Diesel Pump Springs: Function & Replacement

Okay, I've already started disassembling two pumps.

1Z and AFN.

Result!

It appears that the pump pistons are the same, but the pumps differ internally due to the two pressure springs on the valves.

Okay, I'm definitely going to install the stiffer springs in the first pump now, and I'll let you know how it goes!

If I'm wrong, please let me know!

The feathers from 1Z to AFN are slightly thicker and approximately 3mm longer.

Hi,

Even if the springs are different, they only serve to retract the plunger, nothing else.
Take a look at the propeller; it could be different and generate more thrust. Otherwise, to increase the diesel output, you'll need a larger piston – specifically, 11 or 12 mm.

Simply replacing the feathers might work out okay, but it won't achieve anything.

There used to be issues with broken springs, so it's possible that you simply have the newer springs in the AFN pump.

Since I plan to experiment with an 11mm plunger in an AFN carburetor with the original injectors this spring, I'm already researching with various suppliers. I've now encountered this statement for the second time: that the return springs, including the holders, would need to be replaced, depending on the wear of the pump.

Old feathers, new pistons?!
I'd like to hear your opinions on this.

Best regards.
peter

Hello.
These feathers? They actually sometimes break.

The springs are independent of the piston, so in theory, you could reuse the old springs, but since they sometimes break, I would just replace them.

Best regards, Heri.

Are the return springs actually the same across different engine variants, or do they just look similar? Since yours were broken, you probably didn't have a direct comparison.

Theoretically, it would make sense to use stronger return springs for a larger piston. After all, this is the only force that draws the diesel fuel into the high-pressure chamber. I can't calculate off the top of my head how much more force would be needed if the diameter of the piston increases by 10%, but it's clear that more force is required because more diesel fuel needs to be 'sucked' in. The force required is also greater at higher speeds. It's possible that it could be so large that the piston with the weaker springs doesn't fully retract anymore!?

Best regards.
peter

PS:
I'm not sure yet how much the feathers and holders cost individually, but you're probably right, heri, and the investment will pay off just because of the amount of work it saves.

Okay, I would estimate the force using the physics principles taught in 10th grade. I'd use A2 to represent the area of the 11mm piston and A1 to represent the area of the 10mm piston.

So, that's 1.1 squared, which equals 1.21.

m;

Not ³ cubic? Actually, it's about the volume.

'21% more power? - If so, that doesn't sound like a piston replacement would cause the spring to move outside of its tolerance range.'

Quote:

neubaupe: Since I plan to experiment this spring with a 11mm pump piston in an AFN engine with the original injectors

What do you hope to achieve with this? I'd be interested to know what changes you expect to see.

Hello,

neubaupe wrote:

Ultimately, this is the only force that draws the diesel fuel into the high-pressure chamber. I can't calculate off the top of my head how much more force is needed if the diameter of the piston increases by 10%, but it's probably clear that more force is required because more diesel fuel is "sucked" in. At higher speeds, the required force is even greater. Perhaps so great that the piston with the weaker springs doesn't retract completely anymore?!

To prevent any rumors from circulating, here's the correction: the fuel is not drawn in, but is pushed into the high-pressure section by the internal pressure of the pump. And this force acts in the same direction on the piston as the springs. Since Force = Pressure x Area, the 11-size piston is pushed back with 1.21 times the force by the internal pressure compared to the 10-size piston.

Best regards, Uli.

neubaupe wrote:

not ³ cubic? Actually, it's about the volume. 21% more power? - If so, that doesn't sound like you'd be moving outside the tolerance range regarding the spring when replacing the piston.

Well, since the hub remains the same, you can shorten that part.

m;

...the fuel is not drawn in, but is pushed into the high-pressure section by the internal pressure of the pump. And this force acts on the piston in the same direction as the springs. ...

Completely forgot to check the impeller pump.
Interesting... that raises the question, what are the feathers for?

Best regards.
peter

neubaupe wrote:

Completely forgot to check the impeller pump. Interesting... that raises the question, what are the feathers for?

The piston experiences significant inertia at high rotational speeds. Additionally, the inlet valve has a relatively small cross-sectional area, which restricts flow and causes throttling at high speeds or high flow rates.

Then the stiffer springs are also explained. More pistons -> more mass -> more inertia -> more springs.

So, I've already started disassembling two pumps.

1Z and AFN.

Result!

It appears that the pump pistons are the same, but the pumps differ internally due to the two pressure springs on the valves.


The fuel injectors are also different! While not really visible to the naked eye, they are definitely different. The AFN fuel injector has a different geometry and, ultimately, injects more diesel into the combustion chamber per revolution -> resulting in more power.

Best regards, from Haza.