1982 Yamaha XS400 Seca

hdscarbro

Active Member
Found this sad 1982 Yamaha XS400 Seca on Cragislist for cheap. Bought it as a project to work on with my 14 year old son. I thought it would be fun to see if we could get it running again. The bike came from a guy who cleans out houses in exchange for the unwanted contents.

The original gas tank is missing. The tank in the photo doesn’t fit, but was included in the deal. I think it’s from a Suzuki. The carburetors are also missing.

This project is also documented (with more photos) in my XS400 blog. We started this project a while back. I'll do a couple more posts to bring things up to date soon.

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Interesting project. I've considered that model for a few reasons, not the least of which is cheap insurance in my area. That said, I'd prefer a twin shock bike.

The tank has potential. The shape isn't bad, and the flip top cap is a bonus. I see from your blog that you've found a different tank, and it looks like the stock type.

Nice job on the seat, as found in your blog.
 
I found a stock tank on eBay a while back. I like the shape and it avoids the whole problem of fitting a different one.

Here's the bike with the beginnings of a seat. I'm using 2" insulating foam from my local building supply to fabricate the seat. It's glued using spray styrofoam adhesive from Michaels. Regular spray adhesive dissolves styrofoam.

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The ultimate shape. I tried to carry some of the angles and shapes from the tank to the seat.

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Replaced the styrofoam base of the seat with a rigid one made of wood and fiberboard. All of the shaping was done using a sanding block and 60 grit paper. As I a shaped the seat paper templates were used to help maintain symmetry.

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Plug coated with tape and wax. The recess was created taping down split plastic wire loom that I cut in half. I tried using tubing on my first seat and it was a difficult to tape in place.

I am using Butchers Wax to keep the epoxy from sticking. It's available from woodworking suppliers . You can also get special mold wax, but I already had the Butchers Wax.

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After several layers of fiberglass. I've tried both mat and cloth in previous fiberglass projects. Mat is cheap and really messy to work with. I decided that I like 6oz cloth best. It can be purchased from West Marine (a local store) or ordered from many suppliers. I like Jamestown Distributors. Ordered a gallon of epoxy and batch of fiberglass from them a while back.

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I made the bead using split wire loom that was cut in half using a razor blade. Here's a photo of it. It's available at electronics supply stores if you don't want to order it. There are perforations opposite the split that makes cutting it straight easy to do.

There are lots of photos of my SR250 on the blog I wrote after the build. I'm still adding details, but it's worth a look.
 
So you're the other guy building a twin cam XS400. I'm pretty sure that makes two of us in the world lol. I'm hoping I might be the first Seca to get a feature on BikeExif. Don't do anything too crazy and beat me to it OK :)

Earlysport
XS400 DOHC build
http://www.dotheton.com/forum/index.php?topic=61363.0
 
Maybe our DOHC XS400 builds are really ahead of the curve and by this time next year nearly every new build thread will be titled "Yet Another Twin Cam XS400"

I am happy to cede the BikeExif slot to you. I am not planning anything too crazy.
 
Made another seat. The first one was too big and square. Also, I decided to have the seat sit over the back of the gas tank. The first wasn't wide enough at the front.

New seat being shaped.

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After fiberglass layup. I tried release fabric on this seat. I think it makes for a better initial finish. The epoxy is evened out better and there won't be nearly as much sanding.

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Here's the seat on the bike. Planning to use these "free" mufflers from a Yamaha Radian that I got from my cousin. They're currently loose fitted using Emgo upswept muffler adapters. WDYT?

The bits of paper on the floor are CAD (cardboard assisted design) scraps.

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Selfie showing the tail light that I am planning to use. I originally bought it for my SR250 project. I think it complements the shape of the seat pretty well.

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That's some solid glass work you are doing there. Nothing like taking your time on the plug to get a good finish. I agree, cloth is the way to go. It's usually lighter, stronger, and easier to work. The only time I use mat is when i'm making molds. It's just cheaper. Generally speaking Aircraft Spruce has the best prices on cloth, its around $8 for bi and $9 for uni per yard.
 
