Ranger's 1980 CB650C Scrambler build
Ranger's 1980 CB650C Scrambler build
Howdy from Texas! I picked up a 1980 (my birth year) CB650 Custom a month or so ago from a friend of mine in exchange for getting his Harley up and running. I've build a few bikes (mostly choppers) and have been riding since I was 18. This is my first foray into the world of 4 cylinder bikes.
The bike wasn't running when I got it, but did have compression. I was originally going to get it running before modifying (usually the smarter thing to do), but since I have a cracked coil, and I'm going to have to rebuild the carbs (as well as rejet them for intake/exhaust changes), I decided to go ahead and start on teardown.
I know, I know... the factory airbox is there for a reason... but I'm all about making things more difficult than they need to be. That said, I ordered a breadbox air filter from Steel Dragon Performance http://www.steeldragonperformance.com/air_boxes_7.html ... Their website doesn't list a CB650 option, but the air filter for the CB750 PD cards will also fit on the CB650 PD carbs. I emailed them measurements to verify before I ordered. Their breadbox uses UNI filter material and has integrated velocity stacks.
I'm also going to run a vented oil "catch can" by Pingel with a Uni Filter attached. I'll plumb this to the vent.
Additional plans for this bike include 17" wheels front and rear with Kenda Big Block tires, an inverted (USD) front end, 4-1 stainless exhaust, sprocket offset to accommodate the 150mm rear tire and reworked seat/hoop area.
Re: Ranger's 1980 CB650C Scrambler build
I hate the shape of the 1980 tank, so I'm planning to replace it with an early- to mid-70s Honda tank. I'm not really sure what tank, I just want a Honda tank with a non-keyed popup cap. I'll rework the frame mounts to make one fit. I like the SOHC CB750 (before 76), and some of the CB500 and CB450 tanks. Probably others as well. If anybody has one that's straight that they want to get rid of, let me know. The prices on ebay are just ridiculous.
Re: Ranger's 1980 CB650C Scrambler build
I've already started fitting up the rear wheel from a 1992 CB750 Nighthawk. It's a 17x4 drum mag, so the 150/70/17 Kenda Big Block tire fits it perfectly.
However, it has a 17mm axle instead of a 20 mm axle and is, of course, wider, so all of that has to be taken into account. If I center this wheel, then the sprocket mounting surface is actually about .3725" closer to the left axle plate than factory.
So basically, here's what I did to make the axle/wheel work:
I'll post a picture of the setup once that parts are back from the machinist... probably next week.
Then all that was left to do was to figure out how to offset the front sprocket. I looked, and I couldn't find anybody that makes an offset front sprocket for the CB 650... That said, there are a couple of options out there for the CB750. Since the CB650 and CB750 share the same sprocket shaft splines, I took a chance and ordered a 17-tooth 520 3/8" offset sprocket from Cognito Moto. https://cognitomoto.com/collections/all-products/products/17-tooth-3-8-9-5mm-offset-sprocket-for-cb750-cb550-cb500t
The sprocket did fit on the splines, but it was to thick to allow the retaining ring to rotate into place in the notch on the sprocket shaft.
It got a little confusing, since the sprocket is actually indexed off of the retaining ring (and thus the notch), rather than being indexed off the bearing surface on the side of the motor. But I figured out that if I had a little material machined off of each face of the sprocket, I could have it line up perfectly with my new rear wheel, and trim enough off of the back that there was clearance between the sprocket and the bearing. So I sent it to my machinist with instructions on how much material to remove.
It's kind of a shame to oursource this stuff since I just bought a lathe and mill last summer... but unfortunately I haven't had the time to go through them and sort out a couple of issues so I can run them. Guess I've been spending too much time working on bikes...
The last thing I needed to do on the drive line was figure out the gearing and purchase a sprocket for the rear. I used the gearing calculator at https://gearingcommander.com/ and figured out, that with a 17-tooth front sprocket, and a shorter rear tire, a 41-tooth sprocket would get me close to factory gearing. So I ordered a custom sprocket from Rebel Gears. http://www.rebelgears.com I've ordered sprockets from them on several occasions for strange applications. They're always super fast and very reasonably priced.
I'm assuming that once I get the bike going I'll need to tweak the gearing a bit, but I figured I'd start out at factor gearing as a baseline.
However, it has a 17mm axle instead of a 20 mm axle and is, of course, wider, so all of that has to be taken into account. If I center this wheel, then the sprocket mounting surface is actually about .3725" closer to the left axle plate than factory.
So basically, here's what I did to make the axle/wheel work:
- 1. I'm using a 17mm axle (not the one that came on the 1992 nighthawk, as it was too long, but I had one that was the right length in my stash... no idea what it came off of).
2. I'm using the CB650 axle adjusters to keep things simple.
3. I had 2 flanged bushings made out of 1.25" stainless steel round stock. They are 1" long, with a .25" shoulder, and a 17mm bore all the way through. .75" of the overall length has been turned down to 20 mm. These will slip through the axle plates/adjusters on each side of the swingarm.
4. Then I had the factory wheel spacers from the CB750 cut down to the proper length, and cut a .25" deep 20 mm counterbore on once side of each.
5. The Nighthawk drum looks like it will work fine with the CB650 brake rod and stay. Once I get everything bolted up, I might end up swapping the arm on the brake plate with the one of the CB650, but just eyeballing it, it looks like the nighthawk one will work.
6. I'm going to need to trim the sprocket studs a bit. At the moment, they hit the lower shock bolt. But I'll wait until my bushings/spacers arrive to do that. Absolute worst case, I'll rework the shock mounts.
I'll post a picture of the setup once that parts are back from the machinist... probably next week.
