Author Topic: Nighthawk wheels on 75 CB750F (Read 17382 times)

Alan F. · « **Reply #50 on:** November 09, 2008, 05:21:54 PM »

Sounds like you're a busy man Bill, I could probably make up a set of spacers for you if I can prove they actually work first. Or I could send you a drawing of them. I still will have to figure out a sprocket and a tire size though, so any pointers would help me out.

DollarBill · « **Reply #51 on:** November 09, 2008, 06:52:34 PM »

Just a mandate from the wife to finish out this "bonus" room above our garage before Christmas. I've been dragging it out for two years now... Finally got the flooring in today but like my bike having a devil of a time with the electrical. Evidently I am a retard when it comes to electricity.

I did some looking around at tire sizes and this is what I have found:

Stock NH Front Tire: 110/80/18
Stock NH Rear Tire: 140/70/17

Stock CB750F Front: 100/90/19
Stock CB750F Rear: 120/90/18
*don't know if the K model shared the same sized tires as the F or not?

The NH front and rear tire will be 1.393" shorter than the CB750F
NH Front tire is .393" wider
NH Rear tire is .787" wider

Looking at my bike I have a good .75" distance to the swingarm on each side of the tire. Because the swingarm flares out as you move closer to the axle and the NH wheel/tire is shorter there should be plenty of room to use a 140 and possibly a little wider tire.

Alan F. · « **Reply #52 on:** November 10, 2008, 06:39:22 AM »

I'm skeptical about a 140 rear tire fitting, while it may physically fit inside the swingarm... will it come in contact the chain? probably. I've read plenty of threads here that say that the brake arm will be the first to touch the sidewall, this may not be a problem seeing that we're not talking about an SOHC 750 wheel or brake. I've got to buy a new tire for the nighthawk, which I'll have mounted to my spare NH rear wheel and use for proving/disproving whether a 140 rear will actually fit, before it goes on the NH in the spring. This is a 17" wheel for anyone just tuning in.

DollarBill · « **Reply #53 on:** November 10, 2008, 07:46:58 AM »

Looks like you are right. I did some searching on the forum too and it looks like 130 might be the widest we can go. I have seen some posts about offset sprockets that allow for more room. Any thoughts on that?

Alan F. · « **Reply #54 on:** November 10, 2008, 06:15:01 PM »

I'm keeping the offset front sprocket as a very last resort. I'd like to adapt the wheel using as many stock, unmodified parts as possible, so that anyone can do it.
I'm wondering about other sprocket carriers having different offsets... maybe a CBR one will fit the NH wheel? for that matter maybe my K3's carrier will fit... I'd like to find a simple solution before I modify and possibly destroy a perfectly useful part. The NH sprocket carrier has five protrusions that fit into the cush drive rubbers, maybe a little ebay shopping will show me some clues as to what might be close and which will not...

I'm not really worried about running a 140 rear tire, I'm sure a 130 or maybe even a 120 will fit the rim just fine.

754 · « **Reply #55 on:** November 10, 2008, 06:26:08 PM »

140 should fit, i got a 150 on my K3

if you run offset front sprocket you may be able to run wheel w/o mods..

Alan F. · « **Reply #56 on:** November 10, 2008, 07:21:04 PM »

Yup, CycleX's offset front sprocket is now on sale for $69

it's a 3/8" offset, that's .375" I'm working with a .320" offset right now! .055 is less than 1/16", I think I can make a shim to fill that space pretty well.

I'll still have to trim down the sprocket studs a little so they don't grind on the swingarm...

I'm beginning to think this can be done with off the shelf parts and a few simple to make spacers!

