1983 Honda 750 Nighthawk

chickenStripCharlie

Been Around the Block
The DOHC 750s have their fair share of challenges to build up. I would say the Nighthawk more so. But, I attempted to make it look half-decent and i think I did, so time to document it in one place.
Truth be told, i wasn't sure if i'd ever get this bike done so i never created a build thread, but have posted all over other threads that it's time to consolidate. (With Tim's help).

Going to put a few threads together into one, and i'm going to fill in A LOT of gaps with additional pictures


The start - As it looked on craigslist.
Kept indoors. Maintained well, then neglected for a long time. It was cranking over but not a runner.

1617814025817.png


I got it running just enough to know it had potential, and started taking it apart the same day. I liked things about it. And i hated A LOT of things about it.
Always loved the inline 4, ever since i was a kid, but couldn't stand anything else on it.
Hated the 4-4 exhaust, the 16" rear wheel, the forks, the weird shape tank, the auger handlebars ...

The carbs were a mess and a reason for the no-run condition. Sat for a long time. Gummed up, but otherwise fine.

1617814063254.png


cleaned them and spiffed them up a little with a polish and new stainless steel hardware and new gaskets.

1617814084964.png


Did i mention i was new at this? .... i did not know the forks had any air in them. I was wrong.

1617814109772.png


Starting at the back - I threw on a 17" wheel from a 1992 nighthawk. I wanted the 17/19 setup for better tire availability and i liked the look of this wheel.
I also wanted drum in the rear and dual disc in the front. Centered the rim. got new spacers machined and bearings to fit the older 20mm axle and it worked well.
The chains are not the same, but the original 1983 sprocket bolted on perfectly.

1617814137264.png


Threw on a new chain and shinko tire

1617814157208.png



when you tell them slip-fit for the spacers, but they make them press-fit

1617814182988.png



At this point i decided to just go ahead and do the front-end swap and accept the fact that bike will be out of comission for a while.

BELOW (pages 1- 12) ARE THE FRONT-END SWAP AND SEAT PAN BUILDS COPIED OVER BY TIM FROM OTHER THREADS




My DOHC 750 has a less than ideal frame shape for a seat pan. I've got the first bend done and happy with it. How do I make the second, without ruining the first in the process?

I'm using 18 gauge steel.

I know I can just use lots of clamps to get it to sit the way I want, but I also know the moment I take those clamps off the pan will spring back.

Ideas?

Below is an example of the shape I want. However the thread where I found that pic is long dead.

I spent some time beating a stock pan to fit and wasnt happy with the results yet.
 

Attachments

  • 20200401_213021.jpg
    20200401_213021.jpg
    1.6 MB · Views: 151
  • c53b0ffa5c82fb88b1f6418b0d30647e.jpg
    c53b0ffa5c82fb88b1f6418b0d30647e.jpg
    520.7 KB · Views: 155
Last edited:

chickenStripCharlie

Been Around the Block
I wonder if bending a 1/8" flat bar that is about 10" long and 1/2" wide would be easier, then tack welding the pan to it ... 9r if that would be too weak and straightened out somewhat by the pan as well ‍♂️
 

Tim

Administrator
Staff member
I'm no metal shaping genius, but my brain tells me to cut a piece of 3/4" plywood or take a chunk of a 2 x 8 or 2 x 10 on top of the flat section, and clamp that to the frame. This will hold the flat section in place, with an emphasis on getting nice support along the current crease to prevent it from warping there.

Then bend away.

The 2nd pic of the target shape looks like a very thin sheet of what almost appears to be galvanized sheet metal which would have made it easier to shape and retain the shape, but wouldn't be a very solid seat pan.
 

SONICJK

Reminds me of...me No, I'm sure of it. I hate him
Basically you'll need to clamp down the bend you have done, and then overbend the next one so that when it springs back the profile is right.

Find a pvc pipe or similar that's close the the radius that you need and use that as a bending form. You'll never get it to bend correctly on the frame because as you mentioned it's just going to spring back every time and you don't have any way to overbend it while on the frame.

I would clamp what you've got to 4" pvc pipe (or whatever is close the the frame radius) and wrap it around the pipe slowly removing it incrementally to check the bend until you have a good fit.
 

chickenStripCharlie

Been Around the Block
I found this in a CX500 build thread, and i think it's about the only option for the rims I have. Comstars, with through holes on the hub. Original used two rotors and 110mm bolts, but the bolts had nuts from the other side.

