Mechanical fuel pump spills its guts

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...

Part 2

The battle continues:



When the only tool you have is a mill, every problem starts to look like a ....?



Because this is a family friendly forum, I'll spare you all of the magic words that are required to remove the rocker arm pivot pin.
However, if you ever do face this task just think like a sailor who just dropped the anchor on his toe! Blood is also an excellent lubricant.
Once this pin is clear, just pull firmly on the rocker arm. It and it's pivot bushing will pop out.



As I said in the first part, it only gets harder from here. This picture represents an hour or so of increasingly desperate attempts to figure out how to remove the diaphragms and the pull rod from the upper housing. I even got so far as to consider cutting a big hole in the side of the casting to get a better look at the mechanism in there.
Turns out all you have to do is pull harder---it just pops right out!



Victory! From bottom to top you can see the two diaphragms, center pull rod, the main spring, the pull rod bushing, a keeper that prevents the pull rod from falling out the bottom, and a smaller spring that keeps the keeper in position.
The inside of the upper housing is on the left.



There is an interesting oil channel on the side of the upper housing that connects to a port on inside of the mounting flange.



Here's another view of the pull rod assembly.



The only way I could see to get the diaphragms off was to drill down the center of the pull rod and liberate them one at a time. The ends of the rod are formed at each end and this "swages on" each metal disk.



This is the thinner "fuel diaphragm." Both diaphragms have a formed suspension around the edge to give them more travel. Take a look at the edge of a speaker driver and you'll see what I'm referring to.



Oil diaphragm.



This spring scares me a bit. I can just see it trying to take off my finger as the last plate lets go.

Continued in part 3...

Part 3



All fingers survived!



This is the seal/guide assembly attached to the pull rod. I'm not sure whether the hard rubber was broken already or failed sometime during the disassembly process. The diaphragms attach at the left end.



Here's the rocker arm end of the pull rod. While I couldn't see it prior to disassembly, I think the rocker arm goes between the knob on the end and the first disk. The tan plastic piece is the part that snaps into the bottom of the upper housing half.



I think we just found out why this pump was leaking oil and removed from service. The "suspension" part of the diaphragm I mentioned earlier is clearly visible too.



A slow build pump kit?

In the pump, the only rubber components exposed to fuel are the pulsator diaphragm, check valves, and fuel diaphragm. The pulsator diaphragm looks particularly easy to fabricate from a ethanol resistant material, but the valves and diaphragm would probably be a bit more difficult.
This is where I hope the creative minds here at VAF will step in...

Lastly, I hope you enjoyed this little side project. I couldn't find any documentation on these pumps out there, and hopefully this will be as useful as it was fun for me.
Also if you have one of the "old style" fuel pumps that you'd be willing to donate for teardown, that would be interesting as well.

Now I know what's inside the fuel pump. Thanks for detailed description David.

Very interesting, nice photography.

Are you currently or planning to run autogas? I ask because I have found problems with the stuff beyond the ethanol. It absolutely dissolved (on my RV-12) the pipe joint sealer which had worked fine with my 6A's avgas. If allowed prolonged (maybe an hour or two) contact, will very effectively remove paint on the belly.

Jim
RV-12 N233TX

N223JH said:

Very interesting, nice photography.

Are you currently or planning to run autogas? I ask because I have found problems with the stuff beyond the ethanol. It absolutely dissolved (on my RV-12) the pipe joint sealer which had worked fine with my 6A's avgas. If allowed prolonged (maybe an hour or two) contact, will very effectively remove paint on the belly.

Jim
RV-12 N233TX

Click to expand...

First off, thanks to David Carr for posting the images and report on the mechanical fuel pump. Very interesting, indeed.

I've been in contact with Aero Accessories in NC regarding a fuel pump designed to run on mogas with ethanol. Here is the response I received from Vic Harris as of 10/26/2010 on the subject.

David,
We are currently testing rubber materials that will be compatible with
ethanol.
Testing has been very promising. The actual FAA approval process will take
some time to complete.

Victor Harris
Aero Accessories, Inc.
1240 Springwood Avenue
Gibsonville, NC 27249
800-822-3200
336-449-5054

Marvel-Schebler Carburetors LLC.
125 Piedmont Avenue
Gibsonville, NC 27249

I will call them in a day or so to see where the project is today.

Great write-up and dissection, David. I now know why they cost so much.

Fantastic information David. Now I see how the pump keeps oil and fuel separated. And how the overboard, or vent, works.

Thanks very much!

digidocs said:

I'll try to run them through a mass spectrometer soon to identify the exact rubber composition.

Click to expand...

