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  1. #1

    The way I see it

    To make a long story even longer, I think I'm in the market for another Honda, but after what I have been reading here and on other forums, I'm not so sure now. I've been riding and wrenching for over 50 year. I have built and rebuilt motorcycles from the ground up, including 4 Hondas (50,305,450,750), 2 Yamahas, 1 Kawasaki, and 3 Harleys. I have wrenched professionally.

    I rode Harleys exclusively for the last 30 years but am itching for another CB750. I am very concerned about reliability issues I have been reading about, especially with regard to ethanol in the gas -- something I can't escape where I live. I realize that buying a used motorcycle is like inheriting a disease. You can't be sure about the reliability of the work done on any MC unless you've done it yourself.

    The fact that my age (71) is not conducive to be tinkering with bikes the way I used to (however Harleys are extremely easy to maintain and rebuild), I'd much rather purchase something solid, but I don't believe that is possible. I don't fancy modern styling, especially on the later 750's. I'm a 1976 or earlier guy. But between sticking carb float needles, worn out cam chain tensioners, and fried exhaust valves, I'm wondering how reliable even I could build one to enjoy a couple of years of easy riding.

    Can someone convince me otherwise?

  2. #2
    CB750 Guru amc49's Avatar
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    The ethanol issues may not be nearly the problem on later stuff like mid '90s and later with all the emission equipment in place. Similar to how the cars get away with it now. The older stuff was much more exposed to the atmosphere with venting and such, newer will avoid that to lower HC emissions like the cars do. That alone lowers ethanol caused issues quite a bit. The rest you learn by messing with the fuel, like keeping tanks closed as quick as possible and draining fuel to help not sticking the carbs up inside. Ethanol is pretty transparent if you drive the vehicle every day, it's when you don't like a bike stuck in garage for a week that problems happen. I've left a lot of ethanol fuel in a well sealed fuel tank on a car for years before to zero issues but have also failed a brand new fuel pump in 3 months when the tank was not airtight and the bottom of the pump corroded off due to the ethanol phase separating to make acids in the fuel. It's b-tchy stuff and you MUST keep it from atmospheric exposure or there WILL be problems.

    Unless you drive the wheels off one the engines will commonly make 30K miles before tensioner problems if they began new. That in hotter climates like Texas here, colder they will last longer. Many of the newer models use hydraulic tappets which pretty much makes bad valves caused by not setting them a thing of the past too but you have to also be aware of the finickiness that juice lifters can bring to the table. Not hard if you understand them.

  3. #3
    I appreciate you taking the time to respond. My problem with many of the later model Hondas is that they are made for a different generation's tastes. I am not a cafe rider. I have been looking at the CB1100EX, love it, but the pegs are set back to far for me. I would stick with a twin if I could find one that was not trying to look like a Harley (450 Rebel). I had a CB450 (74) which was a sweet ride, but with their oil flow to the heads issue and the irregular maintenance you find these days, it's a tough sell.

    I kick myself for all the bikes I've sold over the years -- but if that's my biggest regret in life, I guess I can live with it. I passed up a very clean looking '74 CB750 last night for a very reasonable price.

    I live outside Indio, Ca. where the temperature is now 110. That will be our low for the next 4 months. It really won't start cooling down until the first week in November, and I'm fully aware of the importance of weather in bike maintenance.

    I've seen the shoddy maintenance that can be performed by shade tree mechanics. The over torqued bolts, improperly adjusted this and that. It can be maddening. I'd probably take a deep dive into anything I bought, just to try and make sure I wouldn't get stranded. That takes 3 months off the front end of the owning experience, and upwards of $2500 in parts. Been there before.

    If I can find away to vanquish the ethanol issue I'd feel better prepared.

    Oh, one word to anyone doing their own valve jobs. I learned a long, long time ago from an expert mechanic that all new valves must be ground before use. None are perfectly concentric out of the box. They are not supposed to be. The difference is night and day. Proper grinding before lapping will give you a top end that purrs like a kitten. I've seen it before and after, where no other changes were made to the bike.

