Plastic fuel tank repair -Report

Hello, all,

I made my own fuel pump for my lawn tractor. (Long story,

1968 Wisconsin one-cyl engine, carb vibrated to bits, poor fuel feed when on hills, etc. So, I put a Kei Hin carb off a Honda 450 motorcycle engine on it, and it runs great, but needs a head of fuel above carb.) So, I made a little pump out of a floppy drive motor, eccentric, rubber diaphragm, and valves made out of ball bearings, springs and standard flare fittings.

This all works great, but the diaphragms keep wearing out. I started with some .060" Neoprene sheet that works well, but lasts only 3 years or so. When it fails, it starts spraying gasoline all over the place, which is NOT a good idea! I bought some material specifically sold as "a diphragm material for fuel pumps, etc." from MSC. It has nylon or similar webbing in it. It is too stiff, but mostly works, but it only lasts about ONE YEAR! What happens is the "rubber" ,material swells up and disintegrates after long exposure to fuel. The fuel pump diphragm in my 1989 Toyota is the original factory piece, and is still working, after a LOT more time and 137,000 miles. Does anyone know where to get this kind of material, used in auto fuel pumps? I need something that is pretty soft, as the motor doesn't have much power, and that will last a long time, as I'm tired of rebuilding this thing. Also, letting it run until failure is going to involve me in a big fireball on of these days, and I want to avoid that!

Hmm, maybe I already know the answer, JC Whitney?

Thanks in advance for all suggestions!

Jon

Al A. wrote in article ...

There is a two-part Devcon product called "Plastic Weld" that I used to sell to snowmobilers specifically to repair the ABS plastic noses.

It is, in a manner of speaking, an epoxy that actually works on plastics.

Bob Paulin - R.A.C.E. Race Car Chassis Analysis & Setup Services

Jon,

That's really the hard way! Why not just get a small Mikunu diaphram pumper and tap into the intake vacumn to pulse it? For the easiest plumming, use a tee connector to feed excess flow back to the tank and leave the carb "as is". If your into hi-G manouvers with your tractor, modify the carb as in shifter kart race carbs...take out the float & needle asm, use two pumps, one in, one out, and stuff the float chamber with fuel cell foam to damp the sloshing. Out fuel pickup is inserted into float chamber with the open end of the tube at the same level the fuel sits at with a working float/needle. Works really slick, but is hardly needed for ordinary purposes.

Why not just fit a standard electric fuel pump?

Yup, I'm not surprised at all. That stuff is great!

Lane

Told you a hot blade was the way to do it. Plastic moulding is my business. Mark K.

Sounds like you are having problems with alcohol in the fuel disintegrating your elastomers. Think methanol/ethanol friendly and it may help.

Gotta be about the best possible place to get info, help, advice, and knowledge is right here on RCM. There seems to be no limit to the talents and abilities of this group. Between the posters here and all the help they provide, and the dropbox which is a HUGE perk for this group, I give a hearty THANK YOU and it's probably the only reason I even stay connected to the internet. Ken.

McMaster Carr sells buna rubber coated material. I thought about using it to fix an acetylene regulator but ended up making a diaphram out of .010 stainless that I had on hand. The diaphram worked well, but the regulator had other problems.

Dan

Does anyone know where to

The diaphragm from the Toyota was probably made from a material called Viton. It is very rubber-like. It smells like cinnamon when it cut or abraded. Mike H

IIRC, the stuff they used to use was nitrile rubber with cloth reinforcing. I don't know what's used these days, whatever it is, if you're using pump gas, it's going to have to withstand MTBE, methanol, ethanol and whatever other mouse milks they're running in the gas these days. As you've discovered, neoprene really isn't suited for today's gas. Might be you could get a fuel pump rebuild kit from(wait for it) JC Whitney for some older model car or truck and use that diaphram material. A junk yard would be another source, dismantle a pump off a wreck and use the diaphram from it. Going to have be a fairly old vehicle, fuel injection has been around a long time. I hope you have some provision for emergency pump shutoff.

Stan

A place you could start is to call Seal Source inc (800-609-SEAL) they don't have a website. Ask them to look up which materials work with gasoline. I think viton is correct, maybe epdm also? They have a huge cross reference that tells what plastics to use with what. They will order for you whatever you need, but they really are a dealer to hydraulic repair shops, so their prices may be steep. They can alse sell pieces of teflon, either virgin, or glass or bronze filled, oil filled nylon, urethane, and phenolic laminate tubes. They can custom machine hydraulic seals for you too.

Good luck

Gene

A regular single-outlet Mikuni fuel pump is under $20... and they normally last thousands of miles. They require no electrical power... just a "pulse" line to a crankcase vent or intake manifold port; and will support at least 30hp (maybe more) on gasoline.

David

Just a thought... Did you design in too much movement on the diaphragm? What sort of pressure limiting do you have in the system (1/2 psi ought to be enough for the carburetor).

Mark Rand RTFM

ya know, an electric fuel pump for a carburreted car is cheap, and a used one ought to cost you no more than $5 - why not use an electric fuel pump?

The little header tank for the carb is 1" copper water pipe, with a float switch in it. If the fuel pump fails to shut off, the air vent back to the tank becomes an overflow drain. The diaphragm has a fender washer about 3/4" OD on each side of it, and the stroke is somewhere around 1/8".

Thanks for all the useful comments, I'll have to do some more research.

Jon

Now don't be too hard on me, I DID take your advice, after all. :)

You did earn the " Told YA so!" for today, however.

I appreciate your (and everybody elses input) very much.

This group has never let me dowm.

Thanks again, AL

I'll second that, Ken. I've never missed here, even with OT stuff like computer problems, car stuff or whatever. A good 80% of my on-the-web time is spent perusing this group. I often wish I had more to offer in return.

Now, anyone wanna talk gun control? Heh. (Couldn't resist. Excuse me while I don my flameproof suit and hide under the desk...)

-AL