Topic: '78 CB750K Project #1 - Cafe-like Racer-ish Bike

[Stoli]

And, here is the seat cutout from an old foam seat pad...



She'll have some nice lines once I cover the seat. 

[Blitzburgh207]

Lookin good man, I like it.  It kind of reminds me of the F model seats.

Something to think about though is that if you are going to use that as your male mold, it's going to be tough to get those tight turns for that band on top.  Might be worth making it flat and adding that strip on after w body filler or something? ...not sure - I'm no expert 

[Stoli]

I'm sure you are right about that. I'd like to make a female mold but from what I have read, the materials to do that are very expensive. I think I will flare out the edges of that top band and hope for the best. It will also match the tank a little closer if I do that way.  If it doesn't work, I'll throw it away and try something else.

[xnoahx]

Looking good

[snowman]

Knee Dents -

Hard choice, made much easier by the fact that there was a big dent in the tank already, presumably from the bike tipping over at some point. I was worried about the bottom edge of the tank getting pulled up and in by the hammering so I cut out a couple pieces of wood that followed the contour of the bottom of the tank and placed the tank on top of them while I hammered. That little flange along the bottom of the tank hugged the wood so it kept it's shape. Say what you will about the 77-78 CB750s but I really like the big tank. Sort of bad ass. I think I am going to have a problem with the clubmans though. In order for them to clear the tank, I need to rotate them up and forward and me thinks its a little too far forward.



Here is the tank in it's current state, primed but not quite ready. I still have another afternoon of bondo and fill primer work to get it right before painting. I plan on painting it gloss black, which will show every little ding, I'm sure. This has been my first experience with bondo. Man that stuff hardens fast. Wish I could play with it a little longer before if starts firming up.

I have the same tank and was thinking about knee dents and would appreciate any additional tips about making the knee dents.  Love the build and can't wait to see where it goes.

[Bankerdanny]

Stoli, when you did the wheels did you retain the original nipples or get new ones along with the spokes?

[SF]

that tank looks awsome. nice work. i like where your going with the look

[Stoli]

I have the same tank and was thinking about knee dents and would appreciate any additional tips about making the knee dents.  Love the build and can't wait to see where it goes.

Knee dents -

Not much to it. I cut out a couple of 2x10s to match the base of the tank as you can see in the pic.  I cut them so they fit snug in the bottom of the tank. Note the hole for the petcock flange (arrow is pointing to it). Not sure if it really mattered, but if nothing else it provided a nice platform while I hammered on the tank and protected the petcock flange. I used a template (also in pic) to trace guides on each side of the tank for symmetry during the assault. The mallet I used is shown as well. It is made of hard rubber. I had it lying around so not sure what its original purpose is. I use it to tap the lids back on paint cans. I think the key is to use a plastic mallet or a rubber one that is hard enough so it won't tend to bounce but soft enough to shape the metal without digging into it. I also think that the larger the surface area the better to minimize the small dents that will result from the pounding. The face of the mallet is also slightly rounded (convex) which I think helps as well.

For the process, there is a good video on YouTube  - search for "Sully's Garage Episode 2" .

Start in the center of your planned "indent", then work your way outward in a circular pattern. Repeat until you have the rough depth and shape you want, then fine tune the edges. It gets a little tricky by the contoured edges along the top sides of the '78 tank where the metal is stronger. Only took me about 30 minutes of hammering. The bondo and sanding to smooth the surface is a skill that I do not have so that is taking me a while. I've been through about 4 cycles of bondo-sand-prime to get it where it is and I think I'll need a few more to get it to where I am happy. Just when you think you have it, you look at the tank in a different light and the shadows magnify the imperfections. At some point I will have to say "good enough" and move on to paint.

[Stoli]

Stoli, when you did the wheels did you retain the original nipples or get new ones along with the spokes?

Got new nipples as well. I was replacing the original plated spokes with stainless steel so I wanted to match. Not sure if it is a bad idea to use plated nipples with stainless spokes or not, but I never considered it. The stainless spokes are expensive, so it made sense to spend a little more to do it right.

Edit: I just checked and the old nipples are too small for the spokes that Buchanan's sent me so not really an option anyways.

[snowman]

Thanks for the quick response on how you did the Knee Dents.  With your tips and the video you suggested, I going to give it a shot.

God I love this forum........

[Stoli]

I'm spending more time on this forum than I am working on the bike.  Currently waiting for some parts, so I thought I would post some more info that might help save the next guy some time.

Chain & Sprockets:

I decided to go with a 530 chain. No reason, other than it seemed like the thing to do. One thing I had a hard time finding is how many links I would need on the chain. Maybe because there are so many combinations that there isn't a set number, but for my K8 I went with 18/48 sprockets and a 108 link Tsubaki chain. I needed to cut off 4 links, so in the end I have 104 links.

[Stoli]

While I was picking up my shop today, I found a little home made gadget that I should have mentioned in my engine post. I thought this was a great tool for chasing the crud out of the cylinder stud holes. Not my idea - found it somewhere else in this forum while I was researching the replacement of cylinder studs. This is one of the old studs, bent at an angle on one end, with a slot cut in the other end with a hacksaw. You thread it into each hole then when you take it out, all the crud that was in the hole is caught in the slot. Clean out the slot and move on to the next hole.  #$%*ing brilliant.

