Topic: Clutch Noise Even When Pulled In

[Ellz10]

So I started up my bike yesterday for the first time finally, after over 2.5 years of this total rebuild. She started up on the 3rd try. Definitely the top 3 best moments of my life. She was obviously idling rough. I was able to sync them after almost 2 hours. Then I took it for a ride up and down the street. Now I want to mention that the bike had no clutch noise (rattle) at all until I took the ride. So while gentle going down the street, when I shifted from 1st to 2nd, I heard this insanely loud clunk but it rode fine. Then the same loud clunk from 2nd to 3rd. Now it only did this once until a minute or so later and after I had shifted a few times. Any ideas what it could be?

Next issue. When I parked the bike and let it cool down, I went back to start it to make sure the carbs were still in sync and they were off just a tad, however now I get this really loud rattling, but when I would pull the clutch in the noise went away and I read here on the forums that that's normal. So I zip tied the clutch and went about fine tuning the sync. Got it all dialed in and then took the zip tie off and let it out then started the bike. Once again the noisey rattle, but this time when I pulled the clutch in the sound won't go away like it did before. And the clutch lever feels weird like I lost some slack somehow.

My valves were adjusted before sync, timing was set correctly. Airbox is on. The motor sounds much smoother now with the carbs in sync. But the clutch rattle can't be a good thing, nor can the slack appearing.

Bike is a 1977 Honda CB750 K

Bored to 836
Crank and alternator lightened and balanced
Carillo rods
Undercut gears
Barnett Clutch with HD springs.

[newday777]

Remove the valve caps and inspect each lock nut is tight.
There was a post not long ago of one coming loose.

[HondaMan]

Well, the nature of the 750 gearbox is to 'clunk' when shifting, due to the weight of the gears (they are almost 150% overbuilt!). Since you also had the gears undercut, the 1, 2 and 3 shifts will clunk even more during engagement(!) because of the extra slot clearances in the gears.

The clutch in this engine (and others like it) wear the most when the clutch is pulled in. That's when the plates slip over one another. So, I'd imagine that the clutch has now worn itself smooth, as compared to when new and the cork blocks have some sharp edges on them. This usually takes about 1000 miles of normal rising to do. There is also a little bearing in the center of the clutch lifter plate, which is intended for occasional (e.g. intermittent) use, and in those engines that spends lots of time idling in traffic with the clutch pulled in, can develop some slack. So, running it with the clutch forced 'on' like you did has probably forcibly worn the parts to their normally-achieved 1500-mile point. I've not seen that done before, but the solution at this point would likely be to readjust the clutch lifter to get normal lever action again.

As for the rattling: did you already check the spark advancer for 'jitter' under a timing light? If the shaft there got bent from turning the engine via that big nut, the timing will 'jitter' when s strobe light is shined on the timing marks, indicating a bent shaft that needs to be straightened.

[Ellz10]

Remove the valve caps and inspect each lock nut is tight.
There was a post not long ago of one coming loose.

I will check in a moment!

Well, the nature of the 750 gearbox is to 'clunk' when shifting, due to the weight of the gears (they are almost 150% overbuilt!). Since you also had the gears undercut, the 1, 2 and 3 shifts will clunk even more during engagement(!) because of the extra slot clearances in the gears.

The clutch in this engine (and others like it) wear the most when the clutch is pulled in. That's when the plates slip over one another. So, I'd imagine that the clutch has now worn itself smooth, as compared to when new and the cork blocks have some sharp edges on them. This usually takes about 1000 miles of normal rising to do. There is also a little bearing in the center of the clutch lifter plate, which is intended for occasional (e.g. intermittent) use, and in those engines that spends lots of time idling in traffic with the clutch pulled in, can develop some slack. So, running it with the clutch forced 'on' like you did has probably forcibly worn the parts to their normally-achieved 1500-mile point. I've not seen that done before, but the solution at this point would likely be to readjust the clutch lifter to get normal lever action again.

As for the rattling: did you already check the spark advancer for 'jitter' under a timing light? If the shaft there got bent from turning the engine via that big nut, the timing will 'jitter' when s strobe light is shined on the timing marks, indicating a bent shaft that needs to be straightened.

So I didn't know that at all. Even with that being said, I'm curious to know HOW LOUD is acceptable and what level of clanking would be considered not okay and indicating something is wrong.

Because it's a loud clanking from the moment I turn the bike on and the whole time I take it up and down my drive. It's very unnerving and I've never heard any other CB750 making the noise mine is.

