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  1. #21
    CB750 Guru amc49's Avatar
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    Not a matter of like or dislike, only the reality of working on them. I am pessimist by nature, it allows me to see through all the BS and it got me paid very well for many years.

    In the light of being more pertinent to the thread, I have to ask Dave or dirtdigger, I've heard that the later CB750F SOHC had issues with the hot rod cam that went into it as well as the valves, they lead to more issues with the motors there. Anything on that? I'm no SOHC expert but ran across that one once, in a buyers' guide, they said to stay away from those F's because of the low reliability. The mods Honda made were problematic it was said.

  2. #22
    Moderator dirtdigger's Avatar
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    The issue is with the F2 head. The cam isn't the issue. there are several things that all contribute to the issue. One issue is they had an issue with the valve guide material wearing out prematurely, it almost always seems to be the exhaust that is the worst. Aftermarket guides seems to fix the issue. Another issue is in the valve components, the F2 valve stem keeper groove is just that, a narrow groove not a nice wide notch like the k valves, they had a tendency to break off in the groove sending the valve into the engine. The tips also prematurely wore because of the very thin hardened tip. The F2 also used a very steep valve spring keeper angle, the stamped steel retainers wore and the keepers and valve would pull through the retainer. Much stronger valve springs contributed to that issue. The F2 had bigger valves and a higher rpm limit and a more aggressive cam...thus stiffer springs. Why Honda did so many changes which each caused there own issue, who knows other then a rush to keep up in the hp war and limited time to test parts. They had an issue with parts in these to final years of the sohc but parts available today fix all the problems. New valves with better material, better material for guides, titanium retainers, better matched valve springs. They are not an issue if you use the right parts and do the right fixes with todays components. I run one on my street 970 motor and have pictures of some of the parts and the build in one of my photo albums in my profile.

  3. #23
    CB750 Guru amc49's Avatar
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    And thank you for that...............

  4. #24
    CB750 Guru amc49's Avatar
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    The 24 hr. 900F roadtest................late but here 'tis..........

    http://www.cb1100f.net/Other/Motorcy...icleCB900F.PDF

  5. #25
    CB750 Addict Flogger's Avatar
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    Quote Originally Posted by amc49 View Post
    The 24 hr. 900F roadtest................late but here 'tis
    Thanks, great reading... have to save a copy!
    1981 CB750 "four" Custom
    1983 GL650i SilverWing
    1996 GL1500 Goldwing SE
    1981 CM400 (Newest Project)

  6. #26
    ridersup ridersup's Avatar
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    I have k7 and k8 engines. The SOHC4 Owners Club lists that the last 2 years of the sohc engines were internally the same as the f engines( latest improvements). I do not think they shared the same carb specs -jets/pilots , they may be good starts for performance upgrades -without the smog carbs.

  7. #27
    Moderator dirtdigger's Avatar
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    The late K and F engines are definitely not the same internally. The bottom end for the most part are the same but the cylinder head, all valve train, pistons and some other small things are very different. The F was made for more power the K was made for the continued use as a cruiser, touring bike, etc.

  8. #28
    CB750 Enthusiast KIRBY's Avatar
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    I think Flogger must be thinking of the 750A. These are the comparative numbers from Wikipedia:

    1976–1978 CB750A,
    736 cc, SOHC, 47 hp @ 7500 rpm, 578 lb dry, 2-speed w/torque converter, chain.

    1969 CB750,
    736 cc, SOHC, 67 bhp @ 8000 rpm, 481 lb dry, 5-Speed, Constant Mesh, Gearbox, Final Drive Chain

    1978 CB750K,
    748 cc, DOHC, 67 hp @ 9000 rpm, 509 lb dry, 5-Speed, Constant Mesh, Gearbox, Final Drive Chain

    1979–1980 CB750F,
    748 cc, DOHC, 67 hp @ 9000 rpm, 503 lb, Dry, 5-Speed, Constant Mesh, Gearbox, Final Drive Chain

    1991–1993, 1995–2003 CB750 (Nighthawk)
    747 cc, DOHC, 75 hp @ 8500 rpm, 463 lb, Dry?), 5-Speed, Constant Mesh, Gearbox, Final Drive Chain

    https://en.wikipedia.org/wiki/Honda_CB750

  9. #29
    CB750 Guru amc49's Avatar
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    The '79-'83 750 DOHC is not 67 hp., more like 75 hp. but depends on the exhaust pipe layout as to the last couple of hp.

    CB 900 was around 89hp. CB1000 a few over that and CB1100 was 108.

  10. #30
    CB750 Enthusiast KIRBY's Avatar
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    Sorry, amc, just quoting Wikipedia. Do you agree with the 750A figures and the SOHC figures?

  11. #31
    CB750 Guru amc49's Avatar
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    There may be a '78 or so 750F SOHC in there with a bit more, the common poster here 'dirtdigger' could tell you more about that.

  12. #32
    Moderator dirtdigger's Avatar
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    Those hp numbers are very generic. The 67hp was a listed crank hp from honda for the early K's, it was undocumented by honda but as the years went on the k lost several hp compared the the original, many small changes in the engine sucked up some of the power. Common rear wheel is in the low to mid 50's from what I have seen. The 750a hp number seems low...unless it is a rear wheel hp number then it may be reasonable as the A used smaller carbs and different cam and the trans was less efficient. The F motor sohc motors definitely had more hp then the K

  13. #33
    CB750 Addict Medyo Bastos's Avatar
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    Honda claimed 12 extra ponies on the 78f, but I think that was a claimed 67hp on that particular engine


    Sent from my iPhone using Tapatalk

  14. #34
    CB750 Guru amc49's Avatar
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    'Those hp numbers are very generic.'

    Absolutely. The engines alone can vary up to 5 hp. easy simply by how the cams go in timing wise engine to engine, and the different exhaust systems used on same engine can make another 2-4 hp. change too.

    Then you get the small losses as mentioned due to the increasing emissions changes of the times, the airboxes change slightly to do some of that. Minor carb changes to do the same do the rest.

    I've seen the same early DOHC 750 engine rated from 72 to 79 hp. and the engines used the exact same cams in all of those. DOHC cam timing errors in install vary the power more there though.

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