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Author Topic: Ultra Budget Bum-stop seat  (Read 6520 times)
Andy
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« on: November 10, 2009, 07:34:20 PM »

Everyone likes and wants a cafe racer right (runningdog, bear, looking in your directions haha)?  Well I do anyway.  When I think cafe racer I am thinking under 600 cc.  I think of smaill bikes with good handling whose speed is mostly because of their light weight and capable riders.  I know everyone doesn't agree with me, but Carpy's cb750's are a bit big for me as a cafe racer.

that is why I got the GS400.  Problem is, the GS is ugly, it's an L with a stepped seat and cosmetically is the antithesis of a cafe racer.  BUT, it's a 6 speed 400 twin and is light light light by my standards and experience.

so I needed to ditch that king queen seat ASAP.  I looked at ebay, I found www.roccitycafe.com and others but frankly, I am not about to spend $250 USD plus shipping for a seat to go on a $300 bike.  I'm sure most of you would agree!  It's not Bear's BSA after all, it's a UJM lump (I have taken to calling it the lump or the Scuzi, as in x-cuse-me).  

what does a poor, partly employed, slightly bored, largely crazy young fool do in this situation?  Fudges things.  Fibreglass cloth will take the shape of whatever you drape it on more or less.  I considered making forms of wood (too heavy, slow to work with, wood on a motorcycle?) and other things, and decided on a leftover 4x8 sheet of hard styrofoam thermal barrier.  When I was a kid my parents took me to a shipbuilders and we made little sailboat hulls out of the stuff (1 foot long).  

Step 1:
I measured and cut 4 sheets of 2 inch thick foam to the approximate length and width I wanted my bum-stop seat to be, plus about 1 inch on all sides.
Step 2:
I put one sheet on the frame of the GS, and thumped on the top.  The foam dented wherever it made contact with metal
Step 3:
carve out the dents.  I used sandpaper, a utility knife, basically anything other than a bar of used soap will carve this stuff.
Step 4:
repeat steps 2 and 3 until the foam fits flush with the frame or is aligned along the plane you want it to sit.  I wanted the bottom edge to be horizontal with a rider on the bike so I fudged around until I got that.
Step 5:
using wood glue or what have you that doesn't eat the foam (anything petroleum based will destroy the foam, I used wood glue) glue the 5 layers so you have a laminated block.
Step 6:
Wait.  Watch jeopardy, claim they are wrong when you are.
Step 7:  
Put the foam blockback on and shape to your heart's content.  shop vac very handy.  I started out using a palm sander and coarse paper but it made a lot of fine dust, even with the vacuum hooked up.  I switched to a small, palm sized drywall rasp and it worked great.  the lines separating the laminated sheets are also handy guides when evaluating symmetry.  I never did get mine perfect, but you have to stop at some point or else you'll end up with a pocket bike seat.  It was like trimming your sideburns and ending up with a mohawk.

Here's what mine looked like to this point.
« Last Edit: November 10, 2009, 07:58:18 PM by Andy » Logged
Andy
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« Reply #1 on: November 10, 2009, 07:49:17 PM »

Moving on..

Keep on shaping.  The foam is $20 a sheet or so, and you can get two full tries out of a sheet.   I used 2 inch thick stuff.

Step 8:
once you have your shape, cover your piece in aluminum tape, the kind that is used for ducts but it not called duct tape.  Who decides these things anyway?  Be carfeful to overlap the tape a bit because the fibreglass resin you'll be using will eat the foam.  I used aluminum tape in the hope that the finished piece could be pulled off.  More on that in a bit.

step 9:
Take a sheet of fibreglass cloth and lay it over your form.  I suppose you could use matting too but it's harder to shape.  Tug at the edges of the fibreglass until it is essentially the same shape as the form and is touching nearly everywhere.  I used a bunch of T-pins to hold the cloth at the front, around compound curves etc so when I was working on other areas it wouldn't shift.  This was a huge help, it was like having extra hands and made the next step much easier.

Step 10:
Apply the resin.  I had an extra 4 inch paint roller laying around that wasn't cleaned and was hard with dried paint.  I mixed up a batch of resin in a roller tray, rolled the roller in it, and then rolled the resin on the mold.  This was probably the smartest thing I had done so far (in no small part because the rest wasn't exactly rocket surgery).  If you roll from the centerline toward the edges the roller will press the resin into the cloth and stick the cloth to the alum tape below.  I have used a brush in the past but it dragged the cloth around, pulled it apart, made it all strandy... basically a disaster.  the roller was great, and I didn't get a single bit of resin on me.  This is unheard of, I am basically the personification of Pigpen when I am painting, fibreglassing etc.


step 11:
wait to dry.  This takes particularly long, I found out, when the outside temp is <5 C and you don't feel like killing your brain by letting it sit inside.

that is as far as I am now.  The fibreglass is stuck to my mold, but I am sure it could be pulled off.  I plan on leaving the foam in there for added strength, it is only about 0.5 kg at most.
I have to put at least 2 more layers of cloth on there.
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Andy
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« Reply #2 on: November 10, 2009, 07:50:10 PM »

pics continued
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Andy
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« Reply #3 on: November 10, 2009, 07:55:46 PM »

Product testing has shown that the bum stop is too small, or my arse is too big.  I'm leaning toward the former but I've been accused of the latter.

