Topic: cams cams cams cams | cams cams cams cams | cams cams....

[grumpy]

I'm trying to decide on a cam.
750K3, stock airbox, stock 4-4 pipes,  bored to second step, new Ape guides (shorter than OEM), Hondaman porting...
General street use, lots of freeway miles while commuting.
would like to juice the mid & upper end for, um, passing purposes.

Comparing DP117khd v. Web Cam 41a v. Megacycle 125-00


     lift      dur     lobe center
in  .345    277   106.5   
ex .325    294   110

     .335    242     ??
     .335    239     ??

     .340    246   104           
     .330    247   104.5     


They all look similar on paper, except for the huge duration of the 117. From what I've been reading, duration like that really only helps at high RPMs and can cause problems at idle. Is that right?

Can anybody give me some quick pros/cons?
I searched but there's nothing really concise. Seems like everyone has a favorite regardless of what the numbers say...

[Old Scrambler]

I also like to have a passing gear

My K3 has 1st-over pistons, a valve-seat grind, stock pipes and box, and 18-48 final drive.  4th-gear power to 10,000+ RPM is aided by a mild DIY porting job, a K&N filter with a few extra holes drilled in the bottom of the case, and 120 main-jets.  Next time I take the motor down I plan to install an F2 cam.

Regarding your cam selection..............wide lobe centers tend to cause the motor to stumble when getting away from the stop-light. Although each of those cams are "safe" to run with stock springs and retainers..............I think they would shorten their life and would tend to cause the rocker-adjusters to "pound' the valve-stems causing dimples. 

[Don R]

 The long exhaust duration was thought to air in cooling the exhaust valves and associated parts.

[grumpy]

Dennis - we have just about the same bike.

So that's an OEM F cam you're considering?

Not sure I get what you're saying about the springs. I understand how pounding the stems will deform the adjuster face but where do the springs come in?

[PeWe]

If you can think about using the saw in your beloved motorcycles frame... 
Install a frame kit and you can change cam during a weekend without much job. Remove tank, frame part unbolted, lift valve cover, off with the valve train, cam sprocket, cam..... Oil, carbs, exhaust still on.
Check with 754 on this forum for a frame kit.

I was sure about to never cut my frame in my beloved bike I had own in 35 years.
Then I had to take out the engine again and I changed my mind. I did not want to scratch the fresh painted frame and engine.
I realized that my bike is no mint OEM CB750 and will never become one anyway even if it now is closer to OEM style than it has been after 1980. The engine is modified since 1983 and I'll have fun with it again now restored/repaired.

Trying other cams can be a future amusement. I have CX-7 now, next can be a DP295, then maybe back to my old Action Fours SS-1 (that was a great cam for touring as well as driving hard in the city, sprockets 17-48).
Change the cam just for fun is not fun when the engine has to be pulled out and all parts that must be removed before that including drain the oil.

[Old Scrambler]

Grumpy............the ramps on the cam-lobes become quite steep as you add duration..........and the taller the lift..........the more compressed the springs are on each actuation.  Missing a shift with a stock motor is not a big deal..........but missing one with a hot-cam means the over-rev is putting a higher level of stress on the motor parts.

Your cam selection is still on the mild side...........and won't really be noticed until 5,000 or more RPMs.  I'm just trying to let you know what you may be getting into.............could be Fun