CB750 pre-78 post-78
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CB750 pre-78 post-78

This is a discussion on CB750 pre-78 post-78 within the General forums, part of the Caferacer.net Forums category; Folks: Friend of mine is looking to pick up a nice reliable CB750. He heard that the 79 DOHC CB750 had issues, since it was ...

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  1. #1
    Senior Member Pete Casper's Avatar
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    CB750 pre-78 post-78

    Folks: Friend of mine is looking to pick up a nice reliable CB750. He heard that the 79 DOHC CB750 had issues, since it was the first year of the DOHC. Can anyone confirm this? If you could choose would you buy the SOHC pre-78 or DOHC 79-82 CB750. Your answer should be based on reliability not asthetics.

    Yeller'
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    Ask not what the wanker can do for you, but what you can do for your wanker!

  2. #2
    Senior Member catboy's Avatar
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    i've not heard of any reliability issues with the '79 but it seems they all have issues with pulse generators and spark ignitors. if you were to upgrade to a dyna ignition, these points become mute.

    check out the 1100F.net site too. those guys KNOW the DOHC front, back, in, out, up, down and sideways.

    "Better a cruel truth than a comfortable delusion." -Edward Abbey

  3. #3
    Senior Member catboy's Avatar
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    i've not heard of any reliability issues with the '79 but it seems they all have issues with pulse generators and spark ignitors. if you were to upgrade to a dyna ignition, these points become mute.

    check out the 1100F.net site too. those guys KNOW the DOHC front, back, in, out, up, down and sideways.

    "Better a cruel truth than a comfortable delusion." -Edward Abbey

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    Senior Member catboy's Avatar
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    ...your friend should also consider his size too; the DOHCs are all around bigger than the SOHCs.

    "Better a cruel truth than a comfortable delusion." -Edward Abbey

  6. #5
    Senior Member catboy's Avatar
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    ...your friend should also consider his size too; the DOHCs are all around bigger than the SOHCs.

    "Better a cruel truth than a comfortable delusion." -Edward Abbey

  7. #6
    Senior Member Geeto67's Avatar
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    I own both in many different variants.

    The three big issues the DOHCs had were:

    - starter clutch. For some reason the bolts on these rattle loose pretty frequently. I can say with confidence that this has happened to every DOHC on the road right now at least once, that is how often it happens. Basically you open her up put red loctite on the bolts and never worry about it again, but it makes an awful grinding gnashing noise when they back off. This happens to all DOHCs not just the 1979.

    - Cam chain. I am willing to bet that about half the DOHCs that are no longer with us due to mechanical issues died because somebody didn't watch the cam chain. There is no real inherent flaw, just that these are stressed motors and when you abuse them the cam chain tends to stretch a little. If you check the adjustment on them every time you do an oil chain this becomes a non issue. However, if you don't they can do everything from bend valves to saw the block in half. SOHCs can go for 30K at a time with out a cam chain adjustment, but not the DOHCs.

    - Electrics. Basically all late 70's to early 80's honda electrics are junk. The cx's had problems, the Gold wing had problems, and these bikes have problems too. Mostly in the form of pulse controllers and reg/rect. Fortunately Honda makes these parts but a brandy new pulse controller will set you back $100+. I just did one recently on my brother's 1979 and it is a pain in the ass to install too but not brain draining. Watch your charging, if it goes chances are you will need another. These bikes also have been known to have stator problems , but if one goes you are pretty much humped in that you just have to buy a new one and they ain't cheap.

    now the positives. The DOHC F chassis is light years ahead of the SOHC chassis. It is stable, espically at speeds over 120mph, it is flickable when rolling, and surprisingly light feeling. Its long size make the bike feel like a grand touring (for those who don't know GT's are cars or bikes that are high performance but you can take on a long trip, the modern equivalent is a sport tourer) european machine rather than a plucky superbike. However it's freight train stature actually inspires more confidence than the SOHC chassis which is "twitchy" at best at the ton. F bikes have the stiffest frame (the tubing is actually thicker) and if he can afford it tell him to buy a 1982 750F or 900F. The 1982s came with the upgraded brakes and some of the electrical issues were worked out. 1979s have a lot of carry over pieces that make it a bitch to restore since they are one year only (the 150mph speedo is a $200 item alone).

