« previous next »
Pages: [1]   Go Down

Author Topic: Honda CB750F Piston Types  (Read 1888 times)

0 Members and 1 Guest are viewing this topic.

Offline RodSOHC750

  • Full Member
  • *
  • Posts: 94
  • Restoring Vintage Honda Motorcycles
Honda CB750F Piston Types
« on: February 09, 2016, 10:01:41 am »
I'm having difficulty finding 0.5mm oversize pistons for my 1975 CB750F.  I don't have the pistons with me as they were left with a machine shop out of town. I recall the pistons having a flat top and the machinist told me the pistons had a "392" on them. My only source of information is the attached table of Honda 61.0mm pistons.  Some of the information is confusing to me and indicates more than one piston for the F model. I know the number after the piston height (+5) is the dome height (5mm), so a flat top piston would be indicated by "+0".

What is the Honda P/N of the 0.5mm oversize piston I need?  Will a 750K piston work?  I want to maintain the stock compression ratio (9.0:1).
Logged
1979 Honda CB750L Limited Edition
1975 Honda CB750F Super Sport
1972 Honda CL450
1970 Honda CT70

Offline BPellerine

  • Master
  • *****
  • Posts: 2,222
Re: Honda CB750F Piston Types
« Reply #1 on: February 09, 2016, 12:13:30 pm »
75 f are the same as 77,78k I think,only the 77,78f pistons were diff,should be a 392 pt no,later ones had a 410 pt no.bill
Logged
1978 CB 750K ard and webers
another anfob

Offline Kawahonda

  • Full Member
  • *
  • Posts: 73
Re: Honda CB750F Piston Types
« Reply #2 on: February 11, 2016, 08:44:56 am »
That chart says that F0/F1 pistons are not necessarily the same as K pistons.

What a predicament! Is that chart wrong?
Logged

Offline przjohn

  • Expert
  • ****
  • Posts: 948
Re: Honda CB750F Piston Types
« Reply #3 on: February 11, 2016, 10:01:10 am »
Logged
I like poetry, long walks on the beach, and poking at dead things with a stick.

Offline SOHC4 Cafe Racer Fan

  • Speak up, Whipper-Snapper! I'm a
  • Really Old Timer ...
  • *******
  • Posts: 15,721
  • SOHC/4 Member #1235
Re: Honda CB750F Piston Types
« Reply #4 on: February 11, 2016, 10:02:10 am »
CMSNL never is cheap.
Logged
1975 CB550K1 "Blue" Stockish Restomod (http://forums.sohc4.net/index.php?topic=135005.0)
1975 CB550F1 frame/CB650 engine hybrid "The Hot Mess" (http://forums.sohc4.net/index.php/topic,150220.0.html)
2008 Triumph Thruxton (http://forums.sohc4.net/index.php/topic,190956.0.html)
2014 MV Agusta Brutale Dragster 800
2015 Yamaha FZ-09 (http://forums.sohc4.net/index.php/topic,186861.0.html)

"There are some things nobody needs in this world, and a bright-red, hunch-back, warp-speed 900cc cafe racer is one of them — but I want one anyway, and on some days I actually believe I need one.... Being shot out of a cannon will always be better than being squeezed out of a tube. That is why God made fast motorcycles, Bubba." Hunter S. Thompson, Song of the Sausage Creature, Cycle World, March 1995.  (http://www.latexnet.org/~csmith/sausage.html and https://magazine.cycleworld.com/article/1995/3/1/song-of-the-sausage-creature)

Sold/Emeritus
1973 CB750K2 "Bionic Mongrel" (http://forums.sohc4.net/index.php?topic=132734.0) - Sold
1977 CB750K7 "Nine Lives" Restomod (http://forums.sohc4.net/index.php?topic=50490.0) - Sold
2005 RVT1000RR RC51-SP2 "El Diablo" - Sold
2016+ Triumph Thruxton 1200 R (http://forums.sohc4.net/index.php/topic,170198.0.html) - Sold

Offline Kawahonda

  • Full Member
  • *
  • Posts: 73
Re: Honda CB750F Piston Types
« Reply #5 on: February 11, 2016, 11:36:23 am »
In Rod's case, I think he decided to go with a slightly over bore rather than an 836 kit.

The cruisin image seller has this for cheap.

Looking at the chart, it APPEARS (like others have been saying) that the F0/F1 pistons have the same heartline and height as the early K pistons. The only difference is slightly different diameters over the year, but since you're over-boring anyways, it doesn't matter.

.5mm oversized:
http://www.ebay.com/itm/69-76-HONDA-CB750K-0-5mm-OVERSIZE-PISTONS-SET-4-PISTONS-INCLUDE-CI-CB750KPS-1-/131588210647?vxp=mtr&hash=item1ea344bfd7

1.0mm oversized:
http://www.ebay.com/itm/69-76-HONDA-CB750K-1-0mm-OVERSIZE-PISTONS-SET-4-PISTONS-INCLUDE-CI-CB750KPS-2-/131588211611?vxp=mtr&hash=item1ea344c39b

I think you've got your answer on this one.
« Last Edit: February 11, 2016, 11:45:41 am by Kawahonda »
Logged

Offline Jerry Rxman Griffin aka MuthaF'er

  • This MuthaF'er is getting to be a
  • Really Old Timer ...
  • *******
  • Posts: 14,890
  • Bought her new 4/75
Re: Honda CB750F Piston Types
« Reply #6 on: February 11, 2016, 11:52:06 am »
Both of these are -392 pistons. The 'full top' is from my 75 CB750F. It uses standard -300 rings. 1.5, 1.5, 2.5mm. The 'partial dome' is from a 78 K engine. It uses 1.2, 1.2??, 2.5mm rings

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 RodSOHC750

  • Full Member
  • *
  • Posts: 94
  • Restoring Vintage Honda Motorcycles
Re: Honda CB750F Piston Types
« Reply #7 on: February 11, 2016, 01:01:05 pm »
My piston top appears like the piston on the right. . . . 75 CB750F.  Oil ring is 3 parts. 
Logged
1979 Honda CB750L Limited Edition
1975 Honda CB750F Super Sport
1972 Honda CL450
1970 Honda CT70

Offline Kawahonda

  • Full Member
  • *
  • Posts: 73
Re: Honda CB750F Piston Types
« Reply #8 on: February 11, 2016, 01:32:46 pm »
The cruisin image kit appears to have that safe flat top profile with valve cut outs.

So I assume with the cruisin image kit you'd be at 9.2:1 or abouts, same as stock. You certainly don't want to lose compression. I'm paraphrasing big time here, but I remember Hondaman stating somewhere that 9.4:1 (or was it 9.5:1?) was a good healthy limit for street SOHCs, maybe he can confirm.
« Last Edit: February 11, 2016, 01:34:21 pm by Kawahonda »
Logged
Pages: [1]   Go Up
« previous next »