NEED ADVICE ON FULL FRONT END SWAP FOR CB750K7 SOHC '78

[Butterworth7v]

Im having trouble finding forum topics on front end swaps for sohc bikes, dont know if the number of camshafts makes a difference to the triple trees/yokes etc. but i would love to snap on some much newer forks and brakes for my k7.
im no fabricator or welder so im pretty much hoping for a straight swap/bolt-on! does anyone know of any straight swaps? i was thinking maybe cbr600 or a cb900f? please help!

[Lucky 1]

It has been done many times.
Just Google it.

Type in: :   "CBR front end on a CB750"

[shinyribs]

Hmm...let's see if this helps.

I know a front end off a DOHC CB750 will bolt right on to a SOHC if you use DOHC bearings.

That said,I have a DOHC with  '91 CBR1000F forks on it,so I don't see any problem in doing the same swap on a SOHC.

My setup:

-'91 CBR1000F forks (41mm)
-'92 CBR600F2 trees (upper and lower yokes)
-Standard DOHC CB steering bearings

Now,what rims do you plan to run? A modern front end with a 17'' rim will usually put one of these bikes in the dirt. I mean low! Seriously ground clearance issues with some setups.

i.e.





But the CBR front end on my '80 F is waaay longer than the stock legs. See how they stick up past the top clamp?



With the legs that far up you could easily use clip ons above the top clamp for upright seating. Of course,you can always put them under if you prefer. But either way you will have extra tube sticking out of the top clamp. My '80 has about 1.5'' of tube sticking out above the top clamp and that bikes' suspension is raised roughly 1.5'' above stock,so you could be looking at close to 3'' of tube above the top clamp if you go that route. But,that will cure the ground clearance issue usually associated with running a modern front end like such as USD's.

Notice the triangular aluminum blocks at the upper shock mount. That's where the bike was raised.


'01 GSXR 750 USD's on a SOHC. I lost about 1-1.5'' of ride height on this setup. And reusing the stock 19'' rim on this setup causes some pretty serious front tire-to-header clearance.



Something else to consider: If you decide to run a 17'' on the front you will want to consider running a matching rim out back. For one,you probably want them to match anyways. But also, 17'' tires are profiled for cornering. Meaning they are kinda pointed looking if you look at the shape of the tread area. Most 18'' and 19'' tires (stock on your bike) have a really rounded tread shape. Mixing a sport profiled tire (17'') with standard profiled (18''-19'') will most likely cause some funky,unpredictable handling.

Hope this helps!

[bparkzd00d]

Hey there. Also very new to the game. Got my '78 750F yesterday for free. Hasnt ran since 1987 (longer than ive been alive) and started right up with a carb clean and new oil. Front brakes are destroyed and ive toyed with the idea of the swap as well. If I read your post correct, and my train of logic is accurate, I could bolt F2 triples to my '78 SOHC with no mods as long as I use DOHC bearings?

If this is true, you just saved me a lot of time trying to find someone that can press a stem for me haha.

[shinyribs]

No,you still have to swap the stem,but the stem and trees don't need to be modified.

The CB stem using the same diameters in all areas,so the bearings work out just fine. And the top clamp will fit snug on the top of the stem like it's supposed to.

The very bottom of the stem is the same diameter on a F2 or F3 stem and as is on a DOHC 79-83,so it will press directly in to place with no mods needed to the stem. I'm not 100% sure if the stem where it presses in to the lower clamp is the same size on the SOHC aa is on the DOHC.

Long story short. 79-83 CB stem will press directly in to a F2 or F3 lower. Not sure a SOHC will,though. But both the SOHC & DOHC stems are much longer than the F2 or F3,so it will definitely need to be swapped.


Where are you located? I've been doing a lot of stem swaps for guys lately. I can help you out if you can't find help local.

[bparkzd00d]

Cool deal. I appreciate the clarification.  Im out in Long Island, NY. Been toying with front end swaps. Research tells me with the aid of all balls custom bearings, I should be able to throw an early 2000s gsxr triple in my bike with no mods. Aparently the 03-04 is long enough. Ill find out as im ordering a triple tonight to toy with since I could stem swap worst case scenario. I know the gsxr also has 26mm ID bearings so im under the impression a repress should be fine. Where abouts are you?

[DavsDeathtrap]

Hey,

Great information here!

I have a 73 CB750 and am looking into a fork swap to a GSXr 750 or 1000 (which I read is a bit longer). Where do I start as far as gathering the right parts. I would like to stay with a spoke rim as well. I'm in Cali and would appreciate any advice/direction for a smoother process if possible.

Thanks,

Dav

[Re-run]

OK, well I have not seen anyone use a gsx front, not to say it hasn't happened, I've just never seen it.

Your 3 main areas are going to be bearings/spacers, neck, axle, and wheel.

You'll need the tree from the gsx and forks, of course. From there, they will "probably" fit the neck of the cb, you will need to find the right size of bearing. Easy way to do this is just get the O.D. size of the CB750 bearing, and the I.D. size of the gsx bearing. Then see of anyone makes a bearing that size. It is probably likely since the japanese manufacturers use a lot of similar sizes, except yamaha, they like to screw people up with their reverse threads and crap.

You will also need the axle for the gsx as it likely threads into the axle holder, the old cb750s do not. SO, you will need the same as above, the O.D. of the cb750 wheel bearing, and the I.D. of the gsx wheel bearing.

This next part may be tricky, you need spacers to align the front wheel with the calipers. Remember, the outer part of the bearing turns, so the spacer should not touch that part, only the inner race. This is further compounded by having to get get the spacing on the rotor right, especially if you decide to go with dual calipers.

It will be a fair amount of trial and error. Us washers to initially figure out the width of spacing you will need, so you don't buy a shit-ton of spacers.

I would also frequent bike salvage yards for parts. Best I can give you, maybe someone else will have seen it and know more.

[Butterworth7v]

Hi Deathtrap

If you're willing to only jump up a few millimetres I can help you keep it vintage with a bolt-on triple and forks from a goldwing? (dual disc, 37mm, shiiiiiiiny).

If not then bugger awf ;D

[DavsDeathtrap]

Hello,
I have a 73 cb750 and am preparing to do a fork swap to an USD fork. Trying to figure out which fork (CBR600 or GSXR 750) will give my bike an even stance with an slightly oversized front tire and 18" spoke rim. Any help or tips would greatly be appreciated.
Thanks-

[DavsDeathtrap]

Hey Butter,

Appreciate the info and offer but I am leaning more towards the café racer look with the UDS front susp.
Any information in this regards would be appreciated!

Thanks again,

[DavsDeathtrap]

Hey Re-Run,

Appreciate this helpful information! I just found a company out in VA. that actually makes a billet spoke hub that uses the GSXR axle and is setup for the dual discs. Now this trip tree and bearings situation still seems pretty trickyl as I am hoping to run a larger size tire on an 18" rim out front.

All the best-