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CB400T Shitbox Build - Daily Driver

This is a discussion on CB400T Shitbox Build - Daily Driver within the Project Builds forums, part of the Caferacer.net Forums category; Originally Posted by jakejensen ... smaller camshaft for the euro models makes the geometry of the lifter/cam contact more abrupt. ... The purpose of the ...

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Thread: CB400T Shitbox Build - Daily Driver

  1. #251
    Senior Member TrialsRider's Avatar
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    Quote Originally Posted by jakejensen View Post
    ... smaller camshaft for the euro models makes the geometry of the lifter/cam contact more abrupt. ...
    The purpose of the valve clearance adjustment is to accommodate thermal expansion. If your clearance is set correctly, there is virtually no clearance once the motor reaches operating temperature. Any other time the valve springs are compressed and it really don't care what your cam ramp is shaped like.


    That rear wheel problem. <- Either your chain was out of align or the rubber in your cushion drive hub is shot. There would not normally be sufficient side loads on the chain to cause that breakage unless the rear sprocket is trying to rotate in the completely wrong direction.
    One other possibility is the chain was too tight <- do that and something is going to break somewhere for sure and it won't be the chain.

    Increased clearances on pressure bearings causing low oil pressure everywhere. Yes that one is a big problem.
    Last edited by TrialsRider; 10-28-2019 at 08:31 AM.

  2. #252
    Senior Member Cyorg's Avatar
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    Quote Originally Posted by TrialsRider View Post
    The purpose of the valve clearance adjustment is to accommodate thermal expansion. If your clearance is set correctly, there is virtually no clearance once the motor reaches operating temperature. Any other time the valve springs are compressed and it really don't care what your cam ramp is shaped like..
    You might want to do some reading up on that subject. How do you account for engines where valve clearance increases with heat. Not all engines are the same in that department. If the cam and rocker shafts run in aluminum then clearance can increase with heat. Also applies to some push rod engines. I have one where you set lash at zero (cold) just so you can just turn the push rod with your fingers. Because....on that engine clearance increases when hot. Have a look at the CB400 head/rocker assembly. How is it laid out and what is it made of?

    Several other things to consider, like time for the valve to dissipate heat to the seat, valve timing, etc.
    Last edited by Cyorg; 10-28-2019 at 02:03 PM.
    "Non urinat in ventum"

  3. #253
    Senior Member TrialsRider's Avatar
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    Quote Originally Posted by Cyorg View Post
    .... How do you account for engines where valve clearance increases with heat. Not all engines are the same in that department. If the cam and rocker shafts run in aluminum then clearance can increase with heat...
    Lets take one bizarre concept at a time, show me how these valves stems are going to shrink with heat.

    Look at your valve clearance and you will see the exhaust needs more clearance, because burning gas is hotter then intake air. Forget clouding the issue with pushrod engines his is a simple 3 valve Honda on one cam. Cam ramp angle makes zero difference to the clearance setting.
    As for the clearance on your cam shaft spinning on aluminum it doesn't (we hope) it runs on a microscopic thin layer of pressurized oil, or we have a problem Houston. You can't go making the clearances different because your cam shaft is flopping around in the bearing, it won't work long like that if at all. He doesn't even have roller rocker arms or roller bearing on the camshaft in addition to the oil pressure like oh say, my 3 Honda motors have, and this is the fella that has to replace the rocker arms if not the entire cylinder head already, correct?


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  5. #254
    Senior Member Cyorg's Avatar
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    Quote Originally Posted by TrialsRider View Post
    Lets take one bizarre concept at a time, show me how these valves stems are going to shrink with heat.

    Look at your valve clearance and you will see the exhaust needs more clearance, because burning gas is hotter then intake air. Forget clouding the issue with pushrod engines his is a simple 3 valve Honda on one cam. Cam ramp angle makes zero difference to the clearance setting.
    As for the clearance on your cam shaft spinning on aluminum it doesn't (we hope) it runs on a microscopic thin layer of pressurized oil, or we have a problem Houston. You can't go making the clearances different because your cam shaft is flopping around in the bearing, it won't work long like that if at all. He doesn't even have roller rocker arms or roller bearing on the camshaft in addition to the oil pressure like oh say, my 3 Honda motors have, and this is the fella that has to replace the rocker arms if not the entire cylinder head already, correct?