    There are still a lot of speed parts for the DOHCs in production but unless you speak japanese there is very little in the way of cafe body parts. In japan the DOHC is a cult bike there and they have stuff there that would blow your mind. The DOHC F bodywork is naturally beautiful anyway and the only thing I would change is to add a corbin seat (which are still made).

    The DOHC is actually a true 750cc (749cc actually), the SOHC is actually 736ccs. A well tuned DOHC will make close to 80hp at the crank (60's at the wheel), the best SOHCs only made 67 crank hp. Just keep up on the maintenance and the bike will run fast forever.

    SOHCs are not without their pro's and cons too but I am too tired to write them.


  8. #7
    Senior Member Geeto67's Avatar
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    I own both in many different variants.

    The three big issues the DOHCs had were:

    - starter clutch. For some reason the bolts on these rattle loose pretty frequently. I can say with confidence that this has happened to every DOHC on the road right now at least once, that is how often it happens. Basically you open her up put red loctite on the bolts and never worry about it again, but it makes an awful grinding gnashing noise when they back off. This happens to all DOHCs not just the 1979.

    - Cam chain. I am willing to bet that about half the DOHCs that are no longer with us due to mechanical issues died because somebody didn't watch the cam chain. There is no real inherent flaw, just that these are stressed motors and when you abuse them the cam chain tends to stretch a little. If you check the adjustment on them every time you do an oil chain this becomes a non issue. However, if you don't they can do everything from bend valves to saw the block in half. SOHCs can go for 30K at a time with out a cam chain adjustment, but not the DOHCs.

    - Electrics. Basically all late 70's to early 80's honda electrics are junk. The cx's had problems, the Gold wing had problems, and these bikes have problems too. Mostly in the form of pulse controllers and reg/rect. Fortunately Honda makes these parts but a brandy new pulse controller will set you back $100+. I just did one recently on my brother's 1979 and it is a pain in the ass to install too but not brain draining. Watch your charging, if it goes chances are you will need another. These bikes also have been known to have stator problems , but if one goes you are pretty much humped in that you just have to buy a new one and they ain't cheap.

    now the positives. The DOHC F chassis is light years ahead of the SOHC chassis. It is stable, espically at speeds over 120mph, it is flickable when rolling, and surprisingly light feeling. Its long size make the bike feel like a grand touring (for those who don't know GT's are cars or bikes that are high performance but you can take on a long trip, the modern equivalent is a sport tourer) european machine rather than a plucky superbike. However it's freight train stature actually inspires more confidence than the SOHC chassis which is "twitchy" at best at the ton. F bikes have the stiffest frame (the tubing is actually thicker) and if he can afford it tell him to buy a 1982 750F or 900F. The 1982s came with the upgraded brakes and some of the electrical issues were worked out. 1979s have a lot of carry over pieces that make it a bitch to restore since they are one year only (the 150mph speedo is a $200 item alone).

    There are still a lot of speed parts for the DOHCs in production but unless you speak japanese there is very little in the way of cafe body parts. In japan the DOHC is a cult bike there and they have stuff there that would blow your mind. The DOHC F bodywork is naturally beautiful anyway and the only thing I would change is to add a corbin seat (which are still made).

    The DOHC is actually a true 750cc (749cc actually), the SOHC is actually 736ccs. A well tuned DOHC will make close to 80hp at the crank (60's at the wheel), the best SOHCs only made 67 crank hp. Just keep up on the maintenance and the bike will run fast forever.

    SOHCs are not without their pro's and cons too but I am too tired to write them.


  9. #8
    Senior Member Pete Casper's Avatar
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    Great information, I will pass it along. Thanks.

    Yeller'
    ---
    Ask not what the wanker can do for you, but what you can do for your wanker!

  10. #9
    Senior Member Pete Casper's Avatar
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    Great information, I will pass it along. Thanks.

    Yeller'
    ---
    Ask not what the wanker can do for you, but what you can do for your wanker!

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