1981 CB650C Tire and Levers Questions

If it's broken or just needs tweaked

Moderators: Volker_P, tidd650

Bzar
Posts: 3
Joined: Thu Aug 04, 2016 2:24 pm

1981 CB650C Tire and Levers Questions

Postby Bzar » Fri Aug 05, 2016 12:12 pm

I got a 1981 CB650C at the start of the season here (Winnipeg, CAN), and it runs well enough for now. So I'm working on some of the minor esthetic stuff now; then I'll be pulling the engine and tuning it up during the off season. I do have a couple questions for the experts here though.

1) I'm looking to replace the brake master cylinder and clutch levers. I don't like the stock, but finding it hard to get something different. Is it ok just to get something with a 14mm piston that can fit my (new) 7/8" bars? The bike has dual discs on the front.
I'm looking at these suckers... http://www.aliexpress.com/item/CNC-7-8- ... .46.JgRr3O

2) My 81 CB650C came with two different tires. The back is a tubeless Dunlop (looks to be original as the bike only had 17k on it). The front however is brand new so I'm assuming it was replaced for a safety at some point. Problem is it's a tube tire. The bike has comstar rims, and the only manual I could find online said the tires are supposed to be tubeless. Is that for both? is it ok to run a tube tire on the front there for now?

Thanks,
Rick.

User avatar
Volker_P
Posts: 5508
Joined: Mon Mar 06, 2006 1:53 am
Location: southern Germany

Re: 1981 CB650C Tire and Levers Questions

Postby Volker_P » Fri Aug 12, 2016 4:25 am

Welcome here, Rick! :D

1. right, basically you need something with the same piston diameter. However the moved brake fluid volume might still differ depending on how many how large pistons are there in how many calipers so no general answer.

2. Tyres older than say about 7 years start to get hart and slippery. When it comes up to cold and wet roads you are lost.
So I certainly won't like to try a motorcycle tyre of 1981 in Canada.
Usually front and rear are tubeless. This means you need a valve in the rim which is probably cut out in your case. Check out if the rim is drilled or manipulated from inside (!) there to make the tube fit.
Basically there is nothing wrong about tube type tyres on comstars if they are mounted properly. "For now" I would think the tube is not the problem but probably the age of the tyre, too.
Not sure how much it is a problem to run a tube inside an intended tubeless tyre.
Cosky's great (free) online manual: http://cosky0.tripod.com

forum links to common technical issues

If you really like this site and you would not like to see it vanish soon, have a look there: Urgent: Future of HondaCB650.com Forum

Bzar
Posts: 3
Joined: Thu Aug 04, 2016 2:24 pm

Re: 1981 CB650C Tire and Levers Questions

Postby Bzar » Tue Aug 16, 2016 8:21 am

Hey, thanks for the welcome Volker_P :)

Good points I wasn't thinking of. I'll have to double check the volume of the master cylinder before buying too.

Just another quick question on the tyre. If the rim was drilled to make the tube valve fit, does that mean I can't go back to a tubeless? You make a good point on the age of the tyres being a safety concern, so I just want to replace them both to be safe, and that's another reason I want to know if the possible drilling would force me to use a tube tyre again? :?

Absolutely loving working on this old bike. It was in some rough shape, but it's looking and riding good now.......well except a few small things. My front brakes started sticking last night. Almost certain the pistons are dirty. I was hoping to put off cleaning them off until I got the new levers so I wouldn't have to bleed the brakes twice, but it's just not safe with those brakes sticking the way they are.

This guy has a great instructional video on how to clean them if anyone is interested.
https://www.youtube.com/watch?v=qK_BR3UP-u0

Thanks again.

User avatar
Volker_P
Posts: 5508
Joined: Mon Mar 06, 2006 1:53 am
Location: southern Germany

Re: 1981 CB650C Tire and Levers Questions

Postby Volker_P » Wed Aug 17, 2016 1:24 am

Bzar wrote:Just another quick question on the tyre. If the rim was drilled to make the tube valve fit, does that mean I can't go back to a tubeless?

I first would carefully check that rim for cracks just in case there is a "reason" for using a tube. A cracked comstar rim is scrap btw.
If it should be all right, the problem might be that the drilled hole is too large for a valve insert now. The original one certainly won't fit but your tyre shop might have an insert for car rims that will still fit. No further problems to go for tubeless tyres then.

Bzar wrote:My front brakes started sticking last night. Almost certain the pistons are dirty. I was hoping to put off cleaning them off until I got the new levers so I wouldn't have to bleed the brakes twice, but it's just not safe with those brakes sticking the way they are.


I'd suppose that the reason for your sticky brakes rather is a problem with the master cylinder as described here. There are two holes and only one looks drilled through. But there is a second small hole in the center of the only half drilled looking bigger hole.
But in any case it is a good idea to open the calipers to get out all that gunk from decades so do that, too! I also recommend to swap from the 40 year old rubber stuff to stainless steel brake lines. Did it and it was worth it.
And don't forget to clean and lubricate the caliper glider bolts.

Have fun! :wink:
Cosky's great (free) online manual: http://cosky0.tripod.com

forum links to common technical issues

If you really like this site and you would not like to see it vanish soon, have a look there: Urgent: Future of HondaCB650.com Forum

Bzar
Posts: 3
Joined: Thu Aug 04, 2016 2:24 pm

Re: 1981 CB650C Tire and Levers Questions

Postby Bzar » Mon Aug 29, 2016 8:51 am

Well I cleaned out the calipers and so far things are working better. Another issue is I changed my handle bars and the original master cylinder has an odd tilt designed for the original bars. Well that doesn't work with my new bars so I need to get a new one.

I contacted the seller at a few aliexpress sales. Here's some that might work...
13.8mm Piston - http://www.aliexpress.com/item/Motorcyc ... 59973.html
14.5mm Piston - http://www.aliexpress.com/item/Front-Br ... 60753.html

Also the new ones are lower so replacing the brake lines will help clean up the slack. Any suggestions where to get good brake lines?

I will get new rubber for next season, great tip. I didn't see any cracks in the rims, so that's one good thing.

I'm also going to take the whole engine out and replace all the gaskets. I've seen a few gasket kits and it seems the bike has a some small leaks that need attending....so mind as well do them all :D


Return to “Technical Discussion”

Who is online

Users browsing this forum: Google [Bot] and 41 guests