1979 CB750F Tracker (maybe?)

[jordandogtown]

I've spent a lot of time over the past few months trying to squeeze this build into a box. I thought it needed to have a clear cut genre, or theme, or design, and squarely fall between the lines of what another bike enthusiast would think "makes sense". I wrestled with what boxes I needed to check to consider this bike an homage to the vintage Honda dirt trackers from the 70's and 80's - but some things I wanted on the bike had very little to do with that era. Maybe it's a street tracker? Google says sort of. Maybe it's a resto-mod café fighter? Why not. Maybe it's an abomination to the first year DOHC's and I should be burned at the stake for chopping it up and disgracing it's heritage? That one's probably the closest.

In the end, I decided to build a bike with pieces and parts and ideas that I wanted, regardless of what category the finished monstrosity would fall into (if any). This will be an ongoing build that I hope to document all the twists and turns to reflect back on one day, and maybe provide some help/inspiration/what not to do for someone else out there with the same lump of Japanese metal.

So grab a beer (or pitchfork) and follow along for some good ol' hillbilly wrenchin' and the occasional bad idea.



Purchased October 2018

 

[jordandogtown]

Don't let the above photos fool you - the bike is mostly complete, but wouldn't be worth a full restoration to me. The paint isn't salvageable, there's plenty of rust and dents, I was given two sets of carburetors which neither were correct or complete, and the entire charging system needs replacement. I love and appreciate anything with the Honda badge on it, but this bike was always going to be something I could sort of experiment with.

So, the plan:

I've been into motocross since I can remember, and as of late, American flat track. I've got a couple dirtbikes hanging around that would be perfect candidates for actual flat trackers, but being in Central KY, there's not much support for the scene, and I don't want to spend all weekend driving for a couple hours of riding. I figured my next best option was a flat track inspired street bike - nimble, lightweight, no electronics, big single cylinder thumper. I spent a year searching for a Honda Ascott, XR600, etc. and never came across one that quiet fit the bill. I found the CB a few hours north for a steal and liked the challenge of trying to combine the two. I'm planning to swap out the swingarm from a CBR600F3 and convert the bike to monoshock, custom subgrame, strip all electronics except a headlight and tail light, throw in some CR31 carbs and a set of dual sport tires, add lots of paint, and keep the motor stock for the first phase.

Some inspiration I've picked up along the way:

 

[Jimbonaut]

Right on - go the hooligans

Working on an '82 myself, will be following along. Bad decisions man, without a few of those I'd still never know the joys of waking up on a strange hotel room floor feeling like horseshit having gotten cold during the night and somehow pulled the flatscreen off the wall to use as a blanket.

 

[jordandogtown]

Thanks brother!

I have to say, some old motorcycle forums are a little less forgiving when it comes to unnatural mods. I'm more of a "cut it, weld it, see what happens" kind of guy. I've always liked it around here

 

[1fasgsxr]

I really dig the 1st and last examples there. Did you go to the Red Mile in the last 2 yrs? its sad but that was my 1st ever flat track event. It was freaking awesome!
me and my dad have gone the past 2 yrs.

 

[Jimbonaut]

Grip it n rip it. I stuck my current build in the Restorations section but I have absolutely no idea why. There it is parading as a soup-to-nuts resto-mod but it became immediately apparently it will be nothing of the sort. Plans man - best thing about them is to see how far they slid ;D

 

[jordandogtown]

First step was to get the bike running back in stock fashion. The bike would start, idle, and drive fine up to 5,000 RPM. "All it needs is a battery" said the PO.... A few minutes spent with the shop manual and a multi-meter revealed, as often, that wasn't the case.

I found a used stator that tested good, and ended up buying a new rotor.

After dropping those in, the bike was now charging but still not revving above 5k. I was told the carbs were just cleaned, which looked to be true based on an outside inspection, but finally decided to check those after the electrical was sorted. Turns out the PO removed the small accelerator pump altogether and the carbs were starving at high RPMs.

This being my second CB, I'm all to familiar with the CV woes. I decided to skip a few steps and ditch the stock carbs altogether and spring for a set of CR31s pre jetted from DCC. I've sold some woodworking commissions and whatever junk I could find around the shop and am this -----| |------ close to having enough cash to pull the trigger (if any of you knuckleheads tell my wife how much they cost we are both going to be in some trouble).

 

[jordandogtown]

I really dig the 1st and last examples there. Did you go to the Red Mile in the last 2 yrs? its sad but that was my 1st ever flat track event. It was freaking awesome!
me and my dad have gone the past 2 yrs.

Yes! And boy it is nothing compared to seeing it on TV. Really gives a new appreciation to throwing 400+ lbs sideways close to triple digits

 

[1fasgsxr]

I bought a set of 26's for my 350F so I feel ya.. still need to finish that bike....haha

 

[teazer]

My first reaction was that a DOHC is way too large to turn into a tracker, but 1 and 3 look pretty good. And if I can turn a GT750 Suzuki into a tracker, no reason why you can't do something wicked to a DOHC. Go for it.

http://www.pinkpossum.com/GT750/phattrakka2/IRP2013.JPG

 

[jordandogtown]

My first reaction was that a DOHC is way too large to turn into a tracker, but 1 and 3 look pretty good. And if I can turn a GT750 Suzuki into a tracker, no reason why you can't do something wicked to a DOHC. Go for it.

http://www.pinkpossum.com/GT750/phattrakka2/IRP2013.JPG

Man that thing looks like so much fun. I bet she sounds like a nightmare on the pipe(s), too

 

[NoRiders]

1980s Medium Hondas can be taken in many dirrections....here's what I chose to do.....you might get an idea or two

I'll be checking in....

