Topic: Stiff downshifting

[Patrick]

So I've been tooling around on my newly rebuilt big bore K0 750 for the last couple of days and I have something of an issue with the shifter.

The bike runs well, although I don't have the carbs exactly zeroed in yet, and it upshifts just fine. Downshifting, however, is a bit stiff and neutral exists only when the motor is in a dormant state. All the gears are there, upshifting and downshifting, but it doesn't always downshift smoothly. You have to kind of "punch" it sometimes. It is downshifting more smoothly the more I ride it, but I haven't had this issue with any of my other bikes after rebuilds (nine, total).

Full disclosure: the upper tranny is original to the bike. The lower tranny is from a later model 750. I changed the lower because the gear bushings are reportedly better on the later models than the brass gear bushings on the original. Both trannies are in good condition and the gear size and tooth counts are the same on both the original and the donor tranny.  The tranny meshed well when I was working the gears before I put the case back together. And, again, I have all gears and it upshifts just fine.

What should I be looking at? The clutch or the shifting mechanism? Don't tell me the tranny, cuz I can learn to live with this. 

Patrick

[scondon]

  What type of oil are you using? This can have an effect on how smooth the shifting is.

   Did you add new friction disks, springs to the clutch or check the shifting mechanism for wear? Adjust the clutch and cable per Honda manual?

    I'm pulling for the thought that your tranny is good and that the stiff shifting can be fixed elsewhere.

[Patrick]

Hi Scondon,

The clutch plates are the ones that were in the bike. The fibers were within spec and the steels had no warpage. The clutch springs are heavy duty, about 4mm longer than stock. Although I haven't had the bike above 6,000 rpm, it performs well off the line and does not slip.

The shifting mechanism is from a K2 parts bike and appeared to be in good condition. The springs are still strong. The shifter that came out of the bike was a Frankenstein's monster of a bastardization, created from two lock tab washers from a front brake disk. It was either ingenious or diabolical. I'm still deciding.

I keep leaning toward the clutch. Or, perhaps, a bit of grunge that made it past me and it somehow affecting the shift drum. I am confused, however, about why it works just fine when under power but seems stiff when the power demand is reversed from acceleration to deceleration. My limited mechanical acumen would tell me that it should be the same either way.

I've got the original clutch springs, and they are within spec, but with the big bore and hot cam I wanted more bite in the clutch. Could I have overdone it?

Patrick

[scondon]

  I'm with ya in leaning towards the clutch, and here's why (minus any useful technical language ).

  When shifting WITHOUT using the clutch, going up the gears (1,2,3,4) is easier than going down. It seems to get a little harder the lower you go and the transition between 2nd and 1st gear can require quite a stomp on the lever if rpm's are already high to begin with. I attribute this upshift/downshift difference to the engine being happy to drop some rpm's while going up the gears and unhappy to be shocked into high rpm's while downshifting.

   I'm leaning away from the transmission 'cause I would think that a problem in the tranny would show up in a specific gear and not over all gears. Three shifting forks, lots of meshing gears, etc.... Not one unifying component that would cause the same problem through all gears, as far as I know.

   The shifter mechanism is a real puzzle to me and I've only really looked at it this year. Still, I would think that problems here would result in things like not shifting at all, frozen lever, shifting in between gears,etc...

   I've had to re-adjust the clutch on a couple engines after the first 100 miles or so. Once everything's settled, I guess. Also, the heavy duty springs seem to need a lot less slack at the lever than the stock ones. My buddy liked about 1/2" free lever play(sloppy loose) on his stock 750 clutch. I've had to take all the slack out of the lever, and even more on occasion, in order to get the clutch to fully disengage when using heavy springs w/ new clutch pack.


    By the way, congrats on getting the bike up and running so quick. I'm impressed

[mkramer1121]

First off, are all your clutch plates aliged the same way?  This could cause the clutch to be stiff/not work.

