Topic: clutch problems, need diagnoisis from Dr. Honda

[greasy j]

ok, I was almost home when my clutch went out on my 1971 CB750 K1. I am not sure what happened but here are the symptoms. by the way I checked the FAQ first.

I can change gears without using the clutch lever as if it is permanently depressed, when it is in gear it does not catch it just revs as if it were in neutral. at first I was hoping I just snapped the line but the opposite would happen then, right? before this happened I had some problems going up into second, like it would kinda take a little effort to clunk it in there. but I've had other Hondas with loud clunky clutches that ran fine for years so I didn't worry about it. also sometimes it wouldn't go all the way into 4th. it would actually be in neutral between 3rd and 4th until I pulled the toe lever up into 4th all the way. not really a big deal. it never bothered me before, but I'm mentioning it in case it helps with a diagnosis.

so, I figure unless it's something simple I might have to take the engine out to get at the clutch. If so I would like to do a rebuild. I've seen the 20 page rebuilding topic. that's awesome. it's what inspired me. how hard would it be to rebuild the clutch and the engine, though? I've never done this before but everyone seems to think that the CB750 engine is one of the easiest to do. I am mechanically inclined, at least in as much as I really dig working on my bike. and I have a garage. even if it's not completely necessary I would like to have a bullet proof, like new, engine in my baby. I plan on keeping her. forever. so I want to do a good job and have it last.

and I have always wanted a nickel plated frame. one of my teachers had a suzuki with nickel frame and it looked awesome. super stealth. I don't know how much this would cost, but I figure if I got the engine out, what the hell do up the frame as well. excessive cost would change my mind about this pretty quick, though.

any advice would be great. thanks.

[bistromath]

One thing at a time! You don't have to remove the engine to get the clutch out. You should be able to fix the clutch without doing any other major engine work.

[greasy j]

well, I have just been fixing one thing after another. I was thinking maybe I should be thorough. do it all at once.

[greasy j]

You don't have to remove the engine to get the clutch out.

actually I wasn't sure about that. that's quite a relief.

[Tower]

Have you tried adjusting the clutch?  If you don't have a manual, use the manuals found on this site.

[mystic_1]

before this happened I had some problems going up into second, like it would kinda take a little effort to clunk it in there. but I've had other Hondas with loud clunky clutches that ran fine for years so I didn't worry about it. also sometimes it wouldn't go all the way into 4th. it would actually be in neutral between 3rd and 4th until I pulled the toe lever up into 4th all the way.

This sort of thing is not uncommon for the 750's, it's not so unusual to end up in a false neutral between some gears.  It's often a sign of wear in the gear selector forks or transmission gear dogs.  Based on your hard shifting into second, I'd guess your shift forks are worn at minimum.

As to your clutch problem, I'd be taking a close look at the lifter mechanism built into the inner clutch cover, which consists of two discs with three ball bearings sandwiched in between them.  The discs have small ramps machined into them, and when you pull the clutch lever this is the assembly that actually applies pressure to the center of the clutch pack.  If nothing is awry there, check the condition of your clutch center and lifter plates - these are known to crack sometimes.

BTW, score a manual HERE, if you haven't already.  Get the Parts List too, if for no other reason than the excellent exploded diagrams.  The Honda Common Service Manual is a good read, too.

Best of luck

mystic_1

[greasy j]

that is great advice Mystic 1. you guys really are beyond helpful.

I think I figured it out, though. I don't know how to explain it but I took off the cover and inner cover fiddled with it and put it back together and all of the sudden it seems to work now. go figure. I still want to do a complete rebuild at some point, though. because it seems kinda on the way out. and it'd be funner than anything else I have to do with my time off.

I guess I should delete this thread now, right? I don't know the proper forum procedures and whatnot, I'm kinda new.

[mystic_1]

No, leave the thread so that others might benefit from the info.

As to the clutch, if you look at those two discs, you can see how, if you rotated them too far, the balls would ride up out of the ramps and sit on the surfaces of the discs themselves, and would not roll back into the grooves when you let go of the lever.  That's my guess as to what happened.  Adjusting the clutch center screw as per the book should keep this from happening in the future.  Make sure to back off on both cable adjusters first.

Cheers
mystic_1

[greasy j]

thanks a lot! good explanations. I feel like I'm going to have to go back in there sooner or later so I'll probably be needing help at some point. for now it's working and thats all that matters.