This design would have the bolts threading directly into the aluminum, plus the bolts would be longer by whatever the adaptor thickness is.

Would this still be a viable solution for me? Any reason this would be less safe to run?



 

doc_rot

Oh the usual... I bowl, I drive around...
DTT SUPPORTER
DTT BOTM WINNER
I don't see any problem with that. those bolts are mostly subjected to shear forces so they don't need to be torqued very much. Seems like that assembly is adding unnecessary weight though. Are these a product you can purchase? Or would you have to make /source your own. I bet you could come up with a lighter solution, perhaps adding a threaded insert into the existing holes so you dont have to through bolt.
 

teazer

Over 1,000 Posts
DTT BOTM WINNER
I agree with Doc-rot. check your existing rotors for pitch center for the holes and diameter of the center and see if EBC lists a disk rotor with the same/less/more dish but the same center.

You can often find a similar rotor for a different bike that will work with your set up of forks, hub and calipers. Modern hubs are usually wider than our old bikes that came with skinny forks, so think about what you are trying to fit together and see if there's something available that might work.
 

chickenStripCharlie

Been Around the Block
I've come across A LOT of threads and never see a anyone mention anything but:
1. Adaptors/spacers for rotors
2. Running the stock sport bike 17" front wheel
3. Custom rotors.

I have to get calipers before I figure my exact measurements, but I doubt I'd find a rotor that matches not only offset but diameter and bolt pattern.

A member on here did go with custom rotors, which is the nicest solution, but they are a little out of my budget for now.
 

teazer

Over 1,000 Posts
DTT BOTM WINNER
Probably right, but it's worth checking to see what's out there before embarking on a more expensive path.

Which rotors are you using - stock or something sexy and newer and lighter?
 

chickenStripCharlie

Been Around the Block
Probably right, but it's worth checking to see what's out there before embarking on a more expensive path.

Which rotors are you using - stock or something sexy and newer and lighter?

yes, that's why i'm still in the "design" phase.
The forks are '99 GSXR750. The rotors too.

The rotors were an eBay fail. They are at minimum thickness, and someone had attempted to turn semi-floating into full floating rotors but i guess it proved too much work so they just got 3 of the 5 bobbins done on one of the rotors. The things dumba$$ kids do, because some guy on the internet posted this "cool new mod" is ridiculous.

So it likely won't take much for me to ditch these rotors. If it drags out long enough, maybe i'll just convince myself to get new custom ones. Would probably be around $600-650 CAD for me i think. But, they'd be new *shrug*

Getting the GSXR front wheel is the easiest solution and seems the one most guys go after, but i just don't like the look of the small 17" front wheel. I like the 17 rear 19 front look. (Yes, that has its own challenges (like header clearance) but hoping we'll be fine. Others have done the same)
 
Last edited:

teazer

Over 1,000 Posts
DTT BOTM WINNER
I think SRAD fork are 214mm between centers and they use 5 hole 320mm disks with 4 pot calipers. Hubs are 130mm across (side to side) and disk rotors are pretty flat (zero offset) so they would have to be spaced out a long way from the hub to avoid calipers and spokes intersecting if you use a narrow hub and spoke up a new rim. On Comstars I have no idea how much clearance you will need. Time to start taking a lot of measurements.

750 SRAD disks were 5mm stock and 600 were thinner at 4.5, so your rotors might work as long as you get a set bobbins to make them fully floating. The centers will wear much faster with floaters, but I don't expect that you will be doing lots of fast miles on the bike.

The other alternative is to get a wide CognitoMoto front hub which I thing is designed for a spoked wheel with GSXR forks and brakes.

Or, as you said, use the GSXR forks and brakes with that Comstar front wheel and get custom rotors made or buy that conversion kit - if it fits.

That's why most guys go full matching GSXR front end, wheel and all. The bits work well together and it's cheaper in the long run.
 
Last edited:

chickenStripCharlie

Been Around the Block
The comstar is 80mm, so 50/2=25mm or 1 inch per side. That is not bad, considering its 6061 aluminum for the adapters.

For this reason I went with older GSXR forks instead, because they are not radial mount calipers. Therefore if necessary, I can space the calipers in/out a little bit to get everything to line up right, so it's definitely a bit more flexible.

I need to get calipers before I can really get serious about measurements, but I'm having a hard time deciding which calipers to go with. I'm still trying to find dimensions on the gsxr calipers so I can see how far they stick out on the inside to see how much room there would be (if any) against the comstar spokes.

