New project - Yammy conversion

Meadowhawk

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Hi all,
I recently purchased an '82 Yamaha Seca 400 with the aspiration of turning it into a tracker/scrambler style. She's been sitting in a barn for 15 years and after a little love (AKA carb cleaning) is running fine, so now I'm turning my attention to dressing her up to look less like a prom queen and more grungy post-apocalyptic.
Like many of you, I've been perusing the interweb for ideas and I came across the youtube video below where the stock tire rims are used but with larger, more gnarly tires. Would anyone know what maximum sized tires would fit on the stock rims?
I was also looking to change the fuel tank but it appears the stock tank in the video looks fine (for me, anyways.)
Thanks so much in advance...have an awesome day.
Youtube video

IMG_4720.jpg
 
Welcome to the site! The stripped-down everything, headlight, and seat make the bike in the video in my opinion.

Look at Avon and Shinko and look into 3.00-18, 90/90-18, or for the front, and 3.50-18, 100/90-18, or 4.10-18 for the rear.

Here's some good info on tire sizes:
https://www.denniskirk.com/learn/tire-sizes-explained

Aspect ratios on inch size tires are typically 100%. You can compare the tire sizes by converting the inch to metric (*25.4) and using a tire size calculator. This tire size calculator is for trucks, but it seems to work fine for motorcycle tires too: https://www.tacomaworld.com/tirecalc?tires=90-90r18-100-90r18
 
Greatly appreciated, Travis. Definitely a fantastic resource I'll be bookmarking. I already have a replacement seat on order, not unlike the one in the video. Although I think his is custom built the way it tucks in under the fuel tank. Front and side fairings have already been removed and I'm on the lookout for a 7" headlight with grill. Painting the motor is next on the agenda. Taking my time and enjoying the process. I wish I started doing this 30 years ago.
Thanks again.
 
I was also looking to change the fuel tank but it appears the stock tank in the video looks fine (for me, anyways.)

The angular tank on the DOHC bikes makes it tough to put a flat seat on and make it look good, but I have to hand it to those Italians for making it work! That subtle seat to tank transition really pulls the whole thing off. I look forward to seeing how you progress!
 
Oh yeah, one other thing - save those plastics and other removed items and put them up here for sale in the Classifieds. Somebody with a Seca is going to want those as they look to be in nice shape.
 
Yeah decent Seca 400 tanks are nearly unobtanium. Mine was rusted out beyond saving, so I ended up mounting an '83 maxim tank on. The pucks fit and petcock mounting is compatible but the lines don't match the plastics.

I'm going to be experimenting with mounting Marauder forks on the bike- bearing sizes and orientations and axle size is identical and the forks are A LOT stiffer, probably would be good for playing around on dirt etc. I don't have a solution for bars or control yet but that shouldn't be complicated.
 
Oh yeah, one other thing - save those plastics and other removed items and put them up here for sale in the Classifieds. Somebody with a Seca is going to want those as they look to be in nice shape.
Yeah, unfortunately the plastics in the photo look good from far but are far from good...cracks everywhere. I attempted to paint them for an old-time patina look, which would compliment the cracks, but the technique didn't work so now she's getting stripped down to the basics.
Your motorbike is supposed to be a reflection of who you are (at least that's my understanding) and I'm a rather quirky individual so just stripping her down won't do. My new plan is to add an extra "component" of the likes that no-one has ever seen before, guaranteed to make other commuters smile.
I will periodically post progress photos for anyone interested.

I strongly believe in the words from the famous Dr. Seuss, "Why fit in when you were born to stand out."
 
My new plan is to add an extra "component" of the likes that no-one has ever seen before, guaranteed to make other commuters smile.

Okay, I'll bite....

In my neck of the woods, just owning and riding an XS400 makes you stand out. But if you want to stand out amongst us XS400 owners and do something that's never been done, well I can think of only one thing that will do that. My guess is that you are going to put a side car on it. Don't tell us the answer (but please, please let it be a side car!) It certainly would be quirky and if Dr. Seuss owned a motorcycle, I can only imagine that it would be a side hack.

I am so sure that I am willing to wager a candy bar on it. Anyone want in on this action?
 
Okay, I'll bite....

In my neck of the woods, just owning and riding an XS400 makes you stand out. But if you want to stand out amongst us XS400 owners and do something that's never been done, well I can think of only one thing that will do that. My guess is that you are going to put a side car on it. Don't tell us the answer (but please, please let it be a side car!) It certainly would be quirky and if Dr. Seuss owned a motorcycle, I can only imagine that it would be a side hack.

