CB450 K7 Fiberglass Tank Build

This is the story of building a fiberglass tank for my CB450.

Before I get into the meat of the build, allow me a few minutes to explain a few of the reasons I decided to go this route and why the design turned out as it did.

The reasons:

1. I wanted to end up with something unique and one-of-a-kind.
2. I like building things.
3. I like doing things the hard way.
4. I'm not very smart.
5. I like doing things the hard way.

The design:

Since this was going to be a one-off tank, I saw no reason in going to the trouble and expense of making a plug and female mold. Althought a male mold has its own challenges (getting a good finish on the exterior and getting the foam out of the interior) I figured it would take less time and material to do it this way.

My design was overly complicated due to way I wanted the tank to work with my seat pan/cowl. When I built the seat pan (another story), I left a fairly long "skirt" around the bottom. I wanted the tank to match up with the pan, which required the tank to be low and actually wrap around the engine head. I 'm still not sure if this was a good idea, we'll have to wait for the bike to come together and see how it all looks finished. My seat also ended up with a pretty large cowl (recessed tail light and hiding a full sized battery), so I wanted a large tank to balance things out visually.

The materials:

The mold was made out of your basic polystyrene building insulation. I work in the civil engineering/surveying business and I was able to collect some nice 3" thick scraps of insulation from a construction site where I was working.

The fiberglass cloth I used was given to me by a friend in the aerospace industry. I'm not exactly sure what it is, but I believe it's "S" glass.

I used West System epoxy (slow cure) from West Marine. It's pretty expensive at about $140 for a gallon of resin + hardner, but it's really good stuff, has almost unlimited shelf life and there's plenty of left over from this seat/tank project for a bunch of other stuff. They also sell a pump kit that makes measuring out the resin properly (very important) a no-brainer.

The original tank was fairly rusty on the inside and not worth much so it became the donor for the filler neck, petcock bung and mounting points

Sorry about the long-winded intro. Next post: The build begins.

CC

Ooooo, this sounds cool.

Flugtechnik said:

Ooooo, this sounds cool.

Click to expand...

Yup, I can't wait. I've been going over the process in my head for a while now and have a few areas that I'd like to see done. Want to see how CC executes it.

just my 2c worth here, but when you build the tank, you will find that you have fewer problems if you build it in two sections, contrary to the idea that it will be "easier" to build a whole tank around the foam and "dissolve" the foam out with acetone or gasoline. It's much better to mechanically remove the foam and seal both sides together, then make sure you seal the tank with a good urethane based sealer, I don't recommend Kreem, I've never used it but I've heard horror stories. So yeah, coming from someone who has and still builds tanks, I'd do it that way and save yourself a lot of headaches

rockcitycafe said:

just my 2c worth here, but when you build the tank, you will find that you have fewer problems if you build it in two sections, contrary to the idea that it will be "easier" to build a whole tank around the foam and "dissolve" the foam out with acetone or gasoline. It's much better to mechanically remove the foam and seal both sides together, then make sure you seal the tank with a good urethane based sealer, I don't recommend Kreem, I've never used it but I've heard horror stories. So yeah, coming from someone who has and still builds tanks, I'd do it that way and save yourself a lot of headaches

Click to expand...

But then there's another option. You can build as one piece, split it into two, remove the foam and then make it whole again (of course I won't deny the headaches) . Stay tuned.

CC

Sorry I don't have pix of the first couple of steps, but it's pretty easy to follow without.

First I cut out the foam into rectangles a little bigger than the profile of the tank. These were glued together with Super 77 spray contact adhesive to build up the width of the tank. Using a hot wire cutter I squared up the front and rear of the blank. I made U-shaped cutouts in some thin fiberboard to guide the hot wire cutter and glued those to the front and rear of the blank to cut the frame tunnel. Then I glued fiberboard templates of the tank profile to the sides and cut out the basic shape with the hot wire cutter. That gets us to here:







As I said in the intro to the thread, the tank has to fit down around my seat pan and engine head so the next step involved routing out the underside of the mold to clear everything. For this I used mostly a small wire cup brush on a high speed grinder and a small (about toothbrush sized) hand wire brush to dig out the foam.





I just noticed that in the pic above you can see one of the templates for cutting the frame tunnel under my die grinder to the left of the mold. Maybe that helps with the explaination a little.

After the bottom of the mold was routed out to clear the seat pan and engine head, the foam was sculpted into the rough tank shape. (Sorry for the grainy pix. My camera doesn't do too well inside sometimes)



Next post: Fabbing the rear mount.