Also, I have two sets of tubes. 1999 750 and 2001 1000, the mounts are different but I dont know if the calipers are. Part of me thinks maybe just adapting original 1983 honda calipers on here wouldnt be a bad idea because they are the sliding type (with pistons on one side only) so I know they would clear for sure.

Here is the bike as it sits with the front fork and 19" wheel. I'm using the stock 25mm gsxr axle with 42x25x9mm bearings and custom machined spacers

Below is the comparison between the 1999 and 2001 forks. You can see the difference in mounting brackets between the two. The '99 is on the left.

Interestingly, the 2001 forks are slightly shorter. Not by much, but I need all the height I can get so it will likely be the '99 tubes.


20200329_214015.jpg
20200307_142152.jpg



Here is how the forks ended up going on: I had a local shop machine a new stem that was 15mm longer than original GSXR so it would fit in the neck. Worked out quite well and less expensive than getting the cognito moto stem when you factor in the shipping costs and exchange for CAD/USD

88921228_891575767961687_5705528872092119943_n_17907912472419096.jpg


83857913_1349494045253803_6222987393087566211_n_18081412705197441.jpg


87660762_1526557474172880_8392916449597737208_n_17908829431413629.jpg


The temp bars got replaced with real Renthals i found used for $20


87329131_851886345332476_8890224559041346799_n_17851756942884087.jpg


I used 3/8" Al plate to strengthen the top clamp. JB Weld is just to hold it in place really, nothing else. Milled the bottoms flat just to make sure everything was nice and square

82568109_774391132968056_7204047776834164960_n_18097243312193611.jpg
 
Last edited:

ex119x

Been Around the Block
The Honda brackets for the sliding calipers probably use different spacing than the suzuki forks. Look at the calipers from an SV650. They are also dual piston sliding type caliper and I think the mounting spacing is compatible some of the GSXR forks. They are available pretty cheep on ebay.
 

chickenStripCharlie

Been Around the Block
The Honda brackets for the sliding calipers probably use different spacing than the suzuki forks. Look at the calipers from an SV650. They are also dual piston sliding type caliper and I think the mounting spacing is compatible some of the GSXR forks. They are available pretty cheep on ebay.

Yes, I'd have to make an adapter to fit the calipers onto the forks. More work but maybe not a bad thing because it could help make the hub spacers that much thinner and lighter. I have lots of 1/4" and 3/8" aluminum plate around here.

I will certainly look into SV650 calipers. Very well possible they might fit. That would be ideal. Might have to join a SV650 group for this. Thanks!
 

teazer

Over 1,000 Posts
DTT BOTM WINNER
SV calipers are similar mounting bolt spacing as the 2001 forks/caliper, but not the same. I would just use the 1999 calipers with the matching forks.

In my stash I found two pairs that appear to fit 1999 but very different thickness overall and different piston diameters and I have no idea what the second pair came from.
 

teazer

Over 1,000 Posts
DTT BOTM WINNER
So here's what I found.

Bottom right: 1991 GSXR Nissin caliper, 91mm bolt spacing, 34/30 pistons x 2
Top right: 99 GSXR ??? Tokico, 91mm bolt spacing, 30/27mm pistons x2
Top left corner: 2001 GSXR 62mm bolt spacing, 30/27mm pistons x2
Bottom Left: SV650 sliding caliper, 55 mm bolt space, 30/30 x1 pistons

Interesting that the Top right will fit a set of 99 forks but has the same piston pairs and the later 2001 caliper.

I cannot tell you what master cylinder bore went with those, but I found a couple of charts on line that suggests that all TL1000 had 320mm disks and 91mm bolt spacing. TL1000S were 4 pistons and TL1000R were 6 piston. I was led to believe that the Nissin small piston 91mm space calipers were from a TL1000. Forks supposedly also but the lower triple said 99 GSXR. SRAD and TL1000 were 214mm fork centers.

SRAD (99) GSXR also had 320mm rotors and 91mm bolt space.

2001 (k1) came with 320mm rotors, 4 piston calipers and 207mm fork centers.

I can confirm that my 99 SRAD or TL1000 forks are 214 and my K1 (2001) are 207mm fork centers.

You can create your own spreadsheet to calculate the force at the bars with different piston diameters and caliper bores. Your bike should be lighter than an SRAD so the same force at the lever may well genearet excessive braking force. Kevin Cameron included his calcul;ations which are more sophisticated than the Michael (Mercury) Morse table on Vintage Brakes web site. It allows for teh effect of disck roto diameter and bike and rider mass.
 

