Topic: Who was trying "other" pistons in a CB750F rebuild?

[HondaMan]

Hi, all:
A couple of weeks (or maybe longer than that!) I was reading here where someone was trying to use pistons from [something else] to rebuild a CB750F engine (I think?). There was a dome on top, and the wristpin height and skirt lengths were real close to the right ones. Does anyone else remember this, or is my neighbor kid's (now legal) pot-smoking activity starting to get to me? 

I need a set of OS pistons for a 750K7, hopefully w/o going to 65mm...

[MiGhost]

Is it possible that you were think about the 76-82 KZ650 pistons being used in the big bore builds?.
62mm with 15mm pin, and a rounded dome.

[HondaMan]

Is it possible that you were think about the 76-82 KZ650 pistons being used in the big bore builds?.
62mm with 15mm pin, and a rounded dome.

That might be it: do you know where to find this thread?

[MiGhost]

I'll locate, and post here.
Not sure if it was strongperf, or Soos.

[MiGhost]

Planning thread:
http://forums.sohc4.net/index.php?topic=28641.0

Build:
http://forums.sohc4.net/index.php?topic=44678.75

Pics in both.

[HondaMan]

Planning thread:
http://forums.sohc4.net/index.php?topic=28641.0

Build:
http://forums.sohc4.net/index.php?topic=44678.75

Pics in both.

Thanks, MiGhost, You're the Search Wizard! 
I think that's the one(s) I was trying to remember. The 'thing' was: the 750 DOHC pistons StrongPerf was trying out. I gotta find one somewhere and see if they might make a decent "F" piston for us in overbore sizes.

Anyone happen to have one?

[MiGhost]

Planning thread:
http://forums.sohc4.net/index.php?topic=28641.0

Build:
http://forums.sohc4.net/index.php?topic=44678.75

Pics in both.

Thanks, MiGhost, You're the Search Wizard! 
I think that's the one(s) I was trying to remember. The 'thing' was: the 750 DOHC pistons StrongPerf was trying out. I gotta find one somewhere and see if they might make a decent "F" piston for us in overbore sizes.

The dome on the DOHC pistons is quite different. Besides the 4 valve reliefs. The dome starts further towards the center. I just picked up some DOHC cylinders with pistons for research info on the big bore build up for a 650.

Here are some of the specs that I have gathered.
Note: Measurements within the accuracy of my el cheapo digital caliper. Use only as a rough guideline.

SOHC CB650 Piston
13101-426-003 PISTON (STD) (79-82 CB 650, 650C, 650SC)
PISTON DIA.: 59.8mm (published spec)
PISTON PIN  C to DOME: 26.50mm
PISTON PIN  C to DECK: 23.0mm
SKIRT @ PISTON PIN: 3.60mm
DECK to SKIRT @ PISTON PIN: 42.6mm
DECK to SKIRT: 52.90mm

DOHC CB750 Piston
13101-425-000 PISTON (STD) (79-82 CB750 C\F\K\L, 82-83 CB750SC)
PISTON DIA.: 62.0mm (published spec)
PISTON PIN  C to DOME: 29mm
PISTON PIN  C to DECK: 24.5mm
SKIRT @ PISTON PIN: 9.95mm
DECK to skirt @ PISTON PIN: 46.5mm
DECK to skirt: 51.7mm

650  (SOHC) Cylinder
12100-426-010 CYLINDER (79-82 CB650, CB650C)
12100-460-780 CYLINDER (82 CB650SC)
Bore center 1-2: 76mm
Bore Center 2-3: 112.5mm
Bore Center 3-4: 76mm
1-2 gap: 2.0\11.1mm Top/Bottom
3-4 gap: 2.0\11.1mm Top/Bottom
SLEEVE LENGTH: 105.0mm
Flange O.D. (Outside diameter) 73.5mm
SLEEVE O.D. (Outside diameter) @ base gasket 65.1mm
SLEEVE I.D. (Inside diameter): 59.8mm

