Topic: CB750-stock cam specs?

[MCRider]

Does anyone know the stock cam specs for a CB750. I know they've changed from beginning to end, so something early in the K0 to K2 range is most relevant to my curiosity, but anything would be helpful.

I did a search for about 10 mintues and best i could come up with is about .314 lift on the intake of an early stocker and .29? on the exhaust. Nothing for duration or from where it was measured.

I've just bot a cam and was curious to compare to stock. It's .360 lift In and Ex and 250 duration measured at .050.

Its the most conservative offering WebCam had.

Thanks.

[michrobi]

I just finished my rebuild with that same cam Ron. http://forums.sohc4.net/index.php?topic=55056 is what it actually measured with a dial indicator at 0.050

The only info I found on stock cams were the open and close degrees listed in the supplement charts.

[MRieck]

Megacycle lists stock as .315 220degrees (intake) .313 235 degrees. That 41 will never measure up to that lift or duration......it is as close to stock as you can get

[MCRider]

Thanks Michrobi and MRieck! That is exactly what i wanted.

I'm fine with as close to stock as possible, that was my goal for cams. i have a frame rail kit and a cam swap could be done on a Saturday morning if i ever felt the need. I've done em before, though many years ago.

I once had a K0 cam, with the Honda marking "R1" in an 836 with a ported head one time. Nice streetable power band, great gas mileage, went a little flat earlier than some would like, 8500rpm or so, but just right for me. Great wheel spinner. I'll bet the 41 is a bit hotter than that was.

A man's gotta know his limitations...or at least what he wants.

I never degreed a cam though, so I'm looking forward to learning that trick. Always just dropped it in and ran it. Always with acceptable results.

Next motor may be made to rev. I'm liking the idea.

[MCRider]

Hi Michrobi: went back and looked at your engine build thread. It looked like maybe there was green plastigage on all 10 bearing shells? Should only have been 5. It may just be oil I am seeing. Nice job getting that back together so quick!

The 41 will run different in a 736 than in my 888, but I'll still like to know what you think.

[michrobi]

Yeah that Spectro oil has a greenish shine heh, I threw away a whole quart thinking it was contaminated at first 

[Bill/BentON Racing]

RC sold only one cam back in the day that would work with stock pistons,it was #240,duration 296,lobe centers 118,lift .327,intake,.330 ex.Intake open 9.5 BTDC,closes46.5ABDC.EX opens 46.5BBDC,closes 9.5 ABDC.This was a regrind cam.The 315 MC you would surely notice,but the 295 might suit your style better.295 specs Duration In-306/-296,lobe centers 105, lift In .390.In opens 19 BTDC,closes 46 ABDC. Ex lift .360,opens 45 BBDC,closes 15 ATDC.315 specs (the one I liked the best)Duration 310,lobe centers 104. Lift .365,Opens 23 BTDC,closes53 ABDC.Ex opens 53 BBDC,closes 23 ATDC.They made 2 more,a 327 and 454 valve bender!,Bill,TG, in the early days RC sold a sprocket with 3 holes,yeah the customer(me) got to file like you ,slotted much better.Bill

[MRieck]

RC sold only one cam back in the day that would work with stock pistons,it was #240,duration 296,lobe centers 118,lift .327,intake,.330 ex.Intake open 9.5 BTDC,closes46.5ABDC.EX opens 46.5BBDC,closes 9.5 ABDC.This was a regrind cam.The 315 MC you would surely notice,but the 295 might suit your style better.295 specs Duration In-306/-296,lobe centers 105, lift In .390.In opens 19 BTDC,closes 46 ABDC. Ex lift .360,opens 45 BBDC,closes 15 ATDC.315 specs (the one I liked the best)Duration 310,lobe centers 104. Lift .365,Opens 23 BTDC,closes53 ABDC.Ex opens 53 BBDC,closes 23 ATDC.They made 2 more,a 327 and 454 valve bender!,Bill,TG, in the early days RC sold a sprocket with 3 holes,yeah the customer(me) got to file like you ,slotted much better.Bill

Dynoman is selling those 295's new....I have one in the shop right now. He also has the 315

[Bill/BentON Racing]

Thanks for the info.I think I need a 315 for next build.Always look forward to your posts and replies.Keep up the good work!,Bill

[Caminokid]

This brings back the days when I used to build 750s to flat out run! I dont remember the size of the stockers...but back then I didnt care. I always had a guy that knew what the biggest that was made for these bikes and got me the cam I needed. from 82 to 88 I was doing all this. Miss doing it now.