Ooooh, forgot to list that on the "magic tool" thread

erich

Interesting. That's an old Lycoming pump. The newer pumps are much simpler inside from the rubber diaphragms up, and don't have two springs inside them. The pump I disassembled is an AC pump.

Great effort

It was only a matter of time before someone got behind the effort
to produce an ethanol tolerant mechanical fuel pump.
http://www.edelbrock.com/automotive_new/mc/fuel_pumps/fuel_pumps_main.shtml
My plan was to get Edelrock to produce a pump(kit) since we do not need
an FAA approved version.
A little competition is good for business.

How ethanol resistant are the other materials in the fuel system? Tank sealant (Proseal), aluminum, teflon, steel, etc?

Ethanol subsidy may be ending

Start of a return to sanity? Thursday June 16, the Senate voted 73-27 to eliminate billions of dollars of subsidies for the ethanol industry. Now if the government could be persuaded to repeal the mandate to include "renewables" such as ethanol in motor gasoline, we wouldn't have to worry about ethanol tolerant components.
http://www.reuters.com/article/2011/06/16/us-usa-senate-ethanol-idUSTRE75F5IN20110616

Thanks to everyone for the positive feedback and suggestions so far.

Using ethanol laden motor gasoline has significant technical and operational challenges. However I think there are few other avenues that can offer as significant of an hourly cost reduction. I'm still young, and I want nothing more than to see sport flying still healthy when I'm old.

David Domeier,

Please let me know what you hear from Aero Accessories. That is a very interesting development.

Very interesting

And I'm so glad I don't have one..

Frank
7a, IO360..Autofuel all the way baby!

Great Job!!

Thanks for the fantastic tutorial on mechanical fuel pumps! That was great!

it was here

hey, I googled this subject trying to find a cross section of the mechanical fuel pump but there's not much out there. then I found it here. great job!

Verrrrrry interesting.

Thank you for taking the time to present this interesting topic.

digidocs said:

Thanks to everyone for the positive feedback and suggestions so far.

Using ethanol laden motor gasoline has significant technical and operational challenges. However I think there are few other avenues that can offer as significant of an hourly cost reduction. I'm still young, and I want nothing more than to see sport flying still healthy when I'm old.

David Domeier,

Please let me know what you hear from Aero Accessories. That is a very interesting development.

Click to expand...

In a subsequent conversation with a tech rep at Aero Accessories, I was told the certification process had been terminated. The guy I spoke with did not know, or would not say, why the effort was scrubbed.

I did post that information on another thread, sorry I did not present it here.

Is there an automotive or marine fuel pump that fits our Lycoming engine?

Here is a link to an interesting video on fuel pump operation.

https://youtu.be/PYKoLUsTJU4

Discusses basic operation with great graphics.

Outstanding video!! Thanks for posting it Dan!

Link

Yes, Thanks for the video link as well.
Most interesting part was the end.
Pump will make TBO or 10yrs whichever comes first.
also I did not exactly understand how the drain actually worked!
Seems I should put a new pump on the Preventive Maintenance To Do list.

Mechanical Fuel Pump

I was told, somewhere, that the same Lyc fuel pump we use here is the same part number that is used in South America. Some places (Brazil?) run alcohol, up to 100 %, without problems.
This is second hand information, and I cannot verify this to be true.
I do not have a mechanical fuel pump, so the resistance of the fuel pump to alcohol is not a factor in my build.

Great video...THANK YOU!

Fulfilling the "education" component of "education and recreation".

longline said:

I was told, somewhere, that the same Lyc fuel pump we use here is the same part number that is used in South America. Some places (Brazil?) run alcohol, up to 100 %, without problems.
This is second hand information, and I cannot verify this to be true.
I do not have a mechanical fuel pump, so the resistance of the fuel pump to alcohol is not a factor in my build.

Click to expand...

Note that this is a pretty old thread.

I've talked with a tech person at M/S on a couple of occasions (several years ago) about this and related issues. He told me that the old 'soft' stuff in the pumps had problems with ethanol, but that while they were not marketing the pumps as E-gas safe, current production used soft parts that had no issues with automotive gas, including E-gas. He hinted that they could no longer even get the old materials in the soft parts. My take (not what he actually said, but my take) was that these pumps really are automotive/industrial designs that are re-purposed for aviation. If M/S is buying components from automotive/industrial suppliers, it makes sense to me that any new production would be E-gas safe, since any auto/industrial use in the USA will almost certainly see E-gas.

FWIW,

Charlie

RVDan said:

Here is a link to an interesting video on fuel pump operation.

https://youtu.be/PYKoLUsTJU4

Discusses basic operation with great graphics.

Click to expand...

That was good. Thanks for posting that link.