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CA77 vs CB/CL77 pistons?

Alan F.

Veteran Member
Joined
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Total Posts
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Location
Haverhill, MA, USA
A question to those that might know, are these inter changeable? It appears so but I'd rather hear it from someone more qualified.
 
I don't know from actual experience, but the part numbers are different between the CA (13101-266-020) and the CB/CL (13101-275-000) and that often, though not in every single instance, means there's a difference. In this case it could easily just be the dome configuration/compression ratio since the displacement and wristpin size is the same (assumedly on my part)
 
I understand standard bore is 60mm with up to 4th oversize available. 15mm wrist pins all around.

I'll copy and paste the part overlap that I find listed on cmsnl.com for pistons, rings and wrist pins.
 
From cmsnl.com:

Honda product number:
Piston CA77
13101-266-020
FITS MODELS
C77 1960
C77 1960
C77 1960 1961 962 1963 1964 DREAM (142592)
C78 1960 1961 1962 1963 1964II 1964III DREAM (142592)
CA77 1960 1961 1962 1963 1964I 1964II 1964III DREAM USA (142592)
CA77 1961

Honda product number:
Piston CB77
13101-275-000
FITS MODELS
CB77 GENERAL EXPORT (142683)
CB77 SUPER HAWK 1961 USA
CP77 GENERAL EXPORT (142683)
CYP77 POLICE GENERAL EXPORT (142683)

This would appear not to be a match, but the 3rd superceding part number for CB77 piston rings, 13012-275-000 is listed all the way back to the first CA77 in 1960.

Honda product number:
Third superceding piston ring p/n
13012-275-000
FITS MODELS
C77 1960
C77 1960
C77 1960 1961 962 1963 1964 DREAM (142592)
C78 1960 1961 1962 1963 1964II 1964III DREAM (142592)
CA77 1960 1961 1962 1963 1964I 1964II 1964III DREAM USA (142592)
CA77 1961
CB77 GENERAL EXPORT (142683)
CB77 SUPER HAWK 1961 USA
CL300 JAPAN
CL77
CL77 SCRAMBLER 1965 USA / 305
CP77 GENERAL EXPORT (142683)
CYP77 POLICE GENERAL EXPORT (142683)

And wrist pins:
CB77 wrist pin
Honda product number:

13111-251-000
FITS MODELS

C75 C76 CS76 1958 1959
C75 C76 CS76 1958 1959 1960 DREAM GENERAL EXPORT (142532)
C77 1960
C77 1960
C77 1960 1961 962 1963 1964 DREAM (142592)
C78 1960 1961 1962 1963 1964II 1964III DREAM (142592)
CA77 1960 1961 1962 1963 1964I 1964II 1964III DREAM USA (142592)
CA77 1961
CB77 GENERAL EXPORT (142683)
CB77 SUPER HAWK 1961 USA
CL300 JAPAN
CL77
CL77 SCRAMBLER 1965 USA / 305
CP77 GENERAL EXPORT (142683)
CYP77 POLICE GENERAL EXPORT (142683)

So I'm concluding that they're interchangeable, but confident input from the voice of experience would really make a difference for me.



 
Looking at the pictures of the 2 different pistons there's obvious differences in the dome. I suspect the CA piston will have a higher compression ratio.
 
I also checked on cranks the same way, the CB crank was only sold as an assembly, but the CA crank had part numbers for all of the individual parts.
Connecting rods had crossover between CA77 and CB77 but most of the other crank components that would determine piston stroke did not cross between these models. So different compression is a possibility. I'll check the manuals and post back here.
 
Ok, so CA77 and CB77 have a 60mmx54mm bore and stroke.

CA77 has 8.3:1 compression
CB77 has 9.5:1 compression

I'll have a look for cylinder head, cylinder and head/base gaskets cross over.
 
Mu suspicion was that the Dream would have the lower compression ratio (single carb, touring intent), so the pictures may well have been incorrect or there's a significant difference in combustion chamber size on the Dream head (which seems less likely)
 
Cylinders are a direct crossover between CA77 and CB77.

Base and head gaskets do not appear to cross over but some are shared with C77 the common ancestor.

And cylinder heads do not appear to cross over.

__________________________________________________

I could guess that base and head gaskets varied in thickness and were given different part numbers that won't interchange, but with cylinder heads also not life-changing there could have been oiling system improvements or combustion chamber differences that I would have no idea about.

I'm off to eBay for combustion chamber photos for comparison sake.
 
Chambers all look the same, the big difference is that CA77 ran a single carburetor, and CB77 ran two.

Different heads entirely.

But AD already replied that while I'm not paying attention!
 
EDIT: The CA77 was also a 360 degree engine, single carb, one set of points.


EDIT: CB77 was a 180 degree engine, two carbs and 2 sets of points.

So there are the crank differences as well. There must have been quite a few custom built 305s trying to keep up with the 450s.
 
The CA77 was also a 180 degree engine, single carb, one set of points.

CB77 was a 360 degree engine, two carbs and 2 sets of points.

So there are the crank differences as well. There must have been quite a few custom built 305s trying to keep up with the 450s.

Actually those are reversed - the CA had the 360° crank (hence the single points, both fire and one is on exhaust stroke), the CB/CL (except limited versions like some domestic models or sent somewhere other than the US) had a 180° crank.
 