I already thought this thing was too short front to back and bottom to top, but I continued with it in the hopes that if I completed it I'd have more experience and hopefully head some problems off when I do get the shape I want.

Anyhow, I am into this whole thing for the tidy sum of $30, which is right up my alley, and the finished product will be custom fitted to my frame, so no need to alter an already finished product (which was a big concern for me when purchasing a $200 or $300 universal fit).  Plus, it kept me out of trouble for a few evenings.

I'll update as things progress, but once you have reached this point there's not much left to do.

It does look a little silly right now, but I have the stock bars from my KZ on the GS.  I am going for clipons or clubmans, think of the look if I was grabbing the front signals instead of those bars!
« Last Edit: November 10, 2009, 08:01:42 PM by Andy » Logged
Runningdog
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« Reply #4 on: November 10, 2009, 08:03:47 PM »

Dude!!!!

I really like the write-up....rigid insulation, glued together...poifect.

How do you plan on attaching the seat to the bike?  Could hardware be integrated into the laying up process?  I'm stoked...rethinking the bobbed-fender and enduro tail-light idea....
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I fear nuthin' for Dog is on my bi@&h-pad....
Past:  '82 Suzuki GS400E
'82 Suzuki GS750E
'81 Yamaha Virago 750
'82 Suzuki GS650GL
'77 Yamaha DT250  
Present:  
'78 XS400 (Collector Plate)
'80 GS 850 (Collector Plate)
'73 Yamaha RT360 (40-year old sullied virgin)
Andy
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« Reply #5 on: November 10, 2009, 08:16:02 PM »

Dude!!!!

I really like the write-up....rigid insulation, glued together...poifect.

How do you plan on attaching the seat to the bike?  Could hardware be integrated into the laying up process?  I'm stoked...rethinking the bobbed-fender and enduro tail-light idea....

Glad I could contribute for a change instead of just taking free windshields, mounting brackets, wiring diagrams and advice.

Rethinking it eh?  well I must admit I was thinking of your XS when I decided to post this.  I wanted an XS but there weren't any $300 ones when I was looking lol.

For attachment I am not entirely certain.  there are hoops on the GS frame I was considering sliding a piece of metal through which would slide through similar holes in the seat.
I am now thinking it would be best to just use clips, like 290 degrees of a circle and glass them to the seat and have them hook the frame tubes.   Or you could set threaded steel inserts into the foam and glass them in and use u-shaped brackets and screws with lockwashers.  I kinda want mine to be secure but not need tools to remove it.  You could glass the stock hinges and lock hardware in I am sure, but I am removing it (lightweight!)
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Andy
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« Reply #6 on: November 10, 2009, 08:20:27 PM »

Oh yeah, this is it for me tonight, but I had to mention

I originally wanted to make a 1 piece tank and tailpiece bit using this method, which I would then saw in half to separate the thank/seat (I figured it would crack up as 1 piece) this would allow me to flow everything together.

In the end I couldn't figure out an easy way to get the petcock, tank cap, etc in there.  Also, ethanol eats fibreglass and I'd have to buy an expensive sealer.  you can get the foam out of the tank by drilling the hole for the cap and adding a little acetone... at the risk of eating your F/G tank a bit.  So I ended up with just a seat, and a little practice.

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Runningdog
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« Reply #7 on: November 11, 2009, 09:02:12 AM »

Oh, I'm sure the Suzi will turn out to be good choice.....better handling from the factory than the Yammie, and that 2-valve motor lasts forever.   The "L" model means that you have a peanut-shaped tank (always good), and a slightly higher seat height/steering head ratio (conducive to a dirt-track sort of look). 

Plus, there are a thousand cafe'd xs400s out there, but very few GS400s....singularity!!!!
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I fear nuthin' for Dog is on my bi@&h-pad....
Past:  '82 Suzuki GS400E
'82 Suzuki GS750E
'81 Yamaha Virago 750
'82 Suzuki GS650GL
'77 Yamaha DT250  
Present:  
'78 XS400 (Collector Plate)
'80 GS 850 (Collector Plate)
'73 Yamaha RT360 (40-year old sullied virgin)
Frank Passmore
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« Reply #8 on: November 11, 2009, 10:27:23 AM »

the seat looks good man i hope you can get it to fit. your inspiring me to maby try my hand at fiberglasing later.
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1976CB550F
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« Reply #9 on: November 11, 2009, 10:34:14 AM »

Awesome Job!! An inspiration to us all. Let us know how the fastening to the frame goes.
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dano
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Seat dude


« Reply #10 on: November 11, 2009, 11:04:53 AM »

