Topic: Tank mounting cups too wide?

[dpuma8]

The original 1971 tank was rusted so the PO gave me a spare tank that was clean with the purchase.  Problem is the cleaned tank does not fit on the front rubber tank mounts.  The mounting cups are probably a half an inch wider on each side.

The tank sits on there but bangs and vibrates over bumps and higher speeds.  One of my rubber mounts broke off so I need to get new ones.  I am assuming that in some year, the mounting points on the tank got wider.  When did it gets wider?  If I know this then I can hopefully get rubber mounts that fit perfectly.

Thanks.

[luap]

if the rubber is to wide for the tank your going use trim them down. angle grinder an a cut wheel

[754]

Sometimes tanks get wider by usig air to try to pop out a dent.. if that is so you might be able to push it back but it will be tricky...

[nokrome]

Sometimes tanks get wider by usig air to try to pop out a dent.. if that is so you might be able to push it back but it will be tricky...

+1 but if you try to push it back together it might develop a crease along the top (ask me how i know)
  maybe you can shim out the rubber mounts on each side to get the tank to fit a little better

[dpuma8]

It looks like the new tank was made wider than the perfect fitting but rusted out one that came with the bike.  So there is no year where the tank mounts got wider?

[MCRider]

I had this issue with my project bike. I wanted to go from a rt side petcock to a left. I got hold of what i thought was a CB750 tank, a little later model where they moved the petcock over, from a salvage yard. it was not identified, I labeled it CB750. Years later when i went to fit it i had the same problem you have. Also the rear tab was just a skosh too far back. I had the tank altered, welded tabs on the cups to narrow them and cut some of the rear tab off.  Then time passed and when i went to use it discovered it was rusted out.

I've since scored a left side petcock tank from eBay and it fits beautifully.

My conclusion is I never really had a CB750 tank. I think it was a CB450 or such which are visually near identical. Is your ill fitting tank a left or right side petcock?

There are wider rubber bumpers I scored at the salvage yard to help mediate the problem with the ill fitting tank. Check the microfiches to see if the 450 bushes are longer than the 750 ones. i may still have them kicking around.

[MCRider]

To my knowledge the CB750 frames never changed at least in that area, and each tank should fit up to at least K6. The only change i ever knew of was they swapped the petcock from the rt side to the left side around K4.

[dpuma8]

It isn't the frame that changed.  It is the tank mounting points that are wider on the new tank.  I am starting to feel that this probably isn't a SOHC 750 tank then.  Maybe a DOHC?  The tank is the same size shape, and it is a Honda one.  The petcock is on the right side as well.

[MCRider]

It isn't the frame that changed.  It is the tank mounting points that are wider on the new tank.  I am starting to feel that this probably isn't a SOHC 750 tank then.  Maybe a DOHC?  The tank is the same size shape, and it is a Honda one.  The petcock is on the right side as well.

I know about the frame, or I assumed. I was responding to someone who asked if the frame had changed.

It is an unsolved mystery to me. CB450 is the only one that could be near that close. Remember they used the entire disc brake front end off a CB750, except for the instruments. So it was a hand me down cousin.

I was hoping yours would be a left side petcock like mine. But the 450s could have had the same issue, rt side for a while than swap over. When I get some time I'll check the fishies.  How about your rear mount tab. Does it fit comfortably or is it a force to get the rubber band on?

Doesn't help your problem though. Helps to know someone else has been there?   

[nokrome]

It isn't the frame that changed.  It is the tank mounting points that are wider on the new tank.  I am starting to feel that this probably isn't a SOHC 750 tank then.  Maybe a DOHC?  The tank is the same size shape, and it is a Honda one.  The petcock is on the right side as well.

  pic of tank?

[754]

 The 450 tank will have crossover tubes at the lower rear corners.. I have one I could try to measre the cups.. but they probably need slight mods to fit and tank is narrower.
 The 450 used lower legs, wheel and brake, same as 750.. springs and tube length are different.. not saying they Wont work though..

[MCRider]

The 450 tank will have crossover tubes at the lower rear corners.. I have one I could try to measre the cups.. but they probably need slight mods to fit and tank is narrower.
 The 450 used lower legs, wheel and brake, same as 750.. springs and tube length are different.. not saying they Wont work though..

You are correct about the crossover tube. My ill fitting CB750 tank did not have a crossover tube, so that shoots the theory that maybe it was a CB450.