I don't know how to go about checking the spark advancer for jitter under a timing light. I will have too go buy a timing light and watch some YouTube videos on how to do it hopefully.


Edit***  So I just went and looked and there's no nut loose. I also went to start it up just to see what noises it would make and while it was idling in neutral, the bike shot into gear on its own and the whole damn thing #&@ing fell on me! I am so effing pissed right now. When I rebuilt the motor, I made sure, I triple checked, that the shifter went thru all 5 gears smoothly and they did! Now this is happening and I am at my witts end. Over 2.5 years and over $18k into it. I've about had it.

And its not like I can have a mechanic look at it, none of them will touch an old 750K.

So if anyone is anywhere around Northern Michigan and wouldn't mind making a few bucks, shoot me a DM. I need to figure out what is wrong with this.

[HondaMan]

Yeow!
I've seen 2 other 750s that did that. It was a long time ago, but the cause was common to many others that were knocked over in their respective garages (onto their left sides), when their shifter lever was pushed up toward 2nd gear (engine not running) and left there for more than 5 minutes or so. This bent the "L" shift fork(s) in those bikes far enough that the C2 gear's dogs were barely touching the C5 gear whenever the engine was in Neutral, 3rd, 4th or 5th. Then, if the bike was leaned over toward the kickstand side with the engine running it made clattering noises, or if the engine was cold, it could drop (temporarily) into 2nd gear. It would pop right back out, but it would also move the bike forward a couple of feet in the process.

It turned out there was a way to test for this without taking the engine apart. I found it on the 2nd one, and have used it since, many times. When the bike is on the centerstand (it MUST be level for this test), starting with the tranny in Neutral and the engine off, slowly turn the rear wheel while also slowly pushing the gearshifter toward 1st gear. When it clicks (more like 'clunks') into gear the rear wheel will lock. Note how far the lever had to move to engage 1st gear. Then go back to Neutral, and repeat this process while shifting the lever up toward 2nd gear. It should move the SAME DISTANCE to shift into either gear. If the "L" fork is bent in the usual way, it will engage 2nd with a much shorter 'throw' to the lever.

On the countershaft (the bottom gearshaft cluster in the engine) there is also a circlip in between 2 gears, near the middle of this shaft. This circlip has a rounded surface on one side and a ground-flat surface on the other. As experienced here by at least one of our members (Gammaflat) some years ago, this can be assembled backward: in his case, it came that way from Honda. If assembled backward, it can actually climb out of its groove on the countershaft, pushing the C5 gear toward the C2 gear and mimicking the same action as a bent shift fork while failing the 'test' outlined above (i.e., it seems like the "L" fork is bent, but acts much like it is not bent, having equal shifting distance-before-engagement for both gears 1 and 2). This one can best be detected on a warmed-up, running engine when the oil is thinner: leaning the bike toward the kickstand side causes the gear to shift over far enough to start clicking against the slots of the adjacent gear, and if the circlip has moved fully off its groove it can cause a momentary gear-dog engagement (which immediately bounces backward and disengages) which is known to be strong enough to take the bike off its sidestand, then disengage. We have a lengthy discussion about this one, somewhere in the archives, when it happened to Gammaflat. While I have never seen any Service Bulletin about this from Honda, I know it has happened to Suzukis and Kawasakis, especially their much-thrashed dirt bikes.

[Shtonecb500]

Honestly, I wouldn't worry about the clunking noise, all of my Hondas are kinda loud in that regard and it changes i've noticed. We are in Waterford, MI and  I can get Phil to look at your bike for you if you wanna bring it down to us...if you get desperate enough.

[Tracksnblades1]

Honestly, I wouldn't worry about the clunking noise, all of my Hondas are kinda loud in that regard and it changes i've noticed. We are in Waterford, MI and  I can get Phil to look at your bike for you if you wanna bring it down to us...if you get desperate enough.

If it’s shifting into gear by itself, I’m betting the noise he is hearing is abnormal…

Wondering out loud which gear it’s shifting into..?

High idle rpms and tacky oil can be clunky, but one usually knows when it’s loud enough to be concerned…

Maybe a video….?

