Author Topic: Gears not shifting properly on my CB750K3  (Read 754 times)

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Offline Northern Flyer

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Gears not shifting properly on my CB750K3
« on: April 26, 2017, 08:59:00 pm »
Hoping someone can shed some light on this.
The engine is out of the bike on a stand and I've only removed the side covers, oil pan, valve cover, etc for cleaning. I had also removed the neutral switch and had difficulty reinstalling it because the "gearshift drum" was inwards too far - I could see a "shoulder on the drum through the hole for the neutral switch that was preventing the switch from seating all the way. I used a screwdriver to pry the drum outwards slightly so that the neutral switch seated properly.
I then put on the shift lever to try the gear changes and found that some gears would not fully engage; the "stopper" would not seat between the "rollers" on the end of the drum. I then noticed that there seems to be a fair amount of backlash in the drive shaft that the sprocket attaches to and that if I put a little rotational pressure on the drive shaft, then the gears would change properly.
It appears to be about 1/2 a spline of backlash on the drive shaft - is this normal (engine has about 35K on it to the best of my knowledge).
I did drive the bike around the block when I bought it before taking it apart and never noticed any issue with gear changes at the time.
Any help or information would be appreciated, thanks.

Offline ekpent

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Re: Gears not shifting properly on my CB750K3
« Reply #1 on: April 27, 2017, 04:28:28 am »
 Usually turning the rear wheel or the countershaft sprocket will help it shift into gear if not rolling /running. Can't really comment though on what you are feeling with confidence.Might very well be normal.

Offline evanphi

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Re: Gears not shifting properly on my CB750K3
« Reply #2 on: April 27, 2017, 04:58:09 am »
Usually turning the rear wheel or the countershaft sprocket will help it shift into gear if not rolling /running. Can't really comment though on what you are feeling with confidence.Might very well be normal.

All sounds normal to me.

There's a video out there somewhere of someone bench testing their motorcycle trans (i think it was a CB) using a drill to keep things "rolling".

As far as a bit of "slop" in the sprocket, that is normal.
--Evan

1975 CB750K "Rhonda"
Delkevic Stainless 4-1 Header, Cone Engineering 18" Quiet Core Reverse Cone, K&N Filter in Drilled Airbox
K5 Crankcase/Frame, K4 Head and Cylinders, K1 Carbs (42;120;1 Turn)

She's a mix-matched (former) basket case, but she's mine.

CB750 Shop Manual (all years), searchable text PDF
Calculating the correct input circumference for digital speedometers connected to the original speedometer drive

Offline flybox1

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Re: Gears not shifting properly on my CB750K3
« Reply #3 on: April 27, 2017, 06:51:47 am »

It appears to be about 1/2 a spline of backlash on the drive shaft - is this normal (engine has about 35K on it to the best of my knowledge).
Cases need to be mated to prevent this.
If it shifts thru the gears with sprocket rotation, carry on.
'78 750K (F3 engine) PD42b's, Modified airbox w/K&N  filter, 40/110 jets, 1 needle shim, IMS@ 1 turn out. Kerker + Cone 18" QuietCore

Past Bikes
1974 550K0 (stock), 1973 CB350F (stock), 1983 Yamaha XS400K (POS)
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