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melchiro
Silver CB900F
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Joined: Aug 10, 2003
Posts: 1495
Location: Mill Creek, WA.

PostPosted: Tue Sep 16, 2014 2:27 am Reply with quote Back to top

Here are the numbers between the two pistons..

900 on the left, CBX on the right..
Image

Same but showing the bottom..
Image

900 piston..
Image

CBX piston..
Image

900 piston..
Image

CBX piston
Image

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1983 Modified CB-750/1123F Track bike
1980 GS1000GT Project
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Ridem32
MB-5
MB-5



Joined: Sep 15, 2014
Posts: 9
Location: Mississippi

PostPosted: Wed Sep 17, 2014 3:33 pm Reply with quote Back to top

If the cbx is on the right it has a dome top, making it taller! But your guage shows the cbx being shorter! I know they use the same rings! I put 900 rings in my cbx
Michael
 
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nathanhouse
Silver CB900F
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Joined: Oct 05, 2008
Posts: 1490
Location: Dover, NH

PostPosted: Wed Sep 17, 2014 4:02 pm Reply with quote Back to top

when measuring the piston you don't count the height of the dome into the compression distance equation only the the flat of the piston. On these CBX pistons it looks like there is no flat so you measure to the very outside edge of the piston as melchiro did.
Thanks for the comparison!
 
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Jebbysan
Red CB1100F
Red CB1100F



Joined: Dec 08, 2007
Posts: 7125
Location: New Braunfels,Texas

PostPosted: Wed Sep 17, 2014 4:26 pm Reply with quote Back to top

nathanhouse wrote:
when measuring the piston you don't count the height of the dome into the compression distance equation only the the flat of the piston. On these CBX pistons it looks like there is no flat so you measure to the very outside edge of the piston as melchiro did.
Thanks for the comparison!


+1

Jebby

_________________
Ass, Grass or Gas....no one rides for free....
1979 CBX
1972 Corvette Stingray Coupe 406/4spd
1982 Z/28
2011 Silverado Crew Cab


"I don't do T and A...because I don't have much of either" Tea Leoni 
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sonicrete
Red CB1100F
Red CB1100F



Joined: Aug 19, 2003
Posts: 15486
Location: Lancaster,Ohio

PostPosted: Wed Sep 17, 2014 6:25 pm Reply with quote Back to top

You also measure from the pin center or same pin diameter from the top edge.
 
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DOHCRob
Black CB750F
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Joined: May 23, 2011
Posts: 827
Location: Hinckley, OH

PostPosted: Wed Sep 17, 2014 8:46 pm Reply with quote Back to top

nathanhouse wrote:
when measuring the piston you don't count the height of the dome into the compression distance equation only the the flat of the piston. On these CBX pistons it looks like there is no flat so you measure to the very outside edge of the piston as melchiro did.
Thanks for the comparison!


I am not sure I understand what you are saying? Please elaborate!

If all other things were exactly the same, except one piston would have a dome, this piston would create a higher compression ratio, because the volume of the combustion chamber at TDC would be smaller.
 
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Jebbysan
Red CB1100F
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Joined: Dec 08, 2007
Posts: 7125
Location: New Braunfels,Texas

PostPosted: Wed Sep 17, 2014 9:20 pm Reply with quote Back to top

We are not speaking of compression ratio....it is from the piston DECK
to the center of the pin....this is called the C/D or compression distance...
If you whacked the dome off of the CBX piston...what is left is the deck....
Use also use the piston deck to determine piston to head....at the quench
area....there is Piston to Valve and Piston to head at the dome too...but these
Honda pistons are not a "Max Dome" design like my 15:1 540 Chevy's are....
It should be "Clayed Out" as good practice but it is not close as Nathan's photos
show in his 985 thread.....
Optimum is "zero deck"....and most steel rod applications call for .040
rod stretch.....a crushed gasket is .040....soooooo....piston flush with deck
is ideal.....
This will effect compression ratio as well.....but indirectly....it is factored in
when calculating CR....
Hope that helps!

Jebby

_________________
Ass, Grass or Gas....no one rides for free....
1979 CBX
1972 Corvette Stingray Coupe 406/4spd
1982 Z/28
2011 Silverado Crew Cab


"I don't do T and A...because I don't have much of either" Tea Leoni 
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nathanhouse
Silver CB900F
Silver CB900F



Joined: Oct 05, 2008
Posts: 1490
Location: Dover, NH

PostPosted: Wed Sep 17, 2014 11:02 pm Reply with quote Back to top

Right it would be measured from the pin centerline but just for comparison this works well. Jebbys right, compression ratio and compression distance or height are two very different things.
 