[Ellz10]

Yeow!
I've seen 2 other 750s that did that. It was a long time ago, but the cause was common to many others that were knocked over in their respective garages (onto their left sides), when their shifter lever was pushed up toward 2nd gear (engine not running) and left there for more than 5 minutes or so. This bent the "L" shift fork(s) in those bikes far enough that the C2 gear's dogs were barely touching the C5 gear whenever the engine was in Neutral, 3rd, 4th or 5th. Then, if the bike was leaned over toward the kickstand side with the engine running it made clattering noises, or if the engine was cold, it could drop (temporarily) into 2nd gear. It would pop right back out, but it would also move the bike forward a couple of feet in the process.

It turned out there was a way to test for this without taking the engine apart. I found it on the 2nd one, and have used it since, many times. When the bike is on the centerstand (it MUST be level for this test), starting with the tranny in Neutral and the engine off, slowly turn the rear wheel while also slowly pushing the gearshifter toward 1st gear. When it clicks (more like 'clunks') into gear the rear wheel will lock. Note how far the lever had to move to engage 1st gear. Then go back to Neutral, and repeat this process while shifting the lever up toward 2nd gear. It should move the SAME DISTANCE to shift into either gear. If the "L" fork is bent in the usual way, it will engage 2nd with a much shorter 'throw' to the lever.

On the countershaft (the bottom gearshaft cluster in the engine) there is also a circlip in between 2 gears, near the middle of this shaft. This circlip has a rounded surface on one side and a ground-flat surface on the other. As experienced here by at least one of our members (Gammaflat) some years ago, this can be assembled backward: in his case, it came that way from Honda. If assembled backward, it can actually climb out of its groove on the countershaft, pushing the C5 gear toward the C2 gear and mimicking the same action as a bent shift fork while failing the 'test' outlined above (i.e., it seems like the "L" fork is bent, but acts much like it is not bent, having equal shifting distance-before-engagement for both gears 1 and 2). This one can best be detected on a warmed-up, running engine when the oil is thinner: leaning the bike toward the kickstand side causes the gear to shift over far enough to start clicking against the slots of the adjacent gear, and if the circlip has moved fully off its groove it can cause a momentary gear-dog engagement (which immediately bounces backward and disengages) which is known to be strong enough to take the bike off its sidestand, then disengage. We have a lengthy discussion about this one, somewhere in the archives, when it happened to Gammaflat. While I have never seen any Service Bulletin about this from Honda, I know it has happened to Suzukis and Kawasakis, especially their much-thrashed dirt bikes.

Thanks Mark! I will be doing both of the practices you mentioned TODAY. I will get back to you with the results.

Honestly, I wouldn't worry about the clunking noise, all of my Hondas are kinda loud in that regard and it changes i've noticed. We are in Waterford, MI and  I can get Phil to look at your bike for you if you wanna bring it down to us...if you get desperate enough.

I may very well take you up on that, I'll make the drive no problem if it means figuring out what's wrong. I'll be in touch!

Honestly, I wouldn't worry about the clunking noise, all of my Hondas are kinda loud in that regard and it changes i've noticed. We are in Waterford, MI and  I can get Phil to look at your bike for you if you wanna bring it down to us...if you get desperate enough.

If it’s shifting into gear by itself, I’m betting the noise he is hearing is abnormal…

Wondering out loud which gear it’s shifting into..?

High idle rpms and tacky oil can be clunky, but one usually knows when it’s loud enough to be concerned…

Maybe a video….?

I'm definitely going to take a video and post it here because I feel thats the only way everyone will know exactly what I'm seeing and hearing.

Stay tuned!





Aside from the shifting into gear on its own, I'm curious about the clutch. I'm wondering if the clutch plates are stuck or if something else is stuck regarding the clutch. I installed it correctly (Barnett Clutch with HD springs), however that was more than a year ago when I rebuilt the motor and its been sitting on the stand ever since. Thoughts?

[newday777]

When it shifted into gear on it's own, was it on the side stand?

[Tracksnblades1]

I’ve ran Barnett’s springs on Honda clutch plates (fibers).

I think the Barney heavy spring on the factory separator plate causes to much deflection. Especially at a stop sign, it seems like it’s not fully disengaged. However with the right components and clutch cable it will work wilth heavy springs..

If your basket isn’t the source of the noise, can you inspect your primary chain and tensioner with the “Sumpthing”?

Did you replace the rubber dampeners in the clutch drive..?

If it’s a hard metallic knock, bang, clunk, etc, it may do the same with just the starter. Perhaps limiting further damage or uninitiated gear selections..

[Shtonecb500]

my mistake on the clanking, i thought you were referring to the clank dropping it into gear, if its clanking while running, riding, then someone thing is probably off/wrong.

