Author Topic: K0 gearshift drum swap Q?  (Read 343 times)

0 Members and 1 Guest are viewing this topic.

Offline Don R

  • My Sandcast is a
  • Really Old Timer ...
  • *******
  • Posts: 19,857
  • Saver of unloved motorcycles.
K0 gearshift drum swap Q?
« on: February 13, 2024, 02:18:54 PM »
 Can the early, K0 style narrow groove shift drum be swapped for a later upgraded shift drum with the wider grooves, and are the shift forks different? 
 It appears that partzilla lists the cb750K through K6 having the same shift fork part numbers.
« Last Edit: February 13, 2024, 02:25:54 PM by Don R »
No matter how many times you paint over a shadow, it's still there.
 CEO at the no kill motorcycle shop.
 You don't need a weatherman to know which way the wind blows.

Offline bryanj

  • Really Old Timer ...
  • *******
  • Posts: 13,980
  • CB500 Number 1000036
Re: K0 gearshift drum swap Q?
« Reply #1 on: February 13, 2024, 02:45:59 PM »
There is a bulletin about the later drum somewhere, i seem to remember the slot is the same, its the flat spot on top of the peaks that is wider.
I have posted the bulletin recently
Semi Geriatric ex-Honda mechanic and MOT tester (UK version of annual inspection). Garage full of "projects" mostly 500/4 from pre 73 (no road tax in UK).

Remember "Its always in the last place you look" COURSE IT IS YOU STOP LOOKIN THEN!

Offline HondaMan

  • Someone took this pic of me before I became a
  • Really Old Timer ...
  • *******
  • Posts: 13,810
  • ...not my choice, I was nicknamed...
    • Getting 'em Back on the Road
Re: K0 gearshift drum swap Q?
« Reply #2 on: February 13, 2024, 06:59:40 PM »
You can use the later shift drum in the early 750, but not always vice-versa. The pins on the shift forks got longer in the K4, while the grooves in the shift drum got deeper in the late K2. The early drum's shift grooves can sometimes then drag on the longer pins' edges in the later forks, requiring some filing/grinding to shorten them a little bit. It's do-able in a pinch.

But, using the later shift drum in the early engines always fits. It has one distinct characteristic that made me do it in my early K2: the Neutral 'bump' is wider and makes it easier to find Neutral, although if you're going racing it also slows the 1-2 shift a little bit as it makes the lever 'feel' heavier if trying to shift it quickly. I swapped mine at 121k miles because my Neutral Bump was getting worn and this would let it slip past Neutral easily when going from 2-to-N while rolling to a stop. For me it was an overall 'win'.
See SOHC4shop@gmail.com for info about the gadgets I make for these bikes.

The demons are repulsed when a man does good. Use that.
Blood is thicker than water, but motor oil is thicker yet...so, don't mess with my SOHC4, or I might have to hurt you.
Hondaman's creed: "Bikers are family. Treat them accordingly."

Link to Hondaman Ignition: http://forums.sohc4.net/index.php?topic=67543.0

Link to My CB750 Book: https://www.lulu.com/search?adult_audience_rating=00&page=1&pageSize=10&q=my+cb750+book

Link to website: www.SOHC4shop.com

Offline bryanj

  • Really Old Timer ...
  • *******
  • Posts: 13,980
  • CB500 Number 1000036
Re: K0 gearshift drum swap Q?
« Reply #3 on: February 13, 2024, 07:48:17 PM »
Bulletin
Semi Geriatric ex-Honda mechanic and MOT tester (UK version of annual inspection). Garage full of "projects" mostly 500/4 from pre 73 (no road tax in UK).

Remember "Its always in the last place you look" COURSE IT IS YOU STOP LOOKIN THEN!

Offline Don R

  • My Sandcast is a
  • Really Old Timer ...
  • *******
  • Posts: 19,857
  • Saver of unloved motorcycles.
Re: K0 gearshift drum swap Q?
« Reply #4 on: February 13, 2024, 10:27:14 PM »
 Thanks, believe it or not I did search for #40 bulletin. I'll try to get a picture of these two side by side. Who knows maybe it's an optical illusion, but I thought one was significantly wider than the other one. That bump is where it hangs up when I test shift it. There's a good chance they are both early type.
No matter how many times you paint over a shadow, it's still there.
 CEO at the no kill motorcycle shop.
 You don't need a weatherman to know which way the wind blows.