Excellent post! Great job on the seat, you're on the right track. There is foams that won't get eaten by the glass, they are pollyester based and can be found at pro supply stores but are quite expensive compared to styrofoam.They are denser and offer more strucural strength, because you are bonding the glass to it, and of course are designed for that purpose, where as styrofoam is an insulator, and the cells are less compact and contain more air pockets. You can achieve the same results by continuing on the same route you are on, carve out the inside where you don't need to 1/2-1". then tape and glass agian. You will get a lot of strength out of the double wall and be feather weight. If you are building a mold, then use a mold release, but you are only building one piece, so this is how you do it. I have an industrial strength self adhesive velcro that I use on the seats I build for seat atattchment, don't use hardware store velcro, the adhesive isn't strong enough, give me a call and I'll set you up with some. I can also supply you with the right foams for the seat and material and instructions if you want to do that part as well......and I'm pretty sure you do  Grin Dano
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PAST BIKES; KD125,250S1C,'76 400FOUR S.S.                                            
CURENT;'89 ZX10, '79GS750E collector plate, '80CBX project                                                                                        If I had more, I'd have more
paulh
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« Reply #11 on: November 11, 2009, 11:13:36 AM »

Great job Andy.Its starting to look more and more like my GS 400 boat tail.lol
Are you going to encorporate lighting on the tail and how are you going to attach it?
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bear
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« Reply #12 on: November 11, 2009, 11:23:41 AM »

Andy,

Back in the day I built a lot of car bits and MC bits with fibreglass and Polyester resin. I even built a bum stop seat for my friend's Vincent. I don't think I would do that for a Vincent these days with the average price at $150,000 - $250,000.

Dano is the man on seats for sure and the best results are with structural foam and mold release and making a negative mold. Then you can get what will be the finished surface very smooth and spray in gelcoat before you lay in the glass to get a very workable finished surface. It has the advantage of allowing you to make more than one (when you get it right) without making up the blank each time.

Well done !

Bear
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Past rides:
1965 Suzuki 80cc K10                  1966 Honda 305 Superhawk CB77                              
1957 Triumph TRW 500               1967 Yamaha Twinjet 100 YL1
1967 BSA 500 Royal Star              1967 BSA 650 Dunstall
1967 Suzuki S32 150cc                 1981 Honda 500 Siverwing GL500
1982 Honda 750 Sabre V45           1984 Honda 750 Interceptor V45
1984 Yamaha XJ650RJ                  1985 Suzuki GSXR750M
1975 Suzuki GT750M                    1966 Yamaha 250 Catalina YDS3

Present Rides and Projects:
1971 BSA A65 650 Thunderbolt                      1983 Triumph TSX750
1975 Suzuki GT750M Lemans                         1975 Triumph 750 Trident T160
1982 Honda CBX 1047 Super Sport                 1977 Triumph 750 Bonneville T140
1982 Yamaha 650 XJ650LJ Seca Turbo            1972 BSA Dunstall 650
1955 Royal Enfield Bullet 500 clubman             1982 Honda CX500TC Turbo
1971 Norton Commando Roadster 750             1984 Honda VF1000F Interceptor
1986 Suzuki rg250 Gamma                             1983 Honda CB1100F
bear
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« Reply #13 on: November 11, 2009, 11:33:31 AM »

Andy, Sorry I got interrupted and did not finish my train of thought.

I would take Dano's advice and aluninum tape the underside of the foam and glass over if you want to preserve the fit you have for frame to seat. The foam will deteriorate and will lead to a poor fit and may even lead to cracking the glass if left as is.  Most high end boats and even Ambulance bodies in New Zealand are glass/foam/glass and I have seen a dump truck perched on the body _ now that is strong!.

Bear
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Past rides:
1965 Suzuki 80cc K10                  1966 Honda 305 Superhawk CB77                              
1957 Triumph TRW 500               1967 Yamaha Twinjet 100 YL1
1967 BSA 500 Royal Star              1967 BSA 650 Dunstall
1967 Suzuki S32 150cc                 1981 Honda 500 Siverwing GL500
1982 Honda 750 Sabre V45           1984 Honda 750 Interceptor V45
1984 Yamaha XJ650RJ                  1985 Suzuki GSXR750M
1975 Suzuki GT750M                    1966 Yamaha 250 Catalina YDS3

Present Rides and Projects:
1971 BSA A65 650 Thunderbolt                      1983 Triumph TSX750
1975 Suzuki GT750M Lemans                         1975 Triumph 750 Trident T160
1982 Honda CBX 1047 Super Sport                 1977 Triumph 750 Bonneville T140
1982 Yamaha 650 XJ650LJ Seca Turbo            1972 BSA Dunstall 650
1955 Royal Enfield Bullet 500 clubman             1982 Honda CX500TC Turbo
1971 Norton Commando Roadster 750             1984 Honda VF1000F Interceptor
1986 Suzuki rg250 Gamma                             1983 Honda CB1100F
Frank Passmore
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« Reply #14 on: November 11, 2009, 11:39:37 AM »

hey man you still lookig for the mirrors that go on the end of the handle bars ?
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