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This is a discussion on this will probably start a fight within the Technical forums, part of the Caferacer.net Forums category; What's the verdict on refacing cb350 valves? I set up my surface grinder and whirlygig and refaced a set of them, they look perfect, but ...

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  1. #1
    Senior Member roccitycafe's Avatar
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    this will probably start a fight

    What's the verdict on refacing cb350 valves? I set up my surface grinder and whirlygig and refaced a set of them, they look perfect, but the more I heard about it, if you take more than a few tenths off the face, you've cut through the stellite coating and the valve will prematurely wear out. Then some other people cited articles about stellite being only on the stems, then others said it was stems and faces, then... on it goes. I'm not above buying a new set of valves, but fuck, if I've got the tools to regrind them, why not?

  2. #2
    Senior Member irk_miller's Avatar
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    I'm not going to argue the metallurgy of the valves, but my practice is always to recut the seats and replace the valves. Valves are too cheap and not exactly rare, so there is no reason not to replace them when rebuilding.

  3. #3
    Senior Member Cyorg's Avatar
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    Well if someone wants to start a fight, take this, wrap it around a lead pipe, and present it to them up side of their head. The bulletin isn't crystal clear which valves it applies to , but whenever we did heads in the (Honda) shop, we would cut the seats, but if a valve was questionable, it was replaced. I believe the valves that you are referring to fall into this category. Do you have a factory manual? If so I assume it only mentions refacing the seats.

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    This is from a 1979 CBX factory manual

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    Last edited by Cyorg; 02-15-2019 at 04:27 PM.
    "Non urinat in ventum"

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    Senior Member Teazer's Avatar
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    What do they know?....... Oh yes. They are the guys that designed the motor to run for a million miles - or whatever the requirement was back then. So they probably know what they are talking about and for a bike designed to last a lot of miles, that makes sense, but for a race bike or one that is hardly ridden any miles it comes down to how much are valves and how often might you need to replace them? On a race motor, the head is probably coming off once a year or two with very few miles per year. Worth the risk of some wear? Quite possibly. Rebuilding a motor for a client that runs it hard at every AHRMA and WERA etc event all year? The economics might be different.

    For my own race motors, I'd cut the valves if they needed it and plan on replacing them every second strip down. For a customer, I might insists they replace the valves because I hate it when a customer says, "let's take the chance" and when it doesn't work out they expect me to eat the work and parts.

  6. #5
    Senior Member Cyorg's Avatar
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    Actually thought about including something about cutting them, although it was more geared towards the current "builds" ...if you aren't going to wear the nubbies off the clown shoes, then why worry about how much you cut off the valves. I don't disagree with you about race bikes, but cheap as I am... I still replace valves out of habit. Not trying to apply logic here. I won't cut stellite valves, but reuse some torque to yield rod bolts as in SBC. That make some people foam at the mouth.
    I no longer do any work for anyone else so any budget concerns are my own. I have the good fortune? misfortune? of having about 10 years worth of my own shit to do and not sure I have 10 years left where I can physically schlepp motors around. Anyway... folks that cut them generally don't seem to run into difficulties as long as they don't carve off too much. CB350 valves are one thing, but would really be gun shy about cutting DOHC Honda valves such as the CBX. On the car side, they even started grinding cranks which were never intended to be ground for the same reason. If I recall correctly, there was place in Aus that made the bearings, because Honda obviously didn't sell them.
    Last edited by Cyorg; 02-15-2019 at 10:25 PM.
    "Non urinat in ventum"

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    Senior Member XB33BSA's Avatar
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    on my m350 twin i went with nos honda parts from the head bgasket up
    i did back cut the valves though
    if i had not gotten ,my nos head and valves at a yardsale for pennies on the dollar
    i wouldn't mess around with the honda stuff why not just put some guides in the head thatare not prone to seizure in extended high rpm runming
    use significantly lighter smaller stemmed modern valves
    the smaller stems aid slightly bettter flow
    Ti retainers aswell. and it shiould enable a bit lighter spring weight and less seat pressure/spring peload
    a huge bonus because honda rocker arm folower pads simply have a too thin
    hard facing
    i have been wanting to do plastic cam lobes

  8. #7
    Senior Member XB33BSA's Avatar
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    as far as hardness after a regrind just do a before after scratch test
    using new swedish chain file like you can get at the stihl saw shop
    the are harder than a normal file and very sharp
    using your machinssts pro ball player hands gently try to pull a chipo of the valves hard face
    after doing a regerind on a valve face that was not pretty
    using the same feel ,see if a chip can be curled

  9. #8
    Senior Member roccitycafe's Avatar
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    someone on hondatwins suggested sectioning and acid etching a valve, I think that's a cool idea since I have a lot laying around. I found cmsnl or whatever has sets for about $100, I think I'll go that route for now, but it would be good to know the stellite thickness for when cb350 valves become completely unavailable. though, someone will probably figure out which honda car valves are close enough with a little modification and we'll all start using those.

  10. #9
    Senior Member TrialsRider's Avatar
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    Quote Originally Posted by roccitycafe View Post
    someone on hondatwins suggested sectioning and acid etching a valve...
    You don't need to acid etch it once you cross section the embedded piece you just stick it on top of an 80 thousand dollar microscope and measure it optically

    ... the stellite will probably measure about 7 micron in thickness.

  11. #10
    Senior Member Cyorg's Avatar
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    ......

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    "Non urinat in ventum"

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