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Discussion Starter #1
So, had a question for all you experienced bike builders/fabricators. I just got a '78 yamaha xs400, and as far as finding a seat goes...not much luck. Am I better off taking the stock seat, stripping all that ugly foam out of it and working off of the bottom structure of the seat and trying to make my own? That way I at least have the same mounting capabilities.... Or should I just mock up a piece of wood that fits the dimensions and get a fiberglass one made custom? If I go that route, how do you usually mount that on the bike?
here's a before pic and one after a couple hours of tear down.

So far, plans include rear sets that I already found, 2-2 exhaust, bars and new guages, and a new seat. the stock tank looks decent...for now.








that's gonna leave a mark.

Edited by - lilhit on Feb 05 2008 12:03:22 AM
 

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hey man, sweet bike!

i had an xs360(virtually identical to the 400), and i just tossed the seat...the pan was big and bulky and wide...also if your seat is like mine was, you have 2 swivel points on the side of the frame, and you could easily fabricate something to keep that swiveling action on a fiberglass seat.

though i would just mount a seat (no swivel), and gut the airbox/relocate the battery..like this guy did...

http://www.bikepics.com/pictures/493248/

"Never mind the track. The track is for punks. We are Road People. We are Cafe Racers." -Hunter S. Thompson
 

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Discussion Starter #3
thats a good idea...cleans up the look a lot. where are good spots for the battery???

that's gonna leave a mark.
 

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under the tail bubble.

you can get a generic fiberglass seat pan from many mfgs (I recommend glass from the past as bret is a member here).
 

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Geeto67,

I was thinking of stuffing the battery under the seat bubble on my cb750 and leaving the stock seat pan in place. Do you have any idea how high the rear wheel travels up into the wheel well? I am having a hard time measuring that myself but it seems that the risk of having the battery up there is that the wheel could bump into it.

Mut
 

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quote:
Geeto67,

I was thinking of stuffing the battery under the seat bubble on my cb750 and leaving the stock seat pan in place. Do you have any idea how high the rear wheel travels up into the wheel well? I am having a hard time measuring that myself but it seems that the risk of having the battery up there is that the wheel could bump into it.

Mut
off the top of my head this is a bad idea because you are going to be tipping the battery on its side every time you open the seat (if you are using a stock pan. You would have to run a sealed battery and even then I am not exactly compfortable with the idea of the battery cables streaching out when you open the seat. The battery under the bubble is more a setup for fixed seat pans than for ones that tilt.

There is a guy on ebay that sells a fiberglass pan for the cb750 that uses stock hinges and you can probably make the battery stationary while the seat hinges over it. In that case you want to make sure the battery tray is above the frame cross brace.

as far as how high the wheel goes into the wheel well, If you remove the shocks the rear inner fender will sit on top of the tire. If you remove the inner fender the wheel will sit on the frame cross brace.

If you are talking about how much will your suspension bottom out, well that all depends on what type of shocks you are running and what size tire and rim. I know you can run an 11" shock, bottom it out and there is still enough clearance and the 11" shock is 2 inches shorter than stock.

The best way I can think to measure the suspension compression is to take one of your shocks, remove the spring, and then compress the shock and measure it (eye to eye). Then take a piece of bar stock, drill it to the measurements and install it in place of your shock (remove both shocks BTW). This way your bike is now fixed at the lowest compression point on the suspension and you can check for clearance. You will want to leave at least an inch and a half of clearance to accomidate the growth of the tire at speed.

if you keep the rear cross brace in the frame that will stop the tire before it ever gets to the seat pan (which sits on top of it)

If it makes you feel better I have ridden my stock suspended cb750K with over 600lbs of people and gear on it and the rear tire did not hit the inner fender (although the shocks did bottom out a few times). Clutch smelled real good after a few highway miles like that.
 

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mut,

do you own an F or a K bike? SOHC or DOHC? I wrote that last response with a 69-76 SOHC K in mind forgetting about the F bikes. Still the basic frame geometry applies. If you build a battery box to replace the F storage unit on a stock setup you should be ok with a stock suspension or higher. If you are moving the bubble forward then pretty much what I said about the K bikes applies regarding the cross brace.
 

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need a roomate??

orange lockers kick ass!



jc

i dont know shit
 

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Discussion Starter #11
uhm actually that's my friends house, and i'm not sure he needs any room mates. but yea. orange lockers are rad. i think. at least they're rad as long as we have a garage to work on the bike haha.

so i'm having trouble finding a wiring harness cuz we're gonna scrap the original wires, they're all torn up. any suggestions?

that's gonna leave a mark.
 

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Discussion Starter #12
so, after some searching, and plenty of 'unervisal' seat pans that might....keyword...might fit. we decided to try and make our own. so far, here's the progress. a $20 block of foam, cut down to size and lots (I mean lots) of freaking foam dust and pieces that are impossible to get off you....and here's where we're at so far. still have some more fine tuning to go, but so far I kind of like it. hopefully it works out. we just need to figure out how to fiberglass it once we're done.....









that's gonna leave a mark.
 

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Looking good. I may try making my own seat for my CB450T. I picked up a book on CD from eBay for $5 about fiberglass molding. Seems pretty straight forward.

“Riding is and always will be my first priority. Through the distractions and inevitable failures in other parts of my life I know that all I have to do to feel better is ride.”-Ryan Clark
 

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cant you just lay the glass and resen on the foam and when your done and everything is set melt the foam out with gas or something like that?

There is the right way, the wrong way and the british way to do anything!
 

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quote:
cant you just lay the glass and resen on the foam and when your done and everything is set melt the foam out with gas or something like that?

There is the right way, the wrong way and the british way to do anything!
thats what I've heard also, so if you do this how you gonna get to the battery, I've been wanting to do the same to my bike, just a little lost on how I'm gonna be able to open the seat to access the battery without tilting it.
 

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Discussion Starter #16
i'm thinking the way we are going to do it, is leave the bottom portion 'open' if you will....because the whole seat pan area is going to sit on the frame anyway, and for the underside of the bubble just make a template and cut out some aluminum that can mount to the frame/lip of the bubble. that way its a 2 piece deal that still allows access.....

that's gonna leave a mark.
 

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Discussion Starter #18
anybody know whether its better to use fiberglass 'matt' which is kind of randomly laid down strands of fiberglass...or 'cloth' which is neatly woven together?
 

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hey man,

if youre in the bay area, check out TAP plastics...they have everything you need...if i remember correctly the guy recommended the cloth...but cant remember for sure....anyway they are friendly and know their stuff....
 

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cloth/fabric is generally considered better. More predictable, stronger structure wise - but really doesn't matter so much in this kind of application. I think cloth is less annoying to handle over mat.
 
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