[Stoli]

Did some more work on the rear fender. Unfortunately the rest will have to wait until the weather warms up because making the fiberglass mold made my house uninhabitable for two days. The fumes just kept rising up from the basement even with a vent fan running. Stage two will have to be done outside in a few months.

After much reading on the art of fiberglass I determined that to do this right, I would need to make a mold out of fiberglass, then make the fiberglass fender from the mold.

Here is the "plug" used to make the mold. It was first shaped from 3 layers of a 2" rigid insulation panel. Then skim coated with bondo, then primed, sanded, and finally coated with 8 layers of Carnuba wax and two coats of PVA mold release.



Then, 2 coats of gel-coat (pigmented yellow) followed by 5 layers of fiberglass mat (pigmented black, although I don't know why I did that - maybe the fumes from the gel-coat). Probably should have gone with 7 layers of mat but ran out of resin and patience.



The mold released from the plug without too much trouble. Now I need to repeat the above process (using the mold instead of the plug) to make the fender.



I was hoping to complete the fender before I moved on to the seat but I can't wait until spring so I'm now in the process of learning how to pad and cover a seat. Hopefully the wife's sewing machine will be able to stitch through the vinyl I use for the seat cover.

[Blitzburgh207]

Lookin good! You're making a fender too?  Which one?

[Stoli]

I was planning on going with the stock front fender to start. Will probably paint it black since the chrome is too rusted to simply polish up with some WD-40 and steel wool. The rear fender is what I am referring to above, which (in theory) will look something like this when I am done (still need to play with the curve of the line along the sides to get it to look the way I want - this is just a touched up photo of the plug) :



I wanted to finish this before I started the seat because my intent is to shape the rear of the seat so it blends right into the line of the fender. I guess I can use the plug to get it close enough.

[snowman]

I'm spending more time on this forum than I am working on the bike.  Currently waiting for some parts, so I thought I would post some more info that might help save the next guy some time.

Chain & Sprockets:

I decided to go with a 530 chain. No reason, other than it seemed like the thing to do. One thing I had a hard time finding is how many links I would need on the chain. Maybe because there are so many combinations that there isn't a set number, but for my K8 I went with 18/48 sprockets and a 108 link Tsubaki chain. I needed to cut off 4 links, so in the end I have 104 links.

Having to replace my chain I decided that while I'm at it may as well replace the sprockets (more for my own peace of mind) and was pondering wether to go with a 530 set up and what made you decide to go with the 18/48 sprocket sets.

[brandEn]

Lookin good man!

[Stoli]

Snowman - I'm new to this so take everything I say and do with a grain of salt. That said, the 530 seemed to be more common with more options. As far as the ratio, I thought I read somewhere that 18/48 was a good option for "around town" riding with occasional highway. I'm not building a drag bike nor will it be an everyday commuter.

Sorry I can't be of more help. Everything I know to this point is from reading, not experience.

[Stoli]

Thanks Branden. I'm having fun with this and am totally hooked at this point. Already looking for a 3rd bike. I have another 78K which I feel compelled to restore to stock even though I am not crazy about the look. It is in decent shape however and a great candidate to keep stock. I really want to build a nice cafe though. I don't know what this current project is other than a rebuild of an old bike. Nothing fancy but hopefully unique.

[deafcaferacer]

This is an excellent thread. Thanks for the detailed notes and photos. Will help when I overhaul my engine this fall.

[Raymax]

Looking awesome so far! I really like the knee dents, they look great on that tank. Keep up the progress, I can't wait to get my engine finished up so I can start on the frame work!

[Stoli]

OK, here is a stupid question...

I was doing some work on the front end today and noticed that my tire was not exactly centered on the rim.  So I deflated it , pulled the sidewalls away from of the rim then re-inflated. Looks great now, but should I have noticed some magical "pop" at some point when the bead seats? Didn't notice anything like that.

Tubeless Avon Road Rider (100/90-19) on stock rim with Metzler tube.

[Blitzburgh207]

Sorry, I can't answer your question....but thanks a lot - now I want new wheels and spokes 

[chris mcshifty]

Nice build . How much room do u have with those tires. Could you fit a 120 on there

[Stoli]

I'm not sure about that. I know I read somewhere that you can go 110 on the front without any problem. Might have read about one guy who managed a 120 but can't remember what year or rim he had. There are some good threads that address that so a little searching and you'll find your answer.  Just don't ask anyone what brand/type of tires to get.

Edit:  Now, if you are asking me if I have enough room, then yes. There is 15mm of clearance between the tire and the left fork. A little more on the other side (I think that is normal. Hondaman addresses that offset somewhere on the forum). So, I could go to a 120 and still have 5mm of space. I don't think I could use the stock fender bracket in that config though and I would need to reroute the brake line since the stock hard line coming out of the caliper is bent to run inside the fork. Theoretically, I can also retorque my spokes to pull the rim over to the side with more space but that wouldn't get me a whole lot more clearance. Bottom line: I'm not the guy to ask such questions of as evidenced by my original question about the tire bead. I really don't know what the #$%* I am talking about.