I was preparing to change out the steering bearings on my cb750 and noticed that the Nighthawk 750 uses the same bearing kit. Since the Nighthawk Swingarm swap went fairly smoothly with a moderately low effort installation, I figured.... 'what the heck', I'll order the $8 lower triple from eBay (plus $20 shipping) and see how difficult a swap would be.
My justification: I figured I could practice removing the lower bearing as well as get a measurement to compare the stem lengths. So not a complete loss even if I don't use it. However, if they are close enough, I can probably adjust or shim the installation enough to make it a direct swap.
My dilemma: removing the old triple to get the measurements is a must and while everything is out, it doesn't make sense to put everything back without actually swapping the bearings. If I eventually do the swap, I would need another bearing kit and would essentially be throwing out the money spent on the first bearing kit, once everything is moved over.
I guess I could justify riding 1 season on the new bearings before tossing them but that's just kind of wasteful. It's bad enough that I've swapped the rear tire before the 2 year old tires got any use. Doing the same thing for the front is another waste of money.
Dang, I might have attention deficit disorder.
This bike has been a wonderful waste of money for me, but I could lose interest in a year and never ride it again making all the money spent on upgrades (not just those steering bearings) lost to a deep, dark hole, but at least I'm stimulating the economy and keeping someone employed along the way.
Oh, the opportunity cost of the compound interest lost on all the money I've thrown at this bike.
There's plenty of references to the stem sizes and bearings that many bikes have, but virtually no measurements of stem length for a real good understanding of what can easily swap. I already know that if I can move to a Nighthawk front end, I would gain the ability to upgrade to 41mm regular (as opposed to upside down) forks, lighter wheels and bigger brakes, but the question is how difficult would that swap be?
In addition to about $300 for the forks, I would expect another $250 for the wheel and tire and other ancillary stuff like springs, so I know it's not going to be cheap but it's not crazy expensive either. I'll need to be careful and methodical so I don't order the wrong items.
I think I need to compare wheel specs to get a better understanding of a way forward after measuring everything, so a riding season with the old forks and new bearings sounds reasonable while I collect the parts for the swap perhaps next winter.
I've stepped on a slippery slope.
During my research, I discovered that a VFR750 triple also uses the same bearings and thus is a possible swap candidate. The parts seem to be cheaper than Nighthawk parts too, so I ordered a lower triple for $20 shipped because the stem looks like it's the same length as the CB750c based on an eBay vendor who likes to post pictures with a ruler next to his parts. Since I'm a cheap squeaking bastard at heart, I have to justify this purchase so here goes:
By purchasing the VFR750 lower AND the Nighthawk 750 lower, I can check the stem length as well as check for the interchangeability of the fork spacing between the NH and VFR.
I already know that the wheel, axle and tire sizes are the same but purchasing this extra extra lower for research purposes will give me the understanding if I can use NH and VFR parts interchangeably. Single or Dual caliper? matching wheels with the back or mismatched? Nighthawk upper with a VFR750 lower?
After receiving both lowers, I started dismantling the front end of my CB750c and discovered very quickly that both the Nighthawk and the VFR do not fit. It was a long shot, but ..... nothing ventured, nothing gained. The bearing looked like it was updated and fairly fresh compared to the bearings on the Nighthawk and VFR lowers I had, however I felt a slight catch in the range of movement, which would be indicative of a need for attention. I could have tried to re-grease them and install everything back, but I have the replacement bearings and the old ones looked kinda dry, so it made sense to go ahead and replace them. That slight catch could have been an out of round roller or a worn race even though the bearing looked nice and fresh.
Part of me feels a sense of relief at not being able to spend the money on the upgrade parts, but it does not mean I've closed the book on this effort. I've probably just kicked the can down the road a little until I find a place where I can do a stem swap or a way to do it. I'm going to grind off the stem weld and give a couple of good wacks with my BFG (big friggin hammer).
I have measured the triples using the following generic diagram by referring to A, B, C for measurements
A: distance from top of the lower to the seat for the upper bearing
B: distance from top of the lower to the top of the stem
C: distance from the outer edge of the fork clamp to the other side
I would love to keep expanding these dimensions to other bikes since there is no compilation of them anywhere. If you have any, provide them in the comments and I'll update the table.
