1979 CB750 DOHC Monoshock Build

[bananas]

Update:

Time to make the undertray/electronics box. Have never worked with fiberglass before so hopefully this first attempt is also the last. I've been checking up on it and so far it seems to be curing quite nicely. Used a combination of mat and cloth, however in the future I'll probably be using mostly cloth because it's soooo much easier to work with.


For anyone interested materials needed are:
-Epoxy Resin, 1 Med-Size Jug
-Epoxy Hardener (Came with the resin)
-Fibreglass mat - 1 pack
-Fibreglass cloth - 1 pack
-Mold release agent (I'm using a regular good quality car wax so I didn't have to buy anything proprietary)
-Cheap paint brush
-Metal Roller
-Good pair of scissors
-3M Breather mask
-Nitrile or rubber gloves
-Lots of plastic bags
-Plastic beer cups and shot-glasses (for measuring)
-Boxcutter for air bubbles (if you get any)
-Heater to assist curing because Vancouver is beginning to get cold


Mockup of the to be welded-on frame gussets. They're designed to completely hide the under-seat electronics box. A very sad blown up '79 Kawasaki KZ200 hibernates in the background

Making sure everything fits. Forgot about the solenoid so I guess the RR will be mounted underneath instead. A little wind should be good for heat dissipation anyways.

Kept the tank on underneath the plastic sheets for part 2 of fibreglassing -- building the seat pan & foam mockup on top of the battery box.

First 2 layers of mat down + a bit of corner reinforcement. This still is awful to work with!! It got everywhere!!! The only good thing about this stuff is that it doesn't have any problems with air bubbles. Was pretty annoying to deal with strands of it getting stuck all over the brushes and roller while applying resin. I'm thinking I should've waited longer between coats?

Fibreglass cloth as the third layer. This stuff was great. No complaints.. Cut out a basic pattern and used a metal roller to get out air bubbles.

Edit: Checked up on the curing a couple of times. its 90% dry now. Two smaller air bubbles formed next to the upswept compound curve, cut 'em open with a boxcutter. Will probably need a bit of sanding all around and maybe a finishing layer. Also realized I forgot to impregnate the overpriced washers i picked up this morning. Damnit.


Next update hopefully coming soon 8)

 

[motonick34]

Wow!!! I love you and hate you all at once! Ive been working on a similar build but ran into some road bumps early on. My gsxr swingarm actually rubs the back engine case!

 

[motonick34]

Just mocked up at the moment

 

[bananas]

Wow!!! I love you and hate you all at once! Ive been working on a similar build but ran into some road bumps early on. My gsxr swingarm actually rubs the back engine case!

Nice! Matt (750mors) also has a DOHC build with GSXR suspension going -- you should check out his thread. It's kind of hard to get good shots as everything is still wrapped up in plastic while I do a undertray/fender and the seat pan.

I'd apologize in advance to the purists for this photo... but I realize this entire thread is probably sacrilege. ;D

In regards to your problem.. The back of the case was shaved to make it fit. I will clean it up a bit along with a ton of other stuff after she's running.

Mounted using the stock swinger bolt/mounting location. Custom races/ spacers on both sides. A main difficulty is getting the wheel centered. I mean it's not terribly important as there are factory bikes out there with offset wheels but I can't live with that kind of thing. Welded two sprockets together to make a (16T) 530 offset front sprocket (In hindsight I should've just ordered a custom sprocket from one of the many custom sprocket manufacturers). Used a (Driven 42T) 530 rear sprocket from a 2003 GSXR 1000 and visually it looks like it'll just clear although I might change this up later for more teeth. No other modifications.

Also, my suspension setup is still not ideal so don't get too many ideas... I'll adjust it somewhat with linkages or worst case scenario completely scrap it for a stock GSXR setup. Right now it functions kind of like a hardtail haha...

 

[motonick34]

What did you have to do to the you swingarm to fit... im scratchin my head here..