I am so sure that I am willing to wager a candy bar on it. Anyone want in on this action?
I am so thankful to not have been drinking while reading your response else liquid would have shot out my nose at terminal velocity. Been awhile since I laughed that hard. I even got the side-eye from the wife before she went upstairs to bed.

Truthfully, the idea of a side car was entertained but I suspect it would exceed my abilities to construct.

In searching the interwebs for unique ideas, I came across one weird build that takes the cake...the bike with the canoe.

I won't say what it is I'm doing, but you would have lost a candy bar.
 
Hmm... A trailer for your dog? Wait.. A cat cage.. It's a cat cage isn't it?
None of the above, but the dog comment reminded me of a pic I found online which I think is both awesome and hilarious.
I'm hoping to have an update photo of my build for you guys in a couple of weeks.
Cheers for now.
 

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Hello again, friends - I was hoping to write an update sooner but errors have occurred and lessons have been learned.
The errors -
The fuel tank cap was seized so I needed to break it to remove it, problem is most of it fell into the tank and was painfully difficult to remove.
Twice I ordered a new fuel cap from Amazon, both times neither of them fit correctly. Walked into a Yamaha dealership and priced out a new cap...I didn't expect the $102 price tag so I did not purchase...will need to find one elsewhere.
I attempted a gas tank rescue, spending time to remove the internal rust and purchasing a can of POR15 Fuel Tank Sealer. I also wanted to improve the previous repairs so I went at it with my torch only to make things much worse. After I picked up the tank, I heard rattling inside and upon shaking it upside down, discovered several large chunks of rust that became dislodged while I used the torch. At this point I was frustrated, gave up and just ordered a new tank from Amazon (one that comes with a cap)
I attempted to return the can of POR15 tank sealer but the seller refused to take it back even though the can was not yet opened. So now I have a can of tank sealer and new fuel tank. My question to anyone out there - can I add the sealer to the new tank to prevent future interior rust?

Lesson learned - of the main styles that are used in these conversions (Cafe Racer, Tracker, Bobber, Scrambler, Brat-style) I decided I like the Scrambler the best because of the bad-ass knobby tires. I ordered some Kenda K270 dual sport tires, placed them on the rims and for the life of me could not get them to inflate. Brought them to my mechanic near work and he could not get the bead to seat properly to add the air. I took them to another shop and even they could not get air in them. I purchased the same size as were meant for the rim so I contacted the folks I got the tires from. This is when I was informed that dual sport tires require inner-tubes. <insert eye-roll here> So now those are on order.

For those of you who recall that I was going to do something very unique to my 400, the next paragraph will describe my intentions. So if you still want to try guessing, stop reading now and wait for photos to come much later.

My first car was a Honda Civic which, for lack of money, I learned to repair things myself. The rear windshield wiper was broken off and the washer fluid nozzle had a chunk broken off on the side so with a lack of pressure, the fluid would just dribble out. Since this nozzle was only plastic, I placed a needle in the hole and melted the surrounding area so that when I removed the needle, the hole would be smaller which theoretically would increase the pressure and shoot fluid straight down onto the glass. Well this plan worked all too well, because there was so much pressure it would squirt the vehicle behind me. That was wayyy so much fun. On a cloudless summer day I would come to a red traffic light and when the driver behind me was not looking I would squirt their car windshield. Once they realized their windshield was wet they would look up into the sky for rain clouds that were not there. I'd squirt them again and they'd laugh when they realized where the water was coming from. So I decided to do the same with my Yammy, but another one of my new hobbies is robotics so I decided to build a robot/droid to sit on the back of my bike spraying the vehicles behind me. So there it is, I'm pretty sure you have never seen a motorbike with a droid on the back squirting water.

I appreciate any advice regarding the new fuel tank, to add sealer or not.

Thanks
 
sealers only fail because the tanks were not prepped properly.
I have two bikes with sealant in and no issues. That ethanol attracts water and rusts tanks from the inside out as water sinks due to being heavier than fuel.
 
sealers only fail because the tanks were not prepped properly.
Right on! +1 on this. Prep has to be extremely thorough for the sealer to last and work. I believe too many think sealers are the magic bullet to take care of rust scale when the truth is you have spend effort to get that crap out of the tank and down to bare metal before the sealer even gets stirred up. I have worked with epoxy coatings a lot and for me to rely on sealer adhesion I would have to use a boroscope to inspect the inside for proper prep before pouring in the sealing fluid.

The problem is, by the time I get down to bare metal or pretty close to it the tank is usually good to go as is, and the sealing step becomes something I don't do. I will say that I am pretty fastidious with the tanks though, and they get emptied and steel ones coated with two stroke oil inside if not used.
 
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