Ambac M-50 Rebuild w/ pics (MEP-003A)

Mr4btTahoe

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Hey alls...

Just buttoned up the rebuild on my MEP-003a injection pump (Ambac M50) and documented the process. Member "jamawieb" gave me a write up on the tear down and it was very straight forward.

I'll post his write up in steps with pictures from my rebuild and some details on what I had to do.

--
Removed from engine
44527274640_d0e490c3bf_k.jpg

On the bench ready for disassembly. Be sure to MARK the pump body and housing as far as orientation goes!

46306598202_c50c835dde_k.jpg
Step 1 - Take the throttle linkage out (take the flat head screws out and then it slides out). Mine was stuck pretty good so a couple flat screw drivers and a bit of prying was in order.

46357426841_d9dd9945dd_k.jpg

Make sure this little piece came out with it. It sticks in the end of the throttle shaft.

45444960055_83d737fb13_k.jpg

Step 2 - Back the inlet and outlet adapters out or take them out completely. (I removed them)

44540678240_5330b81e0e_k.jpg

Step 3 - Take the 4 allen screws off the housing and then push the pump out of the housing. (On mine, this took a bit of effort. I used a thin putty knife and tapped it between the pump and housing at the lip where the 4 clamp screws held it in place. Then gradually worked it up taking care not to damage the housing.)

45634446994_0e6dfc38bb_k.jpg

32485448178_d2eb1ad1eb_k.jpg

Step 4 - Remove the big c-clip off and separate the pump, you'll have the gear set in one hand and the ports for the injectors in the other.

32485401368_9055f6c95c_k.jpg

The gear set will have the plunger sticking out of it and if you look at the end, that the plunger is protruding from, you'll see a flat piece, that is the plunger guide. The plunger guide will be broken in half or it will be rounded off, where the plunger will just spin.
Step 5 - take the cap off the end of the gear set. (Pry it up with a flat blade screw driver carefully. Just an o-ring holding it snug). When you take the cap off you'll see the button under it.
Step 6 - There is a little clip that holds the button in place that has to be removed. I use a little pick to pick it out but be careful because it will fly off and you'll never find it. (I placed the entire assembly in a gallon ziplock bag and used a pick to work the clip loose. When it popped off, it was caught by the bag.)

31418110477_bb44e799b4_k.jpg

From let to right... Cap (tappet), wire clip, timing button.

46357346691_f21b5b546f_k.jpg

Step 7 - After you remove the button. You'll see the end of the plunger under the spring. It's held in place with 2 half circles (best way I know how to describe), you have to depress the spring and get the half circles out. This is the hardest part of the whole thing. I have a pair of need nose vice grips that I cut the nose off of to make them flat. Then set them far enough apart to go around the plunger so I can put the plunger on a hard surface (Like a desk) and depress the spring with the vice grips to get the half circles out. (This is setup just like a valve spring/retainer. I just used some needle nose pliers to push down on the retainer while the plunger was held in a vice with soft jaws. Then a magnet to pull the little clips up out of the retainer.

45634375214_b8760470ad_k.jpg

The little clips are on the right. Spring/retainer under the tappet and to the left of the spring/retainer is a spring shim (that is under the spring when assembled).

31418088327_af5d710459_k.jpg

Step 8 - Remove the spring, plunger and guide.

Plunger

45634357694_a5328d6444_k.jpg

Plunger guide. This is the item that likes to fail after the pump sits and gets gummed up. Mine was nearly rounded out in the center and cracked.

31418100847_641e9fb242_k.jpg

Put back together with new plunger guide and everything clean. When I reinstalled the retainer clips, I placed them on top of the retainer. When I pushed down the retainer using the needle nose pliers, I nudged the clips into the hole and they worked themselves into place. Very easy.

46357314231_4d6f30e087_k.jpg

New plunger guide in place.

44540567030_f5220d43d5_k.jpg

Timing button back in position with wire lock in place.

31418050417_1137121088_k.jpg

Tappet back in place.

45634321894_981519590e_k.jpg

Delivery valve components. Cap, Holder, Spring, Valve, and tiny spacer (orange piece).

31418034287_ea13a689af_k.jpg
 

Attachments

Last edited:

Mr4btTahoe

Active member
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Indiana
After cleaning. Piece on the left is the plunger metering sleeve. The little piece on the end of the throttle shaft slips into the groove on the sleeve and controls it's position.