CC

Looking Good...... I figure you'll only have to fill up once a summer. ;D

CCRider said:

But then there's another option. You can build as one piece, split it into two, remove the foam and then make it whole again (of course I won't deny the headaches) . Stay tuned.

CC

Click to expand...

a good method when you do that is to build only the top half first, then trim the edge, remove about 3/4" of foam around the perimeter, put some aluminum foil around that perimeter, then glass the bottom half. Trim the edges together and remove the bottom half, then remove the foam, and you're left with a nice lip to epoxy the halves together, remember, the final bond with epoxy is really going to be mechanical only, epoxies don't remain chemically active after curing like polyester or vinyl does, and you have to be really careful in secondary bonding, secondly, i really really don't recommend "sealing" the tank with epoxy resin for this same reason, I think someone mentioned that earlier. I did that on a tank way back and the epoxy peeled up from the inside of the tank because it didn't chemically bond to the original material. So.... go with a urethane sealer, which is flexible and even though it won't necessarily chemically bond to the fiberglass, it won't crack or peel....


my .... 57c worth?

Mossy21 said:

Looking Good...... I figure you'll only have to fill up once a summer. ;D

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Yeah, it's a bit bulky. It has trimmed down some since that last picture, but it's still pretty large - we'll call it an endurance cafe racer.

CC

rockcitycafe said:

a good method when you do that is to build only the top half first, then trim the edge, remove about 3/4" of foam around the perimeter, put some aluminum foil around that perimeter, then glass the bottom half. Trim the edges together and remove the bottom half, then remove the foam, and you're left with a nice lip to epoxy the halves together, remember, the final bond with epoxy is really going to be mechanical only, epoxies don't remain chemically active after curing like polyester or vinyl does, and you have to be really careful in secondary bonding, secondly, i really really don't recommend "sealing" the tank with epoxy resin for this same reason, I think someone mentioned that earlier. I did that on a tank way back and the epoxy peeled up from the inside of the tank because it didn't chemically bond to the original material. So.... go with a urethane sealer, which is flexible and even though it won't necessarily chemically bond to the fiberglass, it won't crack or peel....


my .... 57c worth?

Click to expand...

Good tip on the sealer. Unfortunately, I've already sealed with epoxy. I did scuff up the inside surface w/80 grit paper to increase the mechanical bond so maybe I'll get lucky.

Thanks, CC

The rear of the tank will bolt to the seat pan through a roughly 2" wide tab formed into the tank. There will be about a 1/4" gap between the tab and the seat pan for a rubber pad.

To build the base for the tab I started by hot wire cutting a piece of foam 1/4" thick by about 6" wide and long enough to wrap around the seat pan. I covered the foam with packing tape to serve a a mold release and taped it to the seat pan centered at the rear end of the tank mold.

I layed up two layers of fiberglass about 4" wide on the foam pad and made a vacuum bag around the end of the seat pan to hold everything tight around the pan. This piece will be the base of the mounting tab and will also form the lower rear edge of the tank so that there's a nice uniform gap between the tank and seat pan.

The 1/4" pad before glassing:


The seat pan with vacuum bag:


After curing, the tank mold was sanded out a little more to clear the new piece and the tank mold was glued down to the piece with epoxy thickened with micro-balloons (a light weight filler).





When that all cured, the front of the mounting pad base was trimmed and feathered to blend in with the underside of the mold and the underside was final sanded to prep for the first couple layers of fiberglass.





Next time: Underside glassing and final shaping.

CC

Next, two layers of fiberglass cloth were layed up in the frame tunnel and the recesses in the underside of the tank. The strange gray colored squares you see under the cloth are just pieces of tape covering a few accidental deep gouges in the styrofoam mold.





In the pix above the excess cloth that was left above the flat bottom surface of the tank has been trimmed off. The excess is easily trimmed with a sharp razor knife after the resin has set but before it fully cures.

After the resin fully cured, the finishing touches were put on the tank shape. Handlebar and knee dents were formed and the mold was sanded with 220 grit to prep for glassing.

I came really close to screwing up at this stage. While i was sanding out the right side handlebar dent, I didn't have the throttle cable installed. Luckily I caught the mistake and enlarged the dent or the cable attachment would have hit the tank at that point.









The top side of the tank got two layers of cloth plus another couple of layers on the mounting tab extending 3"-4" up the back end of the tank.





The foam blocks were beginning to delaminate a bit in a few places, so the tape you see below the glass is just there to hold the gaps tight together during glassing. (They'll come out later)

The only thing left on the exterior shell now is to glass the flat bottom side. Since the glass won't wrap around the sharp corners, they have to be treated a little differently. Using a razor blade, I cut out a chamfer about 1/4"-1/2" deep in the foam along the edge of the previously layed up bottom and side surfaces. The foam was removed from the chamfer and the inside surface of the glass was cleaned and roughened with the edge of a razor knife. The chamfer was then filled with epoxy thickened with milled fibers (a structural filler made of tiny pieces of glass fiber). When the filler cured , it was sanded down flat with 80 grit paper.







