Topic: DOHC?

[millerza]

So whats the scoop on the DOHC's. Are they any good? Pros/Cons

[HondanutRider]

I think this may be the wrong place to ask this question  ...but I'll offer an answer as I do have a 1981 CB750-K.

When the original SOHC 750 was retired in 1979 and the DOHC was released, it was technically an improvement in several ways.  The motor has a larger capacity with 749cc (I believe) and with the two cams came four valves for each cylinder.  However, they are more troublesome to adjust, as the clearances are adjusted with shims rather than tappet screws.  There are no points on the DOHC, as the system uses one of the first electronic ignitions.  The charging system seems somewhat taxed, and if the battery is weak it seems that it can't keep up enough of a voltage to run the sparks let-alone start the motor - as it doesn't have a kick.  The frame and suspension is supposedly improved (my 1981 has air-loaded front shocks).

Overall, I find the DOHC a nice machine, but it never was as accepted as the original SOHC.  Besides, the market at the time it was sold was slow for motorcycles, and Kawasaki had their famous DOHC on the market since shortly after the Honda SOHC 750 was introduced.  Many thought Honda was slow to respond to the Kawasaki competition, but the truth was that they were selling plenty of the SOHCs for a very long time, so had no need to change the technology.

[MoMo]

I think this may be the wrong place to ask this question  ...but I'll offer an answer as I do have a 1981 CB750-K.

When the original SOHC 750 was retired in 1979 and the DOHC was released, it was technically an improvement in several ways.  The motor has a larger capacity with 749cc (I believe) and with the two cams came four valves for each cylinder.  However, they are more troublesome to adjust, as the clearances are adjusted with shims rather than tappet screws.  There are no points on the DOHC, as the system uses one of the first electronic ignitions.  The charging system seems somewhat taxed, and if the battery is weak it seems that it can't keep up enough of a voltage to run the sparks let-alone start the motor - as it doesn't have a kick.  The frame and suspension is supposedly improved (my 1981 has air-loaded front shocks).

Overall, I find the DOHC a nice machine, but it never was as accepted as the original SOHC.  Besides, the market at the time it was sold was slow for motorcycles, and Kawasaki had their famous DOHC on the market since shortly after the Honda SOHC 750 was introduced.  Many thought Honda was slow to respond to the Kawasaki competition, but the truth was that they were selling plenty of the SOHCs for a very long time, so had no need to change the technology.

That is a good synopis.  I was a Honda  mechanic until 1985 or so.  I'd add that in my opinion the dohc were a smoother running and riding bike.  However, the sohc just has IT...Larry

[lone*X]

I agree completely with this synopsis with one exception:
Quote:  "Overall, I find the DOHC a nice machine, but it never was as accepted as the original SOHC."
The SOHC was produced for 10 years, the DOHC for about 28 years.  The name may have changed to Nighthawk but it is basically the same drive line.  It was accepted very well by the buying public.  It just did not have charisma of the SOHC that started it all.

Models
[edit] SOHC

The single overhead cam models were produced from 1969 through 1978.[14]

    * 1969 CB750K or CB750K0
    * 1971 CB750K1
    * 1972 CB750K2
    * 1973 CB750K3 (US-only, K2 elsewhere)
    * 1974 CB750K4 (US/Japan-only, K2 elsewhere)
    * 1975 CB750K5 (US-only, K2/K4 elsewhere), CB750F, (Canada-only CB750A)[15] The 1975 CB750F had a more streamlined look, thanks in part to a 4-into-1 exhaust and cafe style seat with fiberglass rear. Other changes included the use of a front disc brake and a lighter crankshaft and flywheel.
    * 1976 CB750K6, CB750F1, CB750A
    * 1977 CB750K7, CB750F2, CB750A1
    * 1978 CB750K8 (US-only), CB750F3, CB750A2

[edit] DOHC

    * 1979–1982 CB750K
    * 1979 CB750K 10th Anniversary Edition (5,000 produced for U.S.)
    * 1979–1982 CB750F
    * 1980–1982 CB750C "Custom"
    * 1982–1983 CB750SC Nighthawk
    * 1984–1986 CB750SC Nighthawk (Horizon in Japan) (CB700SC Nighthawk "S" in U.S.)
    * 1991–2003 CB750 Nighthawk
    * 2007 CB750 (Japan-only)

[weekend_junkie]

I've only had good experiences with the 7 different DOHC bikes I've had.  Yes, weak charging system and shim valve adjustments are 2 faults, but no reason to avoid these bikes.

I would say they have a different "it" than the SOHC bikes.  Simply said, they are a bigger bike and can really kick some ass if you're into that kind of thing.  However, you can all too quickly spend modify those bikes to the point that you are left wondering "why didn't I just but an '06 CBR for less money and more performance?"  Rebuild a CB1100F motor with a CB900F/CB1000C crank, put in a WISECO 1123 kit, ditch the CV carbs, get some CBR600F2 wheels, and you will have a sh!t eating grin that will last a long time.

Ask me how I know...

[millerza]

thanks for the info, i didnt do any search for myself just wanted to start conversation. Sorry bout putting the thread in the wrong place.

What causes the diff performance of the kawi?

[HondanutRider]

What causes the diff performance of the kawi?

...like maybe a 900cc and then a 1000cc vs 736cc.

[weekend_junkie]

What causes the diff performance of the kawi?

...like maybe a 900cc and then a 1000cc vs 736cc.

The Honda DOHC head had limiting flow characteristics, making the Kwak a lot easier to hop-up.

[Gordon]

I agree completely with this synopsis with one exception:
Quote:  "Overall, I find the DOHC a nice machine, but it never was as accepted as the original SOHC."
The SOHC was produced for 10 years, the DOHC for about 28 years.  The name may have changed to Nighthawk but it is basically the same drive line.  It was accepted very well by the buying public.  It just did not have charisma of the SOHC that started it all.

Models
[edit] SOHC

The single overhead cam models were produced from 1969 through 1978.[14]

    * 1969 CB750K or CB750K0
    * 1971 CB750K1
    * 1972 CB750K2
    * 1973 CB750K3 (US-only, K2 elsewhere)
    * 1974 CB750K4 (US/Japan-only, K2 elsewhere)
    * 1975 CB750K5 (US-only, K2/K4 elsewhere), CB750F, (Canada-only CB750A)[15] The 1975 CB750F had a more streamlined look, thanks in part to a 4-into-1 exhaust and cafe style seat with fiberglass rear. Other changes included the use of a front disc brake and a lighter crankshaft and flywheel.
    * 1976 CB750K6, CB750F1, CB750A
    * 1977 CB750K7, CB750F2, CB750A1
    * 1978 CB750K8 (US-only), CB750F3, CB750A2

[edit] DOHC

    * 1979–1982 CB750K
    * 1979 CB750K 10th Anniversary Edition (5,000 produced for U.S.)
    * 1979–1982 CB750F
    * 1980–1982 CB750C "Custom"
    * 1982–1983 CB750SC Nighthawk
    * 1984–1986 CB750SC Nighthawk (Horizon in Japan) (CB700SC Nighthawk "S" in U.S.)
    * 1991–2003 CB750 Nighthawk
    * 2007 CB750 (Japan-only)

Only if you're talking strictly about the 750.  The sohc4 line (in the U.S.) went through 1982 with the CB650SC.