[MCRider]

RC sold only one cam back in the day that would work with stock pistons,it was #240,duration 296,lobe centers 118,lift .327,intake,.330 ex.Intake open 9.5 BTDC,closes46.5ABDC.EX opens 46.5BBDC,closes 9.5 ABDC.This was a regrind cam.The 315 MC you would surely notice,but the 295 might suit your style better.295 specs Duration In-306/-296,lobe centers 105, lift In .390.In opens 19 BTDC,closes 46 ABDC. Ex lift .360,opens 45 BBDC,closes 15 ATDC.315 specs (the one I liked the best)Duration 310,lobe centers 104. Lift .365,Opens 23 BTDC,closes53 ABDC.Ex opens 53 BBDC,closes 23 ATDC.They made 2 more,a 327 and 454 valve bender!,Bill,TG, in the early days RC sold a sprocket with 3 holes,yeah the customer(me) got to file like you ,slotted much better.Bill

Dynoman is selling those 295's new....I have one in the shop right now. He also has the 315

I had spoken to Brent? i think it was at Dynoman about the 295. It was tempting, but i opted for the 41. In 10 words or less, would you give me your comparison of the 295 to the 41.

I may have undershot myself, but my goal was, out of those available, to get the first step up away from stock.

I had forgotten about MegaCycle. Looks like some of their offerings are between stock and the 41, though its hard for an amateur to compare apple to apples with these things. Field observation is proably the final arbiter.

[bucky katt]

i'm not really sure if this has been asked before, my short term memory is shot, but i did search and i couldnt find it so here goes. what are the cam specs for a stock k-6 cam compared to a stock 75 750f cam? is there enough difference to make swapping the 2 worthwhile? i really cant spend the money on a hi-performance cam right now. i've unshrouded the valves in the chamber and thats it for head mods. i'm also running the stock carbs from that 75 750f and tuned to work with the stock airbox and k+n filer inside it as well as the kerker header with supertrapp baffle holding 12 discs

[HondaMan]

My notes from actually-measured engines "in the day":
(I used to only measure the intakes at the time.)

1969 K0 sandcast engine:
Intake opens 7 BTDC, closes 45 ABDC
Lift (4 lobes measured): .3150", .3155", .3157", .3225"

1969 diecast engine:
Intake opens 7 BTDC, closes 42 ABDC
Lift: .3150" all 4 lobes.

My first K1, a late 1970 build:
Intake opens 5 BTDC, closes 35 ABDC
Lift: .3150" all lobes.

Honda's spec for K1-K6 (which would be the "2nd generation" K1 and later engines):
Intake opens 5 BTDC, closes 30 ABDC
Lift: .3142"-.3158", .3122" lower limit.
Exhaust opens 35 BBDC, closes 5 ATDC
Lift: .2945"-.2961", .2925" lower limit.

The truth-in-measurement: many, many cams I've measured in very young engines had lift figures on the order of .310" to .315" intake, .285" to .295" exhaust, very common. I have several cams here now, all from young engines, and they also fall into these lift numbers. Honda states that 1.411" total height over the base circle is the lower limit on K0 engines, but I have yet to see a K2 (late) or later engine that even has this much height on ANY lobe.

Honda's spec for "K76/77/78" engines, generally considered to be the "F" and K7/K8:
Intake opens 0 BTDC, closes 40 ABDC
Exhaust opens 40 BBDC, closes 0 ATDC
(I have no lift numbers for these cams.)

[NitroHunter]

Here are measured figures for the 77-78 F-2 (broken band) cam:
Lift - Int. .318", Exh. .302"
Duration - 225 deg @ .040
Lobe centers - 107.5
Overlap - 10 deg @ .040"
       
I would question the wisdom of any larger than .360" lift cam in a stock head, the flow just isn't there. You may be surprised at how quickly (lift wise) these heads stop flowing with even the best port jobs.   
My experience is that long duration cams (over 250 @ .040) makes a sloppy around-town ride with even a 10:1 motor. They have lots of power when turned at big rpm, but suck riding between stop lights.
 
It's all a compromise, so target for your personal fun zone.

[754]

I looked at dynomams site. The cam specs for the  supposed 315 seemed to have different #s.. and is the 317 & 327 copies running .012 and .014 clearance? They either are the same, or it is a different cam.

 RCs, at least some were made by Engle.

