Topic: CB550K vs CB750K Gas Tank Differences Throughout the Years

[itzjoker]

I recently purchased a 75' CB550K, and was wondering which gas tanks were compatible with each other (with minor modifications).

I did some research and read that a 70-77 CB750 K tank should fit a 550K pretty nicely. Not sure about petcock sides.

How would the recessed cap (K7/K8?) 750 or 550 gas tanks would fit on a 75' CB550K? Were there a difference in the length of the tank or is the length the same and gas cap only changed?

All 550 and 750 F tanks were all too long by 1-2 inches.

I'm mainly looking to put a recessed gas cap CB550K or CB750K gas tank on my 75' CB550k.

Also, were there any difference between a K7/K8 550K tank vs 750K tank? 750K tank wider?

[Bankerdanny]

The 77-78 recessed cap K tanks are basically identical to the 75-78 recessed cap 550F tanks. The easiest way to put one of these on a 74-76 550K is to get a seat from a 77-78 K or any year 550F.

I haven't measure my 750F tank and compared it to the 550F tank I have in my parts stash, but I am pretty confident the 750F tank is longer than the 550F.

[brewsky]

Also, were there any difference between a K7/K8 550K tank vs 750K tank? 750K tank wider?

The 77-78 750K tanks are a good 2" wider than the same year 550K tanks, and more "angular" than the 550.
The 750 tanks also have a raised middle section the entire length, vs just around the flip door itself on the 550.

[itzjoker]

The 77-78 recessed cap K tanks are basically identical to the 75-78 recessed cap 550F tanks. The easiest way to put one of these on a 74-76 550K is to get a seat from a 77-78 K or any year 550F.

I haven't measure my 750F tank and compared it to the 550F tank I have in my parts stash, but I am pretty confident the 750F tank is longer than the 550F.

I'm going brat style seat. So it is safe to say that a 750F tank would be the longest and not fit. It is ~2" longer and would extend past the vertical bar on the frame.

I want a 77-78 550K or 750K gas tank because the 75' 550K tank does not look aggressive enough for me.

The 77-78 750K tanks are a good 2" wider than the same year 550K tanks, and more "angular" than the 550.
The 750 tanks also have a raised middle section the entire length, vs just around the flip door itself on the 550.

If they are the same length then both 750K & 550K tanks should work.


Here is an example of what kind of tank I would like on my 550K:

This guy is running either a 750K or later 550K tank on his 75' 550K. Not sure which.

[trigger]

Interesting ! I have a CB 750F2 tank on my K6 mongrel which is a perfect fit.
Tried to fit a CB 750 F2 tank to a CB550 F2 and the front tank mounts are not wide enough for the tank to go over the mounting rubbers. Also the 750F tank is a lot longer.

[Scott S]

The 77-78 recessed cap K tanks are basically identical to the 75-78 recessed cap 550F tanks. The easiest way to put one of these on a 74-76 550K is to get a seat from a 77-78 K or any year 550F.

I haven't measure my 750F tank and compared it to the 550F tank I have in my parts stash, but I am pretty confident the 750F tank is longer than the 550F.

I'm going brat style seat. So it is safe to say that a 750F tank would be the longest and not fit. It is ~2" longer and would extend past the vertical bar on the frame.

I want a 77-78 550K or 750K gas tank because the 75' 550K tank does not look aggressive enough for me.

The 77-78 750K tanks are a good 2" wider than the same year 550K tanks, and more "angular" than the 550.
The 750 tanks also have a raised middle section the entire length, vs just around the flip door itself on the 550.

If they are the same length then both 750K & 550K tanks should work.


Here is an example of what kind of tank I would like on my 550K:

This guy is running either a 750K or later 550K tank on his 75' 550K. Not sure which.

 The '77-78 550's had the tank with the flip up filler door.
 The tank on the bike in the video looks to be from a '78 750.

[Bankerdanny]

 The '77-78 550's had the tank with the flip up filler door.
 The tank on the bike in the video looks to be from a '78 750.

The 77-78 750K had a flip up door too. That's a '76 or early 550K or 750K tank.

[Bankerdanny]

The 77-78 recessed cap K tanks are basically identical to the 75-78 recessed cap 550F tanks. The easiest way to put one of these on a 74-76 550K is to get a seat from a 77-78 K or any year 550F.

I haven't measure my 750F tank and compared it to the 550F tank I have in my parts stash, but I am pretty confident the 750F tank is longer than the 550F.

I'm going brat style seat. So it is safe to say that a 750F tank would be the longest and not fit. It is ~2" longer and would extend past the vertical bar on the frame.

I want a 77-78 550K or 750K gas tank because the 75' 550K tank does not look aggressive enough for me.

That is not a later 550K tank because, as I said above, the later 550K tank is identical to the 550F tank.

You are overthinking this.

If you plan to use an aftermarket seat then the length of the tank shouldn't matter. Fit whatever tank you want and then adjust the seat position to fit. If you plan to use a seat hoop like the bike in the video and a pre-made seat then install the tank you want, mock up the seat, then use that to properly position the hoop.

[754]

500 or 550 with flip cap is not in the middle it's a 750 K tank.
 Petcock is on left side in 75 and 76.

[itzjoker]

That is not a later 550K tank because, as I said above, the later 550K tank is identical to the 550F tank.

You are overthinking this.

If you plan to use an aftermarket seat then the length of the tank shouldn't matter. Fit whatever tank you want and then adjust the seat position to fit. If you plan to use a seat hoop like the bike in the video and a pre-made seat then install the tank you want, mock up the seat, then use that to properly position the hoop.

Length of the tank matters to me. I guess I should say that it is not about the fitment with the seat, but more so the aesthetics. I've seen a 750F tank on a 550 and it looks out of place. Too long (extends past the post on frame), big, and bulky looking on a 550 body.

I just want to make sure the tank I'm looking for is the right look.

[Bankerdanny]

When you say post do you mean the frame rail that runs vertically behind the engine? Here is a side shot of my '75 550F (blue) and my '77 550K (brown). The back of the tank is basically even with the back of that frame tube. The early 550K tank is even with the front of the tube. It isn't a big difference.

The last picture is a 550 Brat photo I grabbed from hondabrats.com (there really is a website for everyone). This bike has a 550F or late model 550K tank on it.

[itzjoker]

Thanks for the pictures! And yes that is what I am referring to. So it seems like an early 550F tank should fit the 550K well.

Here is a 750F tank on a 550 that I found. You can see what I was talking about in my previous reply.

[Can550]

I have been doing similar research since my cb550f tank has pinholes and paint is faded. Thought of securing a blue cb550f tank but so far no luck. Got myself a cb550k (78) tank that sits perfect but need to get it painted unless I can get one clean blue tank.



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