Putting an early 70s CB750 tank on my '81 650

If it's broken or just needs tweaked

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CBDCL
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Joined: Sat Apr 11, 2015 2:17 pm

Putting an early 70s CB750 tank on my '81 650

Postby CBDCL » Sat Apr 11, 2015 9:13 pm

I'd like replace the tank on my '81 CB650 with an older CB750 tank, '71-'76. Should be a 73/74. I've asked and they don't know the year or style. http://pages.ebay.com/link/?nav=item.vi ... 1675491734 I'm thinking it's a K. Anyone know if it will fit? I'm comfortable with modifying holes or creating a tab. Not necessarily wanting to bang out the underside to get it down. Thanks!

hocus82
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Location: Norway

Re: Putting an early 70s CB750 tank on my '81 650

Postby hocus82 » Sun Apr 12, 2015 12:17 am

If you want me to I can try to put one of the 750 k1 tanks I have on my 79 650 and send you photos. Let me know what you need.
1979 Honda CB650Z
1971 Honda CB750 K1

CBDCL
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Joined: Sat Apr 11, 2015 2:17 pm

Re: Putting an early 70s CB750 tank on my '81 650

Postby CBDCL » Sun Apr 12, 2015 12:30 am

hocus82, that's very generous! Thank you very much!

hocus82
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Location: Norway

Re: Putting an early 70s CB750 tank on my '81 650

Postby hocus82 » Sun Apr 12, 2015 1:26 am

I don't think you are going to have any big issues fitting it, it's actually a pretty good fit and I like the fact that it's a bit shorter than stock.

Obviously you need to fab up something to hold it, and the aft of the tunnel is just a smidge too tight for the downtube, so either fab a spacer for the rear mount or widen the tunnel a little bit (we're talking a couple of mm's).

Looks kinda cool being a bit short and stubby :)

Let me know if you need anything else...

Oh, and excuse the crappy pics... lots of sunlight in the workshop, coupled with a iphone with a cracked lense :shock:
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1979 Honda CB650Z
1971 Honda CB750 K1

hocus82
Posts: 47
Joined: Thu Jun 19, 2014 12:23 am
Location: Norway

Re: Putting an early 70s CB750 tank on my '81 650

Postby hocus82 » Sun Apr 12, 2015 1:27 am

Couple of more...
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Knee indents, early 750 tank
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Last edited by hocus82 on Sun Apr 12, 2015 1:35 am, edited 1 time in total.
1979 Honda CB650Z
1971 Honda CB750 K1

cb650
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Re: Putting an early 70s CB750 tank on my '81 650

Postby cb650 » Sun Apr 12, 2015 1:30 am

It might be a closer match to the 81. The 79 tank and mounts are longer.
Did you clean the tank out?!?!?!?!

CBDCL
Posts: 14
Joined: Sat Apr 11, 2015 2:17 pm

Re: Putting an early 70s CB750 tank on my '81 650

Postby CBDCL » Sun Apr 12, 2015 10:25 am

Thank you so much for testing this! I too like that it's short and stubby. It will play well with how I'm simplifying the 3tree and my flat seat can move up a bit, not hanging over the rear wheel as much. It appears to be a success and thanks again!

You mentioned either create the spacer for the mount OR widen the aft. Can you explain why those mods are optional? Opening up the tunnel a bit might hold it well enough that the spacer to the mount may not be necessary?

You clearly have some rad projects going on in your garage and I hope to see them develop. When I get the tank, I'll be sure to post the result.

CBDCL
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Joined: Sat Apr 11, 2015 2:17 pm

Re: Putting an early 70s CB750 tank on my '81 650

Postby CBDCL » Sun Apr 12, 2015 10:31 am

"CB650", can you clarify? Thanks!

hocus82
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Location: Norway

Re: Putting an early 70s CB750 tank on my '81 650

Postby hocus82 » Sun Apr 12, 2015 11:10 am

Happy to help. The aft portion of the 750 tank is now resting on the tube, and leaves a gap (between the tank mount and the frame mount), so either you have to widen the tank to drop down to the frame, or space up the aft mount.. I would consider the latter as I like the way it's almost perfectly horizontal like that..

My 650 project is on the home straight, even though it might not look like it.. waiting for new rear shocks+mounts and to get the seat cover made.. deadline is may 1st... will post pics soon.

Keep it up, get shit done!
1979 Honda CB650Z
1971 Honda CB750 K1

cb650
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Joined: Fri Mar 03, 2006 7:20 am
Location: Denver CO USA
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Re: Putting an early 70s CB750 tank on my '81 650

Postby cb650 » Sun Apr 12, 2015 11:34 am

79 tank is longer than the 80 up. Mounts are in a diff position.
Did you clean the tank out?!?!?!?!

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Volker_P
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Re: Putting an early 70s CB750 tank on my '81 650

Postby Volker_P » Tue Apr 14, 2015 1:57 am

Here is an example of a CB750 tank on the RC05 frame:
viewtopic.php?f=4&t=2659
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

MiGhost
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Re: Putting an early 70s CB750 tank on my '81 650

Postby MiGhost » Mon May 04, 2015 11:21 am

Volker_P wrote:Here is an example of a CB750 tank on the RC05 frame:
viewtopic.php?f=4&t=2659


That would be the later 77-78 750K tank. It will require a small bit of trimming on the side covers to fit.
~ Ghost

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dbiz509
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Re: Putting an early 70s CB750 tank on my '81 650

Postby dbiz509 » Mon Oct 12, 2015 2:59 pm

Hocus82 - what year 750 tank is that?

CBDCL - have you been able to try this out yet? If so, I'd love to hear an update on how the install went and possibly see some after-photos. I'm considering doing the same thing. I love my 650 bike but I really don't like the shape of the tank and I'm looking for a compatible tank, preferably with some 70s styling.

CBDCL
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Re: Putting an early 70s CB750 tank on my '81 650

Postby CBDCL » Mon Oct 12, 2015 4:09 pm

Hocus82 and folks, I'm so sorry for not updating. It was very generous to put in findings for me. I ended up keeping my original tank. Oddly enough, the teardrop tank actually looked great with my bratstyle build, so I kept it. I haven't seen many bikes like this work with this build so had to run with this unique look. She's attached.

The 750 behind my 650 pictured (of the same year) had a tank swap. As Hocus82 mentions, it seems to fit the 650. If they tank mounts don't line up, you should be fine to do what I did with the 750 and Dremel cut the tank mount into a tab that's bendable, then zig-zag it to recess enough to line up. The mounts are workable, where's the underside of the tank would be very difficult to retrofit. Also, if there's a little wobble-room around the frame, wrap it in industrial strength velcro.

Andrew
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