CB400 / CB750 F2 Fork Upgrade

[SirFallalot]

More of post for any fellow owners than asking for help.

The CBR F3 forks can be transplanted to either of the bikes without additional mods, and possibly any more with the same diameter stanchion.

You just need the CBR internals and uppers. The CB uppers WILL NOT allow the internals to fit unless you machine out the inside, there's a narrow bit on the bottom that prevents the CBR internals from passing through, as the cartridge is wider.

Here's a pic of everything side by side.
https://i.ibb.co/nrLWGKn/20210615-142723.jpg

Also the oil in my forks was absolutely disgusting

I bought YSS springs for the CB750 at the same time I got these forks in case it didn't work, haven't opened them yet so I'll try returning them as they won't fit the CBR internals.... Then might need a stronger CBR springs. Not sure how much of a difference this will make, we'll see.

Not sure how much of a difference the CBR forks will make
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Lexmoto Valiant 125; 94 CB400; 96 CB750F2; 81 CB750 (restoring, lol not gonna happen); 2001 ZX9R(It's about to go :c); 2012 R1200R; 2015 R1200RS

[SirFallalot]

Also, anyone know where from I can get fork oil real quick? I....thought I still had some...guess not! Halfrauds the only option? Would it be...."ok" to stick the old one in for a couple days so I can order some proper oil?
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Lexmoto Valiant 125; 94 CB400; 96 CB750F2; 81 CB750 (restoring, lol not gonna happen); 2001 ZX9R(It's about to go :c); 2012 R1200R; 2015 R1200RS

[Robby]

Halfords sell it. Otherwise you could use engine oil, or ATF.

[SirFallalot]

Halfords only had the halfords oil, wherever it is from.
I forgot motorcycle shops were a thing just went to one.
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Lexmoto Valiant 125; 94 CB400; 96 CB750F2; 81 CB750 (restoring, lol not gonna happen); 2001 ZX9R(It's about to go :c); 2012 R1200R; 2015 R1200RS

[SirFallalot]

Update, excellent mod, can be done for the price of new springs (£80-120) but much better results.

Unsure if the springs on the CBR were original (supposedly they'd be too soft) as sag is fine, dive on braking is fixed but it's still comfy on bumps.

One of the rebound adjusters is stuck though and I pretty much ruined the screw even with the right size driver. Also the working one doesn't click (it works tho as I tried one of them before mounting), not sure if assembly problem or just need new fork caps. I bought the forks for £60 just to see if it was possible so not too bothered.
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Lexmoto Valiant 125; 94 CB400; 96 CB750F2; 81 CB750 (restoring, lol not gonna happen); 2001 ZX9R(It's about to go :c); 2012 R1200R; 2015 R1200RS