79 cams in an 80 engine


itsacbx
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79 cams in an 80 engine

Post by itsacbx »

Hey all, Im about to get an 80 engine rebuilt and I have bought a parts inventory which included a quantity of what I think is 79 cams and assorted paraphenalia...
so my question is - "how do you tell what is 79 cams versus 80 and later cams?"
I have four sets of carbs so finding a set of 79 carbs is also not an issue.
Thanks
Al

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Re: 79 cams in an 80 engine

Post by daves79x »

Measure the lobes. Specs are in the shop manual, I don't know them off the top of my head.

Dave

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Re: 79 cams in an 80 engine

Post by itsacbx »

will do, thanks
Al

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Re: 79 cams in an 80 engine

Post by bobcat »

Whoever is rebuilding your motor should know the difference. However,
unless the cams will be degreed, you would be better off using the 81-82
intake cam(s) due to the stock timing specs. Except for the 80 cams the
exhaust are all the same. The only difference with the 80 EX cam is the timing
(sprocket bolt hole location). The lobe profiles are all years the same.
Bob
82 CBX, 81 CBX, CB1100F, 79/82 CB900F (avatar)

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Re: 79 cams in an 80 engine

Post by daves79x »

Bob - Are you saying that the lobe height specs are the same on all years? No, they are not. The lobe height specs are clearly different from '79-'80 and then different again for the '81-'82 intake. I can dig up the specs if you want.

Dave

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Re: 79 cams in an 80 engine

Post by EMS »

Here is an excerpt from a write-up I did years ago:
1980 CBX
The exhaust cam was advanced by 5º and had less overlap. The exhaust cam lift was reduced from 7.5mm to 7.0 mm, the intake cam lift was reduced from 8.3 to 7.8 mm.
...
1981/82 CBX:
New cams closed the intake now 5º earlier, both opening and closing of exhaust was retarded by 5º. Intake valve lift was increased by 0.2mm to 8.00mm, and exhaust valve lift changed to 7.5mm from 7.00mm. A new cam profile with a different rise and fall was supposed to reduce tappet noise.
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Re: 79 cams in an 80 engine

Post by bobcat »

daves79x wrote:
Thu Dec 08, 2022 7:19 am
Bob - Are you saying that the lobe height specs are the same on all years? No, they are not. The lobe height specs are clearly different from '79-'80 and then different again for the '81-'82 intake. I can dig up the specs if you want.

Dave

Yes, please post them.
I was referring to the EX being all the same except 80. Just repeating what I've been told
or read about. Read what you said about the EX cams in my R&D platform thread, p.2-3.
Both you and EMS claim that the EX are the same, except 80. I had also speculated that the
80 IN cam had the lift reduced (you verified it) but nowhere have I found that the EX also had
reduced lift.
Yes EMS, the 81-82 rise/fall (acceleration ramps) were changed but that did not change
duration or lift. Based on the valve open/close numbers in my Honda Specs books and the
FSM specs, the 80 EX cam(s) was advanced to close the EX valves at TDC. Nowhere could
I find any lobe height specs for the 80 cams. The LC numbers for 79,81, 82 are all 107.5.
The 81-82 IN cam was advanced 2.5 degrees to LC 105 for better low end/mid range.

I stand by my original suggestion that the 81-82 cams would be the best choice (unless the
cams are degreed by slotting the sprocket bolt holes).
Bob
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Re: 79 cams in an 80 engine

Post by bobcat »

EMS wrote:
Thu Dec 08, 2022 8:10 am
Here is an excerpt from a write-up I did years ago:
1980 CBX
The exhaust cam was advanced by 5º and had less overlap. The exhaust cam lift was reduced from 7.5mm to 7.0 mm, the intake cam lift was reduced from 8.3 to 7.8 mm.
...
1981/82 CBX:
New cams closed the intake now 5º earlier, both opening and closing of exhaust was retarded by 5º. Intake valve lift was increased by 0.2mm to 8.00mm, and exhaust valve lift changed to 7.5mm from 7.00mm. A new cam profile with a different rise and fall was supposed to reduce tappet noise.
What was the source for the 81-82 info. ?
Bob
82 CBX, 81 CBX, CB1100F, 79/82 CB900F (avatar)

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Re: 79 cams in an 80 engine

Post by EMS »

bobcat wrote:
Thu Dec 08, 2022 4:13 pm
Nowhere could I find any lobe height specs for the 80 cams.