 

[motonick34]

Sorry I just saw your reply! I thought about that and kind of cringed... but if it works ill look into it! What about adapting to the smaller pivot bolt? Great build btw! I envy your progress! Bike is turning out great sir

 

[bananas]

Haha. I figured I should add a bit of info as the original reply was a bit vague. I can't take too much credit I have quite a bit of assistance from a great machinist. He found the stock axle to be the best solution.

 

[motonick34]

Thats awesome you have help like that. I know an amazing bike builder (jesse srpan) 10 minutes away... id just rather not ask for his help. I was seriously about 5 seconds away from chopping the frame and making a new swingarm mounting location when I found your thread

 

[bananas]

A link to 750mors thread: http://www.dotheton.com/forum/index.php?topic=57807.0 if it helps!

 

[motonick34]

Thanks! I found the thread earlier, great stuff here! I thought I was the only one digging the dohc retro mod haha

 

[bananas]

Thanks! I found the thread earlier, great stuff here! I thought I was the only one digging the dohc retro mod haha

Nick, make sure to check out the cb1100f.net forums for a nice wealth of info on the DOHC bikes. There are a number of guys on there with gsxr rear ends as well (which is where I got the idea).

 

[bananas]

Update:

Finished trimming up the battery box. My first attempt at fibreglassing so I'll give it a pass. It definitely would be considered quite shitty if it were a commercial product but for now it's strong enough and it works.. There were a few air bubbles and I found some of the layers were compressed poorly and seperated. I will have to touch it up with a a bit of body filler and sanding before receiving some plastic-friendly paint.

Fortunately the visible undertail section did turn out quite nice. The carnauba wax worked perfect as a mold release.

My major problem was that the resin was too thick/sticky and difficult to apply quickly enough before it hardened so this round I added a cap of acetone to each batch -- so far it seems to have worked perfectly.

So on to the seat pan!


First I made a duplicate form of my Shorai battery using a styrofoam core sandwiched between cardboard and wrapped in tape. Holy fuck do I ever hate styrofoam. Worked great however.

Set the form into the electronics tray along with a cardboard surround. Tried to save some money by buying some unbranded tape. It is the shittiest tape I have ever used in my life. Two layers of it to smooth out the area and to ensure the resin doesn't soak through. In hindsight I should've made a cardboard template to reinforce the tape.

Side-shot. You can see how much the battery extends vertically. It will however be completely hidden within the seam foam once it's upholstered. I could've had it hang lower but I didn't want too much of a visible box under the seat. My thinking is a rectilinear form in that area would detract from the visual "floating" effect in the rear created by the combination of negative space from the monoshock suspension and the visual mass of the inline-four.

Fully glassed with 3 overall layers and a bit of reinforcement along the "box" area. Base layer of mat, with pre-cut cloth on top. This time around I added acetone to the resin to thin it out. Worked flawlessly, however I have noticed it is drying slightly slower than last time. Left a space heater to help with the curing.

Next and final glass part will be the front fender. I haven't really figured out how its going to be mounted but I'm going to leave that problem for future me.

 

[dualero]

Next and final glass part will be the front fender. I haven't really figured out how its going to be mounted but I'm going to leave that problem for future me.

Hi there bud, I'm following this build patiently from Venezuela! It's turning out really good, keep it coming! I have 2 questions for you. 1) How did you apply the carnauba wax? How much? 2) What are you taking as a mold for the front fender? I'm in the need of one myself, and don't know what to mold the fiberglass from to make it suit well. Thanks!

Sent from my GT-I9300 using Tapatalk

 

[bananas]

Hi there bud, I'm following this build patiently from Venezuela! It's turning out really good, keep it coming! I have 2 questions for you. 1) How did you apply the carnauba wax? How much? 2) What are you taking as a mold for the front fender? I'm in the need of one myself, and don't know what to mold the fiberglass from to make it suit well. Thanks!

