometime after 1967. Also the fitting on the outlet side is a banjo bolt style so 3 copper crush washers in total would be needed. Otherwise everything else is identical to that pictured.

[wwheeler]

I will hopefully do more tomorrow. Bills to pay tonight! Yes, my '68 W111 has the bakelite housing, so that is good know and I will edit the previous post. The W111 also has the banjo bolt on the side as does yours. Interestingly, my W128 220SE Ponton has TWO dampers in line. Not sure why but they are identical except for the fittings. The ID holes for the fittings vary from 8mm to 3mm. So some sort of flow choke I suppose. That is why I mentioned to make sure the fitting go back in the correct location.

[wwheeler]

Now where was I? So with the unit apart, you will want to clean the housing, plate the fasteners and fittings and check the flatness of the sealing surfaces. Check both surfaces of the rear cap and main body where the screws go through. VERY carefully use a flat file to remove any raised burrs. Don't try to resurface it, but simply remove high spots. This aluminum casting is soft and is very easy to over-file. You can also check the area where the seal ring contacts on the fittings. 

The big trick to doing this correctly is to make sure the diaphragm is in its "neutral position" when securing the back plate. The back plate squeezes on the outer edge of the diaphragm and creates a seal and holds the diaphragm. This seal creates an air chamber on one side (side with the spring) and a chamber with fuel on the other. The problem here is the spring must be installed when the back plate is tightened. When the spring pushes on the diaphragm, it causes the edges to wrinkle in the housing. If you clamp the back plate with edges wrinkled, it will leak and you will have both chambers filled with fuel.

So to keep the diaphragm properly positioned, I used a homemade tool. See pic 0621. There are many ways (some simpler) to make this tool. You just need a 14mm x 1.5 threaded bolt and an extension at the end to meet the diaphragm at its neutral position. I used a lathe to machine down a long 14mm bolt to include the extension. When this tool is installed, it will look like pic 0622. You will have to do some measuring to determine how long to make the extension so that it holds the diaphragm in the neutral position. Now we are ready to install the guts.

[wwheeler]

This part moves pretty quickly. First some prep work. Have all of the screws near by with the wave washers on them. I use a very small amount of anti-seize on the screws. I almost always use anti seize on dissimilar metals and always when the threads are in aluminum. Also have the appropriate tool for the screws handy.

Pic 0623 is the back plate with the spring installed on its boss. The part that actually squeezes the diaphragm is the raised, flat area not the surface with the bolt holes. Pic 0624 is the main body with the new diaphragm installed. Note the installation tool is installed and is positioning the diaphragm via the center boss.  Now without the diaphragm but with the spring, test fit the back cover onto the main body. This will give you an idea of the spring strength and ensure that the cover fits in advance. If it doesn't, some polishing is in order.

Its show time! Place the back cover on the main body (pic 0625) and align the screw holes. Place two screws 180* apart into the main body just enough to hold the cover (pic 0627). Now step back and take a look at the position of the diaphragm. It should be flat as in the picture and just slightly higher than where it seats. If you have waviness on the edge of the diaphragm, the tool isn't in the correct position. If it is flat continue to add the other screws and be sure to add the washers (pic 0628). Push down on the back cover until it seats and snug screws to hold in place (Pic 0629). I'll finish up tomorrow. If there are any corrections needed or comments, please pass them along.   

[wwheeler]

OOPS. Ran out of attachments. I need to add pic 0627 and 0628.

[Tyler S]

Very nice Wallace! Now the question. Have you mounted it back to the car and can you tell if theres a discernable difference in the sound?
Mine will occasionally make a hissing sound and a rap with a screwdriver handle hushes it right up. I'd say its due for your procedure.   

[wwheeler]

No, not on the car yet. This 220SE W128 is a long rejuvenation project for a car that sat for a long time. This May will be two years after I bought it and since it last ran. 

I have never heard these make noise, I was just doing a complete flush of the fuel system. I suspect that if it is original, the diaphragm is probably hard and ineffective. Probably doesn't hurt just to leave it that way. The rubber on the diaphragm will harden and could become brittle. But because there is a thin fabric layer that it is bonded to, it won't disintegrate into small pieces.

[Cees Klumper]

Thanks for posting this Wallace, very clear and thorough. Now you've got me worrying about the state of my own damper ...

[wwheeler]

Not much else to do to finish up the damper rebuild. Place the damper assembly back into a vice with soft jaws. Torque the back cover screws using a 10mm socket. The torque value is probably not given in the manual, so just use the standard torque values for this size of bolt. Since it is going into aluminum, I might tend to be on the low side. Next is to install the fuel line fittings as seen in pic 0619. I was given an aluminum seal rings from Mercedes for this application. Use your notes to install the fittings in the correct locations.

Not sure how to test other than to use a blunt rod through the nose of the damper which will compress the diaphragm and spring. It should rebound back to the same at rest position. This will have to be done before the fittings are installed. You can also plug one end and pressurized to 10-15 PSI and see if it holds pressure. If not, air may be escaping around the diaphragm where it is pinched.

Hopefully this has been helpful and if some tech minded soul would like to add this to the tech manual, I would be grateful.