My suspicion was that the Dream would have the lower compression ratio (single carb, touring intent), so the pictures may well have been incorrect or there's a significant difference in combustion chamber size on the Dream head (which seems less likely)

I'd have thought so too judging by its performance, at 4 horsepower less that's 15% less than the CB. But if it's pistons are higher compression than even the CB's there just aren't many ways to have a higher compression piston, same bore and stroke, and still have lower compression. It's gotta be the chamber volumes right?

Some poor pics I screenshot from eBay earlier:

Screenshot_2022-01-09-19-10-59.jpgScreenshot_2022-01-09-19-12-38.jpgScreenshot_2022-01-09-19-19-04.jpgScreenshot_2022-01-09-19-20-21.jpg
 
So all has been explained? The CA pistons have a slightly higher dome than CB pistons and when added to a CB77 will increase compression upwards from 9.5:1
 
Well that wasn't so hard, the world will be forever smaller now though.

Thanks AD, LDR and Mike in Idaho for your help and replies.
 
If only Bill Silver would come back once in a while and engage our 305 owners here, he joined but hasn't been here since. You'd think he'd be looking for someplace that is functional since the Honda305 forum is all but dead.
 
Yeah i've been asking questions of the Internet and it keeps sending me there, but when I get there it's just a clearing in the woods with gravel on the ground.

For laughs I tried to register an account, I wonder if I'll ever hear back?

Is it ironic that the homepage listed in his profile doesn't work at all?
 
I've looked all over that mess and can't even find it, so many links either don't work or are in partial disarray. It's a shame too because we know there's a lot of info there
 
I've looked all over that mess and can't even find it, so many links either don't work or are in partial disarray. It's a shame too because we know there's a lot of info there

He is on 3 maybe more facebook groups. Also has a blog, there is a link on it to his web page. I just popped for his CA77 dropbox download, still reading, 51 PDFs.

More from MrHonda
 
I would like a 305 dream with CB/CL 305 pistons :);I wonder if the CB/CL cylinder head(dual carbs,cam,points,etc.) would swap over,then possibly hook-up the top motor mount to the head differently?
 
I would like a 305 dream with CB/CL 305 pistons :);I wonder if the CB/CL cylinder head(dual carbs,cam,points,etc.) would swap over,then possibly hook-up the top motor mount to the head differently?

Won't fit without major body surgery. Dream lower end has different gearing too.
 
Won't fit without major body surgery. Dream lower end has different gearing too.


Ah,I understand,plus the 360 degree crank in the Dream compared to the 180 degree crank in the CB/CL77's.
I suppose a complete engine swap? most likely not for the same reason of the fit of the frame,because of the dual carbs ?
 
I replaced my cb77 pistons with ca77 pistons about a dozen years ago. I bought them from loud mouse, who told me they would provide a higher compression ratio, as others have said.

Since CB77’s already run a bit hot, I would have preferred the stock cr. In fact, I have experienced a few engine seizures with the new pistons. Going to a larger main jet did not help. Getting my centrifugal advance assembly reworked by Tim so that the full advance was not too great seems to have fixed it.

That was my experience, anyhow. The ca pistons work fine, just be sure the full ign advance and full-throttle mixture are ok.

Larry near Pasadena
63 cb77, 71 sl350, couple of ct90s, couple of Bultaco Matadors, etc
 
In 1965 Honda reduced the compression ratios to 8.5:1 for CB/CLs. There are three different pistons for CB/CL72s in different compression ratios. Just two for 305s.
 
Welcome back Mr. Honda. Thanks for the information. My originals were from a 1965 engine but I’m ashamed to say I don’t know what year the ca77 replacements were.

Anyway, it’s running smoothly for now.
 
Dream pistons only changed in early 1962, when they switched from thick rings to the 275 code CB77 thinner ring sets. Compression stayed the same from beginning to end.
 
Yes thanks, I wasn't interested in sharing the link with the world but so it goes.

I've placed an offer, the price to put that set together with NOS parts is at least 1/3 higher on eBay. Failing that I could call the usual phone-only sources or wait for swap-meet tables to come out...

Edit: What kind of compression do you think those would make in a CB750 with stock combustion chamber volumes ~23.5cc? Stock compression was 9.0:1 with flat topped pistons.
 
That Seller accepted my lowball offer so they're on their way. They'll go into my CB750K8 with a K0 cam I also got a screaming good deal on, that should be fun even if it needs 93 octane only.
 
In 1965 Honda reduced the compression ratios to 8.5:1 for CB/CLs. There are three different pistons for CB/CL72s in different compression ratios. Just two for 305s.

Would you mind expanding a little on this with a timeline, market availability or part numbers?
 
The original note was in reference to CA/CB pistons, so I assumed that that was the subject matter relating to your photos. I happened to check eBay for 61mm pistons and those came up. I assume that they are for an F2 engine with canted valves, but I am not a 750 expert, but F2 pistons are mostly flat on top. I thought they might be Kawi KZ650 pistons, but they are probably race pistons cast off of ART blanks. Good luck.
 
Per the seller they have the cast markings CB77. I don't know why he wouldn't lead with that...
They'll go into my K3 or K8 along with a K0 cam I picked up along the way. I'll assemble cylinder and head with one ringless piston, no base or head gaskets, and I'll lay some clay atop the piston to determine clearance. It's an old racers' trick to make more power in a stock 61mm bore. I'm not sure if these pistons had received any modifications or not, but they appear stock.
 
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