dang injector - PeachParts Mercedes-Benz Forum

TMAllison · #1 08-13-2008, 03:17 PM

You are supposed to "lap" the two halves if they dont fit tight enough to seal.

Pretty simple, get very fine wet/dry paper and a perfectly flat stone or glass work surface. Sand the mating surfaces. Clean them SUPER good before resembling, pop test, adj, test again and install with new heat sheild.

hoborobot69 · #2 08-13-2008, 05:14 PM

Say what!? which surfaces? Not the threads... Right? Also I didn't pop test them.. Don't have a tester.. I'll buy or make one soon.. But please describe to me again in more detail the procedure you suggest?

TMAllison · #3 08-13-2008, 05:25 PM

Take the inj body apart. Set the guts aside. Sand each half of the inj body in circular motion to make the seam between each perfectly flat again so that when you put the two halves back together they will seal.

Or look up "lapped surfaces", "lapping" on google, etc.

PS: your plywood workbench top or the concrete garage floor is NOT a flat enough surface to work upon.

Diesel911 · #4 08-13-2008, 08:48 PM

Quote:

Originally Posted by hoborobot69

Say what!? which surfaces? Not the threads... Right? Also I didn't pop test them.. Don't have a tester.. I'll buy or make one soon.. But please describe to me again in more detail the procedure you suggest?

The flat surfaces. One flat surface on each side of the of that center plate and the flat surface on the bottom of the upper 1/2 of the injector.

Beagle · #5 08-13-2008, 11:51 PM

Quote:

By fine wet/dry paper I would think 600grit or less.
I have been using a plate of glass with 600 grit lapping compound that rock shops (Lapidry?) folks use to lap/tumble/smooth rocks. You can lap a whole set of injectors with 1/4 teaspoon or less and some light oil like sewing machine/gun oil/3 in one oil. Water is OK to.

Don't even THINK about touching these faces with even 1200 abrasive paper let alone 600! These are lapped to a Ra 0.5µm flat and flawless mirror finish on special grooved cast iron lapping plate with a 2 micron diamond lapping paste. The faces must 'Wring' together to hold 140 bar without internal or external leaks. Dirt can be removed by rubbing on paper soaked in silver polish on plate glass.

Alastair · #6 08-14-2008, 12:24 AM

Quote:

Originally Posted by Beagle

Don't even THINK about touching these faces with even 1200 abrasive paper let alone 600! These are lapped to a Ra 0.5µm flat and flawless mirror finish on special grooved cast iron lapping plate with a 2 micron diamond lapping paste. The faces must 'Wring' together to hold 140 bar without internal or external leaks. Dirt can be removed by rubbing on paper soaked in silver polish on plate glass.

Ah, At last! The voice of reason!

I was wondering when someone was going to put this 'Sand-paper' rubbish to bed!

Yup, Those are Precision ground/lapped parts. Sand them with wet/dry 600 or even 1200 grit, and they are Scrap!

--

--IF you have done this and 'got-away' with it, You're bloody lucky!

When doing nozzle-changes, just clean these mating-faces well with cloth soaked in solvents. Nothing more--Finish up by washing Everything in FILTERED Diesel Before assembling -WET- with the filtered fuel....

When everything is Spotless clean, re-assemble and tighten by hand. Then slacken half a turn, and re-tighten. Do this slackening/tightening by hand three or four times Before finally tightening to the right tightness....

IF everything is Properly clean, and you have no damage to any sealing-surfaces (and why should you, as they have always been tight inside the injector until you took them out...)--

--Then you'll have no leaks either internally to the leak-off OR through the threads....

Diesel911 · #7 08-14-2008, 02:17 PM

Quote:

Originally Posted by Beagle

Don't even THINK about touching these faces with even 1200 abrasive paper let alone 600! These are lapped to a Ra 0.5µm flat and flawless mirror finish on special grooved cast iron lapping plate with a 2 micron diamond lapping paste. The faces must 'Wring' together to hold 140 bar without internal or external leaks. Dirt can be removed by rubbing on paper soaked in silver polish on plate glass.

In the Fuel Injection shop I worked in (5 years) when used 500 grit lapping compound for our hand lapping plates and our Automatic Lapping Plate machine 99.9% of our lapping of Fuel Injection Pump Parts and Injector part was done with 500 grit.

We used 1200 grit for our nozzle re-regrinding operation to lap the Injector Pintel seats and on sticky Injector Pintels and Plunger and Barrels (IP Elements).

That shop was in business for 30 years until the owner died. I can't imagine that in all that time he was using the wrong grit lapping compound!

I would prefer not to use the plate of Glass as a Lapping Plate but so far I have always been out bid on Ebay for a real lapping plate.
Also the lapping plates do not have to be grooved and some plates have a grooved side and a flat side; both can be used.

I have lapped 3 (10 Mercedes injectors and 6 Volvo injectors) sets of injectors on the Glass Plate and none of them have leaked.

C Sean Watts · #8 08-14-2008, 03:49 PM

Quote:

Originally Posted by Diesel911

In the Fuel Injection shop I worked in (5 years) when used 500 grit lapping compound for our hand lapping plates and our Automatic Lapping Plate machine 99.9% of our lapping of Fuel Injection Pump Parts and Injector part was done with 500 grit.

We used 1200 grit for our nozzle re-regrinding operation to lap the Injector Pintel seats and on sticky Injector Pintels and Plunger and Barrels (IP Elements).

That shop was in business for 30 years until the owner died. I can't imagine that in all that time he was using the wrong grit lapping compound!

I would prefer not to use the plate of Glass as a Lapping Plate but so far I have always been out bid on Ebay for a real lapping plate.
Also the lapping plates do not have to be grooved and some plates have a grooved side and a flat side; both can be used.

I have lapped 3 (10 Mercedes injectors and 6 Volvo injectors) sets of injectors on the Glass Plate and none of them have leaked.

Didn't you have a diagram of this a few months ago?

Beagle · #9 08-14-2008, 10:12 PM

Quote:

We used 1200 grit for our nozzle re-regrinding operation to to lap the Injector Pintel seats and on sticky Injector Pintels and Plunger and Barrels (IP Elements).

Rubbish!

Diesel911 · #10 08-13-2008, 08:44 PM

Quote:

Originally Posted by TMAllison

You are supposed to "lap" the two halves if they dont fit tight enough to seal.

Pretty simple, get very fine wet/dry paper and a perfectly flat stone or glass work surface. Sand the mating surfaces. Clean them SUPER good before resembling, pop test, adj, test again and install with new heat sheild.

Exactly.
By fine wet/dry paper I would think 600grit or less.
I have been using a plate of glass with 600 grit lapping compound that rock shops (Lapidry?) folks use to lap/tumble/smooth rocks. You can lap a whole set of injectors with 1/4 teaspoon or less and some light oil like sewing machine/gun oil/3 in one oil. Water is OK to.