Have you thought about what you are going to do on the sides to integrate the "funny" tank angles at the rear? Maybe modify the seat base to join to the tank lines?
 
Thanks. Looked at the Aircraft Spruce site. Given the prices, I'm guessing that you're using Rutan cloth What's better about it compared to the stuff you get from marine suppliers? I've been using 6oz cloth from Jamestown Distributers. It costs
$5.60/yard for 10 yards.

Sav0r said:
That's some solid glass work you are doing there. Nothing like taking your time on the plug to get a good finish. I agree, cloth is the way to go. It's usually lighter, stronger, and easier to work. The only time I use mat is when i'm making molds. It's just cheaper. Generally speaking Aircraft Spruce has the best prices on cloth, its around $8 for bi and $9 for uni per yard.
 
zap2504 said:
Have you thought about what you are going to do on the sides to integrate the "funny" tank angles at the rear? Maybe modify the seat base to join to the tank lines?

I have given it some thought and have come up with two possibilities (that's where the pile of cardboard scraps came from in one of the photos).

1) As you suggest, extending the seat base forward.

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2) Cut the seat base back at an angle to reflect the angle on the tank.

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Which is better?
 
Here's how I made the fender. I used the old rusty chrome fender from my SR250 as the plug for the fiberglass. I also used this fender for the fiberglass fender that I made for my SR250 cafe.

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I used aluminum flashing to provide a smooth surface for laying up the mount tabs.

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Waiting for the epoxy to harden. Release fabric was smoothed over the final layer of fiberglass.

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After hardening overnight and removing the release fabric.

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Ready for trimming.

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The roughly trimmed fender.

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Closeup showing the nice finish produced by the release fabric.

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Roughly trimmed fender in place. I plan to eventually trim it considerably smaller.

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hdscarbro said:
I like this direction better, but think it would look even better if the bottom of the seat angled forward to meet the bottom of the tank and completely matched the rear tank angle.
 
hdscarbro said:
Thanks. Looked at the Aircraft Spruce site. Given the prices, I'm guessing that you're using Rutan cloth What's better about it compared to the stuff you get from marine suppliers? I've been using 6oz cloth from Jamestown Distributers. It costs
$5.60/yard for 10 yards.

Yes the Rutan cloth. Being able to chose unidirectional and bidirectional cloth is the biggest advantage. Using the two varieties simply allows you to build lighter and stronger pieces.
 
Been working on relocating the electrical bits under the seat and fixing a dent in the gas tank the past few days. I'll have some photos of the electrical soon.

Here's the dent.
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I don't have a stud welder, so I made a dent tool from steel rod to hammer the dent out from inside the tank. I probably re-bent the snake a dozen times to get the tip to the right places for hammering.

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Here's where I stopped. Hopefully, this is good enough to finish up the repair with body filler. There's still a bit of a flat spot below the tank badge.

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Body filler is hardening as I type.
 
Planning to fill them in and use decals instead.

I've been trying to come up with an interesting way to paint the tank that works with the shape. My son wants to paint it yellow. I'm thinking white or silver knee dents. Perhaps yellow tank with a black stripe of some design. Here's a link to a finished XS400 that I've been mining for ideas.

I have dim memories of a bike from the 70's having a yellow tank with white knee dents but can't recall what it was.
 
hdscarbro said:
I've been trying to come up with an interesting way to paint the tank that works with the shape. My son wants to paint it yellow. I'm thinking white or silver knee dents. Perhaps yellow tank with a black stripe of some design.

I have dim memories of a bike from the 70's having a yellow tank with white knee dents but can't recall what it was.
Your tank shape is so pronounced, I think it would be overkill to outline the knee dent area with stripes (came OEM on a couple years) or a lighter paint. I was thinking bright yellow tank, flat black knee dent area (maybe tank gripper material?), flat black underseat area and maybe a small Yamaha block decal on the yellow tank area instead of a "Yamaha" decal. MS Paint is your friend.

I think there were some yellow Yamaha tanks on their dual-sports and off-road bikes back in the '70s but I can't think of a road bike with a yellow tank and white knee dents (maybe burgundy tank with white knee dents like the XS750?).
 
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