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Jebbysan
Red CB1100F
Red CB1100F



Joined: Dec 08, 2007
Posts: 7125
Location: New Braunfels,Texas

PostPosted: Wed Sep 17, 2014 11:33 pm Reply with quote Back to top

nathanhouse wrote:
Right it would be measured from the pin centerline but just for comparison this works well. Jebbys right, compression ratio and compression distance or height are two very different things.


I measure from where you did and add half of the pin Wink Easy!

Jebby

_________________
Ass, Grass or Gas....no one rides for free....
1979 CBX
1972 Corvette Stingray Coupe 406/4spd
1982 Z/28
2011 Silverado Crew Cab


"I don't do T and A...because I don't have much of either" Tea Leoni 
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Shawn_Mc
CB1100F
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Joined: Jul 30, 2012
Posts: 2813
Location: Anaheim Hills, Ca.

PostPosted: Fri Sep 19, 2014 1:55 am Reply with quote Back to top

One of those is a Wiseco (taller dome) and the other is the OEM Honda, correct?

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1100russ
CB1100F
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Joined: May 17, 2010
Posts: 2914
Location: williamsburg, ohio

PostPosted: Fri Sep 19, 2014 3:19 am Reply with quote Back to top

Never seen a 900 piston out but that is a stock CBX piston for sure.

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bobcat7
Black CB750F
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Joined: Oct 03, 2011
Posts: 1011
Location: dallas texas

PostPosted: Fri Sep 19, 2014 4:37 am Reply with quote Back to top

I have CBX 4th over pistons in my 82 900F motor
(20 years now). the CBX piston is shorter (.080")
and in total length but is also lighter, a desirable thing
in a high winding undersquare motor due to piston
speed. in order to use them in a 900 or 750 the cyl.
block base must be milled .080 + to get the desired
piston to head clearance (deck height) and I found
that other mods. were necessary to make this work
right. this motor, and whole bike was a total experiment
but 20 years later it exceeds my wildest expectations
and still runs,rides and handles flawless and requires
only routine maintenance. deck height is .038" and
compression ratio is 11.5/1 .
 
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Jebbysan
Red CB1100F
Red CB1100F



Joined: Dec 08, 2007
Posts: 7125
Location: New Braunfels,Texas

PostPosted: Fri Sep 19, 2014 5:44 am Reply with quote Back to top

bobcat7 wrote:
I have CBX 4th over pistons in my 82 900F motor
(20 years now). the CBX piston is shorter (.080")
and in total length but is also lighter, a desirable thing
in a high winding undersquare motor due to piston
speed. in order to use them in a 900 or 750 the cyl.
block base must be milled .080 + to get the desired
piston to head clearance (deck height) and I found
that other mods. were necessary to make this work
right. this motor, and whole bike was a total experiment
but 20 years later it exceeds my wildest expectations
and still runs,rides and handles flawless and requires
only routine maintenance. deck height is .038" and
compression ratio is 11.5/1 .


I was waiting for you!

Jebby

_________________
Ass, Grass or Gas....no one rides for free....
1979 CBX
1972 Corvette Stingray Coupe 406/4spd
1982 Z/28
2011 Silverado Crew Cab


"I don't do T and A...because I don't have much of either" Tea Leoni 
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melchiro
Silver CB900F
Silver CB900F



Joined: Aug 10, 2003
Posts: 1495
Location: Mill Creek, WA.

PostPosted: Fri Sep 19, 2014 6:28 am Reply with quote Back to top

Shawn_Mc wrote:
One of those is a Wiseco (taller dome) and the other is the OEM Honda, correct?


Image

These are my own pistons, stock CB900, (left piston) and stock CBX, (right pistons}... I replaced my stock CBX pistons with the OMT 68mm pistons.. Here is my CBX thread..
My 1979 CBX Project

I created a the topic here so that I would not muck up Nathan's 985 Project thread.. And because there was so much mystery surrounding the CBX piston's dimensions... Well, some of knew, but I guess without photographic evidence as proof, there was some doubt...