Alan F. · « **Reply #57 on:** December 04, 2008, 05:58:40 PM »

The quest for a suitable steel sprocket on a budget is now over, here's the scoop: The 91-03 750 Nighthawk sprocket carrier has 5 studs, and a 520 sprocket (which is useless for this project) so a suitable bolt-on was required. After a little research at www.jtsprockets.com (which shows a measured diagram of each sprocket they sell) I realized that honda used the same sprocket pattern on a whole bunch of bikes, and they'll all bolt right up, but I'm looking to keep the gearing close to stock, right? I chose 17/44, when Rusty Riders made me a great deal ($22 shipped!) on an NOS 44 tooth sprocket, Honda OEM Part #41200-438-000 which fits CB900F 1981-82 and VF750F 1983-84 and with a little bit of deburring with a rat-tail file, fits the Nighthawk sprocket carrier perfectly. Next I'll make up my stepped spacers and bolt it up! I've planned a stainless steel shim to cover the .055" difference between the NH sprocket carrier and the Cycle-X offset front sprocket's 3/8" offset, it'll have similar swingarm clearance to the Cycle-X offset rear sprocket. And this 17/44 combination works out to 2.588 gearing which should work just fine.

KB02 · « **Reply #58 on:** December 05, 2008, 04:59:22 AM »

Check out this thread in the Tips and tricks section:

http://forums.sohc4.net/index.php?topic=41747.0

It calculates tire size into the gearing equation, too.

Alan F. · « **Reply #59 on:** December 05, 2008, 07:00:33 AM »

Cool links, I've got a spreadsheet somewhere that calculates tire size and maybe a few other things I think, if I can find it I'll post it here.

I haven't decided on tire size yet, I'm thinking of running a 140 which seems like it'll fit, but not sure what aspect ratio I'll use, thinking of 140/80/17 or 140/90/17. The stock NH tire is a 140/70/17 that I'll be test fitting after I make up my spacers, as soon as I buy/mount it up. I'm looking for a beefy rear tire/ hotrod look back there, not the spindly look my NH has out back.

Alan F. · « **Reply #60 on:** December 06, 2008, 05:10:58 PM »

Here's the spreadsheet I was thinking of, it'll helps compare two tires of different sizes and displays all of the vital statistics for each.

coyotecowboy · « **Reply #61 on:** January 08, 2009, 11:43:42 AM »

Bumpity bump

Anyone made any progress on this?

DollarBill · « **Reply #62 on:** January 08, 2009, 11:58:44 AM »

I'm in a holding pattern....$$$

I have thrown a wrench in this deal too because I really want to put a modern front end on my bike. Possibly GSXR so that I am sure is going to require more mods and more $$$

I've got time....it's the patience I am lacking.

Alan, any progress on your end?

Alan F. · « **Reply #63 on:** January 08, 2009, 06:01:12 PM »

Hey Bill!

Yeah, a little. I've cleared up some space to work on it over the past week. So far I'm adapting the nighthawk lower triple to the K3 frame by designing a few spacers, and going with the tapered roller bearings I got years ago. The first will lower the bottom bearing's race about flush with the bottom of the steering neck, the next sits below the lower t.r. bearing at the bottom of the steering stem, spacing it upward about .8" and I'm not sure (without my notes in front of me) if I'll need a spacer above the top bearing between it and the nut above it.

The tricky part that I'm working on is that .8" lower spacer, I'm adapting the NH's steering stops to the K3's steering stops' position, so I don't have to modify the tab on my frame. I really don't want to modify anything, just adapt things to fit. Every part I'm using will fit the other bike I own, so I'd rather not hack anything up.

I've got a chain and sprocket from ebay, and I'm still planning the Cycle-X 3/8" offset front sprocket.

I'll keep this thread updated when I have new info.

coyotecowboy · « **Reply #64 on:** January 08, 2009, 06:29:03 PM »

Cool!! I'm wanting to do cast wheels of some sort, but the vintage stuff is heavy and possibly out of true, and not always capable of handling tubless tires. The nighthawk wheels look trick (doesn't someone here have some vintage five spoke wheels that look similar?) And they have the plus of utilizing modern tire sizes

Alan F. · « **Reply #65 on:** January 09, 2009, 06:21:35 AM »

Uncrash has Hayashi five spokes, got the deal we all dream of ($50 for the pair locally, with decent tires, instead of $3500+), and bolted them right on. They are awesome in the pictures and I'm hoping to see them this summer sometime.

