1985 CB700sc 1st to 2nd gear grind

[OneMoreHonda]

Hi all, I got my first nighthawk this spring and been getting it back on the road after 21 years of sitting in the original owners garage! It has about 11K miles on it, I am the second owner. Needless to say, some things needed service. For engine related stuff I've done the following:

Drained original oil in it (was the color of caramel )
Flushed fresh engine oil after 100 miles...it needed it to get all that gunk out.
Cleaned out gel-like DOT4 fluid from clutch system,
Rebuilt slave cylinder.
Cleaned out master cylinder.
New DOT4 fluid in clutch system and air bled.
New plugs
Cleaned and set gear shifter (was already at oem settings per the notch and dot aligning, so no change)

It runs well for the time being.

My issue I've noticed on it is the shifting from 1st to 2nd likes to make a gear grind and not go in right away like a normal shift going from 2-3 or 3-4 etc. It goes, but it grinds first. Higher rpms, more grind noise usually, real low rpms, less noise, but grinds maybe a tiny bit less. I experimented by going through neutral or slowly shifting it from 1st to 2nd in low rpms, slight improvement but not very usable. I also tried 1st to neutral to 2nd, smoother, but not practical, but it grinds less often.

I haven't taken the clutch plates out yet. Pulling in the clutch allows the engine to rev and not move the bike. When off and in gear, pulling in the clutch and moving it isn't at all as smooth as being in neutral. My other bikes are noticeably easy to push. I dont have another nighthawk to compare to so I assume its either normal or not normal.

Thoughts on what I might want to do or need to check/test out?

[Pete in PA]

I had to put a clutch in my 92. Started slipping.

Even older bikes with the original clutch...Just change it. I believe the friction plates age out just from sitting.

Make sure you use a motorcycle oil.

Could need to further bleed the clutch.

[dickdagger]

I have the same bike with the same problem. The clutch plates are not disengaging fully. I set up a test rig (clamp) for the slave cylinder and found that it is leaking even after replacing all seals in the clutch hydraulic system. Take it off the bike and see if there is any fluid there before you do anything else. I haven't thought of a good way to test the master yet.

I also tried to make a screw type compressor to replace the slave in the hope that I could push the cross shaft as far into the case as it will go, but the force required is tremendous and my compressor failed. At this point I am suspect of the clutch itself, as someone has previously removed the clutch cover and resealed it with orange RTV.

If your slave isn't leaking (and are 100% sure you've bled the line properly), that is the time to open up the right side clutch cover and inspect the steel and friction disks. Typically they oxidize or transfer metal from the friction disk to the steel disk over time, but this problem will resolve itself with use. I have put 2k miles on my bike while nursing this issue, altering my shifting to prevent the grind, and it has not improved. I even tried slipping the clutch intentionally at speed to wear off the supposed corrosion, still no improvement.

Anyway, I will update when I have new info and I hope you will as well. Good luck.

[mollusc]

Aside from clutch issues, the 1-2 shift is also known to be a problem on 1980s Hondas.  The shift fork is somewhat weak and can be easily bent.  Fixing it requires a full teardown of the engine.
Having sporty looks, the Nighthawk S tends to get ridden hard.  Unfortunately, rushing the 1-2 change is a quick way to damage the shift fork.  It's possible that this is actually the source of your problem.  Aside from a deep dive to repair it, the workaround is just to baby the bike through that gearchange as best you can.

[dickdagger]

To me, a bent shift fork would manifest itself in the form of not being able to shift into certain gears or slipping out of gear. The grind happens because there is still torque being applied to both the input and output gear sets by the engine and rear wheel respectively. One of those torques has to be reduced to almost nothing for the dogs to catch and fully engage without being forced back apart.

[Bob H]

My issue I've noticed on it is the shifting from 1st to 2nd likes to make a gear grind and not go in right away like a normal shift going from 2-3 or 3-4 etc. It goes, but it grinds first. Higher rpms, more grind noise usually, real low rpms, less noise, but grinds maybe a tiny bit less. I experimented by going through neutral or slowly shifting it from 1st to 2nd in low rpms, slight improvement but not very usable. I also tried 1st to neutral to 2nd, smoother, but not practical, but it grinds less often.