  4. #4
    CB750 Guru amc49's Avatar
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    I understand why you think that works but it's often death on bikes nowadays. The bikes if Japanese commonly use substandard steels for the valves and heat treat them to get the life back while stlll being dirt cheap. The problem with the heat treat is that it can only be a couple thousandths thick and not much more than .005". If you grind a valve like that you almost guaranteed remove the heat treat and the valve material underneath commonly will not make 10,000 miles, because it is only a very soft steel. BTDT myself to test the idea out. Even lapping can remove the heat treat if you do it too much.

    The new valve does not seem concentric because it was cut while being positively held but no valve runs like that, they run in a hole that can have varying amounts of looseness as well as being out of round. So new part does not seat. Same with recutting one that seems to be out of round, it's simply the difference in one tool holder and another, no two valve machines register the same.

    The early DOHC I advise on here were among the worst as far as valve life, they were designed for low lead fuel and the world used that until finally moving away from it to absolute zero lead around the early '90s. At that time I began to have serious valve problems with machines I had earlier than that, low lead seems close to zero lead but in actuality they were nowhere close. Even the slightest amount of lead helped a LOT but all gone now and why valves go so fast on Japanese stuff now. And why you don't reface any valves per almost all of the service manuals, they replace only and NO cutting on them at all, only light lapping. The only thing you can cut is the seat in head.

    If you grind them they WILL run better at first but not for long at all. Pull head and the valves will have receded whoppingly into the head because the hardness that slowed that is gone. That does not happen on most American stuff like cars because they use the much better steels that are hard throughout the part not just on the surface.

    I've done plenty of my own backyard valvejobs and 100% success doing it as long as you take that into account. You almost have to now as valve job work is becoming unobtainium now like dead-on boring work, it being hard to find real competence doing it, although they will all tell you they can. Most can't at all, it is becoming lost art.

  5. #5
    That is distressing. Surface heat treating is actually harder to perform that a full heat treat. The Germans used to do it on their WWII Mauser actions and you had to be very careful when grinding the front of the action parallel to the barrel not to remove more than about 0.004 or you would loose the hardening and have to re-anneal and quench the action. I have not dealt with low quality steel so never ran into the problem.

    Yes, good machine shops are hard to find -- everything is disposal these days. The way we got around older bikes that were made during the leaded gas days was to replace the seat with a Stellite one. I do know of an excellent machinist down in San Diego. The new seats are machined to size and pressed into the hole made when the old one is removed. It is a straight forward process for a competent machinist, but not cheap by any means. This is the way we have fixed the issue for over 40 years now. Mind you, I have not had this done on a Honda, but I suspect for the right amount of money, it can be done.

    I appreciate your input.

  6. #6
    Moderator dirtdigger's Avatar
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    Only place I would send Japanese stuff to in california is APE. They started out on the old cb750's. The exhaust seats in the sohc are hard. The valves rarely go bad except lot of miles and poor maintenance.

  7. #7
    CB750 Guru amc49's Avatar
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    X2 APE..........the bigger valves don't go bad as easy since the valve stem clearance is relatively small as compared to valve head size, but some of the guides can. The smaller valves like 4 valve head go bad faster as the stem clearance is about the same as the big ones meaning the smaller valve can wallow a bit in the hole even with new valves and guides.

    I've had the smaller engines shuck exhaust valves in less than 6K miles after they were ground, they just melt and distort all over the place. Again like said, the seats in head are no problem. You can tell if you lap too far to break through the hardcoat, the valve will start cutting like lightning even lapping when you hit the softer steel underneath.

    I remember too getting harder exhaust seats installed when unleaded gas showed up, until the OEMs began to induction harden them to not have to any more. Used to scout junkyards looking for later Ford 2.3 SOHC heads with both induction hardened seats and the good D-port intake port. Used to race '74 model with no heat treat and the valve job had to be freshened every 3-4 weeks from valves sinking in the soft seats. Ridiculous.

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