What does this mean:
1980 CBX
The exhaust cam was advanced by 5º and had less overlap. The exhaust cam lift was reduced from 7.5mm to 7.0 mm, the intake cam lift was reduced from 8.3 to 7.8 mm ????
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Re: 79 cams in an 80 engine

Post by bobcat »

EMS wrote:
Thu Dec 08, 2022 4:43 pm
bobcat wrote:
Thu Dec 08, 2022 4:13 pm
Nowhere could I find any lobe height specs for the 80 cams.

What does this mean:
1980 CBX
The exhaust cam was advanced by 5º and had less overlap. The exhaust cam lift was reduced from 7.5mm to 7.0 mm, the intake cam lift was reduced from 8.3 to 7.8 mm ????

What do you mean "what does this mean" ???
Nowhere in my specs books or FSM do I have those specs for the 80 cams. I'll take your
word for it but what was your source for the 81-82 (Pro Link) cams. I read about all the
updates in a lengthy article that summarized all the 81 Pro Link changes.

Personally I don't care about the 80 cams because they are useless junk. We are talking
in circles here. :roll:

The only bit of info. I didn't have is the EX cam lift.
Last edited by bobcat on Sat Dec 24, 2022 12:42 pm, edited 1 time in total.
Bob
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Re: 79 cams in an 80 engine

Post by daves79x »

OK, I've posted these before several times. These are directly from the Honda shop manual, including the '80 addendum (which has some numbers mixed up, you have to re-work the inches-to-mm numbers):

'79 Lobe Height
Intake - 37.30mm-37.46mm
Exhaust - 37.50mm-37.66mm

'80 Lobe Height
Intake - 36.80mm - 37.06mm
Exhaust - 37.00mm - 37.16mm

'81-'82 Lobe Height
Intake - 37.00mm - 37.16mm
Exhaust - 37.50mm - 37.66mm

These are directly from the shop manual and are available for anyone to research. These numbers are much more valuable real world numbers than lobe center shifts, as they allow you to actually determine what cams you have and the wear on said cams. Very helpful when building an engine from assorted parts of unknown origin. All you need is a set of micrometers.

I don't know 'what you heard or read', but these are the numbers.

Dave

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Re: 79 cams in an 80 engine

Post by bobcat »

Thankyou Dave. I haven't seen this posted before.
I am missing the 1980 addendum in my FSM collection although I do have the
1978 pages (same as 79). I wasn't incorrect about the EX cams being the same
for 79,81,82 except for the difference in the acceleration ramps (rise/fall rate)
for 81,82 which doesn't affect duration, lift or lobe height. As well the lobe centers
for those years are all 107.5. I will disagree with you about LC shifts as is evident
in the fact that the IN cams were advanced 2.5 deg. on 81,82 IN cams for better low
end power. If LCs didn't matter, why the change ?

Sorry to hijack your thread Al, but I hope you find some value in the info.
Bob
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Re: 79 cams in an 80 engine

Post by daves79x »

Bob - You misunderstood my comment on lobe centers. My point was that you could not identify which cams are which on the bench by knowing what lobe centers are what. You simply need to know the cam lobe height - period. In service, the lobe centers may do what they do differently between years, but that has no bearing on IDing the cams, which again, was always my point.

Dave

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Re: 79 cams in an 80 engine

Post by bobcat »

Dave, correct, now that you put it that way. You can't identify a cam by
it's lobe center. My suggestion to Al was that the IN. cam(s) from the 81-82
would be the best cam choice due to LC timing. Any cams but 80 would be
better but 81-82 would be my choice.
Bob
82 CBX, 81 CBX, CB1100F, 79/82 CB900F (avatar)

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Re: 79 cams in an 80 engine

Post by itsacbx »

Thanks for all that.....that will be for my Engineer son to sort thru and consider the big box of cams we have and work out which ones are least worn and [Im assuming[] we can find a set whether 79/80 or 81. Im gonna have to read this multiple times to make sense of it.
Background- the engine is presently in multiple boxes and there is no guarantee that the cams/head is the original set.
My question though was much more simple than all that and which I didnt make clear at all......
How do I identify the various years? Surely Honda identified them with some form of casting mark would they not?
Maybe Im making this hard for myself and should just reassemble the engine with the set of cams that is in the big box 'o' parts.
Al

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