Two layers of cloth on the bottom surface and the easy part's done !





And a shot all trimmed up:



Next time we'll cut it apart and start digging out the foam.

CC

That is one awesome tank - love the big size. You make it look easy, and it's about the cleanest looking fiberglass job I've ever seen!

I'm loving this thread. Great work. You make it look very easy.

Like Tim said, I don't know how you work so clean. Whenever I glass, there is a mess everywhere and it never looks neat like that.

Tim said:

That is one awesome tank - love the big size. You make it look easy, and it's about the cleanest looking fiberglass job I've ever seen!

Click to expand...

Thanks Tim. Like my wife says, size does matter. That's why I have to overcompensate with the tank. :'(

CC

HerrDeacon said:

I'm loving this thread. Great work. You make it look very easy.

Like Tim said, I don't know how you work so clean. Whenever I glass, there is a mess everywhere and it never looks neat like that.

Click to expand...

Thanks very much, It hasn't been too hard, but not quite easy either. Of course all the pix are taken after the mess is cleaned up.

CC

Where is the petcock going to go? Crossover tubes?

Flugtechnik said:

Where is the petcock going to go? Crossover tubes?

Click to expand...

Yes. I will hopefully get to that point in tonight's installment.

CC

I really hated to destroy my original tank, but a quick search of ebay showed it wasn't worth much, so it gave up the filler neck, petcock bung and front mounts:









I drilled a bunch of holes in the filler neck flange to increase the mechanical bond, sandblasted everything and shot a coat of dupli-color etching primer on the filler neck:



I cut a template for the filler neck hole out of paper, transfered it to the tank and cut out a hole in the tank for the filler.



Next, I marked the tank where it would be cut and separated. There was nothing scientific about where I cut it, I just wanted to be able to access all the interior areas of the of the tank and have a seam location that would be fairly easy to repair. I also added a few index marks on the tank to help line everything up when it came back together.







If I were a smart man, I would have sanded a groove about 1/8" deep and 2" wide around the foam mold, centered on my cut line before I glassed the exterior. That would have formed a nice recess to lay in 2" wide strips of glass when I joined the two halves back together. Instead I did it the hard way, which you'll see a little later.

I cut along the line with a roto-zip spiral saw bit in my die grinder. Then, I used a hacksaw blade with a point ground into the end to cut the foam and separate the top and bottom pieces.





The foam was removed from the top half by gouging out with a 1/2" wood chisel. The little bit of foam that stuck to the glass was cleaned up with acetone and the interior surface was sanded with 80 grit paper then wiped down with acetone.



The filler neck was glued to the inside of the tank with epoxy thickened with microballoons.



After the filler neck cured all the excess epoxy was sanded down smooth.

Now, back to the hard way of forming the recess around the tank seam. Around the inside of the tank, along the cut, I applied a strip of 3/4" wide double stick foam tape, then a 1" wide strip of white electrical tape on top of that. Then four layers of fiberglass cloth were layed up on the inside of the tank. Once the inside lay-up cures, the original two layers on the outside can be cut through at the tape line and the tape and exterior glass layers removed to produce the repair recess. Hope that makes sense. If not the pictures later on should help.





Here's a couple pix of the foam being chipped out of the bottom half:





Since the tank has a low area on each side, separated by the frame tunnel, I installed fittings for an equilization tube between the two sides. To make the fittings, I bought a couple of 1/4" hose nipples, cut off the pipe threads and ground down the bases to make mounting flanges.





These were glued into the bottom of the tank at the low areas in front.



The petcock bung was trimmed to size and glued into the bottom of the tank just in front of the knee dent on the right side.









All of the tight corners in the bottom half of the tank that would be hard to get cloth to lay into were filled with epoxy and microballoons. Small grooves and bubbles in the exterior glass layer were filled as well. The seam along the bottom half was treated the same as the upper half. I stuck a short piece of rubber hose in the petcock bung to keep the epoxy out and layed in four layers of cloth.







I have not been keeping track of the time involved in the tank (I don't want to know), but I do remember that I spent about 9 hours just laying the four layers of glass in the bottom half of the tank.

Next time we'll prep the two halves and join them back together.

CC

Outstanding! Off topic - have you had any trouble posting your updates to the site? From time to time posting picture-heavy posts doesn't work out so well. I'm hoping those issues are behind us.