Sent from my GT-I9300 using Tapatalk

Hey Duelero, Thanks for the compliment!

I use a mothers wax (just the one I use for my car). I just dumped it on and rubbed it all over with my hands. Probably about 2 tablespoons worth at least. You'll know how much you need when you're applying it -- don't put too much but don't be stingy about it either.

I'm going to be locking the wheel in place.. probably using tape or zip ties or something like that. Taping over the wheel/forks and glassing directly on it. Best part is that the fender will be perfectly mirrored to the shape of the tire. Let me know if this is kosher, but there's a sticky over at the customfighters.com forum where a guy does exactly this (it's where I got the idea).

Link: http://www.customfighters.com/forums/showthread.php?t=32629


Cheers!

 

[dualero]

That's a really good read sir. Thanks for that link. I'll follow your indications in terms of release mold agent concerns and report back

Sent from my GT-I9300 using Tapatalk

 

[hdscarbro]

I'm going to be locking the wheel in place.. probably using tape or zip ties or something like that. Taping over the wheel/forks and glassing directly on it. Best part is that the fender will be perfectly mirrored to the shape of the tire. Let me know if this is kosher, but there's a sticky over at the customfighters.com forum where a guy does exactly this (it's where I got the idea).

Link: http://www.customfighters.com/forums/showthread.php?t=32629


Cheers!

I've made a couple of fiberglass fenders by using an existing fender as a plug. Here's a brief writeup with photos.

 

[bananas]

I've made a couple of fiberglass fenders by using an existing fender as a plug. Here's a brief writeup with photos.

Whoa! I don't know how your glasswork is so clean... makes it looks like mine was produced by a monkey. That's another great way of making a front fender. The technique I plan to use is awesome for us without something to glass over (other than a new tire). In my case I acquired the GSXR front-end piecemeal and normally I'm a big fan of modern sportbike fenders but never got the SRAD fender as its kind of... awfully 90's looking.

Checked out your build the XS looks great!

 

[bananas]

Update:

Prepped & cleaned up the front wheel and glassed it for a fender. This part was a lot easier than the electronics tray and seat pan and all-in took less than 30 minutes. Probably should've done this one first.

Credit for this fender making method goes to Fathead_03 from customfighters.com. Link: DIY: Fiberglass front fender - Custom Fighters - Custom Streetfighter Motorcycle Forum


Started off by cleaning the front tire with a wet paper towel. Make sure to dry it off after for easy tape adhesion. Used some old newspaper and more tape to protect the area from dripping resin.

Taped up an area a bit larger than the actual fender itself. Did two layers, one along the tire and one horizontally this was to both smooth out the area and to protect the tire.

Drew a few lines on the tape with a sharpie beforehand as a general guide for cutting after the part cures. I pre-cut the fibreglass cloth to a general shape and made lots of cuts (about 2" each) along the sides so it will curve around the tire more easily.

Three layers of cloth. Finished up the small can of epoxy resin I've been using for these parts. All finshed!

Still have no clue how it's going to be mounted. Hopefully I can get someone to fab something similar to my Duc. ;D

 

[BigSherm]

Great work, Bananas!

 

[bananas]

Great work, Bananas!

Thanks!


The electronics box I made first turned out great. Just needs a bit of sanding/bondo and some paint. Very strong and definitely hard enough to bash skulls if I so please.

So learning new things is always fun... I've been checking up on the new glass parts all weekend and for some reason I feel like I did something wrong for these two parts. I'm going to guess that I didn't mix my hardener well enough or I added too much acetone to the mix. The parts are somewhat hard but still a tiny bit tacky, translucent and not very strong.

Anyone with fibreglass knowledge want to chime in? I'm wondering what my solutions are... Do I let them cure longer and see what happens? Scrap 'em and start over? Or can I perhaps add a couple more properly mixed layers for some more rigidity?

The electronics box cured overnight with a space heater so my assumption is that a whole weekend should've been ample time?