 

[KPSguy]

I've spent a lot of time over the past few months trying to squeeze this build into a box. I thought it needed to have a clear cut genre, or theme, or design, and squarely fall between the lines of what another bike enthusiast would think "makes sense". I wrestled with what boxes I needed to check to consider this bike an homage to the vintage Honda dirt trackers from the 70's and 80's - but some things I wanted on the bike had very little to do with that era. Maybe it's a street tracker? Google says sort of. Maybe it's a resto-mod café fighter? Why not. Maybe it's an abomination to the first year DOHC's and I should be burned at the stake for chopping it up and disgracing it's heritage? That one's probably the closest.

In the end, I decided to build a bike with pieces and parts and ideas that I wanted, regardless of what category the finished monstrosity would fall into (if any). This will be an ongoing build that I hope to document all the twists and turns to reflect back on one day, and maybe provide some help/inspiration/what not to do for someone else out there with the same lump of Japanese metal.

So grab a beer (or pitchfork) and follow along for some good ol' hillbilly wrenchin' and the occasional bad idea.



Purchased October 2018

Looks like a good place to start.

I wanted to challenge myself on my first time build approx 2 years ago almost to the day . Started with a couple 70s Hondas starting point . 72 cb 500 four and 78 750 F .
After looking at all the stuff on line , it was clearly gonna become a " Vintage Style Cafe " build.
I came up with little 500 four Cafe over approximately 6 month build and 3500.00 back yard buget.

Sent from my SM-G892A using Tapatalk

 

[jordandogtown]

Nice work man. You don't see very many people going from spokes to comstars, but I dig it.

 

[jordandogtown]

Once the title was transferred (always nervous until this point for some reason) I began sourcing some parts. I knew above all else I wanted to try the monoshock conversion. Yea, I know, it'll never handle as well and there's a ton of math and geometry involved and I'm going to ruin the bike forever. Well I got news for ya - I was going to ruin this bike in some form or fashion anyway, and if I wanted a well handling/performing bike I wouldn't have bought one that's 40 years old and dang near 500 lbs (sorry; had to vent).

I found a complete swingarm and shock from a 1996 CBR600F3 for a steal. Turns out parts for less popular mid 90's streetbikes aren't super expensive. There's not a ton of specifics out there, but I was confident enough that I could make it work.

My CB pivot bolt is 14mm, and the CBR is 17mm. I planned to just enlarge the holes in the frame to accept the larger CBR bolt, but unfortunately it was a couple inches too short. I spent a solid 2 weeks trying to track down special bearings/sleeves/bolts and came up empty handed. The closest option I found was a 14mm ID x 18mm OD bronze bushing for some electric motor. I chucked these up on my wood lathe and carefully turned them down to 17mm OD. I used 5 of these spaced across the bearings and entire pivot bolt so I feel pretty good about it (famous last words?)

The next catch was a little clearance issue between the front of the swingarm and the rear of the motor. For some reason Honda left the upper case to hang over about half an inch of the lower case. I made a "do not pass" mark on the top and gently (and nervously) took a grinder to the motor. I could have went further, but didn't want to press my luck.

A quick mockup has me real excited. I also plan to use the original wheel instead of upgrading to the 17" wheels from the CBR which everyone does - albeit for good reason. The axle is a perfect fit, but the caliper hanger will need some attention as well as some new spacers.

 

[jordandogtown]

I finally worked up the courage to start hacking away at the frame. Years of moto have left me with bad knees and a not-so-good back, so I took a break from the bike and put together a work table with whatever lumber I had laying around.

All I had on hand was a cheap motorcycle lift, and a few jack stands, so it was going to take some head scratching.

First, I built the table top and managed to roll the bike on top of it, while leaving enough room for the lift underneath.

Next, I carefully raised the table top and bike with the lift, trying to keep everything centered and balanced. Once I reached the max height of the jack stands, I built some very quick and crude legs just a hair shorter. Lowered the lift and the table landed squarely on the floor.

I can already tell this will save me plenty of agony down the road. With the bike at beer belly level, it's time to start hacking.

 

[jordandogtown]

Quick note: I planned on picking up a cheap Harbor Freight engine hoist/crane when it's time to paint this lump. I'm thinking I can pick the bike up with that, move the table, then set the bike down on the floor, instead of dismantling the table. Fingers crossed, we'll cross that creek when we get to it.

 

[jordandogtown]

I got tired of looking at the sub frame and brave enough to finally do something about it. Time for the angle grinder 8)

I started with the center stand mounts and cut them just inside the top weld. Luckily they are flimsy enough that a set a pliers and a couple wiggles will break the bottom weld. I never was a fan of grinding upside - I'll save that for when the motor is out.

I used the same method without the sub frame and it worked out surprisingly well, with plenty of patience. I suppose if someone was inclined, they could simply weld the stock sub frame back in place with little effort.

A little flap-diskin' and she's ready to be poorly welded on. KY is stuck below 0oF for a few days so it can wait till the weekend.

 

[jordandogtown]

With help from the great Irk I also learned that my bottom cases are the "B" style, which indicates which size crank bearings I need

(I'm still sticking with my story that 1 B = 1 Badass, making this a very cool bike)

 

[Jimbonaut]

Gotta love angle grinders - you weren't kidding about getting tired of looking at the sub frame. You going to be fabricating a whole new rear end?