The shifter/trans is pretty simple to understand once you crack the case and examine it.  The shift arm, attached to the pedal, rotates the shift drum.  This is a cam with grooves in it that the shift forks ride in.  The forks move the gears in and out of postition based on the position of the shift drum.   That's it really, with the tangs on the gears locking them in place.

[Patrick]

I don't think it's the clutch plates. This bike has the square block fibers, which really don't have alignment issues like the spiral fiber plates. I'm thinking it's the new heavy duty springs causing the need for more adjustment. And I spent about two weeks three years ago studying the shifter mechanism on my K5 750 trying to figure out how it went back together. I forgot to take pictures when I took that one apart. That kind of lesson stays with you. I hope it is not the shifter, somehow, because I have applied all of my knowledge already. But I am not a master of the shifter by any means. It shifted as it was supposed to when everything was installed before I started the motor for the first time. I didn't notice a difference upshift to downshift.

No need to be impressed with the speed of the project, Scondon. I had some time on my hands and the bike, when it came, was essentially complete. It was a project bike for the last owner, but he never got around to doing anything except collecting parts. Along with the bike were four bins full of NOS or lightly used parts, so I really only had to buy cables, gaskets oil seals and a few incidentals. Most of the time I have spent on past projects has come because I was waiting for delivery of parts or waiting for finances to allow purchase of parts. With the four bins and the K2 parts bike, I had pretty much everything I needed.

Tomorrow I take the bike for a long shakedown ride. Probably 50 to 75 miles. Short five block to five mile drives have convinced me it will take me where I want to go. Now I just need all the new parts to get to know each other.

First, I readjust the clutch again.

Thanks,

Patrick

[754]

Adjust the clutch!!  amd WHERE did you hear of a bushing change in the Tranny ??

[Patrick]

I heard of the bushing change from another well respected forum member. Then I saw them with my own eyes. The bushings in the K0 were brass and apparently subject to premature wear. The later models were not.

Patrick

[754]

Probably bronze bushings. if you can check number off later partslist I can supply number for 69-71 and see if it was superseded..

[Patrick]

A K2 bushing, I believe for second gear, from a K2 750 is 23425-300-010 and the dimensions were 29X14.
23425-300-010.

[754]

That could be a supersede.. first part would have been 300-000

[Patrick]

And, while not an expert on metals, by any means, those bushings sure look like brass to me. Don't seem ruddy enough for bronze...

[RRRToolSolutions]

Patrick, I've been through this on several bikes - most recently the Honda CB750 K4. The springs have nothing to do with the sticking. The Honda clutch has that bearing surface in the center of the pressure plate. Once pulled - the springs compress just as stock ones would. Sure they "clamp" with more pressure, but the clearance between the fibers and steels is one and same. The stock, factory Honda plates are expensive as are the steels - $13 and $11 each respectively. THEY are worth every penny!! Forget the PNM or Barnetts - I've used them and they will never again grace my door. Get the real deal - don't bead blast the steels - they have a smooth finish for a reason. Blasting is great for stopping a slipping clutch, but hard springs and stock plates -steels and fibers will give you a killer clutch, no slip, and factory -new shifting.

Good luck with your project.

Gordon

[scondon]

No need to be impressed with the speed of the project, Scondon. I had some time on my hands and the bike, when it came, was essentially complete.

Patrick

  Still, It takes me months of fretting and studying up before I even begin a project. Got all the parts on hand, you say? I can waste two weeks trying to decide between the shinier part and the one that has less wear, and another week second guessing my choice   Three bikes in six years at this pace

  When using the HD clutch springs I usually adjust the clutch per the manual (turn in until resistance is felt, then back off 1/4 turn). At the lever I adjust a bit tighter than spec (I forget what spec is but seem to recall 1/8" gap between lever and perch before cable slack is fully taken up). I can push on a stock lever with one finger, about as hard as one would push a baby's nose, and see the play in the lever. With the HD springs, a bit more force is needed before seeing ANY gap in the lever. When I set any looser than this I have to pull the lever all the way to the bar, and even that isn't enough sometimes. Results may vary so this is just for comparison.


