Topic: Stock CB750 Cam Identification

[BPellerine]

I have a ko head and to me the ports look a lot better in the finish area than the 78k that I also have,also not so many sharp edges in the combustion chamber.bill

[kmb69]

.....
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.

All of the points you make are valid.

I would not call the Sandcast heads "ported", but they are pretty "slicked up" compared to K1-K8 heads. The factory definitely spent some amount of time on them.

Pretty sure the carbs, Sandcast through K6, will flow air similarly. Not so sure about how similar the internal fuel passages are. The jetting was obviously different to accommodate air box and exhaust pipe changes.

[Don R]

 The K4 engine in my K0 bike has an 836 kit, light porting (by me) a yoshi clone look 4-1 and a loong muffler. The seat of my pants says the F2 cam is awesome. Maybe more torquey than the Kenny Harmon F cam in it now. Totally not scientific and no data.
If I was going with new springs I'd look for an F2-3 cam. That said, a new cam with no wear might even be better.

[Bill/BentON Racing]

Yo, D, what you mean you don't believe the cams were different? Huh? Heres what you look for to identify a original, early and different cam, the raised rectangle block in the bottom pic on left side of cam. After the first change, the bar was ground down like on upper cam, hopefully kmb69 can find the last one I sold him for better pics! ,Bill .......they are different, I promise you. Oh yeh, dibs on one if anyone has one for sale, thanks, ......you owe me!! Lol.

[TurboD]

Bill The identifying castings is what I am looking to sort out. Until someone actually shows tested specs, I still believe the pre 77 K cams are the same spec wise.

I do want to point out that any of these old stock cam make for a poor choice for any modern performance build, I have run the specs from all of these stock cams through my simulator. The power numbers only vary by a few with all of the cams (auto excluded). As Don posted the F2-3 would be the best choice if stuck with stock parts. 

My only interest is to identify some cams I have on hand. On my latest project (turbo), I am considering all options.

[Bill/BentON Racing]

I hear you...but just disagree about the K cams all being the same. Byron Hines. .. he knows a little,  is quoted as saying he's measured at least 3 different  K grinds,  this was around 75/76. If Keith will find his I sold him, and  place it next to a stocker from 73 on you can visually see the difference. And when you ride a good running K0 like Charlie David's on here...you can feel it! , Bill

[TurboD]

I have stated my beliefs as to why the early bikes would have ran better based on facts that we know. The early cam may or may not be different, I have yet to see actual fact or proof in the form of numbers. None the less, even if it were different in some way, it would still be of no use for todays performance minded rider.

If they were in fact "visually" different (which is a lot in numbers terms) and ran better, I would sure like to think that in 40+ years someone would have specs on them. I have no doubt the early bikes ran better, the changes that we know of could have accounted for nearly 10hp by themselves. 

[gschuld]

Dave,

Would you like to borrow a sandcast/K0 "rectangular pad" cam to measure? I can also send you a very low mileage late k1 cam which was supposed to be around the time of the first of several minor cam neutering changed from the factory.  I'd like to know the difference(mostly for the geek factor), on paper, as well.  I am confident there is a difference as well, but I am equally confident that the less restrictive airbox, exhaust, advancer, fatter jetting, etc of the sandcast/K0 model made far more difference in performance compared to early mid 70s engines than the cam alone.

If you have the tools to measure, I'll get them to you.  Maybe some other stuff as well if you're interested.  Did you get me PM from last week?  It's only if you are interested...

George

[Bill/BentON Racing]

I'd love to know,hearsay  ain't really worth a damn!  And yes a ll those other things added to for sure,  man I thought I might have some in my provisional workshop manual.....but no cam specs at all, it did say they located the rockers high away from heat to help maintain valve clearances,  Bill

[TurboD]

George A degree wheel and a dial indicator are all that's needed to run the numbers on a cam (and a engine of course).

[PeWe]

I found similar discussions in the Sandcast forum
http://cb750sandcastonly.com/smf_forum/index.php/topic,81.0.html
http://cb750sandcastonly.com/smf_forum/index.php?topic=265.0;wap2

Still no timing experiences with measured early Sandcast cam vs later.

I thought that Lotus Root 4-4 exhaust was for racing only. This was on the early CB750, right? This must be one more reason for more power.

[kmb69]

.....
I thought that Lotus Root 4-4 exhaust was for racing only. This was on the early CB750, right? This must be one more reason for more power.

There were at least 3 different exhaust systems on the Sandcast production bikes - Lotus roots, No Number, and some 300's.
SC researchers have demonstrated that there were multiple internal baffling configurations in the No No's and the 300's.
The Lotus roots were essentially straight megaphones when the baffles were removed and came stock on the early SC's.

[754]

Should be able to check cam in a lathe or vblocks..read it through 180 degrees, I think.

[TurboD]

I quickly skimmed over the Sandcast link posted above, seems they are pretty much saying the same as what I have been saying.

 

Should be able to check cam in a lathe or vblocks..read it through 180 degrees, I think.

I would think that to get truly accurate readings it needs to be in a head. The rocker arm effects the readings. I feel that we might be splitting hairs to begin with..

[754]

I usually measure cam lobe itself..as I assume its 1:1 ratio..
 You can bench read them very quickly..

[TurboD]

The rocker is not flat where it follows the cam, and does not touch in just a single area. To map out the lobe we would need to be completely accurate, to settle it once and for all.

I personally do not care how a sandcast cam specs out, I have zero interest in one.

My sole purpose of this post was to hopefully identify the better late K and F cams visually. 

[Bill/BentON Racing]

Yes, but would be nice to know,  Bill 

[754]

The rocker is not flat where it follows the cam, and does not touch in just a single area. To map out the lobe we would need to be completely accurate, to settle it once and for all.

I personally do not care how a sandcast cam specs out, I have zero interest in one.

My sole purpose of this post was to hopefully identify the better late K and F cams visually. 

That last one is easy ..the fat lobe one is the F ..can see it from 10 feet away..