PVC Tank How To

[ferball]

1. Figure tank size. I built my tank to go under my top tube, so I measured the available space from my head tube to my seat tube and the clearance from the top of my engine to my top tube. If you want to go behind the seat measure appropriately, or if you have a rear rack that you want to mount it on measure away. How much your tank will hold use the formula: Volume= 3.14 X Radius Squared X Length of Pipe. This will give you volume in cubic inches, google cubic inches to gallons for a quick conversion tool. Given my parameters I Built my tank out of 3 inch PVC and made it about 14" long.
Volume = 3.14 x 1.5 squared x 14 or 98.91 cubic inches or .42 gallons

2. Cut PVC. I cut a piece of 3 inch PVC about 11 inches allowing about an inch and a half of length for each end cap. put end caps on to make sure it fits in the desired location adjust length as necessary, but don't glue yet.

3. Add fittings. I used a step bit to drill a hole in one end cap. The step bit allowed me to make the hole slightly smaller than my fitting, and with a little bit of muscle I was able to thread the fitting into the pipe. I used scd 40 PVC it was plenty thick, Scd 80 would be overkill. I did the same for my fill pipe fitting on the tube.

4. Glue it. Use Seal All or some other fuel proof adhesive/bonding agent/ glue. Unthread your fittings apply glue and re install. Glue end caps on.

5.Vent Cab I used a standard brass garden hose cap, drilled a hole in the center then inserted a slotted peice of plastic (sHeet metal would work as well) see pictures below.

Materials list for fittings will be in following post. I plan on using a universal shut off kit found at Lowes instead of a petcock to shut off fuel, it will be in materials list.

 

[ferball]

Materials:

Fill pipe 3/4 MHT x 3/4 MHT or 1/2 FHP Hose Adapter. I wanted the finer thread on one side to thread into pvc.

Outlet1/4 x 1/4 brass adapter. As long as the barb side is 1/4" the thread can be what ever you want, I found the smallest thread possible.

Cap 3/4 Inch Garden Hose Cap. Generic cap you will need an extra garden hose gasket to act as a retainer for the plastic/sheet metal vent piece.

PVC Diameter will be determined by desire application and/or required volume just make sure you buy 2 pvc Caps of the same size, I found that anything over 4" diameter gets crazy expensive.

I will hopefully have the tank cleaned and mounted for pics before the week is out.

 

[ferball]

Almost forgot here is the fuel cut off alternative to the pet cock:
Precisefit Gas Shut Off Valve

 

[taddthewadd]

This might be over kill but when I built mine I used a tap to thread the PVC for the fittings. I know you drilled slightly smaller and used the fittings to thread the PVC. I guess Either way works and your way is cheaper. Just a thought. I think your tank looks really good. I don't understand what that red piece is under the cap though. Oh, and one other thought. On mine I didn't vent the tank right on the cap, I used and extra fitting like your fuel line fitting near the seat and put an extra fuel line on it (tucked under the seat) and put a couple of loops in it to prevent it sloshing out and you couldn't see it since it was under the seat. Again I love your tank and just giving some ideas.

 

[taddthewadd]

Oh, I think I get what the red plastic thing is. It prevents fuel from sloshing out of the vent, right?

 

[ferball]

yes the extra piece is to keep fuel from sloshing out as long as none of the slots in the plastic line up with the center hole. You can also buy a hose cap with a 1/4 inch barb attached to it and just add a line and/or filter for a vent, I just wanted something that looked a little sleeker.

 

[ferball]

I also would have threaded the pipe but I could not find the tap and die set so I cheated.

 

[ferball]

Here is the tank mounted and ready to go.

 

[taddthewadd]

That is awesome! I like how the mounting straps location makes the pipe all look one diameter. The caps don't stick out. I am curious about the intake tube. Did you do that to cut down on noise? If so how much did it help?

 

[ferball]

yes I did the intake for noise (plus the soda bottle just adds to the look) It did not reduce sound an awful lot, but it did change the pitch and gave it deeper sound, I still have to add some sort of filter element/packing into the bottle portion of the intake and I believe that will make a noticable difference with the intake noise.

 

[taddthewadd]

Ferball, is the fuel filler neck (brass hose piece) big enough to fill it with a fuel container? Or do you have to use a funnel? One last question, what is that red piece made of and did you have to make it or can you buy it already like that?