When I got my '93 750 12 years ago, it only had 7,000 miles on the clock (had been stored).
It was doing what you describe, and I was bummed out coming from a couple Yamaha that shifted like butter smooth.

I did a deep dive, and PDF'ed several articles that addressed the issue.
--------------------
This article is from a defunct website that was called ridergroups dated 2012:

"My motorcycle shifts rough between first and second gear."  I read a lot of blogs and forums and this is a fairly common concern.  Learning to ride motorcycles correctly can be a life long pursuit. I thought I would post a quick article for people who are concerned about their motorcycles rough shifting and provide a solution that has worked for me.  Maybe some guy frustrated by his rough shifting motorcycle will find this on Google and have a more enjoyable ride by mastering his finicky motorcycle transmission.
Most motorcycles have a rough shift going in to first gear.  It is very typical for a motorcycle to have a thump sound and maybe even a slight lunge forward when shifting in to first gear.  Some motorcycles are even a little rough shifting in to second gear once you are under way.  What is frustrating to some riders is that it does not rough shift every time but just on occasion or every few shifts.  More than one rider has wondered if something is wrong with their motorcycle's transmission.
 
Here is a solution that has worked for me to get a consistently smooth shifting motorcycle
Next time you are out on a ride try this: pre-load your shifter before shifting in to second gear.  What do I mean by preload your shifter?  It's simple, while in first gear and rolling along, start to apply upper pressure with your toe on the gear shift before pulling in the clutch.  Not enough pressure to cause the bike to shift but just enough so that you can feel the gear lever through your shoe.  If you apply pressure like this before pulling in the clutch your bike should shift to second as smooth as butter when you pull the clutch and roll off the throttle.
Try this next time you are out for a ride.  With a little practice this becomes second nature and you can enjoy consistently smooth shifts as you cruise down the road."
-------------

[dickdagger]

Yeah, that makes it worse. Believe me, that's my normal shifting style on every other bike I've been on, but this 700 will grind the 1st to 2nd shift if you don't pull the clutch to the bar and wait a half second before you even think about touching the shifter. This is a clutch disengagement problem. Bike on center stand, first gear, pull clutch in, can't rotate rear wheel by hand. In neutral the rear wheel spins easily.

[Gene]

Hi all, I got my first nighthawk this spring and been getting it back on the road after 21 years of sitting in the original owners garage! It has about 11K miles on it, I am the second owner. Needless to say, some things needed service. For engine related stuff I've done the following:

Drained original oil in it (was the color of caramel )
Flushed fresh engine oil after 100 miles...it needed it to get all that gunk out.
Cleaned out gel-like DOT4 fluid from clutch system,
Rebuilt slave cylinder.
Cleaned out master cylinder.
New DOT4 fluid in clutch system and air bled.
New plugs
Cleaned and set gear shifter (was already at oem settings per the notch and dot aligning, so no change)

It runs well for the time being.

My issue I've noticed on it is the shifting from 1st to 2nd likes to make a gear grind and not go in right away like a normal shift going from 2-3 or 3-4 etc. It goes, but it grinds first. Higher rpms, more grind noise usually, real low rpms, less noise, but grinds maybe a tiny bit less. I experimented by going through neutral or slowly shifting it from 1st to 2nd in low rpms, slight improvement but not very usable. I also tried 1st to neutral to 2nd, smoother, but not practical, but it grinds less often.

I haven't taken the clutch plates out yet. Pulling in the clutch allows the engine to rev and not move the bike. When off and in gear, pulling in the clutch and moving it isn't at all as smooth as being in neutral. My other bikes are noticeably easy to push. I dont have another nighthawk to compare to so I assume its either normal or not normal.

Thoughts on what I might want to do or need to check/test out?

Years ago, I had a 70s 550. Shortly after I got it, 2nd was missing, all the rest worked fine. Result: I replaced the 2nd gear shift fork. Yes, I had to split the case. I sold it shortly after.

