Author Topic: CB750 "R1" camshaft (Read 25918 times)

Bodi · « **Reply #25 on:** December 03, 2009, 11:34:56 AM »

Casting a cam blank is done with sand casting, an age-old process. You make a model cam blank "master" with lobes bigger than the final grind you want out of something fairly hard but easy to shape, wood is the likely material. You put it in a casting box and pack foundry sand around it. You remove the model and pour molten metal into the hole in the sand shaped like the model. When it cools, you remove the sand and have your metal cam blank.
If there are several cam blank masters - necessary if you want a lot of blanks and run several casting lines - you mark them so any defects can be traced to the model: if a bit gets chipped off a master accidentally for example, you can look at the number on a defective casting and then repair or discard the damaged wooden master.
If a new cam grind that wants a lobe bigger than your master is adopted, you will need a new bigger-lobed one. If you have a new grind with smaller lobes you might make a new smaller-lobed master to save grinding effort removing the excess metal. Otherwise there would be no good reason to spend time making a new master.
Suppose your new and revolutionary 1969 CB750 has only one blank cam master at first, the R1 (the R either identifies it as a 750 cam or is there to help you tell a 6 from a 9) but you made two just in case, so the R2 is on the shelf. Then orders start pouring in and you ramp up production, requiring R2 plus new ones, R3 and R4.
In 1976, you've broken and discarded R1 and several others and made quite a few new wooden masters, you are (as a guess) using R2, R3, R5, R9, R10, R11 and R12... the rest are gone. Any 1976 engine would have a camshaft with any of these marks but all cams are ground to 1976 specs.
An R1 cam (in this imaginary scenario) could be any model year up to when the model was retired. An R12 could be any model year since it was first used, until retired.
There is some relationship between cam mark and model year, but not a relationship as simple as R1=K0, R2=K1 etc. I don't think there are any changes between model years that would require a different cam blank (and thus a new wooden model).

mystic_1 · « **Reply #26 on:** December 03, 2009, 01:23:22 PM »

Excellent post, Bodi!

mystic_1

MCRider · « **Reply #27 on:** December 03, 2009, 01:59:52 PM »

Thank you Bodi, all very interesting. So I'm only fractionally right and I can accept that.

So an early R number could appear in a later bike with later specs. But likely an R10 for example would never have appeared in an early bike.

Well the delusion was fun while it lasted.

Back to the original poster lwitchy. He may have an early spec cam, or not. If he had virtually any other R# to look at he could tell.

If the other parts in his box were early that could give him hope.

But as Mystic says without measuring or comparing, one could not know

nobody · « **Reply #28 on:** December 03, 2009, 02:11:25 PM »

well that makes a lot of sense. I'm not so anxious to see my cam now, I'll wait until I actually have a reason to crack open that motor.

MCRider · « **Reply #29 on:** December 04, 2009, 04:55:08 AM »

Quote from: mgab on December 03, 2009, 02:11:25 PM

well that makes a lot of sense. I'm not so anxious to see my cam now, I'll wait until I actually have a reason to crack open that motor.

After doing some more research and receiving some qualified PMs on the subject, it seems...

The R numbers were pretty much sequential and tied to to the detuning process up to 1975. At that point, for some reason, Honda started the numbering process over again, re-starting at R1.

So a low R number in a pre75 K bike is likely a hotter cam, with the R1,2,3 likely K1 and ealier. That explanation makes everyone "right" and restores my impression that the earlier numbers are the hot cams, especially since I know my parts bikes and second hand cams all were K5 or earlier.

No absolutes here, but my limited physical evidence supports it.

A low R number in a 75 or later bike is likely a detuned cam already Now what's going on with the Fs especially F2 and F3 is unknown to me. My assumption is those are hotter cams and may be transferrable to a K. But with the different valve angles I don't know. I'd probably buy an aftermarket cam before doing an F to K swap.

lwitchey · « **Reply #30 on:** December 04, 2009, 06:55:49 AM »

I have to find out more about this cam. I am going to take it out to the shop tonight and set it up on some V blocks and measure the lift. Check back in a couple of days. I will post my results.

