Author Topic: Stock CB750 Cam Identification (Read 13369 times)

gschuld · « **Reply #25 on:** January 26, 2016, 10:54:02 AM »

Quote from: dragracer on January 26, 2016, 10:29:54 AM

So are we to conclude from all posted so far that the sandcast and K/0 cam is the better choice as far as stock grinds are concerned?? Seems the way to go for an economical street build or a stock motored ET bike.

My understanding is the sandcast cam was the most tuned up cam Honda offered on a factory cb750. From there on everything was slowly detuned for various reasons(increased engine smoothness, reduced intake roar from the K0 airbox, glass pack hm300 exhaust to quieter/more restrictive baffled exhaust, less handwork on the heads, dropped jetting on the carbs, advancer pull back, and of course, as Hondaman detailed, the cams were detuned to match.

Mileage got better, engines got quieter, but performance slowly dropped off from 1969 through 1975 or so. There was a renewed effort with the F model to bring some performance back to or perhaps exceed sandcast levels. Those later F cams might be as performance minded as the sandcastle cams.

I would be interested in knowing the details that can positively identify a sandcast/very early K0 cam.

A sandcast/early K0 cam would certainly be the most desirable stock cam value wise, but I would suspect performance wise as well.

Grorge

TurboD · « **Reply #26 on:** January 26, 2016, 11:22:39 AM »

Quote from: dragracer on January 26, 2016, 10:29:54 AM

So are we to conclude from all posted so far that the sandcast and K/0 cam is the better choice as far as stock grinds are concerned?? Seems the way to go for an economical street build or a stock motored ET bike.

Frank this is what I am hearing, however I have not seen any actual specs to back this up.

Measuring a lobe with a caliper is just one small piece of the puzzle when it comes to comparing cams.

George I cannot speak for the "sandcast" cam, but the cams actually got hotter with later production. A 77-8F cam is hotter than a 77-8K, which is hotter than 72-76K cam. A auto cam, well it made the engine run...Lol.

kmb69 · « **Reply #27 on:** January 26, 2016, 11:56:16 AM »

Quote from: TurboD on January 26, 2016, 11:22:39 AM

Quote from: dragracer on January 26, 2016, 10:29:54 AM
So are we to conclude from all posted so far that the sandcast and K/0 cam is the better choice as far as stock grinds are concerned?? Seems the way to go for an economical street build or a stock motored ET bike.
.....
George I cannot speak for the "sandcast" cam, but the cams actually got hotter with later production. A 77-8F cam is hotter than a 77-8K, which is hotter than 72-76K cam. A auto cam, well it made the engine run...Lol.

I have read that the 77-8F cams were actually the "hottest" but I have not confirmed this. Not so sure about the 77-8K being hotter than any previous cams.

The thread Bill mentions: http://forums.sohc4.net/index.php/topic,131229.msg1463544.html#msg1463544

Will also have to confirm but I am not sure the "raised mark" Bill spoke about is on all Sandcast cams.

Jerry Rxman Griffin aka MuthaF'er · « **Reply #28 on:** January 26, 2016, 12:37:17 PM »

Keith, is that a secret raised rectangle on the back side of your right hand?!

kmb69 · « **Reply #29 on:** January 26, 2016, 01:12:04 PM »

Not sure. Those are not my hands. I think they belong to Sammy.

Candice is not here today, so I cannot readily lay MY hands on it to look.

BPellerine · « **Reply #30 on:** January 26, 2016, 01:23:36 PM »

Quote from: dragracer on January 26, 2016, 10:29:54 AM

So are we to conclude from all posted so far that the sandcast and K/0 cam is the better choice as far as stock grinds are concerned?? Seems the way to go for an economical street build or a stock motored ET bike.

I doubt that those sandcast cams are economical ,bet they go for a good dollar when they are found.billp

Bill/BentON Racing · « **Reply #31 on:** January 26, 2016, 04:13:23 PM »

Hard to find, but hell you can see the difference

BPellerine · « **Reply #32 on:** January 26, 2016, 05:15:14 PM »

Quote from: Bill/BentON Racing on January 26, 2016, 04:13:23 PM

Hard to find, but hell you can see the difference

ya you sure can the lobes are much diff!billp

scottly · « **Reply #33 on:** January 26, 2016, 05:59:47 PM »

K7 cam, from engine # 2704603:
Intake base circle 1.104"
Intake lobe height 1.406"
Intake lobe lift .302"

Exhaust base circle 1.106"
Exhaust lobe height 1.390"
Exhaust lobe lift .284"

754 · « **Reply #34 on:** January 26, 2016, 11:26:04 PM »

I would say this the early are hotter than midyear cams..but the 77/78 F cams visually look pretty hot compared to the rest ..look like more duration

Jerry Rxman Griffin aka MuthaF'er · « **Reply #35 on:** January 27, 2016, 10:18:05 AM »

Which F are you referring to? BOTH I'd assume?

PeWe · « **Reply #36 on:** January 27, 2016, 10:40:30 AM »

I measured my 2 std cams I have with a caliper
K6 -1976 from my bike
I got the 1978 cam with complete cam holders I found on eBay. The cam holders and caps have not stamped markings, ink markings.
1978 (probably K7) cam seems to have beefier lobes but slightly less lift than K6 cam

K6:
IN
Base circle 28.1mm
Lobe height: 35.95mm
Lift: 7.85mm / 0.309"

EX
Base circle: 28.1mm
Lobe height: 35.3mm
Lift: 7.2mm / 0.283"

1978 cam:
IN
Base circle 28.1mm
Lobe height: 35.7mm
Lift: 7.6mm / 0.299"

EX
Base circle: 28.1mm
Lobe height: 35.25mm
Lift: 7.15mm / 0.281"

754 · « **Reply #37 on:** January 27, 2016, 10:43:18 AM »

Jerry i have never seen the early F cams.

kmb69 · « **Reply #38 on:** January 27, 2016, 10:49:03 AM »

Quote from: Jerry Rxman Griffin aka MuthaF'er on January 27, 2016, 10:18:05 AM

Which F are you referring to? BOTH I'd assume?

