Topic: degreeing in a cb750 cam for the best performance

[bucky katt]

i have a 74 cb750k with a k6 motor, bored .75mm over. i am installing a 1977 cb750f cam as soon as my adjustable cam sprocket gets here and i was wondering about the best method to do this, where it needs to be set as well. i am running a hondaman ignition, stock carbs with needle set 2nd groove from bottom and 122.5 jets along with a k+n filter in the stock airbox (openings slightly enlarged), and a set of iridium plugs that i will do the modification that the cyclex site mentioned, 17/46 sprockets and a 110/90/18 rear tire (thought the sprockets and  tire size might  be important because of final drive ratio is affected by those 2 things) i have a degree wheel i made with the template i downloaded from someone on the forum.

[bucky katt]

anybody? parts are here and i want to get started but i dont want to have to take the valve cover off more than once 

[kghost]

Hey Fuzzy,

Its a rather laborious post to explain.

Web Camshafts has a page on it.

http://www.webcamshafts.com/

[Jerry Rxman Griffin aka MuthaF'er]

I don't know that anyone has specs on stock cams to do degreeing with. I'd slap it in there and line up the line with the end of the tower as recommended by the shop manual.

I'd defer to Mike or HM however. Hopefully someone can find more detailed info for you.

[bucky katt]

Hey Fuzzy,

Its a rather laborious post to explain.

Web Camshafts has a page on it.

http://www.webcamshafts.com/

thanks a bunch for that Tim!

[turboguzzi]

Dont know how the mark align between cams, Jerry's advice might be spot on, but what if not?

Then regretfully, a degree wheel will not be enough, you will need also a dial gauge to degree a cam with accuracy.

Another tool you'll need is a piston stopper that will let you zero in the your degree wheel with high accuracy too. you werent hoping to have it zeroed on exact TDC just by looking at the marks on the ignition, did ya?  

It's easy to build it with an old spark plug form which you'll have to remove the ceramic core, tap it and screw in a bolt that should protrude say, an inch. That gets screwed into one of the plugs holes after you made sure that pisotn is not nearby.

The process after is quite long, sorry, cant find the time to type it for you but you should be able to locate the whole story googleing "degree cam".

[bucky katt]

hmmm this process is looking worse and worse every time i look at it hmmmmmmmmmm, anyone want an adjustable cam sprocket?

[bwaller]

The K's are what 5-35-35-5 degrees, what are the F'ers though? It's probably on the site somewhere. Just time it straight up or so the degrees of intake opening & exhaust closing are the same.

[Bill/BentON Racing]

CB750Fs '77 were Intake opens 5 BTDC,closes 40 ABDC,ex opens 40 BBDC,closes 5 ATDC,intake 0 on CB750F,75/76.Bill

[mlinder]

It all depends on what you want it to do, bucky. More high end power in a peak-ier, narrower range, or more low end at the expense of top end.

[bucky katt]

i'm thinking of setting it so that the big power strarts coming in around 4k - 4500 or so. this is a 77 750f cam and i can see by looking at it theres way more duration on it than the 75 750f cam

[bucky katt]

i can live with a little less bottom end if i can get more midrange and up top, i'll likely go back to an 18/48 sprocket set up if ya'll think it's neccesary. i have the 17/46 right now
i HAD a 17/50 at first and i couldnt get but 90 mph out of it

[NitroHunter]

Katt,
Forget the advertised open-close numbers - use them for reference only - and degree by the lobe center method. It's the only true way to know where you're at.

That F-2 cam has 107.5 lobe centers. Yeah more duration keeps valves open longer, but once the lobes are moved away from each other (107.5 LC) you have a decreased overlap - good for emissions, but lacks top-end potential of a cam with identical lift & duration numbers ground on 104 Lobe Centers...

With it in my STOCK F'er, I've run 102 (intake) LC, big low rpm grunt and it falls on it's face before 7k. Bumped int. LC to 104, improved but still not right. 106 was much better, the butt dyno said it pulled better than at 108. Maybe at 108 it would have slightly better mph by a couple.
 
I ran that bike in Stock Eliminator (XH/S) 13.07@101mph with the cam set at 106 int lobe center. Top speed was 110-115 range.
And I have the record certificate to prove it. 

[bucky katt]

is that top speed the top end in the 1/4 mile? or top speed out on the road. it runs almost 120 with me on it now, and i go about 370 or so.

[scottly]

Bucky, if I were you, I would install the cam "straight-up", and enjoy your bike, unless you are trying to set new records by trying to second-guess the cam grinder..

[bucky katt]

it's just a stock 1977 cb750f cam. the motor is still all Honda inside 

[lordmoonpie]

If it's a stock cam Bucky, I'd go with the honda manual, there's only minute gains to be had by degreeing although the stock cams can be scribed a good few degrees out it won't hurt your ride or your experience of riding. On a harsher cam for fast street or race, I'd go with degreeing it in every time (and I do :-)). Once you've made the piston stopper like Simon suggested from an old spark plug, have a degree wheel and a dial gauge, you're well away into hours of fun working out numbers of degrees to add and subtract until you get the cam right. In a weird kind of way it's fun to do and get it spot on but with a stock cam, I'd go with stock build techniques...

[bucky katt]

sounds good to me then. it is a stock honda cam, just not stock for the motor it's going into 

[turboguzzi]

Once you've made the piston stopper like Simon suggested from an old spark plug,

LMP, freudian slipping lately ? 

How's you r back BTW?

Nitro, two questions (maybe I'll learn something new:) )

1. How do you obtain the desired lobe center without using the open/close figures? (@0.40 lift of course)
2. The overlap is the delta between inlet and exhaust, how do you change it in a single cam with both IN and EX on the same part?

TG 

[bucky katt]

FINALLY! i'm picking up a set of factory 4-4 pipes tomorrow. theyre 78 model pipes and there is going to be some modifying done to the baffles. i have been trying to get a set of 4 - 4 pipes for 2 damn years. i did the "happy 4 into 4 exhaust dance" in front of the wife and pastor today, convincing them that I am indeed full bore loony 

[MRieck]

Once you've made the piston stopper like Simon suggested from an old spark plug,

LMP, freudian slipping lately ? 

How's you r back BTW?

Nitro, two questions (maybe I'll learn something new:) )

1. How do you obtain the desired lobe center without using the open/close figures? (@0.40 lift of course)
2. The overlap is the delta between inlet and exhaust, how do you change it in a single cam with both IN and EX on the same part?

TG 

Exactly. You are married to the lobe separation ground into the cam. I've talked about it before and the idea of grinding different separation angles.

[bucky katt]

so, am i better off with the k6 cam? the 75 750f cam or the 77 750f cam? i do have an adjustable cam sprocket and i'm putting it in regardless of whether i can adjust the present cam anyways since i WILL get a good street cam as soon as i get some more parts sold.

[Jerry Rxman Griffin aka MuthaF'er]

My vote is the 77 F. It has 5 degrees more duration.

[NitroHunter]

TG,
Of course you are right about the open/close # giving the LC, My thoughts were directed to a valve train geometry change giving a goofy cam number not matching the cam card. My bad! 
 In the overlap example, I was just pointing out the difference when a cam is ground using the same lift/duration master, but to different CL numbers. The closer the lobes, the greater the overlap. Smokey Yunick was a master at understanding how the rules DIDN'T address this!  

The changes I tried worked OK for me - in my own riding situation - is all.  


-

[bucky katt]

IF i get to re-torquing head tomorrow/later today i'm going to install the 77 f2 cam and the new sprocket, installed straight up for the time being.