[Don R]

 My K1 Hot Rod dropped into first every time I tried to kick start it. I thought I was somehow hitting the shifter.
 What it was, I found the shift ratchet pivot stud loose in the engine case. I got helicoils to repair it and then discovered it wouldn't drill since there was a helicoil in there already. I got a different stud with good threads and red loctited it into place.
 It also had a loose band around the clutch basket, that was noisy, I welded it in and later installed an entire F2 clutch with good results. I also have heavy clutch springs that are coming back out when I get time.
 It was a smoker so I finally removed the head and found no cam chain guide. I honed it, re-ringed it and put on the rebuilt ported head that came with it.
 It proves you never know what was done to a 50-year-old bike until you dig in there.

[Ellz10]

When it shifted into gear on it's own, was it on the side stand?

Yes, it was on the side stand. It lurched forward caused the side stand to kick back and go up.

I’ve ran Barnett’s springs on Honda clutch plates (fibers).

I think the Barney heavy spring on the factory separator plate causes to much deflection. Especially at a stop sign, it seems like it’s not fully disengaged. However with the right components and clutch cable it will work wilth heavy springs..

If your basket isn’t the source of the noise, can you inspect your primary chain and tensioner with the “Sumpthing”?

Did you replace the rubber dampeners in the clutch drive..?

If it’s a hard metallic knock, bang, clunk, etc, it may do the same with just the starter. Perhaps limiting further damage or uninitiated gear selections..

I think I'm going to have to take the clutch cover off and take a look at what's going on under there.

I can inspect the primary chain and tensioner if I drop the SumpThing/oil pan.

I had the rubber dampeners replaced by Ken at CycleX when he rebuilt my cush drive including new cush bearing.

my mistake on the clanking, i thought you were referring to the clank dropping it into gear, if its clanking while running, riding, then someone thing is probably off/wrong.

It only made a super loud clunk the one time yesterday when I shifted it into 1st and then from 2nd to 3rd. It doesn't make that sound anymore. Now it's just the constant noise when it's going down the road as you'll be able to hear in the video.

My K1 Hot Rod dropped into first every time I tried to kick start it. I thought I was somehow hitting the shifter.
 What it was, I found the shift ratchet pivot stud loose in the engine case. I got helicoils to repair it and then discovered it wouldn't drill since there was a helicoil in there already. I got a different stud with good threads and red loctited it into place.
 It also had a loose band around the clutch basket, that was noisy, I welded it in and later installed an entire F2 clutch with good results. I also have heavy clutch springs that are coming back out when I get time.
 It was a smoker so I finally removed the head and found no cam chain guide. I honed it, re-ringed it and put on the rebuilt ported head that came with it.
 It proves you never know what was done to a 50-year-old bike until you dig in there.

I might have to take the shift cover off and take a look under there at the same time when I take the clutch cover off.

I rebuilt this whole bike and entire motor.

[Ellz10]

Here is the link to the video. I uploaded it on YouTube to make it easier. It's only about 18 seconds long. You can hear the noise the bike is making as I go by slowly. The faster I go down the road, the louder this noise gets. Make sure you turn your volume up to hear it.

I'd also like to note that for some reason I can't rev past about 5,500 rpms, and that is really pushing it!

[Ellz10]

I also need to further note that shortly after this video ended, I could not move my bike freely. It was stuck in the road. Even with the clutch pulled in, the bike would not move. I tried rocking it back it forth. Nothing. I tried switch gears and rocking back and forth in the next gear. Still nothing. I ended up having to lift the bike, shove an old Craftsman center jack under the rear wheel and carefully roll it back to the house and into the garage. All in 92° heat. Rough.

[denward17]

In the video, near the end when you were slowly going by, what gear were you in?  Was the engine dying, like running out of fuel?

[Ellz10]

In the video, near the end when you were slowly going by, what gear were you in?  Was the engine dying, like running out of fuel?

1st gear. Yes it was about to die from not idling high enough.

[Ellz10]

Anyone know what could be wrong? Stuck in gear, won't move even with clutch pulled in. Loud noise when driving down the road as heard in the video. I'm going to be taking the clutch cover and gear cover off later tonight and see if I can see if anything is amiss.

[Jerry Rxman Griffin aka MuthaF'er]

Pull your oil pan and take a close look inside. That really didn't sound like a clutch to me.