[dickdagger]

Update: I've determined that the clutch hydraulic system is, in fact, operating normally. The fluid leaking around the slave cylinder area was actually fresh engine oil that looked like the slightly aged brake fluid in the clutch system. It had pooled around the slave piston and gave the illusion of brake fluid gushing around the piston seal.

I also made a forcing screw plate to bolt directly to the bike in place of the slave cylinder, so I could be certain that the clutch basket was being fully actuated by the hydraulics. I took off the clutch cover to confirm that the range of travel of the basket was the same when both the slave cylinder and forcing screw were actuating the clutch basket. The results were the same. The outermost friction disc's cogs should travel to the very edge of their grooves in the clutch basket. I also used the plate to check hydraulic efficiency in the clutch; bolting it to the slave and pulling the lever resulted in a rock hard feel after little travel and no sink afterward.

The next test was to check for warpage in the clutch discs. I used a flat pane of glass (that I checked with a straight edge) and feeler gauges to check both the steel and friction discs. The steel discs all had small strips of blueing scattered around the surface, and all seem to be slightly warped but within spec. The friction discs are not given a warp spec in the shop manual, but all were around 5 to 8 thou with the exception of one, which was 15 thou. The friction discs appear to be replacements, as they are all at max. thickness spec and the bike has 30k mi. on it. Someone has been into the clutch cover at some point, as it was reinstalled with orange RTV over a broken gasket. All springs were at factory spec.

Clutch disc warpage measurements (in.):
Steel - 0.009, 0.005, 0.004, 0.004, 0.002
Friction - 0.005, 0.006, 0.005, 0.006, 0.007, 0.015

The max. warpage tolerance for the steel discs is 0.012"
The standard thickness for friction discs is 0.153"
No tolerance given for friction disc warpage
All springs were at their factory spec. length of 1.34"


It seems like this is the cause of the grind; slight clutch plate warpage across all plates induces drag even with the basket fully separated, and this drag transfers enough torque from the engine to keep the 2nd gear dogs from sliding into their grooves. I don't know when I'll end up getting new plates, as I prefer to use OEM and they don't seem to be readily available and are quite expensive.

[mollusc]

Now that's some thorough diagnostics!  Nicely done.
OEM aren't necessary for the clutch plates, honestly.  You should be able to find EBC or (my preference) Barnett online.  Probably a good idea to throw in new springs if you do that, too.  Just remember to soak them in oil overnight before installation.

[dickdagger]

Do you use their kevlar clutches? I've heard mixed results about them in the past. Interested to hear how they worked out for you in this bike

[Larry Fine]

Just remember to soak them in oil overnight before installation.

(The fiber plates, not the springs.)

[mollusc]

I haven't actually replaced the plates in my 700S.  I do have a traditional (i.e. not Kevlar) Barnett set that's still new in the packet that I have never installed.  My bike has been out of action for several years, and I plan to install the new ones when I eventually get it back on the road.

[OneMoreHonda]

Thanks all for providing some feedback. I've tried some preloading and "shifting like you mean it" aka clutch in, movement of shift lever quickly into 2nd vs a more relaxed speed. This helps some, but is more of a band-aid. I did pull off the clutch side, all my thickness measurements show well within specs. I did not check for warpage on mine however, as there are no specs for it. I have a new seal kit for the slave cylinder I just got 2 days ago, and will put that in shortly. I'll report back shortly after I finish my new tire install, and figure out how to do the fork seals or just have the dealer do them, special tools needed.

[dickdagger]

You can make a fork seal tool yourself out of a small length of PVC tubing. The inner diameter for the pipe should be 1 3/4" and the inner diameter for the collet needs to fit the pipe on one side and have a similar thickness to the fork seal. Just go to a hardware store with your tape measure and find out what will work. Cut the pipe and collet in half diametrically and reassemble them on the fork tube. Bind them together with a hose clamp. You should now be able to slowly walk the seal in with a rubber mallet, alternating strikes on each half of the pipe.