digidocs
Well Known Member
It seems to me that the mechanical fuel pump is one of the last alcohol intolerant components left in our fuel systems.
I recently purchased one for science and education and sacrificed it to our noble cause.
A Lycoming LW-15473 mechanical pump. This is the higher pressure type used with mechanical fuel injection systems.
I started by removing the screws from the pulsator cover. The large round disc has a slight wave to it. The screws are tightened to compress it like a spring that applies a semi-constant force the the rest of the stack. Even when torqued, there is about .03" of clearance under the raised portions.
Why is it that gaskets and springs always know when its exactly the most inconvenient time to let go?
The black goo went everywhere except amazingly my pants!
Here is the pulsator cover removed. I'm pretty sure the pulsator diaphragm acts in concert with the sight recesses in the cover to form a sort of pulsation damper.
Maybe it should be called the anti-pulsator?
The pulsation diaphragm came off next. Here you can see the inlet (bottom), outlet, and the two check valves.
I attacked the screws holding in the main diaphragm next. These pumps have two linked diaphragms. The top one keeps out engine oil and the bottom one pumps the fuel. The space between them is vented to the port at 4 o'clock. If one diaphragm ruptures, you'll get a tell-tale leak out the vent port, but no fuel should get into the oil or vice-versa.
Here's the bottom of the valve plate from above. It also serves as the cap for the main diaphragm chamber.
Now we can see our first glimpse of the main diaphragm. Both diaphragms are sandwiched between a set of their own support plates as you can see. The copper colored "rivet" in the center is the end of the rod that connects the two diaphragms and the lever arm.
Now that the screws are out, the diaphragm assembly is starting to separate. You can see here that the "oil diaphragm," here at bottom, is significantly stiffer and thicker than the "fuel diaphragm." Both are fabric reinforced rubber.
I'll try to run them through a mass spectrometer soon to identify the exact rubber composition.
Up until now, the disassembly has been pretty easy. Unfortunately, the rocker arm pivot shaft is now ready to put an end to that. It runs all the way through the body and is retained by a "shop head" on one end.
Let the struggle begin...
I recently purchased one for science and education and sacrificed it to our noble cause.
![img_0352.jpg](/proxy.php?image=http%3A%2F%2Foscar.dcarr.org%2Flyc-pump%2Fimg_0352.jpg&hash=5ac600f750030ae8ecc2c62d4b79a818)
A Lycoming LW-15473 mechanical pump. This is the higher pressure type used with mechanical fuel injection systems.
![img_0355.jpg](/proxy.php?image=http%3A%2F%2Foscar.dcarr.org%2Flyc-pump%2Fimg_0355.jpg&hash=4ed029069791398a25722a0d08862ed0)
I started by removing the screws from the pulsator cover. The large round disc has a slight wave to it. The screws are tightened to compress it like a spring that applies a semi-constant force the the rest of the stack. Even when torqued, there is about .03" of clearance under the raised portions.
![img_0356.jpg](/proxy.php?image=http%3A%2F%2Foscar.dcarr.org%2Flyc-pump%2Fimg_0356.jpg&hash=f91fd7e7688eb8f2bd1e3c3667fe9551)
Why is it that gaskets and springs always know when its exactly the most inconvenient time to let go?
The black goo went everywhere except amazingly my pants!
![img_0359.jpg](/proxy.php?image=http%3A%2F%2Foscar.dcarr.org%2Flyc-pump%2Fimg_0359.jpg&hash=30d384863bcb6ef0a48da37030c3d6cc)
Here is the pulsator cover removed. I'm pretty sure the pulsator diaphragm acts in concert with the sight recesses in the cover to form a sort of pulsation damper.
Maybe it should be called the anti-pulsator?
![img_0361.jpg](/proxy.php?image=http%3A%2F%2Foscar.dcarr.org%2Flyc-pump%2Fimg_0361.jpg&hash=299a1f6ae4b6c29000c0a2b75aca294e)
The pulsation diaphragm came off next. Here you can see the inlet (bottom), outlet, and the two check valves.
![img_0364.jpg](/proxy.php?image=http%3A%2F%2Foscar.dcarr.org%2Flyc-pump%2Fimg_0364.jpg&hash=3f095ae143eb1b0b2c22a1ffd234781a)
I attacked the screws holding in the main diaphragm next. These pumps have two linked diaphragms. The top one keeps out engine oil and the bottom one pumps the fuel. The space between them is vented to the port at 4 o'clock. If one diaphragm ruptures, you'll get a tell-tale leak out the vent port, but no fuel should get into the oil or vice-versa.
![img_0366.jpg](/proxy.php?image=http%3A%2F%2Foscar.dcarr.org%2Flyc-pump%2Fimg_0366.jpg&hash=f5aa9709eb8e1dbd6096f9fa239cb460)
Here's the bottom of the valve plate from above. It also serves as the cap for the main diaphragm chamber.
![img_0367.jpg](/proxy.php?image=http%3A%2F%2Foscar.dcarr.org%2Flyc-pump%2Fimg_0367.jpg&hash=80bf9d634c250beecd565c932687c7bd)
Now we can see our first glimpse of the main diaphragm. Both diaphragms are sandwiched between a set of their own support plates as you can see. The copper colored "rivet" in the center is the end of the rod that connects the two diaphragms and the lever arm.
![img_0371.jpg](/proxy.php?image=http%3A%2F%2Foscar.dcarr.org%2Flyc-pump%2Fimg_0371.jpg&hash=4082f443c6d61081092c0e0dedd10ab2)
Now that the screws are out, the diaphragm assembly is starting to separate. You can see here that the "oil diaphragm," here at bottom, is significantly stiffer and thicker than the "fuel diaphragm." Both are fabric reinforced rubber.
I'll try to run them through a mass spectrometer soon to identify the exact rubber composition.
![img_0373.jpg](/proxy.php?image=http%3A%2F%2Foscar.dcarr.org%2Flyc-pump%2Fimg_0373.jpg&hash=676f0c3c5ff15aee5bbaffb8a9f2a016)
Up until now, the disassembly has been pretty easy. Unfortunately, the rocker arm pivot shaft is now ready to put an end to that. It runs all the way through the body and is retained by a "shop head" on one end.
Let the struggle begin...