750 (DOHC) Cylinder (593 casting)
12100-425-010 CYLINDER (79-81 CB750 F\K\C)
Bore center 1-2: 80.4mm
Bore Center 2-3: 139.1mm
Bore Center 3-4: 80.4mm
1-2 gap: 18.2/11.15mm Bottom/top
3-4 gap: 18.2/11.15mm Bottom/top
SLEEVE LENGTH: 116.2mm
Flange O.D. (Outside diameter): 76.7mm
SLEEVE O.D. (Outside diameter) @ base gasket: 69.1mm
SLEEVE I.D. (Inside diameter): 62.0mm

900 (DOHC) Cylinder
12100-438-000 CYLINDER (80-81 CB900 C)
Bore center 1-2: 80.4mm
Bore Center 2-3: 138.8mm
Bore Center 3-4: 80.4mm
1-2 gap: 1.0/9.5mm Top/Bottom
3-4 gap: 1.0/9.5mm Top/Bottom
SLEEVE LENGTH: 117.6mm
Flange O.D. (Outside diameter): 78.2mm
SLEEVE O.D. (Outside diameter) @ base gasket: 71.3mm
SLEEVE I.D. (Inside diameter): 64.5mm

Anyone happen to have one?

Shoot me your shipping info, and I will get the pistons headed your way!
I am sure you will get more value out of them.

[HondaMan]

Wow! Great info!

I have 2 of the 750F engines here, one apart, one not (yet) for rebuilds.
If we could make these work, it would help everybody! I can cover postage, or something?

Send to:
Mark Paris
8903 W. Florida Ave.
Lakewood, CO 80232

I can compare them with the OEM pistons in both the "F0/1" and "F2/3" and "K7/8" engines, as I think I have stockers from all 3 laying around here somewhere.

Many thanks!
 

[MiGhost]

A similar situation with the 650.
While Dynoman does have the big bore (stock sleeve) kits for both the 650 (674cc), and F2/3 (836/915cc). The $$$ price tag does cause a bit of hesitation.

Correct me if i am wrong.
F0/1 & K7/8 (392 casting) Pie tin dome, Flat outer lip with stepped flat dome.
F2/3 (410 casting) Saucer dome, Evenly rounded to outer edge.

If you can get more accurate measurements on any above specs. Please update.

Pistons in the mail.

[HondaMan]

A similar situation with the 650.
While Dynoman does have the big bore (stock sleeve) kits for both the 650 (674cc), and F2/3 (836/915cc). The $$$ price tag does cause a bit of hesitation.

Correct me if i am wrong.
F0/1 & K7/8 (392 casting) Pie tin dome, Flat outer lip with stepped flat dome.

Most of the time, this is correct. But, there's also another type of piston in these 2 engine types that I see once in a while. It has a rounded dome like the F2/3 pistons, with a "392" casting mark, but has flycuts into the tops for the valves. The dome has an angled quench band around it where the 'pie pan' ones are flat, and the dome is not quite as tall.
I think I might still have a used set of these somewhere, as I rebuilt a virgin, rusted-tight "F"/392 about 2 years ago that had them and tossed the old ones in a box somewhere as curiosities...the skirts have a pronounced slipper on them, too. IIRC, the length of the slipper matches the F2/3 pistons' length, but the sides are cut back up, like we're used to seeing.

F2/3 (410 casting) Saucer dome, Evenly rounded to outer edge.

That's the only type I've seen in the (virgin) F2/3 engines.

If you can get more accurate measurements on any above specs. Please update.

Pistons in the mail.

Thanks! This should be fun!

[MiGhost]

Tracking info sent via PM.

[HondaMan]

Tracking info sent via PM.

Thanks, MiGhost!
I'm chafing at the wrench to see if these can be made to work, or something similar to them. We need a source of post-1975 oversize pistons pretty badly!

[MiGhost]

I think I might be on a similar path looking for big bore pistons as the 650 chamber looks very similar to the F chamber. The tapered quench F0-1 piston looks very close to the 650 piston.

