Bosch injector anatomy question

[nametooshort]

Does anybody happen to know the Bosch injectors?

In the style of injectors thats used in the XUD/TUD range (and a lot of others, VW etc). I know it's kind of not so technical, but I am sure you know the family I mean. The 'double eared' (two leak off pipe connections pressed directly into the top casing) injectors that are used in pretty much most Bosch-injected car engines of the period.

They all have pop-ratings printed on them, as well as the Bosch number of course, on the top casing, like 120bar or 130bar etc.

But, do I understand correctly, that this whole family of injectors has identical top cases, and it's the actual spring and shim that sets the pop pressure? So, different engine systems use different bottom casings (since they have different threads/collar nut sizes, and also some have nozzle shields), but the top casings are all identical?

So, in this picture:



-Part 7 is the nozzle, which come in different 'flavors', and I know a lot of people who mod diesels often change them for different sizes etc.

-Part 6 (the bottom casing) is engine-specific, because different companies heads have different threads etc

-Part 3 and 1 (spring and shim) are the ONLY parts that set the pop pressure

-Part 5 and 4 (I call them the anvil and hammer, although thats neither correct not accurate) are universal to that family of injectors.

Is this correct so far?

So, does that mean, that, for example, if I use the spring, shim and nozzle from a 120 bar injector, and then screw the top casings from a 130 bar injector into them, that it would in fact be a 120bar injector with '130 bar' printed on it?

In other words, the part that carries the pressure rating stamping (the top casing) actually has absolutely no role in setting the pressure?

The reason I ask is because I had some good XUD 120bar injectors, and I disassembled them and left the parts neatly arranged on a clean towel on the floor, and then my friend proceeded to neatly reverse his beetle right over the towel, which went over the top halves and snapped off all their return pipe stubs. The other parts were not run over tho.

I also have some similar injectors but rated at 130 bar, from some other engine, different thread to the XUDs. So can I just use the top casings from the 130 bar injectors, and the springs/shims/bottom casings/nozzles/etc from the 120 bar injectors, and they will still stay 120bar (despite the fact that they will confusingly say 130bar on them)?

PS I know that mix-and-matching used injector parts is never ideal, since they all wear differently etc in theory.

[steelcityuk]

Assuming that you got the shim that belonged to the spring when the injector was calibrated then I'd say yes. But any slight machining difference in the bodies would make this invalid and I think you need to consider machining tolerances. That's why diesel specialists use equipment to test spray pattens, pop pressure and leak off.

Steve.

[nametooshort]

Well, unfortunately all my stuff is in a different country, and me (and this batch of engines) is here, so I have to try to guesstimate. I have a old Bosch testing rig and some other stuff, but it's all big and heavy.

I know machining tolerances can vary, but that's with everything. As far as I know, Bosch injectors are not calibrated as such, serial production models are just made and tested, and any ones not in the range get rejected, that's all. Their manufacturing methods are good enough to not need calibration in everyday use. Nobody hand-picks shims for injectors, they all get the same machining operations, the same springs and the same shims, and turn out the same enough to be usable. It seems that pop pressure is not amazingly critical in 'old style' diesels, once you get to within about maybe 5%, getting any more accurate has little benefit. Everybody who I know who is into tuning diesels has the same story to tell. They pop-test, sit there obsessively grinding the shims to within a tolerance of less the 0.1bar, and nothing changes.

Thats one of the first thing I got warned about when I started messing with diesels. Somebody (who obviously knew me, and how I sit there for hours making my own carb jets on a jewelery lathe, or programming ECU maps manually) said to not get too critical about pop pressure difference, like I do with gasser engine parts.

But, what I was trying to get at is, are the top injector bodies all identical parts? Is the only difference between them the number stamped into them? Or do 120bar and 130 bar bodies have minute dimensional differences?

I think they are an identical standard part, and it's just the spring and shim that sets the pressure. But without a pop-tester here, I can't be sure.

Any Bosch nerds here happen to know the answer for sure?

[steelcityuk]

My local Bosch specialist do pop test the injectors to ensure they are to spec when they service injectors that was my point so if you start swapping parts you'll have to have them pop tested to find out.

[xmexclusive]

Not all Bosch Injectors have common components.
There are quite a few variants.
That said injectors from the same family can be reset to different pressures.
I have a set of KCE S 5 marked 120 bar that were converted to KCE S 6 - 170 bar.
Still marked 120 bar though.
They worked fine.
The diesel man just fitted new nozzels and shims.
Then they were "pop" spray tested.
Running with miss set or defective injectors has been known to burn through the tops of pistons.
If you cannot test or get them tested then do not risk mix and match.

John

[nametooshort]

Oh, well, I finally found out the answer, in case anybody wanted to know. I called a friend of mine who is a real Bosch nerd and they looked around through different spec/parts books and came up with a definitive answer.

It seems the correct answer is, yes, all of the familiar 'double eared, short spring (also applies to the 'long spring' variety) injector's upper casings are in fact the same part, made to the same dimensions and tolerances. The part receives it's stamping according to what shims/spring/nozzle/bottom casing is fitted to it on assembly.

The casings therefore do not bear their own number, they bear the number of the injector into which they are assembled. BUT, ALL of those top casings, no matter which injector they are destined for, are all created equal.

Which is exactly what I wanted to know. Yay!

Well, learn something new every day I guess.