_________________
1979 Modified CBX
1982 Modified CB-750/1100F
1983 Modified CB-750/1123F Track bike
1980 GS1000GT Project
1972 CB500 Four K1 Project 
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Jebbysan
Red CB1100F
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Joined: Dec 08, 2007
Posts: 7125
Location: New Braunfels,Texas

PostPosted: Fri Sep 19, 2014 8:52 am Reply with quote Back to top

No doubt ever here....

Jebby

_________________
Ass, Grass or Gas....no one rides for free....
1979 CBX
1972 Corvette Stingray Coupe 406/4spd
1982 Z/28
2011 Silverado Crew Cab


"I don't do T and A...because I don't have much of either" Tea Leoni 
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orion
Twinstar
Twinstar



Joined: Oct 03, 2012
Posts: 91
Location: texas

PostPosted: Fri Sep 19, 2014 9:24 am Reply with quote Back to top

wtf am i looking at here ?
 
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sonicrete
Red CB1100F
Red CB1100F



Joined: Aug 19, 2003
Posts: 15486
Location: Lancaster,Ohio

PostPosted: Fri Sep 19, 2014 3:29 pm Reply with quote Back to top

Honda changing something. Nothing like the assholes using same parts just to change them.

I measured the aftermarket pistons that have a flat for the headgasket and they measure .060" different.

Just WHY would someone use CBX pistons in 4 just because you had them?
 
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bobcat7
Black CB750F
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Joined: Oct 03, 2011
Posts: 1011
Location: dallas texas

PostPosted: Fri Sep 19, 2014 9:15 pm Reply with quote Back to top

sonicrete wrote:
Honda changing something. Nothing like the assholes using same parts just to change them.

I measured the aftermarket pistons that have a flat for the headgasket and they measure .060" different.

Just WHY would someone use CBX pistons in 4 just because you had them?


because I CAN, I KNOW HOW AND IT WORKS ! just like my carbs! Rolling Eyes Cool

just because you haven't figured it out, done your research, I guess means that
it won't work ! right ?! you are the last word when it comes to criticism ! Crying or Very sad
 
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Jebbysan
Red CB1100F
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Joined: Dec 08, 2007
Posts: 7125
Location: New Braunfels,Texas

PostPosted: Fri Sep 19, 2014 11:06 pm Reply with quote Back to top

orion wrote:
wtf am i looking at here ?


I guess I have to say wtf is that suppose to mean?
I think what you are wondering is this:
A lot of folks in the way back machine used CBX pistons to make a
985....it wasn't easy and the reason being is that the piston pin was
in a different position....you had to machine the jug to make it work.
Just another way to skin a cat....

Jebby

_________________
Ass, Grass or Gas....no one rides for free....
1979 CBX
1972 Corvette Stingray Coupe 406/4spd
1982 Z/28
2011 Silverado Crew Cab


"I don't do T and A...because I don't have much of either" Tea Leoni 
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nathanhouse
Silver CB900F
Silver CB900F



Joined: Oct 05, 2008
Posts: 1490
Location: Dover, NH

PostPosted: Sat Sep 20, 2014 12:41 am Reply with quote Back to top

bobcat7 wrote:
I have CBX 4th over pistons in my 82 900F motor
(20 years now). the CBX piston is shorter (.080")
and in total length but is also lighter, a desirable thing
in a high winding undersquare motor due to piston
speed. in order to use them in a 900 or 750 the cyl.
block base must be milled .080 + to get the desired
piston to head clearance (deck height) and I found
that other mods. were necessary to make this work
right. this motor, and whole bike was a total experiment
but 20 years later it exceeds my wildest expectations
and still runs,rides and handles flawless and requires
only routine maintenance. deck height is .038" and
compression ratio is 11.5/1 .


Happy with that compression ratio Bobcat? Any issues? I've been going back and forth about where I want to land on this subject. I was thinking right about 11.5-1 on pump gas. I think I'll be able to run higher than some because of some of the changes I'm making to the engine ie combustion shape plug location and stuff like that. However, I admittedly don't know as much about this aircooled stuff as others on this site so I'm always looking for good advice and hands on experience!
 
