« previous next »
Pages: [1]   Go Down

Author Topic: Piston ring thickness for CB750  (Read 534 times)

0 Members and 1 Guest are viewing this topic.

Offline timtune

  • Enthusiast
  • **
  • Posts: 188
Piston ring thickness for CB750
« on: July 12, 2023, 07:08:43 AM »
Last time I bought rings they were too thick to fit in the piston grooves. Turns out my franken motor had F and K parts.
I need rings for another project. All I can tell is the grooves in the pistons are .056". Before I order can someone confirm these pistons as F or K?

Thanks
Logged

Online newday777

  • Really Old Timer ...
  • *******
  • Posts: 5,437
  • Avatar is my 76 K6 in Colorado w/Cody on back 1980
Re: Piston ring thickness for CB750
« Reply #1 on: July 12, 2023, 07:46:44 AM »
Any numbers on the pistons at the writ pin recess or inside the piston?
Logged
Stu
Honda Parts manager in the mid 1970s Nashua Honda
My current rides
1975 K5 Planet Blue my summer ride, it was a friend's bike I worked with at the Honda shop in 76, lots of fun to be on it again
1976 K6 Anteres Red rebuilding project, was originally my brother's that I set up from the crate, it'll breath again soon!
Project 750s, 2 K4, 2 K6, 1 K8
2008 GL1800 my daily ride and cross country runner

Prior bikes....
1972 Suzuki GT380 I had charge of it for a year in 1973 while my friend was deployed and learned to love street riding....
New CB450 K7 after my friend returned...
New CB750 K5 Planet Blue, demise by ex cousin in law at 9,000 miles...
New CB750 K6 Anteres Red, to replace the totaled K5, I sold this K6 at 45k in 1983, I had heavily modified it, many great memories on it and have missed it greatly.....
1983 GL1100A, 1999 GL1500 SE, 1999 GL1500A

Offline timtune

  • Enthusiast
  • **
  • Posts: 188
Re: Piston ring thickness for CB750
« Reply #2 on: July 13, 2023, 06:14:45 AM »
Yes
They all have 300 to the left of the pin and then 9, 10 or 11 to the right of the pin. The recess on the other side just says Honda.

The tops have the triangle pointing forward to two valve divets and large valve divet at the rear.
Logged

Offline bryanj

  • Really Old Timer ...
  • *******
  • Posts: 14,092
  • CB500 Number 1000036
Re: Piston ring thickness for CB750
« Reply #3 on: July 13, 2023, 07:34:11 AM »
300 should have the thicker rings, 410 thinner not sure on 390.
This all assumes Honda pistons and rings not aftermarket
Logged
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 timtune

  • Enthusiast
  • **
  • Posts: 188
Re: Piston ring thickness for CB750
« Reply #4 on: July 13, 2023, 12:02:07 PM »
I thought .056 was the thinner ring with the thicker being about .070"
Logged

Offline Jerry Rxman Griffin aka MuthaF'er

  • This MuthaF'er is getting to be a
  • Really Old Timer ...
  • *******
  • Posts: 14,929
  • Bought her new 4/75
Re: Piston ring thickness for CB750
« Reply #5 on: July 13, 2023, 01:31:09 PM »
1.5mm, 1.5mm. 2.5mm vs later at 1.2mm, 1.2mm, 2.5mm
Logged
As of today 3/13/2012 my original owner 75 CB750F has made it through 3 wives, er EX-wives. Free at last.  ;-)

Offline timtune

  • Enthusiast
  • **
  • Posts: 188
Re: Piston ring thickness for CB750
« Reply #6 on: July 14, 2023, 05:17:54 AM »
Quote from: Jerry Rxman Griffin aka MuthaF'er on July 13, 2023, 01:31:09 PM
1.5mm, 1.5mm. 2.5mm vs later at 1.2mm, 1.2mm, 2.5mm

What do these represent? .058" =1.5mm .046"= 1.2. Mine must then be the earlier.
Is there not a difference between K and F or were pistons the same per year
Logged

Offline bryanj

  • Really Old Timer ...
  • *******
  • Posts: 14,092
  • CB500 Number 1000036
Re: Piston ring thickness for CB750
« Reply #7 on: July 14, 2023, 08:47:18 AM »
Only way to be shure is check parts books/fiche
Logged
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 Jerry Rxman Griffin aka MuthaF'er

  • This MuthaF'er is getting to be a
  • Really Old Timer ...
  • *******
  • Posts: 14,929
  • Bought her new 4/75
Re: Piston ring thickness for CB750
« Reply #8 on: July 14, 2023, 12:37:14 PM »
The narrower rings/pistons were installed on late 76 F, 77/78 Fs and possibly 77/78 K's

Agree with Bryan. Most -300 model and -392 model pistons were 1.5, 1.5, 2.5 rings

I don't do SAE with metric old Hondas
Logged
As of today 3/13/2012 my original owner 75 CB750F has made it through 3 wives, er EX-wives. Free at last.  ;-)

Online Don R

  • My Sandcast is a
  • Really Old Timer ...
  • *******
  • Posts: 20,113
  • Saver of unloved motorcycles.
Re: Piston ring thickness for CB750
« Reply #9 on: July 14, 2023, 01:06:24 PM »
 My old 836 was also 1.5, 1.5, 2.5 mm but aftermarket pistons have no rules.
Logged
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 HondaMan

  • Someone took this pic of me before I became a
  • Really Old Timer ...
  • *******
  • Posts: 13,966
  • ...not my choice, I was nicknamed...
    • Getting 'em Back on the Road
Re: Piston ring thickness for CB750
« Reply #10 on: July 14, 2023, 05:05:52 PM »
Quote from: Don R on July 14, 2023, 01:06:24 PM
...but aftermarket pistons have no rules.
Yeah. This has gotten me in trouble before. :(
Logged
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 timtune

  • Enthusiast
  • **
  • Posts: 188
Re: Piston ring thickness for CB750
« Reply #11 on: July 15, 2023, 07:31:42 AM »
Quote from: Jerry Rxman Griffin aka MuthaF'er on July 14, 2023, 12:37:14 PM
The narrower rings/pistons were installed on late 76 F, 77/78 Fs and possibly 77/78 K's

Agree with Bryan. Most -300 model and -392 model pistons were 1.5, 1.5, 2.5 rings

I don't do SAE with metric old Hondas

Ok this finally makes sense. My 300 series have the fatter rings. Before I bought the same rings and then found out my franken motor had a f jugs and pistons which they would not fit.

https://www.vintagecb750.com/products/4/engine/75/piston-ring-sets 
Part # 05-7000 looks like what I need
Logged
Pages: [1]   Go Up
« previous next »