Topic: clutch friction zone

[KeithB]

1972 CB 750K
I  found that my '72 had a very small "friction zone" in relation to clutch lever travel and was a bit "snatchy" as well.
So I replaced all the plates with a new set.
Much smoother on the grab but still a very small friction zone.
I have read and re-read clutch adjustment and followed the instructions closely.
The clutch fully dis-engages, doesn't slip on 4th gear acceleration and the actuator has enough play to not be riding on the release bearing, so adjustment seems correct.
 I can't change the the fact that all the clutch action takes place with very short lever movement.
This is not an issue of where in the lever travel clutch action takes place, but rather the travel distance of the lever in relation to the engagement and dis-engagement of the the clutch.
I don't recall this problem on the '78.
Is this normal or have I overlooked something?

[DJ_AX]

... like my 750. ..
It's only in the last 10% of movement that it begins to engage.
With the old clutch plates and with the new. I searched and searched and couldn't find any info on how to change it.
Now the 550 on the other hand begins to engage with about 80% still left to go.
And then slowly and smoothly engages as you let it out to the end.

I've learned to live with it... Kind of like it actually...

But it would be nice to have more control over the controls! 

[DJ_AX]

to add... I've also fiddled with all of the adjustments ..
and while I've learned to live with it, I would REALLY like to be able to control this.

It seems odd that with nearly all other factors being pretty easily adjustable.. this one isn't?

There must be some way!

[chewbacca5000]

Describe your clutch engagement adjustment process for us.  Maybe there is something you are leaving out that another forum member can help with.

[MCRider]

I don't know about the 78, but on the K2, the friction zone is very small. It is what it is, nothing you can do about it except... add a clutch assist like they use on big dirt bikes. It puts a lever in the cable which primary purpose is to relieve the effort, but side effect is it broadens the friction zone.

I had one on my wife's bike years ago, but can't find a link to it.

Without an add on device however, you're stuck with a sensitive clutch. This was noted on the roadtests done at the time. Just the way it is.

[MCRider]

Found it:
http://www.motorcycle-superstore.com/2/9/192/4223/ITEM/Moose-Racing-Easy-Pull-Clutch-System.aspx

This will probably not work on short handlebars. Should work on stock bars. You need enough free length to fit it in, adds about 3-4" to total cable length. Works great!

[DJ_AX]

Would't it be easier to somehow just move the fulcrum on the lever?

[MCRider]

Would't it be easier to somehow just move the fulcrum on the lever?

Probably not, IMO. The assist device is a 20 minute install without modifying anyhting.

I have seen adjustble levers but you have to buy the perch as well which would make for a fairly cluttered handlebar.

I think its a badge of honor for most of us to just get used to the stock throw and master it. 

[DJ_AX]

Is there not anything inside the clutch basket that can be modified to expand the friction zone?

And yes I am honored.

[MCRider]

Is there not anything inside the clutch basket that can be modified to expand the friction zone?

And yes I am honored.

In my search I found that the Harley guys have something like that. An extended arm on the lifter. I've never seen one attempted on the CB750. Not enough room I'd say and the design doesn't lend itself to that.

[KeithB]

I kind of figured it was a "get used to it" thing. Not that big a deal.
Just completed a removal and re-installation of the clutch and had a good look at exactly how the lever movement is converted to a push against the clutch release bearing.
There is a round plate that has 3 pockets for ball bearings and the same thing on the housing. It's behind the adjustment nut/ screw.
As the lever is moved forward by the cable, it rotates the round plate and the bearings ride up out of the pockets and the plate pushes against the release bearing.
The rate of the movement is based on the slope of the sides of the pockets.
This might be something that was changed on later models.
As it turns out, the springs that I first re-installed were after market with a higher spring rate.
Installed the stock springs (35mm) and the feel has improved but still all the action happens in the last 10%.
Overall, an improvement over the old clutch so I will go with what I can get
Thanks for every ones input.

[MCRider]

From K2 to K8, that's what i compared, one of the 3 pieces of the clutch lifter you described, carries a different part number. It's the most inboard, and carries the adjuster bolt. Its not the cam which is pegged to the cover, or the rollers, its the third part.

IIRC, it has ramps machined into it as well and may feel differently. It is also NLA. It would be interesting to pick one up on eBay and compare.

The change occurred halfway through the K8 production so likely rare. Some K8s carry the original part number, hence the original part.

[KeithB]

That's very interesting MCRider!
I might try to get one and try it out.

[mec]

you can try to bend one of the steel plates so that it is out of planeness by ~0.4mm

mec

[MCRider]

you can try to bend one of the steel plates so that it is out of planeness by ~0.4mm

mec

There's a neat trick I may try!

[catsoup]

I am having a similar issue, where the action only takes up about 10% at the very beginning of the pull / end of release. I can't say I really love it.

However, this only seems to have happened after I replaced my steering head bearings and had the front end off / clutch cable disconnected. I think it may seem worse than it is because I am having a slight issue with my throttle where it is a little tight and slow to return, so it sounds like I'm revving when I shift if I do it the way I was accustomed to. This is not so much a problem, just I've had to get used to a new way of doing it.

maybe this will lead someone to further insight. I was going to go look at it this evening so I will report back if I find any variables that changed.
cb750f 78

edit: quick search turns up this, which seems to have some good information for others with this concern. linked are both the standard clutch adjustment method and hondaman's more involved solutions.
http://forums.sohc4.net/index.php?topic=66353.0

edit2: I will admit I did the calibration process again, more carefully this time, and it seems to have solved my problems.