Topic: 5th gear noise, not quite a grind

[beaniam]

Hi all I just picked up a 78 cb750k earlier this week and today got around to tagging it and taking it out.   Runs great, shifts great, PO told me the clutch slips however I adjusted the cable to spec as per the faq and it doesn't seem to slip at all to me.  However...  Very seldomly in 4th and almost always in 5th I get this sound that sounds almost like a gear grinding but not quite.  Sounds almost like something rubbing on teeth of a gear.  Sometimes if I downshift to 4th then back up to 5th it goes away.  Also if I give it throttle in 5th it seems to go away until cruising/idle throttle.  It feels like it's coming from the left side of the crank cover but it's hard to diagnose when going 45mph.  I'm new to bikes but not to wrenching on vehicles, I'm just not sure where to start looking or which cover to pull first.  It has never popped out of gear on me yet and shifts fine otherwise, there is also no lack of power in 4th or 5th when this noise/vibration starts.


Edit: here's my issue




http://s257.photobucket.com/albums/hh224/beaniamyota/?action=view&current=P1010275.mp4

I have no second or 5th gear issues other than this noise in the video.  None of the gears pop out.

[Gordon]

Is the chain really loose?

[beaniam]

it has a fair amount of play,  I didn't get to adjusting that yet.  Definitely a lot more loose than the chain on my nx650.

[flybox1]

make your adjustment with the bike not on a stand, andwith someone of your stature sitting on it.

[Gordon]

If it's loose enough it will drag on top of the swing arm when letting off the throttle or downshifting.  

[beaniam]

I adjusted the chain, didn't help.  I don't think that's the issue.  Here's a video to better show what I'm talking about.  It comes and goes.  I start up and go through the gears then I go between 4th and 5th during this and you can hear it start and stop.  The entire time it's not popping out of gear and there's power going to the chain.  I read other threads mentioning the loss of second and 5th pops out.  I don't have either of these symptoms.
Now that I can better tell where it's coming from it sounds more like it's coming from the clutch side.  Where should I start tearing things apart?



http://s257.photobucket.com/albums/hh224/beaniamyota/?action=view&current=P1010275.mp4

[Gordon]

Strange.   It sounds kind of like when you push down on the kick-start lever when the engine is already running. 

[beaniam]

When it's running and I push the kick start down on my bike it's very quiet compared to this noise.  I've tried messing with the kick start when it is making the noise but it doesn't change.

[beaniam]

Well I pulled the clutch out checked it over and put it in back and changed the oil.  The clutch lock nut was loose so the whole clutch basket kinda wobbled a little.  One of the corners of the clutch lifter plate was broken off about a 1/3 of the way through the bolt hole.  I managed to break another corner off putting it back together.  I also counted 9 friction discs and I believe the manual said there's 6?  Anyway I either put something back wrong or with the other broken corner on the lifter plate there's not enough pressure on the spring now because the clutch slips so bad I can barely do 40mph.  I heard the noise from earlier real quick in 5th then went away but I'm assuming it's still there and just not coming in yet because I'm not going fast enough.    I'm giving up for the night.

[beaniam]

I'll get back to this in the morning.  Anyone have any ideas? 

[Old75_ratafe]

I think u found the issue, and I've heard of people adding discs to stiffen it up (usually for racing).  I know in cars the automatic clutches this is a real common practice.  Did u find the piece of broken basket? I'd bet its rattling around in there.

[beaniam]

The piece of broken lifter plate was still in place just loosely wedged between the basket and the bolt so there weren't any parts floating around in there that I can put blame on for that noise.  I picked up a couple used complete clutch assemblies on ebay that I can compare and replace my broken plate with.  Also replace one of my apparently missing metal clutch plates.
Reading through some other threads I started thinking maybe a worn shifter drum?  Not completely engaging 5th?  Problem with that is, it is in gear and doesn't pop out.  With the noise I'm still under power and can throttle it (sometimes the noise goes away until I let off).

[beaniam]

Adjusted the clutch adjustment screw, that's why I didn't have clutch.  Took it for a ride, still does it at random in 5th and very rarely in 4th.  Didn't do it at all until about 2 minutes into riding.  I can't really figure out what starts or stops the noise.  It just comes and goes at it pleases.  Rode a couple miles in 5th no noises, come to a stop sign, get back up to fifth and as soon as it clunks into 5th it starts.  When I'm riding it almost sounds and feels like it's coming from the shifter side.

[a700guy]

Are you sure the output shaft bearing is not failed and making what I call a bearing skating sound?

You could test this idea by having the bike in neutral and increasing rear wheel speed to the point it normally starts, engine doesnt even have to be running.

