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  1. #1
    CB750 New Member TheFantasticMrFox's Avatar
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    '92 Nighthawk Cafe Racer build / Fuel tank compatibility questions

    I just bought a '92 CB 750 Nighthawk, intending to turn it into a café racer after deciding not to modify my grandfather's '85 BMW, and I've got a few questions:

    The main two things I'd like to do right away are swap the gas tank, as the original one is dented and repainted poorly, and I'm not a huge fan of the style anyway, and put a nicer looking seat on it, but I'm having a hard time finding out what years or models will be compatible. I'd like a sportier style, like the older 750s had, but I can't tell if they'd match up without extensive modification. As near as I can tell the tanks all attach similarly, but while I know my way around a car, I'm practically a total novice when it comes to bikes, can anyone help me?

    Thanks in advance.

  2. #2
    CB750 Guru amc49's Avatar
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    'As near as I can tell the tanks all attach similarly...'

    Hit the nail on the head there. Similar being the key word. Past that you are in no man's land and on your own. Similar has different meanings to different people as well, it being a subjective thing. There is no interchange book per se. Simply owner liking and deciding to change up whatever he has to to make it work, that can be quite extreme at times. Bear in mind that modern tank lines are made to flow with those of the side covers and seat as well, tank by itself can be somewhat stark looking when you are done.

    The only true 'compatible' you will find is exact parts fit exactly on that model only with only a very few interchanges like with series of same engined bikes like the earlier 1st gen DOHC. Even those don't crossfit to different purpose models using same engine.

    Not to say tanks can't swap but it always requires somebody willing to go the distance to determine it far closer than just a 'looks like it will fit'.

  3. #3
    CB750 New Member TheFantasticMrFox's Avatar
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    Yeah, that pretty much confirms my suspicions. Thanks for your candor though, I guess I'll be doing this the old fashioned way.

  4. #4
    CB750 Member Mcbuckets13's Avatar
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    I grabbed a k series tank from the junkyard and it was super close. Looks awesome on the bike (92' cb750 Nighthawk) lines flow very well, but it hits the top frame downtube and I have to cut it and channel it. Not wanting to practice on my good tank, I grabbed a crap tank off of a mid 90s Katana and took to cutting it up and attempting tack welds with a mig welder. Suffice to say, you pretty much have to tig them from what I understand and after messing with it quite a bit. Best advice I would say is that if you want it done and done right, figure out exactly what you want, and make it happen whether it is going to an expert to rework the tank a bit or figuring it out yourself. The payoff of the accomplishment will be well worth it. I included a pic of the tank I want sitting on the bike as well as the horrible welds I made on a donor. Any advice here from anyone would also be appreciated.


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  5. #5
    CB750 Member jschmidty's Avatar
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    That tank looks AWESOME! What did it come off?

  6. #6
    CB750 Member Mcbuckets13's Avatar
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    77’ k series I believe


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  7. #7
    CB750 Member jschmidty's Avatar
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    forgive my ignorance. Is the k series BMW?

  8. #8
    Moderator dirtdigger's Avatar
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    Ive welded and made several fuel tanks and many oil tanks. You can easily mig weld them you just need correct heat range and make sure your gaps are tight and metal is clean. You can just as easily burn threw with a tig its all in metal prep, heat and experience. Was it mig welding or was it a flux core setup? By the white residue on the metal it looks like it was flux core...not gas shielded. Also gaps way too wide and if you are burning through on the solid pieces of metal you are too hot.

  9. #9
    CB750 Member Mcbuckets13's Avatar
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    Honda CB750 K (K series).


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  10. #10
    CB750 Member jschmidty's Avatar
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    cool, thanks

  11. #11
    CB750 New Member Bezugo's Avatar
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    I've got that same tank on my 95 CB 750 (not Nighthawk)





    Took a little massaging, but mainly had to weld new mounts for the rubbers. Where it mounts at the front. Not hard at all.

  12. #12
    CB750 Guru amc49's Avatar
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    It's too high at the back where seat is supposed to match up, at least better than it does. And where are the side covers?

    If you like it it's fine but many here will not go for that. The mechano punk look of this side is not that bad and I for one could like it but if the other side has the big black wiring mess hole look of so many battery/electric sides then most will not be big on that one.

    I for one could like it but only in ALL black. That means tank and fenders too. Liking it more the more I look at it.

  13. #13
    CB750 New Member Bezugo's Avatar
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    I appreciate your input and agree

    The bike is not finished yet. The covers are yet to be made. The rear fender was something i thought about and wanted to try, but ended up removing. Even the front fender will be replaced.

    The tank could be lowered at the back if i wanted, but i wanted to raise it just a bit to follow the seat line. The gap you see on that side shot is definitely not visible in any way at eye level.

    Even the tank only has a temporary paint job until i decide if i like it that much, which i think i do.

  14. #14
    CB750 Guru amc49's Avatar
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    X2, I caught the seat line thing too, perfect, but many bikes actually set tank back down slightly to seat front down too, it seems to be a design thing in some cases, making you think you are sitting in it rather than on it. The more melding of man and machine idea. My thoughts anyway.

    The only real thing that matters is you liking it, the rest of the planet has no say there. Including me.

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