   When you ride tomorrow, pay attention to whether the downshifting gets stiffer as the bike gets hotter . This won't tell you much about the clutch but might point to lean air/fuel mixture or other condition causing the engine to run too hot. A very hot engine can make shifting a bit harder too.

[Patrick]

The more I think about it, the likely it becomes that my ride tomorrow may be delayed. I have a clutch in a low mileage parts K2 out in the shed. I believe it has seven fibers and six steels. So I should do some comparing. That will be my morning. It's supposed to be low eighties, sunny with a light breeze tomorrow afternoon, so that's when I'd prefer to ride anyway.

The K0 has maybe 10 miles on it now, so I need to recheck the torque on everything anyway.

Patrick

[Patrick]

Too often, when I search the the archives searching for insight and meaning to life, I happen upon a question that mirrors my problem. There is a lot of discussion and some suggestions, and then.... nothing. No postscript. No tie-up-the-loose-ends answer to what the solution was.

So this is a post script. I harvested the clutch from my K2 yesterday and found the fibers and steels to be in remarkably good shape. It also had heavy duty springs, which I did not need. I installed six of the fibers and all of the steels in my K0 this morning. Guess what. Smooth downshifts and... what's that green light... NEUTRAL - WITH THE ENGINE RUNNING. Whoo-hoo!

Needless to say, I did not get around to taking that shake down ride yesterday. After some more adjusting, I think I know what I will be doing this afternoon. It's 75, sunny with no wind and I've got country roads 1/2 mile from home.

Thanks, guys. Another win.

Patrick

[scondon]

  Thanks for the follow-up, Patrick. Now get out and get some wind in yer hair, er...on your helmet......or whatever

[andy750]

Thanks for the post-script Patrick and glad to know you got the problem fixed. Now of course you wont be reading this for a while as you`ll be too busy riding  Enjoy!

cheers
Andy

[azuredesign]

After some more adjusting, I think I know what I will be doing this afternoon. It's 75, sunny with no wind and I've got country roads 1/2 mile from home.

A good ending to a potentially hassle of a situation, congratulations! Reminds me of a story I heard yesterday:

I received a call from Mike, one of the parts guys at my local shop, relating that the jets I had ordered had come in. The parts guys at Arlington Motorsports are friendly and really good to work with. When I arrived, I asked Mike how his ride up to Maine a couple of weeks ago had gone. He kind of grinned and handed me a sparkplug. I looked at the plug which appeared fairly well used and pretty carbon fouled, before I noticed that the threads along one side were completely distorted. When I asked what happened, Mike related that he was riding his '99 Kawa 600 with 158,000 miles on the clock (no joke), down RT 95 when all of a sudden he heard a loud noise and the the dreaded woof, woof sound of lost compression being forced out of some sort of opening, which accompanied significant loss of power. Damn, he said as he pulled off at the exit which happened to be right in front of him, I've holed a cylinder. As he rolled into a vacant lot , Mike said visions of broken twisted alloy castings of varied shapes were running ceaslessly through his thoughts. He pulled into the lot, just as a motorist stopped to say that he had heard the noise, and pointed out a motorcycle shop right behind the lot. The shop turned out to be a metric sport bike shop, and one of the mechanics came out as he pulled in. The fellow listened for a second and said "yup". As Mike shut off the bike, the mechanic reached up into the fairing and pulled out a coil. Imbedded in the coil was the very spark plug I was holding in my hand. The mechanic got another plug, tried it, and lo and behold it threaded right in and snugged up just as it should. 15 minutes later, with the coil replaced, Mike rode home and slept like a baby that eve.

I bet you'll sleep well tonight as well. It's such a good feeling when things work out easily and quickly.
Hope you had a great ride!