One last thing I want to mention here for future readers info is, today I went to OSH to buy a few brass barbs like the ones on your tank and I found one that is a 90 degree elbow. That is the first place I have seen that carries them. It works well for the fuel line coming out of the tank to the carb.

 

[ferball]

I do have a funnel but it came with the fuel can, it is 3/4 inch so it is a bit for a normal fill pipe, but most small engine fuel cans would fit it.

The red piece I fabricated out of a piece of plastic I found in the shed, sheet metal would work, you just want to slot the side enough to let the air by but stay seated between the rubber gaskets. Keep the slots out of the center of the insert so that gas won't slosh through the hole in the cap

 

[taddthewadd]

I wonder if that red gasket is fuel proof. Someone told me the black ones are not for sure but I should look for the red one like you have. I asked them if they knew for sure the red one was ok with gas and they said probably but they didn't know for sure.

If it isn't you could use a fuel resistant o-ring. My local Harbor Freight just started carrying them. The o-rings are brown color and are sold in a plastic box in an assortment of sizes. I do like the idea of the gasket shown in your picture better thought and if it is fuel resistant then that is the way to go.

 

[BarelyAWake]

Jus' a tip to confuse things lol, bear in mind that "fuel resistant" isn't always the same as "alcohol resistant" and with today's Egas, it'd be worth askin' when buying stuff.

As an example, if you can actually find alcohol resistant 1/4" clear fuel line - it lasts FAR longer that regular "fuel resistant" clear fuel line... while I'd not stop projects or worry too much about it, it's still worth askin'

 

[silverbear]

Ferball,
Very nice job on your tank. I'm usually not a fan of anything plastic, but it does have its uses and this looks like a good one. The tank should be durable and last a long time. I'm wondering if there is an elbow set up so that the filler could up a little higher and the cap level. That would be nice. I like the cap and am going to experiment with it. Do you find any leakage at all? Not having a vent line running up under the seat gives a cleaner look which I like. I'm wondering if harness leather gaskets might work... I have scraps of course. That would not be affected by gas I would think. Of course I see your tank covered in harness leather, but you know me. I agree that having your straps where you placed them tricks the eye from seeing the step down from end cap to the smaller diameter. I like your tank and appreciate your sharing the how to.
SB

 

[ferball]

I have not found any leakage at all in the cap.

My dad is a retired plumber so I had a garage full of pvc to play with so One of my original thoughts when I stared seriously considering pvc was to use like a 3 inch T with like an 1 1/2 take off and just cap the ends of the T and use the take off as the filler. I went with the brass fitting because I liked the lower profile and it "fits" the bike better.

My dad is a retired plumber so I had a garage full of pvc to play with.

If I had harness leather and I knew what I was doing with it, I would definitely finish it like one of yours SB but all I had one hand was Smurf blue rustoleum paint...

 

[Bikeguy Joe]

Nice tutorial, it adds another dimension to the biking community.

 

[Maxvision]

yes I did the intake for noise (plus the soda bottle just adds to the look) It did not reduce sound an awful lot, but it did change the pitch and gave it deeper sound, I still have to add some sort of filter element/packing into the bottle portion of the intake and I believe that will make a noticable difference with the intake noise.

Why not turn that soda bottle around to face the front of the bike? Might help get that "Ram Air" effect and would prevent dirt from your rear wheel from getting sucked it...

 

[bfgmovies]

Oh man I was looking for a way to make a behind the seat gas tank when I came across this post, thanks for the 'how to', now I have one that works on this girls Schwinn beach cruiser lol

 

[happycheapskate]

You can cut washers out of plastic from soda bottles, gatorade bottles, and the caps to those. They will hold up to fuel for a long time. I have used gatorade jugs for replacement fuel tanks on resurrected lawnmower engines. Look for baby formula bottles (1Qt size from Similac etc. They have large, soft, flat sides that you can cut with scissors easily. Coffee can lids might be a similar type of plastic. Do not use the green mtn dew bottles for anything with fuel! IT MELTS. I used to carry spare soda bottles full of weeder gas for weed-eating at the cemetary (all day job). The clear ones work ok if they have a pinhole vent. The green ones melt!