Attachments

  • DSCN5118[1].JPG
    DSCN5118[1].JPG
    3.2 MB · Views: 94
  • Fork-Conversion-Details.jpg
    Fork-Conversion-Details.jpg
    498.8 KB · Views: 119

chickenStripCharlie

Been Around the Block
So, for anyone else that comes across this in a search at some point, this is how I'm doing it.

I welded a support through the tube so I can clamp it, then welded a flatbar on top through which to feed the sheet metal.

It's working ok. I bend down and tap tap tap with a rubber mallet.
20200412_102748.jpg
20200412_103738.jpg
 

Attachments

  • 20200412_131657.jpg
    20200412_131657.jpg
    1.7 MB · Views: 125

chickenStripCharlie

Been Around the Block
So here's what I found.

Bottom right: 1991 GSXR Nissin caliper, 91mm bolt spacing, 34/30 pistons x 2
Top right: 99 GSXR ??? Tokico, 91mm bolt spacing, 30/27mm pistons x2
Top left corner: 2001 GSXR 62mm bolt spacing, 30/27mm pistons x2
Bottom Left: SV650 sliding caliper, 55 mm bolt space, 30/30 x1 pistons

Interesting that the Top right will fit a set of 99 forks but has the same piston pairs and the later 2001 caliper.

I cannot tell you what master cylinder bore went with those, but I found a couple of charts on line that suggests that all TL1000 had 320mm disks and 91mm bolt spacing. TL1000S were 4 pistons and TL1000R were 6 piston. I was led to believe that the Nissin small piston 91mm space calipers were from a TL1000. Forks supposedly also but the lower triple said 99 GSXR. SRAD and TL1000 were 214mm fork centers.

SRAD (99) GSXR also had 320mm rotors and 91mm bolt space.

2001 (k1) came with 320mm rotors, 4 piston calipers and 207mm fork centers.

I can confirm that my 99 SRAD or TL1000 forks are 214 and my K1 (2001) are 207mm fork centers.

You can create your own spreadsheet to calculate the force at the bars with different piston diameters and caliper bores. Your bike should be lighter than an SRAD so the same force at the lever may well genearet excessive braking force. Kevin Cameron included his calcul;ations which are more sophisticated than the Michael (Mercury) Morse table on Vintage Brakes web site. It allows for teh effect of disck roto diameter and bike and rider mass.

Hey, great post!

Can you do me a favor and measure the width, especially from the pad toward the rim .... to know how much they would stick "in", for top left and top right.

While I agree those 62/91mm measurements will work with the 01/99 forks, I could have sworn the 99 SRAD came with 6 piston calipers, not 4?!

Honestly, I'd prefer the 4. Less to rebuild and aparently the 6 were never that good anyways.

If the width works, I'd rather just go with stock bolt on ones instead of making adapters for the calipers.

The rotors I have are 5 bolt, 320mm and I think 54mm bore hole, as shown on the chart for 99 SRAD.

THANKS FOR THE HELP!!!!
 

teazer

Over 1,000 Posts
DTT BOTM WINNER
From the center line of the caliper - which is the center of the disk, all three double sided are 41-42mm to the inner side where they are closest to the spokes. TL100R I think was the one with 6 pot calipers, but no need for that complexity and the longer 6 piston caliper is more likely to flex than shorter 4 pot calipers.
 

chickenStripCharlie

Been Around the Block
From the center line of the caliper - which is the center of the disk, all three double sided are 41-42mm to the inner side where they are closest to the spokes. TL100R I think was the one with 6 pot calipers, but no need for that complexity and the longer 6 piston caliper is more likely to flex than shorter 4 pot calipers.

Ok, that seems less than I expected, which is good.

Wheres the mounting point in relation to that centerline? Aka, how far in from the mounting point can I expect the rotor centerline to be with those calipers? I'm sure the mounting point isnt a full 42mm the OTHER way.

I just measured and I have about 66mm on the lower mounting bolt from the mounting point to the spokes and about 80mm on the upper bolt. 66mm sounds a little on the low side if that mounting point is too dar off the caliper centerline.

If I could get that measurement I'd be much obliged. No rush. Whenever you get a chance!
 

DTT Bike Of The Month Gallery

DTT Light or Dark

www.jadusmotorcycleparts.com
shop.themotoworks.com
www.cognitomoto.com
https://www.townmoto.com
www.speedmotoco.com
www.lostapostle.ca/
www.sparckmoto.com
Top Bottom