Then all that was left to do was to figure out how to offset the front sprocket. I looked, and I couldn't find anybody that makes an offset front sprocket for the CB 650... That said, there are a couple of options out there for the CB750. Since the CB650 and CB750 share the same sprocket shaft splines, I took a chance and ordered a 17-tooth 520 3/8" offset sprocket from Cognito Moto. https://cognitomoto.com/collections/all-products/products/17-tooth-3-8-9-5mm-offset-sprocket-for-cb750-cb550-cb500t
The sprocket did fit on the splines, but it was to thick to allow the retaining ring to rotate into place in the notch on the sprocket shaft.
It got a little confusing, since the sprocket is actually indexed off of the retaining ring (and thus the notch), rather than being indexed off the bearing surface on the side of the motor. But I figured out that if I had a little material machined off of each face of the sprocket, I could have it line up perfectly with my new rear wheel, and trim enough off of the back that there was clearance between the sprocket and the bearing. So I sent it to my machinist with instructions on how much material to remove.
It's kind of a shame to oursource this stuff since I just bought a lathe and mill last summer... but unfortunately I haven't had the time to go through them and sort out a couple of issues so I can run them. Guess I've been spending too much time working on bikes...
The last thing I needed to do on the drive line was figure out the gearing and purchase a sprocket for the rear. I used the gearing calculator at https://gearingcommander.com/ and figured out, that with a 17-tooth front sprocket, and a shorter rear tire, a 41-tooth sprocket would get me close to factory gearing. So I ordered a custom sprocket from Rebel Gears. http://www.rebelgears.com I've ordered sprockets from them on several occasions for strange applications. They're always super fast and very reasonably priced.
I'm assuming that once I get the bike going I'll need to tweak the gearing a bit, but I figured I'd start out at factor gearing as a baseline.
Re: Ranger's 1980 CB650C Scrambler build
Here's some pics of the bike mocked up with the tire, and after I mounted the tire on the rim. Still need to trim the sprocket studs and put everything together with my new axle spacers/bushings.
- GeorgeSweety
- Posts: 462
- Joined: Tue Aug 08, 2017 11:47 am
- Location: UK.
Re: Ranger's 1980 CB650C Scrambler build
Hi Ranger and welcome to the site. Well you certainly seem dedicated to your project, I'm not sure if I'd do anything with a CB650 before I got the motor sorted first but each to their own. I only say that because of the problems I've found with my own motor when I just wanted to change the valve stem oil seals, it is now in a bazillion pieces on the garage floor Good luck with the project and as long as you keep posting I'll keep watching. Regards, George.
Re: Ranger's 1980 CB650C Scrambler build
Here’s the parts I’m going to use for the crankcase breather/oil catch can...
Re: Ranger's 1980 CB650C Scrambler build
GeorgeSweety wrote:Hi Ranger and welcome to the site. Well you certainly seem dedicated to your project, I'm not sure if I'd do anything with a CB650 before I got the motor sorted first but each to their own. I only say that because of the problems I've found with my own motor when I just wanted to change the valve stem oil seals, it is now in a bazillion pieces on the garage floor Good luck with the project and as long as you keep posting I'll keep watching. Regards, George.
Thanks! You’re right, of course, but I tend to jump right in without regard to what makes sense. If it comes down to it, and I have to build the motor, I will. Fingers crossed!
- Solomoriah
- Posts: 50
- Joined: Wed Jun 01, 2016 10:18 pm
Re: Ranger's 1980 CB650C Scrambler build
Nice project... watching with interest...
Re: Ranger's 1980 CB650C Scrambler build
Ooh ... shall be watching this build avidly. I’m waiting to collect a barn find CB650, so will be learning as you build, picking up ideas and learning from your successes. Good luck
Re: Ranger's 1980 CB650C Scrambler build
Got my bushings, spacers and offset front sprocket in today from a machinist friend of mine. Looks like I did my math correctly.
Re: Ranger's 1980 CB650C Scrambler build
I’ll need to trim the sprocket studs down a bit to clearance the lower shock bolt. If that doesn’t buy me enough clearance, I might fabricate new lower shock mounts.
I’ll also need to remove the chain guard mounting tab. The chain pictured is just a cheap one I have for mockup. The wider X-ring chain I plan to run will hit the tab.
Can anybody tell me why my images turn sideways? I’m posting from my phone if that matters.
I’ll also need to remove the chain guard mounting tab. The chain pictured is just a cheap one I have for mockup. The wider X-ring chain I plan to run will hit the tab.
Can anybody tell me why my images turn sideways? I’m posting from my phone if that matters.
Re: Ranger's 1980 CB650C Scrambler build
And here’s how the whole thing looks.
Re: Ranger's 1980 CB650C Scrambler build
I’m going to have a bunch of stock parts available for sale if anybody is interested. Wheels, forks, gauges, front end, tank, side covers, seat.
I also have a complete CBR690RR front end with wheel and brakes. I was going to run it, but decided on an R6 front end instead.
I also have a complete CBR690RR front end with wheel and brakes. I was going to run it, but decided on an R6 front end instead.
Re: Ranger's 1980 CB650C Scrambler build
After thinking about it a little more, I think that, rather than cutting down the sprocket studs, I’m going to pull them and replace them with bolts. That will give me more than enough clearance. To keep the bolts from backing out, I’ll have a sprocket lock laser cut out of stainless. Something similar to what Hugh’s Handbuilt makes for the Harley bolt pattern. I’ll drill and tap the sprocket so I can mount the lock plate directly to it. I just ordered a spare sprocket carrier off eBay to play with. I’ll still trim the studs on the one I have so I can push the bike around the shop.
Re: Ranger's 1980 CB650C Scrambler build
I have much more clearance with the sprocket bolts. Now I just need to layout a lock plate and have it cut out of aluminum.
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