MCRider · « **Reply #31 on:** December 04, 2009, 07:06:25 AM »

Quote from: lwitchey on December 04, 2009, 06:55:49 AM

I have to find out more about this cam. I am going to take it out to the shop tonight and set it up on some V blocks and measure the lift. Check back in a couple of days. I will post my results.

It wold be interesting to know.

754 · « **Reply #32 on:** December 04, 2009, 08:20:51 AM »

The F cam is noticeably hotter to the eye..

I want to know if it is THAT NOTICEABLE on early cams?

no need for V blocks, except to mesure straightness. ise a caliper on the lobes.. more lift, it must be larger..

MCRider · « **Reply #33 on:** December 04, 2009, 08:31:53 AM »

Quote from: 754 on December 04, 2009, 08:20:51 AM

The F cam is noticeably hotter to the eye..

I want to know if it is THAT NOTICEABLE on early cams?

no need for V blocks, except to mesure straightness. ise a caliper on the lobes.. more lift, it must be larger..

My R2 is visibly hotter, more lift and duration, than my R10. Pictures this weekend.

We know the HP drop from best to worst in the K lineup was about 6 to 8 depending on who says it. Cam wasn't the only thing, but a big part of it.

HondaMan · « **Reply #34 on:** December 04, 2009, 08:43:56 AM »

The "restart" of the R casting numbers seemed to be tied to the major cam change at the "F" model in 1975. At this cam, the duration was retarded 5 degrees:
K models: IN opens at 5 degrees BTDC, closes at 35 degrees ABDC.
F models (and K7/8): IN opens at 0 degrees BTDC, closes at 40 degrees ABDC.

The "F" cams also have a steeper opening ramp (which is part of the accelerated wear issues on those valve guides). These 3 things taken together meant the "ears" on the cam had to move in relation to the lobes.

This issue was due to emissions limits: retarding any cam will reduce emissions at lower RPM levels, especially hydrocarbons. In the 1975 era, our highly intelligent EPA was edicting that motorcycles suddenly had to pass the "same emissions rules as automobiles", which meant that at 2500 RPM there was a hydrocarbon limit. So, Honda, Suzy and Kawi all retarded their existing cam profiles a few degrees to limit low-end fuel, and voila! the bikes passed the 2500 RPM test (like anyone rides at 2500 RPM...). This same retard business pushes the power peak upward in the powerband, so suddenly the new "F" bikes felt pipey at 6000+ RPM and a little doggy in around-town traffic. You can "fix" F/K7-8 engines by slotting the cam sprocket and advancing the cam 5 degrees, which will result in considerably more low midrange torque.

All of this had to be fitted into an existing engine design, which meant the sprocket was to remain the same, so it appears a new cam mold was started. That's when the "R" number was reset back to "1" again: at least that's what 'we wrenches' surmised at the time...

MCRider · « **Reply #35 on:** December 04, 2009, 08:51:28 AM »

Thanks HM! The plot thickens!

lwitchey · « **Reply #36 on:** December 04, 2009, 10:41:46 AM »

I pulled the cam from the shelf and noticed that it is stamped and not cast into it. That means that it was marked after it was cast. It did not come from the mold. Here is a pic. of it. See if it turns out.

Bodi · « **Reply #37 on:** December 04, 2009, 11:07:23 AM »

It looks like (although picture detail is limited) that the sand casting pebbled texture is inside the stamped R1 character lines. That would mean the number is stamped into the master rather than into the finished cam casting. If the stamped characters are smooth in their indentations, they were stamped on the casting.

ColinMc · « **Reply #38 on:** December 04, 2009, 11:10:44 AM »

My 76 unmolested (but well abused) motor has an R1 cam in it, the 72 motor I got from ebay as a supposed low mileage motor has an R2...have one more motor to check tonight or this weekend that's in my friends garage lol. Might take the valve cover off the Action4 motor I got just to see what cam that has too...not sure if it's even a Honda cam in that one...