My justification: I figured I could practice removing the lower bearing as well as get a measurement to compare the stem lengths. So not a complete loss even if I don't use it. However, if they are close enough, I can probably adjust or shim the installation enough to make it a direct swap.
My dilemma: removing the old triple to get the measurements is a must and while everything is out, it doesn't make sense to put everything back without actually swapping the bearings. If I eventually do the swap, I would need another bearing kit and would essentially be throwing out the money spent on the first bearing kit, once everything is moved over.
I guess I could justify riding 1 season on the new bearings before tossing them but that's just kind of wasteful. It's bad enough that I've swapped the rear tire before the 2 year old tires got any use. Doing the same thing for the front is another waste of money.
Dang, I might have attention deficit disorder.
This bike has been a wonderful waste of money for me, but I could lose interest in a year and never ride it again making all the money spent on upgrades (not just those steering bearings) lost to a deep, dark hole, but at least I'm stimulating the economy and keeping someone employed along the way.
Oh, the opportunity cost of the compound interest lost on all the money I've thrown at this bike.
There's plenty of references to the stem sizes and bearings that many bikes have, but virtually no measurements of stem length for a real good understanding of what can easily swap. I already know that if I can move to a Nighthawk front end, I would gain the ability to upgrade to 41mm regular (as opposed to upside down) forks, lighter wheels and bigger brakes, but the question is how difficult would that swap be?
In addition to about $300 for the forks, I would expect another $250 for the wheel and tire and other ancillary stuff like springs, so I know it's not going to be cheap but it's not crazy expensive either. I'll need to be careful and methodical so I don't order the wrong items.
I think I need to compare wheel specs to get a better understanding of a way forward after measuring everything, so a riding season with the old forks and new bearings sounds reasonable while I collect the parts for the swap perhaps next winter.
I've stepped on a slippery slope.
During my research, I discovered that a VFR750 triple also uses the same bearings and thus is a possible swap candidate. The parts seem to be cheaper than Nighthawk parts too, so I ordered a lower triple for $20 shipped because the stem looks like it's the same length as the CB750c based on an eBay vendor who likes to post pictures with a ruler next to his parts. Since I'm a cheap squeaking bastard at heart, I have to justify this purchase so here goes:
By purchasing the VFR750 lower AND the Nighthawk 750 lower, I can check the stem length as well as check for the interchangeability of the fork spacing between the NH and VFR.
I already know that the wheel, axle and tire sizes are the same but purchasing this extra extra lower for research purposes will give me the understanding if I can use NH and VFR parts interchangeably. Single or Dual caliper? matching wheels with the back or mismatched? Nighthawk upper with a VFR750 lower?
After receiving both lowers, I started dismantling the front end of my CB750c and discovered very quickly that both the Nighthawk and the VFR do not fit. It was a long shot, but ..... nothing ventured, nothing gained. The bearing looked like it was updated and fairly fresh compared to the bearings on the Nighthawk and VFR lowers I had, however I felt a slight catch in the range of movement, which would be indicative of a need for attention. I could have tried to re-grease them and install everything back, but I have the replacement bearings and the old ones looked kinda dry, so it made sense to go ahead and replace them. That slight catch could have been an out of round roller or a worn race even though the bearing looked nice and fresh.
Part of me feels a sense of relief at not being able to spend the money on the upgrade parts, but it does not mean I've closed the book on this effort. I've probably just kicked the can down the road a little until I find a place where I can do a stem swap or a way to do it. I'm going to grind off the stem weld and give a couple of good wacks with my BFG (big friggin hammer).
I have measured the triples using the following generic diagram by referring to A, B, C for measurements
A: distance from top of the lower to the seat for the upper bearing
B: distance from top of the lower to the top of the stem
C: distance from the outer edge of the fork clamp to the other side
| Bike | Dimension A | Dimension B | Dimension C | Offset |
| Nighthawk 750 (93-2001) | 20.5cm | 26.5cm | 23cm | 4cm |
| VFR 750 (90-1997) | 16cm | 22.5cm | 23cm | 3cm |
| CB750c (79-1982) | 17.5cm | 24cm | 21.5cm | 5cm |
I would love to keep expanding these dimensions to other bikes since there is no compilation of them anywhere. If you have any, provide them in the comments and I'll update the table.
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