If it doesn't do it there, then you have a idler gear bearing issue on one of the tranny shafts and will need to seperate the cases to find it, it will more than likely stand right out upon dissassembly.

[beaniam]

It's a very distinct something metal rubbing on a gear type of sound.  Either there 100% or not at all.  No in between.  When moving and it starts I can really only get it to continue if I leave it in 5th.  Even slowing down to about 35 with it still in 5th it's still there.  Downshift once and it's gone.

[beaniam]

Picking up a headless 78 cb750 engine with a complete noise free tranny on Tuesday for $100.  At least I'll have something to compare to instead of a cardboard box of parts like the trannys on ebay.

[scottly]

That is a very odd noise. Time for a stethoscope?

[beaniam]

I suppose but I think I just keep putting off the obvious which is that I need to split the case.  I'll do that when I have my 78 parts bottom half sitting in front of me to compare with.
When it starts it feels like the area right behind the starter.  That's where I could feel the grinding the most when fishing my hand around it when it does it.  It's hard to diagnose because it comes and goes when on a stand.  I can get it to be constant when riding but then it's a little harder to do when you're cruising at 45.

[Old75_ratafe]

started gear not retracting all the way maybe or catching slightly at high speeds? Easy test for that pull the starter and then kick start it and go see if it'll still do it.

[scottly]

Just for grins, remove the chain and see if the noise is still there...

[mystic_1]

started gear not retracting all the way maybe or catching slightly at high speeds? Easy test for that pull the starter and then kick start it and go see if it'll still do it.

Starter gears don't "retract" on a 750, or any other SOHC Honda that I'm aware of, like they do on a car.  Instead they use a one-way roller clutch behind the alternator rotor on the crank.

mystic_1

[beaniam]

Just for grins, remove the chain and see if the noise is still there...

Tried it, still there.  Started stripping the bike down, just have to pull the engine out now.  However I just got a phone call from the guy I was picking the engine up from. He just realized it was a 79 cb750K engine out of the 10th aniversary edition bike. Looking at the 79 transmissions on ebay I can see the clutch is definitely different but would the 79 transmission parts drop in my 78 case? Also would I be able to use the later style clutch with the stronger looking lifter plate? I've gotta decide what I'm doing before tomorrow morning. 

[Old75_ratafe]

started gear not retracting all the way maybe or catching slightly at high speeds? Easy test for that pull the starter and then kick start it and go see if it'll still do it.

Starter gears don't "retract" on a 750, or any other SOHC Honda that I'm aware of, like they do on a car.  Instead they use a one-way roller clutch behind the alternator rotor on the crank.

mystic_1

 Was wondering about that hadn't removed mine yet (one of the few things that worked when I got my bike).  Could still be the roller clutch maybe some rust got in there and its grinding at certain speeds? idk it was just a suggestion.  But I'm kinda leaning twards a shot bearing in the case.  I'm not real familure with our clutches do we have the equivalent of a throw out bearing I know on cars those go under certain strains and will cause noise... although its usually more a humming not gear grinding.

[beaniam]

started gear not retracting all the way maybe or catching slightly at high speeds? Easy test for that pull the starter and then kick start it and go see if it'll still do it.

Starter gears don't "retract" on a 750, or any other SOHC Honda that I'm aware of, like they do on a car.  Instead they use a one-way roller clutch behind the alternator rotor on the crank.

mystic_1

 Was wondering about that hadn't removed mine yet (one of the few things that worked when I got my bike).  Could still be the roller clutch maybe some rust got in there and its grinding at certain speeds? idk it was just a suggestion.  But I'm kinda leaning twards a shot bearing in the case.  I'm not real familure with our clutches do we have the equivalent of a throw out bearing I know on cars those go under certain strains and will cause noise... although its usually more a humming not gear grinding.

Sort of.   There's a bearing in the outer clutch cover that if adjusted properly won't be spinning when the clutch is engaged.  Pull the clutch and it pushes in on the clutch plate.
Other than the exhaust I've got the motor pretty much stripped down to the point of being ready to pull out and split the case.  With theamount of noise it makes I'm guessing on whatever it is being worn enough to see right away.  Not picking up the other engine.  Realized 79 is when they went to dohc.   Nothing in there will work for me 

[beaniam]

Finally made some progess.  ...or just gotten myself further into the point of no return.

Ebay transmission showed up.  Looks good, no obvious wear, worn dogs, broken gears...









My back started hurting around here.

Looks like someone dropped a driver bit down in the starter box and said "oh well"





Split





Some metal flakes, sealant, and gunk.



Looks like someone has had this motor apart before.  I haven't started tearing into the transmission yet but as it sits I don't see anything jumping out at me as a source of that grinding.  Where would it be suggested I start looking for that random 4th/5th gear grind?