46357277441_e52d575c10_k.jpg

Back together with bushing and C Clip in place. You can see the metering sleeve inside the pump body with the plunger through it. There is a little dot on the sleeve that needs to face towards the outputs on the pump (top).

31417993187_c4ae72c8ec_k.jpg

46306405592_380d5218b0_k.jpg


And completely re-assembled with new body o-rings. Make sure when you install the throttle lever, that the little piece mentioned in the first pictures goes into the groove on the metering sleeve. Also make sure your marks line up on the body when it goes back together.

44540516350_2d913e2b81_k.jpg

Now.. This is how I did it. Was very straight forward but this is the first M50 I've been through so be sure to check the manuals. This pump has not been ran on a test stand, etc. Basically, it's just a tear down.. clean.. replace what's broke.. and re-seal job.

I purchased the rebuild kit and plunger guide from Ambac. Shipped price was ~$80. There is a contact number in the info thread.

These are the manuals I used..

https://cdn.greenmountaingenerators...etering-MEP002A-MEP003A-50-2-4A-80A-9540A.pdf

https://cdn.greenmountaingenerators...l-Injection-Pump-Metering-MEP002A-MEP003A.pdf

Hope that helps!

I notice now that I didn't get pics of the delivery valve assembly back together. When the housing is empty, the little spacer goes in first (sits in a little groove you'll see once it's apart).. then the valve (and needle valve). Then the spring and then the holder. After the holder is torqued, the cap can be re-installed.
 
Last edited:

Guyfang

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Insert those missing pictures using the edit function, and then I would say, this should be a sticky. Very well done.
 

Keith_J

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Most importantly, CLEAN!!! No abrasives, ever. Diesel Mechanic in a Bottle, xylene, toluene, acetone or carb cleaner are the best solvents to clean, reassemble using kerosene or bio free diesel.

Getting the metering sleeve, plunger and hydraulic head aligned can be tricky, test fit the plunger into the sleeve and head to check for any abnormal resistance. Always flush with clean kerosene or diesel before assembly, skin debris from your hands can cause these parts to seize or stick. Powder free exam gloves can help.
 

Mr4btTahoe

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Mine went together with out much fuss. I cleaned every component... solvent dipped the case and disassembled hydraulic head. Cleaned everything really well and re-cleaned each part as it went back together with some light machine oil on every moving component.

Spins glass smooth now and everything on it moves like butter.
 

scrapdaddy

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Great write up and will be saving. Where did you purchase parts from? I lost one of the small C clips.

Thanks for taking the time to post this up.
 

Mr4btTahoe

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Great write up and will be saving. Where did you purchase parts from? I lost one of the small C clips.

Thanks for taking the time to post this up.
I ordered everything direct from Ambac. Call this number and leave a message if she doesn't answer.

800-628-6894
 

nothingbutdarts

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Bailey, Colorado
Thank You for the excellent write up and pictures!!! I was hoping you could confirm something for me, I do not have a MEP but have a DJC, I have 3 DJC pumps that I have no idea if they are any good, 1 I can't even turn the gear, the second one I can turn the gear fairly easily but, only about 3/16" back and forth, the third spins completely around quite easily. I guess from what your final write up on the rebuild you said the gear spins really easily, true? So the other two might need some work I would guess.
Have you used it since the rebuild?
Again, Thank You!!
 

Mr4btTahoe

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Location
Indiana
Been a bit since I've been on as the genny took a back seat to a bunch of other things (such as our second kiddo being born).

As far as the pump goes... yes it should spin easily by hand. If it doesn't, it's likely gummed up with old fuel. Don't force it... pull it apart and clean it. Inspect the parts. If you don't force it, it'll likely not need parts replaced. Typically the parts fail from a gummed up pump being forced over via the engine cranking. Anymore, if one has been sitting for a long time, I'd pull the pump and clean it before trying to start it.
 

Guyfang

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I would loosen the screws holding it to together, and sit it in a bath of cleaner. THEN take it apart. And repeat as needed.
 

Philratcliffe

Member
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Location
Florida
Where to buy parts for Mep 002/003

Hey alls...

Just buttoned up the rebuild on my MEP-003a injection pump (Ambac M50) and documented the process. Member "jamawieb" gave me a write up on the tear down and it was very straight forward.

I'll post his write up in steps with pictures from my rebuild and some details on what I had to do.