The 17" drum brake 90's NH rear and 17" 90 CBR1000 front that I have don't seem much lighter, although I've not weighed anything to compare. I'll add that to my to-do list when I've got the NH front end bolted up, and post my results here.

DollarBill · « **Reply #66 on:** January 09, 2009, 06:43:41 AM »

I like that fortune cookie Alan! I thought seriously about some gold 70's Kawasaki mags for a while but decided to stick with the Nighthawks because of the tire size but it was hard to turn down because they were cheap.

Alan, have you seen this thread: http://forums.sohc4.net/index.php?topic=38968.0
It lists the CB750 rear axle as 20mm...or did I read it wrong. Unless my calculations are incorrect I don't think our measurements came out to 20mm did they?

coyotecowboy · « **Reply #67 on:** January 09, 2009, 10:23:37 AM »

Just for arguements sake, how does a 90's NH swingarm measure up against a 750K swingarm? I was checking them out on complete bikes and on the Honda fische. If it would fit in the 750K yoke and was as long (or a little longer) then this could be a really slick setup

Alan F. · « **Reply #68 on:** January 09, 2009, 05:58:34 PM »

That's a good question, I don't have the answers to. I stopped looking for a nighthawk swingarm a while back, I've got the axle and chain adjusters, so a bare swingarm with pivot bolt would be fine...maybe I'll have another look at CL and Ebay...

I'll break out my vernier and remeasure the axle bolts, I'll repost some uncluttered measurements later on.

I was wondering if anyone would be able to read that fortune cookie pic in my avitar....Thanks I thought it was pretty good too.

Alan F. · « **Reply #69 on:** February 01, 2009, 08:12:56 PM »

If anyone's been folowing this thread, I've been making some progress and will be posting in the project shop, here's a pic of where I ended up tonight.

DollarBill · « **Reply #70 on:** February 01, 2009, 08:40:24 PM »

Very nice progress Alan! It's going to look great! I wish I had more progress to report but alas I do not. Keep up the good work.

Alan F. · « **Reply #71 on:** February 02, 2009, 05:54:40 AM »

If you go with 90'S 750 Nighthawk stuff, I can supply drawings of my spacers, maybe even make another set for you - steering stops and all... I'm going to investigate the similarity to early CBR F1/F2 triple trees for possible cross fitment in case you choose CBR stuff.

chickenStripCharlie · « **Reply #72 on:** March 24, 2019, 05:39:57 PM »

10 year Bump .... so, do we know if the rear drum brake is a direct swap between the nighthawk and earlier CB wheels? The brake is listed as 180mm for both, but I'm not certain if it's as simple as just the diameter.

I have a 83 750 nighthawk (chain drive!) And looking to swap a 92/93 17" nighthawk wheel onto it (for better tire availability) so wondering about fitment.

Current tire is a 140/90 16 so width shouldn't be an issue, just not positive on the offset and brakes (ebay sellers dont really provide a whole lot of info)

Thanks!

Bankerdanny · « **Reply #73 on:** March 25, 2019, 09:21:31 AM »

The '83 Nighthawk is DOHC and this is the SOHC forum, so you might not get the info you are looking for here.

chickenStripCharlie · « **Reply #74 on:** March 25, 2019, 10:41:33 AM »

Quote from: Bankerdanny on March 25, 2019, 09:21:31 AM

The '83 Nighthawk is DOHC and this is the SOHC forum, so you might not get the info you are looking for here.

The question about the interchangeability of the 180mm drum brake is still valid..... because if others were able to fit the earlier CB brake into the nighthawk rim, then it would answer a part of my question as well

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Author Topic: Nighthawk wheels on 75 CB750F (Read 17382 times)