1979 CB650; well, mostly

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Chief78
Posts: 6
Joined: Sat Jul 20, 2019 1:30 pm

1979 CB650; well, mostly

Postby Chief78 » Wed Jul 31, 2019 8:08 pm

Hi everybody. I am new to the forum but definitely not new to motorcycles. I bought this 1979 CB650 two and a half years ago and have been working on it little by little ever since. Front suspension has been borrowed from a mid 90s ZX7 and the rear suspension is a mix of CBR F3 and 636 Ninja so I could run a 180 tire. I did most of the work myself to save money, but I am no expert. More than anything, I am happy that it is stable at high speed and not a death trap.
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Volker_P
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Joined: Mon Mar 06, 2006 1:53 am
Location: southern Germany

Re: 1979 CB650; well, mostly

Postby Volker_P » Thu Aug 01, 2019 5:06 am

Welcome here! :D
You did a very interesting project there! This really does not look like a 1970/80's bike any more. Swingarm maybe a bit long, but everything else looks like it could be a Honda design, too. Often it is tough work to make things look fitting unspectacular together so I'd say this is really fine work.
Does it ride like a more modern bike, too? Fork, wheels and swing arm look promising with regard to rideability but there is of course still the weak frame. Did you already try what happens when you really make use of the front brakes capabiiities? :roll:
Cosky's great (free) online manual: http://cosky0.tripod.com

forum links to common technical issues

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GeorgeSweety
Posts: 418
Joined: Tue Aug 08, 2017 11:47 am
Location: UK.

Re: 1979 CB650; well, mostly

Postby GeorgeSweety » Thu Aug 01, 2019 5:08 am

Hello Chief and welcome. Very nice looking bike, I have one of those in my garage awaiting a refurb so I'm looking for idea's at the moment.

Chief78
Posts: 6
Joined: Sat Jul 20, 2019 1:30 pm

Re: 1979 CB650; well, mostly

Postby Chief78 » Thu Aug 01, 2019 5:21 pm

Thank you very much, guys. The CBR swingarm is a few inches longer, but I believe it is a bit stronger. My main goal was to fit 17 inch rims so I could get sportbike quality tires for cornering and extreme riding performance. The tires are Michelin Pilot Power 2ct and Pilot Road 4 on the rear I believe. It handles so well on the tires and suspension that I almost want to attempt knee dragging in corners. I have been thinking that when I tear it down to powder coat the frame, I will have all of the plug welds on the frame completely welded. The removable frame leg will stay removable though which will be a very big weak point. It was easier than I thought it would be to fit that swing arm in the frame. The changes I made have drastically change the image of the bike, but I personally feel being able to use sport bike tires is worth losing the look and originality of the Comstars. If I decide to change the wheels to something more original I could always go with Supermoto rims which are spiked as well as 17 in to fit sport bike tire still.

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Volker_P
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Joined: Mon Mar 06, 2006 1:53 am
Location: southern Germany

Re: 1979 CB650; well, mostly

Postby Volker_P » Tue Aug 06, 2019 1:09 am

Chief78 wrote:..., I will have all of the plug welds on the frame completely welded. The removable frame leg will stay removable though which will be a very big weak point.

When I say weak frame I think of tube diameters and connection geometry. Tubes and welds usually do not crack so steel and welding work seem fine. Instead tubes just bend! Probably this flexibility allows this kind of frame for a bike of that weight at all. Make it stiffer and you run into trouble. Provided you have all the bolts in place and torqued properly, the engine supports the frame around the removable leg. No worry there and no need to loose this advantage.
So I think welding at this kind of frame without real need could make things worse but not better. :wink:
Cosky's great (free) online manual: http://cosky0.tripod.com

forum links to common technical issues

Chief78
Posts: 6
Joined: Sat Jul 20, 2019 1:30 pm

Re: 1979 CB650; well, mostly

Postby Chief78 » Thu Aug 08, 2019 6:28 pm

Volker,

When you mention tube diameter and frame design versus the weight of the bike it brings to my mind the average Harley frame. Those bikes weigh over 800 lb and somehow are supported by frames that are similar to the CB650. Maybe they have thicker tubing. I wonder if there is anybody in here that has welded there frame the way I intend to weld mine? I may start at topic searching out folks that have fully welded their frame with the exception of the removable lower leg. I find it very curious that it could be beneficial to have a frame that bends and twists but I'm no engineer.

Efferdy
Posts: 19
Joined: Tue May 29, 2018 1:35 am

Re: 1979 CB650; well, mostly

Postby Efferdy » Fri Aug 09, 2019 12:30 am

Howdy! That looks like a neat one! Welcome and enjoy your project


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