notes on Hatz Diesel engine 1D81 and Bosch fuel injector pump PFE 1075

Bosch PFE 1075 installed in a Hatz Diesel engine 1D81Z

A Hatz 1D81 single-cylinder diesel engine drives my k5 ATV - and it proofed itself extremely reliable over more than 20 years. The engine and all hoses were certified for RME use from the beginning. Actually the 1D81Z would run on pure rape-seed oil, and most other oils, but a glow-plug would have to be installed then, to start it with oil. With Diesel or RME, it starts without a glow-plug. Hence fuel was either pure RME or, later, a mix of RME and mineral Diesel.

To remove the fuel injector pump PFE 1075/50 in a Hatz 1D81 engine: Remove shut-off magnet, if installed. Remove the low pressure pump. One of the three screws is hard to get to, but manageable. Remove low and high pressure pipes from PFE, and remove the PFE itself.

disclaimer:
Text and images are given without any warranty. Use or ignore at your own risk. High pressure lines and Diesel injectors may pose a health risk. Copyright of images by me.

usage with RME (Rape-seed Methyl Ester) and clogging of fuel lines

The original 20l canister of RME had been perfectly fine and stable for 20 years. But lately a black tar-like residue clogged the fuel system, stopping the engine. This necessitated a full clean-up: removal and cleaning of all fuel components: tank, filter, low pressure pump, high pressure pump - every component except the injector nozzle.
The tar-like substance was surprisingly resistant to non-polar solvents (e.g. petrol, paint thinner, etc). It did partially resolve in Isopropanol. So soak or sink the components over night or even for some days. The tar appears to swell and the brittle bits can be swiped off or removed with compressed air. Thicker layers to be scraped off first.
It might be worth to note that the inner lining of the fuel hoses was completely stable and intact, and not the cause of the clogging.

cleaning of low pressure fuel pump

The low pressure pump was the component most affected by the tar. - Besides the tank itself. The images below show the internals after cleaning with Isopropanol.

low pressure pump clogged by tar-like residue

Bosch Diesel fuel injector pump PFE 1075/50, disassembly and fix

stuck piston - symptom & solution

The Bosch PFE 1075/50 is used in many small (in this case 10kW) Diesel engines, and generally very reliable. However, when the engine sits idle for months (presumably > 6 months), some internal parts may get stuck and it won't start. This may be aggravated by the use of RME as fuel. Note that Hatz does recommend special procedures for longer storage.
Sometimes the main piston gets stuck in the 'upper' position, if the camshaft comes to stop at or near that position after the engine is switched off. If it stays there for months, it may get stuck, and the spring of the PFE isn't strong enough to push it back then. Disassembling the PFE solves the problem (see below).
A more frequent problem is that the controlling trottle pin and ring get stuck (shown in the 'cut-off' position below). The governor 'fork', that matches the pin on the PFE, may then not be forceful enough to rotate the pin from its 'cut-off' position, and the engine won't start. That was fixable without disassembling the PFE itself. What worked for me: Remove the PFE and fill it with Isopropanol, then turn the pin to 'full' and pump, by pressing the spring and piston against something stable. Repeat multiple times and flush with high quality oil thereafter.

When pressing the spring and piston manually: The PFE will emit a burst of fuel after overcoming the outlet valve, so you have to overcome a first mechanical load when compressing the spring. If the throttle is set to ''cut-off'', this first mechanical load does not exist, since there's no fuel to pump. This may serve as a test which end-position of the thottle ring is ''cut-off''.

If you do have a PFE model that can be disassembled, proceed with great care: Disassemble the PFE itself, on a clear desk, with patience and under clean laboratory conditions. Start with releasing the piston from rear spring loaded plate. Then try to unstuck the piston from the bore (items 4 and 5 from left in image) by light slaps with a light hammer. Lubricate everything with sewing-machine oil and re-assemble.
If your PFE is a newer model, which supposedly can't be disassembled, try filling it with Isopropanol. That might work (untested here), but probably takes a day or two to show any effect.

Bosch PFE 1075/50 internals

Bosch PFE 1075 throttle pin in ''cut-off'' position

• The inner piston can be inserted in two ways (rotated around 180 degrees). Only one is correct. Align the notch in the piston with the large hole of the cylinder (see photo).
• Every washer must be re-installed in exactly the same way for correct timing. Your PFE may be assembled differently from the images given here.
• Check the re-assembled PFE by itself first: Fill about 10ml of Diesel, set throttle to max and push piston. It should pump after overcoming the outlet valve. Even more critical, check that it does not pump when the throttle ring is set to cut-off. With the throttle-ring, Cut-off is the clockwise stop when seen from the high-pressure outlet (see photo).
• When inserting the PFE into the engine, check that the throttle pin fits the fork of the speed governor. Otherwise the engine may become uncontrollable after starting.
• After installing the PFE into the engine, test with some Diesel in the high-pressure pump and a disconnected low-pressure pump. The engine should start with that and run a few cycles cleanly.
• As a reserve, I'd recommend to have a solid piece of plastic oder rubber handy when starting the engine for the first time after PFE replacement. In case of a uncontrollable run-away, choking the air intake is the only way to stop it. So the rubber should fit the air intake and should be handy and applicable in a rush.
• Likely end-users are not meant to disassemble a PFE pump. Maybe you want to consider simply getting a replacement part, or take the engine or pump to a Hatz or Bosch licenced workshop.
• You may want to use a specific test stand to re-check the timing and fuel amount of the pump.
• No need to unmount the throttle pin and its supporting ring at the engine-internal side of the pump.
• Very likely this doesn't work for newer PFE models, which are sealed and not possible to dis-assemble.
• Your Mileage May Vary, use this info at your own risk.