FYI: I have a set of the KZ650 pistons coming. Will post the specs when I get my hands on them. Draw back to the KZ650 pistons. Expensive rings!

[Terry in Australia]

G'Day Mark, I've got a set of NOS "Action Fours" 65mm pistons to take a 1970's KZ650 out to 720. (718?) I bought them because they looked almost identical to F2 pistons but never used them. They had one piece rings and 15mm wrist pins, which I used on my RC pistons, from memory?

I can take a pic after work tomorrow if you like, from memory Action Fours used OEM cast pistons, but if so, I don't know what these would be for originally? Cheers, Terry.

[HondaMan]

G'Day Mark, I've got a set of NOS "Action Fours" 65mm pistons to take a 1970's KZ650 out to 720. (718?) I bought them because they looked almost identical to F2 pistons but never used them. They had one piece rings and 15mm wrist pins, which I used on my RC pistons, from memory?

I can take a pic after work tomorrow if you like, from memory Action Fours used OEM cast pistons, but if so, I don't know what these would be for originally? Cheers, Terry.

There they are again! Boy, I sure miss the Action Fours guys. They had the best ideas and good quality parts, except for their cams (too soft, wore quickly). They had one cam I still can't forget: it had 7.8mm lift with +30 degree intake duration and +18 degrees exhaust. This was LESS lift by 0.1mm than most stock cams. It would idle like stock, wind clear off the tach if you weren't careful, and made anyone who toured with it fit the 45T rear and 18T front sprockets to the bike. It pulled like a tractor - for about 10k-12k miles, then the lift was falling off already from softness.

If only I had a cam grinder!

[MiGhost]

G'Day Mark, I've got a set of NOS "Action Fours" 65mm pistons to take a 1970's KZ650 out to 720. (718?) I bought them because they looked almost identical to F2 pistons but never used them. They had one piece rings and 15mm wrist pins, which I used on my RC pistons, from memory?

I can take a pic after work tomorrow if you like, from memory Action Fours used OEM cast pistons, but if so, I don't know what these would be for originally? Cheers, Terry.

Would you be looking to sell those pistons?

[Terry in Australia]

G'Day Mark, I've got a set of NOS "Action Fours" 65mm pistons to take a 1970's KZ650 out to 720. (718?) I bought them because they looked almost identical to F2 pistons but never used them. They had one piece rings and 15mm wrist pins, which I used on my RC pistons, from memory?

I can take a pic after work tomorrow if you like, from memory Action Fours used OEM cast pistons, but if so, I don't know what these would be for originally? Cheers, Terry.

There they are again! Boy, I sure miss the Action Fours guys. They had the best ideas and good quality parts, except for their cams (too soft, wore quickly). They had one cam I still can't forget: it had 7.8mm lift with +30 degree intake duration and +18 degrees exhaust. This was LESS lift by 0.1mm than most stock cams. It would idle like stock, wind clear off the tach if you weren't careful, and made anyone who toured with it fit the 45T rear and 18T front sprockets to the bike. It pulled like a tractor - for about 10k-12k miles, then the lift was falling off already from softness.

If only I had a cam grinder!

Thanks Mark, I suspect that the "unknown" cam I found in a pile of other CB750 cams is an Action Fours cam, it doesn't have any markings of note, looks to be a smilar profile to a K0/K1 cam, albeit with around 2mm more lift.

So far no wear that I can detect, (and it's easy on a CB750 cam, the "foot" of the tappet wears a path in the lobe) and as it came with a non-adjustable cam sprocket I just dropped it in after I removed the Megacycle 125/75, and what a difference! It starts better, idles better, has tons more torque, and the bike is much more happy at traffic speeds.

Hmmnn, it could be an Andrews cam too, I've had one of each many years ago, but either way, it's a beaut! Cheers, Terry.

[Terry in Australia]

Would you be looking to sell those pistons?

I tell you what mate, if you send me an autographed copy of Mark's book, I'll send you the pistons. How's that? Cheers, Terry.