Oh these are all 750K motors I have btw.

MCRider · « **Reply #39 on:** December 04, 2009, 11:23:33 AM »

Quote from: ColinMc on December 04, 2009, 11:10:44 AM

My 76 unmolested (but well abused) motor has an R1 cam in it, the 72 motor I got from ebay as a supposed low mileage motor has an R2...have one more motor to check tonight or this weekend that's in my friends garage lol. Might take the valve cover off the Action4 motor I got just to see what cam that has too...not sure if it's even a Honda cam in that one...

Oh these are all 750K motors I have btw.

So your 1976 R1 is a pollution control cam. The 1972 R2 may be of interest. So now the question arises did they use the same blank (R2) with different grinds? I would have thought an R2 would have been K1 or ealier. Assuming your 1972 is a K2, but it might be a K1.

Lots of motors...cool!

ColinMc · « **Reply #40 on:** December 04, 2009, 11:32:54 AM »

The thing is...i've gotten all these motors from 2nd 3rd...4th...who knows how many people owned them. So I really can't be 100 percent sure they are the original cams. I'm just guessing.

Yeah I need to get rid of some of these things lol.

Spanner 1 · « **Reply #41 on:** December 04, 2009, 04:27:31 PM »

No definitive answer yet, did Honda revert to hotter cams in '77/'78 ? ( K and F pumper carbs ) and R1 or R2(like my K'78) cams to try increase performance to vie with the competitors DOHC bikes?? In other words, if it's stamped R2 irrespective of year is it the same cam as an early( hotter ) R2 cam...??

MCRider · « **Reply #42 on:** December 04, 2009, 07:25:09 PM »

Quote from: Spanner 1 on December 04, 2009, 04:27:31 PM

No definitive answer yet, did Honda revert to hotter cams in '77/'78 ? ( K and F pumper carbs ) and R1 or R2(like my K'78) cams to try increase performance to vie with the competitors DOHC bikes?? In other words, if it's stamped R2 irrespective of year is it the same cam as an early( hotter ) R2 cam...??

Probably not. The R2-2 (post 75) cams have a nod towards emission control the R2-1 cams (pre 75) would not have had. As hondaMan said the F cams also had steeper ramps aiding and abetting the valve guide wear the Fs had.

754 · « **Reply #43 on:** December 04, 2009, 08:26:48 PM »

Found a R13 today,.... what is that from..

..Freakin EH model..

lwitchey · « **Reply #44 on:** December 05, 2009, 07:02:07 AM »

I set this R1 cam up in some centers an ran a indicator over it. I came up with .278 lift on the intake and .258 lift on the exhaust. I figure there might be some wear on them. It could actually be .280 and .260.

HondaMan · « **Reply #45 on:** December 05, 2009, 07:45:43 AM »

Quote from: lwitchey on December 05, 2009, 07:02:07 AM

I set this R1 cam up in some centers an ran a indicator over it. I came up with .278 lift on the intake and .258 lift on the exhaust. I figure there might be some wear on them. It could actually be .280 and .260.

The K0 lifts were:
IN .3142"-.3158" (7.98-8.02mm)
OUT .2945"-.2961" (7.48-7.52mm)
or, for simplicity: 8mm inlet and 7.5mm outlet.

By the time of the K2 mid-year, these numbers were approximately:
IN .3010"
OUT .286"
as measured across several bikes at the time.

By the time of the new K$, which is when I quit taking such measurements on customer's bikes that came in for tuneups, the number were:
IN .298"
OUT .286"

I had also noticed on K4 teardowns (for new rocker shafts, as they wore quickly on the late K4 and the K4 bikes) that the "R" numbers on the cams were like R3 and R4, even saw one R6 in 1975 on a new K5. Then I didn't take notice after that.