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bobcat7
Black CB750F
Black CB750F



Joined: Oct 03, 2011
Posts: 1011
Location: dallas texas

PostPosted: Sat Sep 20, 2014 4:28 am Reply with quote Back to top

nathanhouse wrote:
bobcat7 wrote:
I have CBX 4th over pistons in my 82 900F motor
(20 years now). the CBX piston is shorter (.080")
and in total length but is also lighter, a desirable thing
in a high winding undersquare motor due to piston
speed. in order to use them in a 900 or 750 the cyl.
block base must be milled .080 + to get the desired
piston to head clearance (deck height) and I found
that other mods. were necessary to make this work
right. this motor, and whole bike was a total experiment
but 20 years later it exceeds my wildest expectations
and still runs,rides and handles flawless and requires
only routine maintenance. deck height is .038" and
compression ratio is 11.5/1 .


If I had it to do again, I would shoot for 10.5/1 or 11/1
max for street use. I forgot to mention that I had the head
milled .020" too. not necessary to use CBX pistons but
jumps the compression up ! I just went a little overboard. Razz
the best place to gain compression is deck height (piston to head),
then piston dome or head milling. deck height no.1 priority.

Happy with that compression ratio Bobcat? Any issues? I've been going back and forth about where I want to land on this subject. I was thinking right about 11.5-1 on pump gas. I think I'll be able to run higher than some because of some of the changes I'm making to the engine ie combustion shape plug location and stuff like that. However, I admittedly don't know as much about this aircooled stuff as others on this site so I'm always looking for good advice and hands on experience!
 
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bobcat7
Black CB750F
Black CB750F



Joined: Oct 03, 2011
Posts: 1011
Location: dallas texas

PostPosted: Sat Sep 20, 2014 4:37 am Reply with quote Back to top

Jebbysan wrote:
orion wrote:
wtf am i looking at here ?


I guess I have to say wtf is that suppose to mean?
I think what you are wondering is this:
A lot of folks in the way back machine used CBX pistons to make a
985....it wasn't easy and the reason being is that the piston pin was
in a different position....you had to machine the jug to make it work.
Just another way to skin a cat....

Jebby


Jebby, only the big bore kit for the CBX will produce a 985. 4th over
stock, OEM CBX pistons is what I used which yields 930cc. the 900
and CBX are the same bore but the stroke is dramatically different.
 
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sonicrete
Red CB1100F
Red CB1100F



Joined: Aug 19, 2003
Posts: 15486
Location: Lancaster,Ohio

PostPosted: Sat Sep 20, 2014 5:26 am Reply with quote Back to top

Wow a lot of work to make 930cc. Never made any that small. Mine were 1187cc. 74mm bore and 69mm stroke.

Do your self a favor and order pistons what you want,not try to make shit work and BRAG ABOUT IT.
 
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bobcat7
Black CB750F
Black CB750F



Joined: Oct 03, 2011
Posts: 1011
Location: dallas texas

PostPosted: Sat Sep 20, 2014 5:33 am Reply with quote Back to top

sonicrete wrote:
Wow a lot of work to make 930cc. Never made any that small. Mine were 1187cc. 74mm bore and 69mm stroke.

Do your self a favor and order pistons what you want,not try to make shit work and BRAG ABOUT IT.


come down here and ride this thing before you pronounce your Holy Judgement.

those are the pistons I WANTED !
 
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melchiro
Silver CB900F
Silver CB900F



Joined: Aug 10, 2003
Posts: 1495
Location: Mill Creek, WA.

PostPosted: Sat Sep 20, 2014 1:04 pm Reply with quote Back to top

Jebbysan wrote:
No doubt ever here....

Jebby


Yeah Jebby, I knew I did not have to convince you.. Wink

Nathan, if you are going back and forth, considering using your Wiseco pistons, thinking about shaving more materials to get that 0 deck height and all,...

Have you thought about using the Ebay Cruzinimage pistons? Though it does not have the high dome like the Wiseco,at least with the Cruzinimage pistons, you will have 0 deck height, so it may even out, compression wise. And, Brent likes a flat dome for a better combustion... Food for thought..

_________________
1979 Modified CBX
1982 Modified CB-750/1100F
1983 Modified CB-750/1123F Track bike
1980 GS1000GT Project
1972 CB500 Four K1 Project 
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nathanhouse
Silver CB900F
Silver CB900F



Joined: Oct 05, 2008
Posts: 1490
Location: Dover, NH

PostPosted: Sat Sep 20, 2014 3:14 pm Reply with quote Back to top

melchiro wrote:
Jebbysan wrote:
No doubt ever here....