[MiGhost]

Would you be looking to sell those pistons?

I tell you what mate, if you send me an autographed copy of Mark's book, I'll send you the pistons. How's that? Cheers, Terry.

And not my first born's, first born. A great kid BTW
You drive a hard bargin Mate. Checking availablilty.

[HondaMan]

I just ordered some more, as PeWe wants me to write in a book for him, too.
I dunno...it seems such a crime to scribble in someone's nice book? (You'll understand when you see my handwriting!).

Ghost: I am going to see if my machine shop guys would be able to turn off these shoulders about 2mm on these pistons. If so, we have a good way to match up pistons for the 750F (all 3 versions) and the K7/8 pistons! These stockers would make almost 0.5mm overbore size. They are just 0.1mm less diameter than the 0.5mm overbore 750K0-6 pistons I have (new). So, getting them in any oversize will also give these engines a new future! 

I'm going to get a new set and will install them into the K7 engine I am rebuilding now. I might take the ones you sent me and use them in a "test" K7 engine I'm also doing, which will have other mods and such (it's my experimental engine for the later bikes).

[MiGhost]

I just ordered some more, as PeWe wants me to write in a book for him, too.
I dunno...it seems such a crime to scribble in someone's nice book? (You'll understand when you see my handwriting!).

Ghost: I am going to see if my machine shop guys would be able to turn off these shoulders about 2mm on these pistons. If so, we have a good way to match up pistons for the 750F (all 3 versions) and the K7/8 pistons! These stockers would make almost 0.5mm overbore size. They are just 0.1mm less diameter than the 0.5mm overbore 750K0-6 pistons I have (new). So, getting them in any oversize will also give these engines a new future! 

I'm going to get a new set and will install them into the K7 engine I am rebuilding now. I might take the ones you sent me and use them in a "test" K7 engine I'm also doing, which will have other mods and such (it's my experimental engine for the later bikes).

Don't get in a big hurry stuffing those old pistons into the test K7. I will pass along the stocker KZ650 pistons that I have coming. It would be good to get a go\nogo on those for the F2\3 in particular.

I've got a set of NOS "Action Fours" 65mm pistons to take a 1970's KZ650 out to 720. (718?) I bought them because they looked almost identical to F2 pistons but never used them. They had one piece rings and 15mm wrist pins, which I used on my RC pistons, from memory?

I can take a pic after work tomorrow if you like, from memory Action Fours used OEM cast pistons, but if so, I don't know what these would be for originally? Cheers, Terry.

Could you put up some pics of those. I have a couple questions about them that a pic should answer.

[PeWe]

.....
I dunno...it seems such a crime to scribble in someone's nice book? (You'll understand when you see my handwriting!).
....

The authors handwriting willl make the book very personal.  Handwriting... doctors usually have almost not readable handwriting. Not something bad...

If you want photos of old used Action Fours 65mm pistons for CB750 K engines. I can attach some.

[HondaMan]

Would you be looking to sell those pistons?

I tell you what mate, if you send me an autographed copy of Mark's book, I'll send you the pistons. How's that? Cheers, Terry.

Hey, Terry: can you PM me your address?

[Ibdsharpe]

Mark,
Just trying to.make contact. No replies to my 3 emails and didn't want to bother you but need to
Know you received my carbs.
Thanks,
Dave Sharpe sharpedvs@aol.com

[HondaMan]

Mark,
Just trying to.make contact. No replies to my 3 emails and didn't want to bother you but need to
Know you received my carbs.
Thanks,
Dave Sharpe sharpedvs@aol.com

Dave:
please switch to my other e-mail:
hman750@gmail.com .

For reasons I can't fathom, my Concentric.net mail service seems to have disappeared. They don't respond to my e-mails and I can't get into any of my accounts there, nor my 'personal' webpage stuff they have hosted since 1996. I think they are toast?

I received 3 boxes on Monday and Tuesday, haven't even had time to open them - major car problems since last week. I'll check tonight and write back.