Both 77-8F's use the 14101-410-000 cam. According to the parts book, the 75-6F's and the 77-8K's use the 14101-392-000 cam. The 76-8A's use 14101-393-000.

NitroHunter · « **Reply #39 on:** January 27, 2016, 06:47:04 PM »

The F-2 410 has the 108 lobe centers - less overlap.

TurboD · « **Reply #40 on:** January 27, 2016, 07:58:28 PM »

Here are the cam specs taken from Honda service manuals. I have come up with 4 different cams used. I cannot speak on a early sandcast cam, but one of the manuals is dated 1970.

I have listed these in order by power potential, not only by specs but also by running them on my dyno simulation software. They fall in order just as one would expect by reading the specs. This is only to help rate the stock cams, all of these are very mild by any performance standard and should be replaced if more power than stock is wanted.

Hondamatic
Intake open 5 AFTER tdc
Intake closes 30 after bdc
duration 205
intake centerline 97.5

Exhaust open 40 before bbc
exhaust closes 5 before tdc
duration 215
exhaust centerline 107.5
--------------------------------
K model
intake open 5 before tdc
intake close 30 after bbc
duration 215
intake centerline 102.5

Exhaust open 35 before bbc
exhaust close 5 after tdc
duration 220
exhaust centerline 105
-------------------------
K model 77-78
intake open 0 tdc
intake close 40 after bbc
duration 220
intake centerline 110

exhaust open 40 before bbc
exhaust close 0 tdc
duration 220
exhaust centerline 110
---------------------
77 78 F
intake open 5 before tdc
intake close 40 after bbc
duration 225
intake centerline 107.5

exhaust open 40 before bdc
exhaust close 5 after tdc
duration 225
exhaust centerline 107.5

I hope this helps to answer as to which "stock" cam will make the most power.

Jerry Rxman Griffin aka MuthaF'er · « **Reply #41 on:** January 27, 2016, 09:44:15 PM »

Supplement to CB750F

Intake open 5 btdc
close 35 abdc
dur 220

Exh open 35 bbdc
close 5 atdc
dur 220

PeWe · « **Reply #42 on:** January 28, 2016, 03:00:12 AM »

Info in the Cobra build article about RC327 vs stock cam

TurboD · « **Reply #43 on:** January 28, 2016, 05:37:37 AM »

Quote from: PeWe on January 28, 2016, 03:00:12 AM

Info in the Cobra build article about RC327 vs stock cam

Pewe I agree with that, and I also suspect the actual tolerances varied from run to run as well.

Old Scrambler · « **Reply #44 on:** January 28, 2016, 07:24:07 AM »

Someone will post the sandcast or early K0 cam specs............but I think the extra few-degrees of ignition advance on the early motors had a lot to do with that 'kick-in-the-pants" performance.

TurboD · « **Reply #45 on:** January 28, 2016, 07:49:33 AM »

Quote from: Old Scrambler on January 28, 2016, 07:24:07 AM

Someone will post the sandcast or early K0 cam specs............but I think the extra few-degrees of ignition advance on the early motors had a lot to do with that 'kick-in-the-pants" performance.

Agreed, this along with the fact that they had the richest jetting, less restrictive air box and pipes.

kmb69 · « **Reply #46 on:** January 28, 2016, 08:38:07 AM »

Quote from: TurboD on January 28, 2016, 07:49:33 AM

Quote from: Old Scrambler on January 28, 2016, 07:24:07 AM
Someone will post the sandcast or early K0 cam specs............but I think the extra few-degrees of ignition advance on the early motors had a lot to do with that 'kick-in-the-pants" performance.

Agreed, this along with the fact that they had the richest jetting, less restrictive air box and pipes.

My Aug, 1969 Shop Manual says:

Inlet valve: open B.T.D.C. 5
Inlet valve: close A.B.D.C. 30
Inlet valve lift: 0.3142-0.3158 in.

Exhaust valve: open B.B.D.C 35
Exhaust valve: close A.T.D.C 5
Exhaust valve lift: 0.2945-0.2961 in.

Ignition timing: B.T.D.C. 6° at 1000rpm, 40° at 2500rpm

TurboD · « **Reply #47 on:** January 28, 2016, 08:56:47 AM »

Those numbers look like the same numbers I got for the K models.

754 · « **Reply #48 on:** January 28, 2016, 11:42:08 AM »

Well if the cam aint hotter its the ports and as Lucky says .best dam 750 carbs..
maybe its time to flowtest KO carbs, vs the fork actuated roundtops. ?

TurboD · « **Reply #49 on:** January 28, 2016, 12:16:14 PM »

Here are my thoughts, they are only opinion based on logic and facts that I know of the sandcast stuff. I have not had any of the parts in hand.

We know the sandcast bikes were jetted richer, air box flowed more, pipes were freer flowing and timing slightly bumped. These things alone could account for nearly 10 hp, this would seem like a lot compared to the newer more restricted bikes. Now again without hands on, My current opinion is, I am of the belief that the cams were not different or the heads were polished, even if the heads had some work from the factory, the workers would have not been able to spend much time on each of them to actually increase performance by much. I have had a couple sets of carbs, and the bodies looked to be exactly the same sizing as newer carbs.

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Author Topic: Stock CB750 Cam Identification (Read 13369 times)