--
Removed from engine
View attachment 751156

On the bench ready for disassembly. Be sure to MARK the pump body and housing as far as orientation goes!

View attachment 751157
Step 1 - Take the throttle linkage out (take the flat head screws out and then it slides out). Mine was stuck pretty good so a couple flat screw drivers and a bit of prying was in order.

View attachment 751158

Make sure this little piece came out with it. It sticks in the end of the throttle shaft.

View attachment 751162

Step 2 - Back the inlet and outlet adapters out or take them out completely. (I removed them)

View attachment 751159

Step 3 - Take the 4 allen screws off the housing and then push the pump out of the housing. (On mine, this took a bit of effort. I used a thin putty knife and tapped it between the pump and housing at the lip where the 4 clamp screws held it in place. Then gradually worked it up taking care not to damage the housing.)

View attachment 751160

View attachment 751161

Step 4 - Remove the big c-clip off and separate the pump, you'll have the gear set in one hand and the ports for the injectors in the other.

View attachment 751163

The gear set will have the plunger sticking out of it and if you look at the end, that the plunger is protruding from, you'll see a flat piece, that is the plunger guide. The plunger guide will be broken in half or it will be rounded off, where the plunger will just spin.
Step 5 - take the cap off the end of the gear set. (Pry it up with a flat blade screw driver carefully. Just an o-ring holding it snug). When you take the cap off you'll see the button under it.
Step 6 - There is a little clip that holds the button in place that has to be removed. I use a little pick to pick it out but be careful because it will fly off and you'll never find it. (I placed the entire assembly in a gallon ziplock bag and used a pick to work the clip loose. When it popped off, it was caught by the bag.)

View attachment 751164

From let to right... Cap (tappet), wire clip, timing button.

View attachment 751165

Step 7 - After you remove the button. You'll see the end of the plunger under the spring. It's held in place with 2 half circles (best way I know how to describe), you have to depress the spring and get the half circles out. This is the hardest part of the whole thing. I have a pair of need nose vice grips that I cut the nose off of to make them flat. Then set them far enough apart to go around the plunger so I can put the plunger on a hard surface (Like a desk) and depress the spring with the vice grips to get the half circles out. (This is setup just like a valve spring/retainer. I just used some needle nose pliers to push down on the retainer while the plunger was held in a vice with soft jaws. Then a magnet to pull the little clips up out of the retainer.

View attachment 751167

The little clips are on the right. Spring/retainer under the tappet and to the left of the spring/retainer is a spring shim (that is under the spring when assembled).

View attachment 751168

Step 8 - Remove the spring, plunger and guide.

Plunger

View attachment 751169

Plunger guide. This is the item that likes to fail after the pump sits and gets gummed up. Mine was nearly rounded out in the center and cracked.

View attachment 751170

Put back together with new plunger guide and everything clean. When I reinstalled the retainer clips, I placed them on top of the retainer. When I pushed down the retainer using the needle nose pliers, I nudged the clips into the hole and they worked themselves into place. Very easy.

View attachment 751171

New plunger guide in place.

View attachment 751172

Timing button back in position with wire lock in place.

View attachment 751173

Tappet back in place.

View attachment 751174

Delivery valve components. Cap, Holder, Spring, Valve, and tiny spacer (orange piece).

View attachment 751175
Where did you buy the repair parts for the injection pump? Thx
 

Mr4btTahoe

Active member
118
60
28
Location
Indiana
It has been brought to my attention that one of my details is wrong. Apparently, the image in the Ambac manual is upside down in comparison to every other image in the book with the pump disassembled. The DOT on the "METERING SLEEVE" needs to face the ENGINE side of the pump and not the pump outputs. I have yet to run my engine since the pump rebuild so I will pull mine apart and correct this before running it. I can't edit the original post at this point so figured I'd make note here. Not sure what issues it may cause but better safe than sorry.
 

nothingbutdarts

New member
5
0
1
Location
Bailey, Colorado
I am trying to figure out what dot you are refering to? Is this dot in one of the firts two posts you did in this thread? You have pictures in post #1 & #2. So far I have tried to take apart 2 pumps, both have seen some water are are not coming apart yet, they are soaking in diesel at the moment. I have managet to pull the throttle shafts out of both and on one the gear will turn back and forth just a little and stop. I do not want to force anything, I am hoping to eventually get both apart and repaired.
 
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