[Ellz10]

Pull your oil pan and take a close look inside. That really didn't sound like a clutch to me.

I hate to do so since this oil is so damn expensive, but I'm probably going to have to do it anyways.

Something tells me I'm going to end up going back in and splitting the cases. Awesome.

[seanbarney41]

Pull your oil pan and take a close look inside. That really didn't sound like a clutch to me.

I hate to do so since this oil is so damn expensive, but I'm probably going to have to do it anyways.

Something tells me I'm going to end up going back in and splitting the cases. Awesome.

yeah that sounded really bad, not a normal cb750 sound at all, to me sounded like drive chain and/or sprockets contacting something heavily

[Ellz10]

So I pulled the gear shift cover and this is what it looks like.

I'm not seeing anything abnormal.

[Ellz10]

This is what clutch side looks like.

I drained the oil (obviously) before this and there weren't any metal flakes. So I assume that's a good thing.

Edit* I took the entire clutch assembly out and the bike is still stuck in gear. Won't budge.

I literally have no clue what to do at this point or how to go about getting it unstuck.

[denward17]

What gear do think it is stuck in, 2nd?

If you put your gear shifter mechanism (lever) back on, can you try to find neutral and take a video of the shifting mechanisms while trying to shift into a gear.

The detent appears like it could be in 2nd gear.   Engine off while trying..


EDIT: I just saw where you have the clutch out, I would wait on trying to shift until the experts chime in.

[denward17]

Cross referencing CMSL diagrams, on a '78 CB750K, it shows 7 friction plates, it appears you have 8.

Also the diagram shows 6 clutch plates, with one in the middle being different.  You appear to have 7.

Not saying it is wrong, just pointing out difference.

[Ellz10]

What gear do think it is stuck in, 2nd?

If you put your gear shifter mechanism (lever) back on, can you try to find neutral and take a video of the shifting mechanisms while trying to shift into a gear.

The detent appears like it could be in 2nd gear.   Engine off while trying..


EDIT: I just saw where you have the clutch out, I would wait on trying to shift until the experts chime in.

It didn't make any difference, it moves the same short range of motion as it did before I pulled the clutch components.

Here's the video of me shifting it as far as it will go.

[Floshenbarnical]

I'm bookmarking this thread. I've been having some transmission oddity, and this seems like a good learning experience. I have my fingers crossed for you OP. For what it's worth, if anyone can help you figure it out its these guys.

[HondaMan]

Hmm...first, a 'try this' thing if you haven't already: the rear wheel (or at least the drive sprocket) needs to be rotating when the engine is not, if you want to attempt a 'manual' shift (so to speak...). This is because of the dogs-and-slots arrangement of the typical constant-mesh gearbox (all of them, not just this one). The gears that are disengaging (like when going into Neutral) will be fine, but the dogs of the next gear will not be lined up for the shift, on purpose, by design. That's why these 'clunk' like they do when entering the next gear: the dogs forcibly accelerate the new gear to the present gear's speed.

I have had just one of these engines go together (in a hurry, and in the dark on my patio one night) when the "C" shift fork did not drop into the slot of the mainshaft where is was supposed to while the engine was upside-down, and the result was a bike that would shift fine into 1st, and maybe into 2nd, but that was all. After that there were no more gears as the drum wouldn't turn until the 3rd gear would slide into the 2nd for the 2-3 shift. I was able to [just barely] see the error by looking up into the (dripping on my face..   ) oil pan's opening, from under the bike, and knew I had to pull the engine out just to pull the cases apart, align the "C" fork correctly (the next time I did it at high noon...) and re-drop the bottom case onto the top case...again...and then put all those other pieces back on... And about the other noises coming from below: if the 2nd gear's dogs are TRYING to engage with C5 because of the loading of the "C" shift fork resting against it, this will make the whole gearbox "jitter", which means all those other unloaded gears are rattling their dogs and slots together because they are not being orchestrated by the "C" fork dampening their minor movements.

The only part of this story that aligns with your engine is the "looking up into the (dripping on my face..   ) oil pan's opening, from under the bike", but this means once again taking off that Sump Thing to do it (and probably another gasket set?). A word of advice if you then have to [re]pull the engine out to fix this situation: put the bottom oil pan onto the bottom of the engine after removing the Sump Thing's raised housing. It is EXTREMELY easy to dent the bottom oil pan surface while removing/installing this 200+ pound engine, and the dented pan surface will forever leak oil. (Don't ask how I know this, because I won't tell you! ).