Nitro, I ran the 315 with stock head & valves, and Webers, and found I had exceptional midrange, certainly more fun in town than a stocker.( you could short shift and it would pull hard) Part, but not all of that time I ran my turbo header high pipe, and am starting to think it maybe is a bit torquier, due to smaller primaries.

[MRieck]

Here are measured figures for the 77-78 F-2 (broken band) cam:
Lift - Int. .318", Exh. .302"
Duration - 225 deg @ .040
Lobe centers - 107.5
Overlap - 10 deg @ .040"
       
I would question the wisdom of any larger than .360" lift cam in a stock head, the flow just isn't there. You may be surprised at how quickly (lift wise) these heads stop flowing with even the best port jobs.   
My experience is that long duration cams (over 250 @ .040) makes a sloppy around-town ride with even a 10:1 motor. They have lots of power when turned at big rpm, but suck riding between stop lights.
 
It's all a compromise, so target for your personal fun zone.

I support those statements 100%.

[michrobi]

Hi Michrobi: went back and looked at your engine build thread. It looked like maybe there was green plastigage on all 10 bearing shells? Should only have been 5. It may just be oil I am seeing. Nice job getting that back together so quick!

The 41 will run different in a 736 than in my 888, but I'll still like to know what you think.

I love it! Noticeable as hell when on an incline like a freeway on-ramp. It seems like it cut my 4th gear time before shifting to 5th in half. Screams to 8k RPM like it was cool! It's hard to say how much of that is the cam though, Ron. The engine only had ~62 lbs of compression in 3 and 4 to begin with.

[MCRider]

Hi Michrobi: went back and looked at your engine build thread. It looked like maybe there was green plastigage on all 10 bearing shells? Should only have been 5. It may just be oil I am seeing. Nice job getting that back together so quick!

The 41 will run different in a 736 than in my 888, but I'll still like to know what you think.

I love it! Noticeable as hell when on an incline like a freeway on-ramp. It seems like it cut my 4th gear time before shifting to 5th in half. Screams to 8k RPM like it was cool! It's hard to say how much of that is the cam though, Ron. The engine only had ~62 lbs of compression in 3 and 4 to begin with.

That's what we like to hear. What displacement are you running?

Cerainly the lack of compression was a problem. Its been a while for me, but i remember what a fresh 736cc stocker felt like. Sure it wold rev to 8K no problem, but it would feel like a little less of a motor above 5.500k. If the motor is "coming alive" above 4.5k, then its likely the cam. Sounds like good mid-range too, which is where we live.

[754]

Most of you guys are missing what big squirters can do at the lower RPMs and midrange.

 I think the 77/78 carbs, squirt maybe 1/3 as much as on the Webers !

[michrobi]

736cc is the displacement aint it?

[NitroHunter]

Frank I'll bet your squirters do make a big difference in ridability.
When I had that 315 cam in the 970 motor, my 29mm Smoothbores got many jet changes trying to compensate for weak vacuum and intake reversion at low rpm, with the resultant crummy transitioning. In time I got it OK - but not really good. I ended up buying the aftermarket accelerator pump kit, I don't know what the squirt was but yes it helped a lot, it just was never really smooth.
My commute just didn't have enough 'play areas' for a cam so lumpy. Way too much 3-5k usage involved.
 
Believe me, I'm not saying that (on the weekends) the duration-related horsepower rush from 6k to redline+ wasn't a blast - quite exhilarating, actually     - just that the 'milder' cams give a more satisfying overall experience when WOT isn't practical.

And not everybody can get their hands on a set of Webers...  


 

[MCRider]

736cc is the displacement aint it?

Yes if its stock. Sorry I've read so many threads I can't keep it straight who's doing what.

It would be real easy to "over-cam" a 736, so it sounds like you've got a good one.

Generally, the more displacement, the lower rpm the power comes in, and ends. So my 888 should do what I want with the 41.

[michrobi]

Oh yeah, bone stock except the cam. Well, and the exhaust, carbs and ignition are also upgraded.

[Bill/BentON Racing]

I went looking for what I thought was an Engle cam,but was Norris R grind,Anyone used,familiar with,let me know.MC good to see your progression,I think your bike is gonna do just what you want,however if you want to borrow a Sat morning cam ,we will fix you up! Bill

[michrobi]

Hey Bill my Cobra used a Norris custom grind cam. I have the specs somewhere on here. Based on that alone it's a good bet that's a quality camshaft.