    Ok forget my pushrod engine... it was just an example of an engine where valve clearance increases with heat... didn’t think it was that bizarre. How do you arrive at “there is virtually no clearance when the engine reaches operating temperature”? Yes the valve stems expand... so does the head of the valve and more importantly in this situation.... what about the aluminum cylinder head? I not referring to clearance between the cam and the journals in the head. If the rocker assembly is made from sintered iron or something similar instead of aluminum, then the effect would be less. Think about the relationship between the cam and the rocker shaft..... not just the valve stem. What about the distance between the valve seat and the spring seat... does it remain constant in an aluminum head? To be honest I don’t know exactly what his valve clearance will do when hot... I do know it won’t drop to virtually zero. Are there not other SOHC Honda engines out there where clearance increases with heat? Personally I wouldn’t make an assumption about that engine. If I really needed to know, I would set it cold and recheck it hot.
    "Non urinat in ventum"

  6. #255
    Senior Member Teazer's Avatar
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    Now that "we" have solved the problem, what exactly was the question that was being addressed? Just askin' for a friend.

  7. #256
    Senior Member jakejensen's Avatar
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    Quote Originally Posted by Teazer View Post
    Now that "we" have solved the problem, what exactly was the question that was being addressed? Just askin' for a friend.
    I think the question I'm asking myself is why did I take the damn engine apart in the first place???

    Replacement parts (new ones) cost more than the bike itself. lesson learned.
    TrialsRider likes this.

  8. #257
    Senior Member 8ball's Avatar
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    Quote Originally Posted by jakejensen View Post
    I think the question I'm asking myself is why did I take the damn engine apart in the first place???

    Replacement parts (new ones) cost more than the bike itself. lesson learned.

    Unfortunately, that is a question that is addressed in the “read first” thread in the New Member’s section. Specifically in post #3.
    https://www.caferacer.net/forum/new-...ead-first.html

    You aren’t the first to realize how expensive it gets, real quick.
    I always find a soap box useful to get on my high horse.

    Quote Originally Posted by roccitycafe View Post
    .... same thing with furniture, it doesn't have to be straight or not wobble, or keep thing from rolling off it, or not collapse when sat upon, it's personal taste man... if I want a dining room set that endangers the life of my dinner party guests, then it doesn't need second hand approval

    My GS550 Build Thread

  9. #258
    Senior Member TrialsRider's Avatar
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    Jake, we keep telling people they are sinking so much money and effort into fixing these old cheaply built, abused and worn out motors it would make better economic sense to buy a new motorcycle :/ but most respond with it being a learning experience they seem to need to experience first hand.


    Cyorg, you are talking nonsense, i
    f you have a way of measuring valve clearance on a Honda overhead valve engine while it is still at operating temperature, please share with us how that can be done.

    re: “there is virtually no clearance when the engine reaches operating temperature” <- Because the valve has elongated due to heat to a point where the valve clearance you previously set at room temperature, is all but gone! As in, close to zero excess backlash between the mating parts as possible, without actually making the valves leak.

    re: "
    Are there not other SOHC Honda engines out there where clearance increases with heat? No! because then it would not be a valve clearance adjustment, that would make it a pre-tension adjustment.



  10. #259
    Senior Member jakejensen's Avatar
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    Quote Originally Posted by TrialsRider View Post
    Jake, we keep telling people they are sinking so much money and effort into fixing these old cheaply built, abused and worn out motors it would make better economic sense to buy a new motorcycle &#x1f615; but most respond with it being a learning experience they seem to need to experience first hand.


    I heard that haha

  11. #260
    Senior Member Cyorg's Avatar
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    Quote Originally Posted by TrialsRider;
    Cyorg, you are talking nonsense, i[/COLOR
    f you have a way of measuring valve clearance on a Honda overhead valve engine while it is still at operating temperature, please share with us how that can be done.

    re: “there is virtually no clearance when the engine reaches operating temperature” <- Because the valve has elongated due to heat to a point where the valve clearance you previously set at room temperature, is all but gone! As in, close to zero excess backlash between the mating parts as possible, without actually making the valves leak.

    re: "
    Are there not other SOHC Honda engines out there where clearance increases with heat? No! because then it would not be a valve clearance adjustment, that would make it a pre-tension adjustment.


    I think I get it... you’re just trolling. Right?
    "Non urinat in ventum"

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