Jebby


Yeah Jebby, I knew I did not have to convince you.. Wink

Nathan, if you are going back and forth, considering using your Wiseco pistons, thinking about shaving more materials to get that 0 deck height and all,...

Have you thought about using the Ebay Cruzinimage pistons? Though it does not have the high dome like the Wiseco,at least with the Cruzinimage pistons, you will have 0 deck height, so it may even out, compression wise. And, Brent likes a flat dome for a better combustion... Food for thought..


I already have the Wiseco pistons, but even though I have them I can still adjust the CR. I just going back and forth between running closer to 10-1 or 11.5-1. The pistons will be zero deck and the domes will be modified but how much will depend on the piston deck thickness. If there is enough material I'd like to cut some of the dome down on the exhaust side of the piston to help with mixture motion and to help push the compressed A/F over toward the exhaust side of the chamber. I also want to flatten the top of the dome down a bit to help with flame propagation. I may do a little bit to the exhaust valve notches as well to help with mixture motion but like I said, all this depends on how much material I have to work with. I'll probably look into this a bit more this next week.
 
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Shawn_Mc
CB1100F
CB1100F



Joined: Jul 30, 2012
Posts: 2813
Location: Anaheim Hills, Ca.

PostPosted: Sat Sep 20, 2014 11:14 pm Reply with quote Back to top

Personally, I think he's better off with the Wisecos because theyre forged as opposed to the cruzin image that are cast.

Im just wondering if decking the cylinder to get to zero, or if decking the cases to get to zero is better. Seems like you'd want to keep the cylinder deck as thick as possible to wick heat. Or maybe split the difference...4-5 ways to skin that particular cat.

Most of the Wiseco pistons Ive worked with have a pretty generous dome thickness. And being forged, it doesnt have to be .250 thick to live through some detonation.

Kinda wonder also if milling the head off to the point where the intake valve is right at deck height isn't a bad idea either. It'd help unshroud the cylinder side of the valve and take out some of that volume so you could mess with the domes for motion and still retain some C/R and build a better wedge. Hell, you could angle mill the head a tad to aid that too. It'd require you to degree the cams, but hell, you're already quite a ways down the rabbit hole, why not look for the bottom? Laughing

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nathanhouse
Silver CB900F
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Joined: Oct 05, 2008
Posts: 1490
Location: Dover, NH

PostPosted: Sun Sep 21, 2014 1:22 am Reply with quote Back to top

Getting off subject of the original post but yeah I'll probably drop the base gasket and then I'll only have .020" to remove. .010" on the case and ten off the deck, not sure that small amount will count for too much even if I took it all from one place. Discussion on motion mixture and such can con't in my build thread if you like so we don't get this one too far off track.
 
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melchiro
Silver CB900F
Silver CB900F



Joined: Aug 10, 2003
Posts: 1495
Location: Mill Creek, WA.

PostPosted: Sun Mar 19, 2017 6:08 pm Reply with quote Back to top

"Bumping", this post because there is talk of, "CBX Piston" comparisons..

Also, while surfing the net, I found this place below. Andrew Motorsports. They sell DOHC 750/900 piston upgrade items. One, which is "68mm" Wiseco pistons.
Image

http://andrewsmotorsports.mybigcommerce.com/honda-cb-750-dohc-79-82-902cc-big-bore-wiseco-piston-kit-k902/

They also sell "turn key", ready bolt-on stuff, for our 750 motor, the above pic. With the Wiseco 68mm pistons, this makes 901/902cc.

What has me wondering with these, Wiseco 68mm Pistons, model #12029M06800, could this be a "0" deck height piston????? This could be a different piston, vs, the low deck height, 67.5mm, that we have come to know.

The low deck height Wiseco piston's part # is 4218M06750 .

Hmmmmmm

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1979 Modified CBX
1982 Modified CB-750/1100F
1983 Modified CB-750/1123F Track bike
1980 GS1000GT Project
1972 CB500 Four K1 Project 
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1100russ
CB1100F
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Joined: May 17, 2010
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Location: williamsburg, ohio

PostPosted: Sun Mar 19, 2017 6:54 pm Reply with quote Back to top

Still the same wiseco old school style big barrier to flow and flame propagation "dome" piston. I'm going a different direction.

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