Custom frame build cb360

The back story to this new project is about a year ago I picked up an old school looking cruiser bicycle to give away as a promotion for my boxing gym. The promotion didn't really go over well, and this thing has been sitting in the place ever since. So for a year now I've been looking at it thinking how much the overall shape would make an awesome looking motorcycle frame. Hell, the tubing is plenty thick, large enough diameter, and has beautiful mandrel bends in it. Why not just cut it up and use the tubing?

Here's the plan. I've had a cb100 motor kicking around for some time now, and the only part that's up in the air is I which motor to use, my 175 or the 100. If I use the 175 I will be riding this a lot, as I will the take the wheels, front end, etc off the bike for this project. If I go with the 100 I will have to buy everything else for it. Certainly not in the finances at the moment, so will take longer to build. Also, it would be ridden a lot less if I go with the 100.

Here's my plan for the frame. Single 1.5 inch OD downtube running down and under the motor, single 1.25 inch OD backbone, will fab up proper mounts depending on motor. Rigid rear, and still unsure if I want to weld a seat to the frame or run a monoshock under it. 1 inch tube for the rear of the frame, will bend it up to house cb175 rear wheel correctly. Thinking a 2 to 4 inch stretch in the rear section over a stock cb175 frame.

Here's the list of questions I'm in need of input on.

Which motor should I use and why?
Would the 175 be too much stress for that backbone/downtube combination?
Head tube angle?
Anyone machine head tubes and can give a little input?
I can do it no problem on my lathe, just curious what material and how to cut for bearing cups. I read 2 1/4 inch OD with 3/8 wall is what I'm looking for, would like to confirm.
How much would you stretch the rear? 2, 3, or 4 inches?
Any other advice?

Frame will be getting chopped up today, will post some pics as I go!

Re: Ground up custom frame cb100 or 175, need help!

Ok really premature but im stuck in bed with the flu its all i can muster. Has not been my week. The plan is lathe a real neck, obviously change the rake. Probably around 45 degrees. Yes I know the trail will be ridiculous, no I'm not using a different tree to lower the rake, bike is going to be for show just to have a little fun.

Have to chop the frame apart yet, will be changing the space between the backbone and downtube by changing the downtube angle a bit. That combined with the rake im trying to get it as low to the ground as I can (again show bike). Will be removing the lower backbrace, the seat post, and everything behind it will be all new. The front end is of a '70 cb175 for $40 ala ebay. Will clean up just fine

Also as im writing this im thinking maybe the thread should be in specials..... oops!

Re: Ground up custom frame build, need help!

Been rather busy lately, just getting to this now. The front end has been mostly refinished, frame is completely hacked up, going to start on the neck on my lathe. Still up in the air on engine choice. I've had 2 more options present themselves, both 350's, one twin and one four. I figure once all the materials are ready to start making the frame I will try both and see what I like better, but I think the twin will be a better choice.

Re: Ground up custom frame build, need help!

Did I get that straight. You plan on putting a 350 twin motor in that bicycle frame? It won't run will it?

Re: Ground up custom frame build, need help!

teazer said:

Did I get that straight. You plan on putting a 350 twin motor in that bicycle frame? It won't run will it?

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Haha I'm actually only using the downtube and backbone. It's the correct gauge steel, and has some beautiful bends. Backbone is 1.25 OD and the downtube is 1.5 OD. This is really just for show though, it'll run and could be ridden but looking to build an extreme trailer queen. I'm gonna be playing with it in an hour or so I'll take some photos of what is actually being kept.

Re: Ground up custom frame build, need help!

Well... This should be interesting.

Re: Ground up custom frame build, need help!

yes....curious

Re: Ground up custom frame build, need help!

Well... This should be interesting and yes....curious.

Re: Ground up custom frame build, need help!

Love the interest!!!

Here is what I was left with. I will make a neck for the front end this week. Looks like I need 2 inch OD with a 3/8 wall. already have a bearing kit with races, will just turn the inside down for a snug fit. Once thats done I will start bending up more tube so I can get somewhere on this.

Re: Ground up custom frame build, need help!

Jig jig jig jig jig jig jig. Did I mention get a jig?

Re: Ground up custom frame build, need help!

Tim said:

Jig jig jig jig jig jig jig. Did I mention get a jig?

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LOL. So your saying I might need a Jig?

Already in the works. I'm not rushing anything on this project because for one its supposed to be a challenge to my skills and just a fun project, not to mention its not like I'm building it to ride. I'm hoping my wife will let me use it as art to adorn the great room

Re: Ground up custom frame build, need help!

Curiously, I am finding myself interested in this project.

Re: Ground up custom frame build, need help!

I decided to dig into the front end and square that away today. Have to remove the tumbler from the bottom triple, the bottom bearing race (which looks like a pain), get those pesky trim pieces off the lowers, and grind down the fender mounting points. Can anyone confirm they are solid attachment points and I'm not going to run into a hollow cavity?

Re: Ground up custom frame build, need help!

jag767 said:

Love the interest!!!

Here is what I was left with. I will make a neck for the front end this week. Looks like I need 2 inch OD with a 3/8 wall. already have a bearing kit with races, will just turn the inside down for a snug fit. Once thats done I will start bending up more tube so I can get somewhere on this.

Click to expand...

What kind of bearing kit did you get and how much were they?

Re: Ground up custom frame build, need help!

jag767 said:

Been rather busy lately, just getting to this now. The front end has been mostly refinished, frame is completely hacked up, going to start on the neck on my lathe. Still up in the air on engine choice. I've had 2 more options present themselves, both 350's, one twin and one four. I figure once all the materials are ready to start making the frame I will try both and see what I like better, but I think the twin will be a better choice.

Click to expand...

I am new to the forum and can't believe your attempt. Looking forward to the results. What kind of lathe do you have?

Re: Ground up custom frame build, need help!

Meanmcqueen63 said:

What kind of bearing kit did you get and how much were they?

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I picked it up a few months ago for my 175 but didn't wind up using it. Just a replacement all balls kit. Since this is the same front end I figure I'll donate it to the cause. As for the lathe it's actually a friends, would have to check next time I'm there. He's pretty Damn good on it, has been turning components for the rearsets on a 550 build which came out fantastic I'll have to take some picture to post. I definitely don't have any high level of proficiency, but with proper measuring this seems fairly straight forward that I can manage it.

Re: Ground up custom frame build, need help!

I think you would be better with the CB100 motor (or XR75, etc)
You could probably pick up one of the Chinese clone motors pretty cheap

Re: Ground up custom frame build, need help!

Well after going through what was available got a motor out of a cb360. It need to be completely rebuilt but it'll work to build a frame around!

Re: Ground up custom frame build, need help!

Wow, I think!?!?

Re: Ground up custom frame build, need help!

Those frame pieces + a cb360 motor = bad things...

I'm all for going off script but do some research on frame fabrication first. I know you say this is just for show but why not make it functional too?