Honda had a habit of reducing cam lift on all of their bikes, but most of them did not enjoy 10-year sales runs: I suppose it to be from a combination of reducing their warranty costs due to wear issues and also their manufacturing costs by stretching out the life of the mold models, like Bodi noted above. Models are expensive to make, and with as many 750s as they were building at the time, they had to have several copies of the cam molds going at once, just to keep up. It was once said that they were building one 750 every 40 minutes. Thus was the enormous popularity of this bike! I don't think you can make a cam that quick from one mold (Bodi?).

eurban · « **Reply #46 on:** December 05, 2009, 10:28:42 AM »

Quote from: MCRider on December 03, 2009, 10:58:14 AM

Quote from: mgab on December 03, 2009, 10:47:47 AM
Haha, well you've been plenty helpful thus far so I'll take your word on it.
According to one of the CB750 books i have, the Fs with the head/valve angle change (77/78?) were pepped up to compete with the DOHC suzis, etc while waiting on the Honda DOHC. The Ks were left as they were for the Windjammer Fairing crowd.

Not really sir. The 77 and 78 Ks got the performance enhancements that were introduced in the 75 and 76 F models. This includes a compression ratio bump from 9:1 to 9.2:1 along with a better breathing head and a hotter cam profile (don't know how it compares with the earliest profiles) The accelerator pump carbs also helped with performance. Weight was up significantly from the very early bikes yet according to period magazine tests 1/4 times were similar. The late K engines or early F engines (without the larger valves) are solid starting point for a performance motor build. All stock cams are relatively mild but it would be interesting to know the evolution of the profiles.

HondaMan · « **Reply #47 on:** December 05, 2009, 11:05:05 AM »

Quote from: eurban on December 05, 2009, 10:28:42 AM

Quote from: MCRider on December 03, 2009, 10:58:14 AM
Quote from: mgab on December 03, 2009, 10:47:47 AM
Haha, well you've been plenty helpful thus far so I'll take your word on it.
According to one of the CB750 books i have, the Fs with the head/valve angle change (77/78?) were pepped up to compete with the DOHC suzis, etc while waiting on the Honda DOHC. The Ks were left as they were for the Windjammer Fairing crowd.

Not really sir. The 77 and 78 Ks got the performance enhancements that were introduced in the 75 and 76 F models. This includes a compression ratio bump from 9:1 to 9.2:1 along with a better breathing head and a hotter cam profile (don't know how it compares with the earliest profiles) The accelerator pump carbs also helped with performance. Weight was up significantly from the very early bikes yet according to period magazine tests 1/4 times were similar. The late K engines or early F engines (without the larger valves) are solid starting point for a performance motor build. All stock cams are relatively mild but it would be interesting to know the evolution of the profiles.

The thunbnail sketch version of the profiles:
K0 inlet duration: 5 BTDC to 30 ABDC, Outlet 35BBDC to 5 ATDC.
By the K4: drop the duration about 5 degrees, evenly split.

My estimate of these changes are that the models were wearing down and Honda was detuning.

The later cams move the above numbers "back" 5 degrees, but they started with the full duration again.

MCRider · « **Reply #48 on:** December 05, 2009, 11:34:17 AM »

Whew! My head is spinning. Suffice it to say, the 69s were the fastest and some cams are different from others.

eurban · « **Reply #49 on:** December 05, 2009, 01:01:23 PM »

Quote from: MCRider on December 05, 2009, 11:34:17 AM

Whew! My head is spinning. Suffice it to say, the 69s were the fastest and some cams are different from others.

No, the fastest stock 750s were the 77 and 78 Fs. They were also the heaviest. According to Cycle's test of the 77K it was also faster than the 69 they tested way back when and heavier too. Some here dispute the tested 1/4 mile times of the 69 (ragged out bike, improper technique on this new kind of beast etc etc) but who knows as there seems to be a good bit of nostalgia mixed in. I would think that with the higher compression in the late Ks combined with the better breathing heads and pumper carbs that more power was being generated. This was certainly blunted somewhat by the weight gains and perhaps by the quiet exhausts. . . .

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Author Topic: CB750 "R1" camshaft (Read 25918 times)