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Thread: 450/500 Valve Adjustment

  1. #1
    Supporting Member Rich Ard's Avatar
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    450/500 Valve Adjustment

    Putting this together following my frustration as it was difficult to source a .0012"/.03mm feeler gauge. Experts, please weigh in for completeness and accuracy.

    Basic procedure from the CB450 service manual:

    Valve Tappet Adjustment

    Excessive valve clearance will cause tappet noise and negative clearance will cause valve damage, excessive wear of the cam follower, and loss of power.

    Therefore, the valve tappet clearance should be maintained properly.

    Turn the fuel valve to the "STOP" position, remove the fuel lines from the fuel valve body, raise the seat and remove the fuel tank.
    Remove the cylinder head cover A (inlet side) and B (exhaust side).
    Remove the point cover and the dynamo cover.
    Rotate the generator rotor counterclockwise and align the "LT" mark (1) on the generator rotor with the index mark (2) on the stator. If the index marks of both the inlet and exhaust camshafts are aligned to the index marks on the bearing holders, this position is the top dead center of the intake stroke, therefore, the rotor should be turned one complete revolution to bring it to the top dead center of the compression stroke, in other words, the purpose is to place the left hand piston at the top dead center of the compression stroke.

    Check the left hand cylinder tappet clearances in the exhaust and inlet valves. Insert the feeler gauge (3) between the cam and the cam follower. If a slight drag or resistance is felt as the gauge is inserted, the clearance is correct. If the clearance is too close or too loose, adjust the tappet. The standard clearance for both the inlet and exhaust valves is 0.0012 in. (0.03 mm) when the engine is cold. Adjustment by loosening the cam follower shaft lock nut (5) and turning the cam follower shaft (4) with a screw driver as shown in the photo. Specific clearance can be obtained at two positions of the follower shaft, but only one of these is the correct adjustment point.

    The clearance is reduced when the adjustment is made as shown in the table below.

    [attachment=1:3o1qaiov]1.jpg[/attachment:3o1qaiov]
    [attachment=0:3o1qaiov]2.jpg[/attachment:3o1qaiov]

    Right side

    Inlet: Turn counterclockwise
    Exhaust: Turn clockwise
    Left side

    Exhaust: Turn counterclockwise
    Inlet: Turn clockwise


    NOTE: The check or adjustment of the tappet clearance should be performed while the engine is cold. The clearance may tend to increase as the temperature rises. Make sure that the adjustment has not been disturbed while tightening the lock nut, by rechecking the clearance after the lock nut has been tightened.

    Next, rotate the generator rotor 180° counterclockwise to bring the right hand piston to the top dead center of the compression stroke and then check both the right inlet and exhaust valve tappet clearances in the same manner as for the left hand side.

    Following is a discussion from the old MSN CB450 forum - notable experts weighing in are Bill Lane (tpbmusic here, stillstanding462 in the below); Terry Naughton of Team Hansen (honda3370).

    From: bobm (Original Message) Sent: 1/18/2008 10:45 AM
    I am in the process of tuning a '73 CB 450. Starting with the valves, I have not been able to find a .0012 feeler gauge in any auto shop. The best any of them can do is .0015. Any thoughts on where to get one?
    Thanks.


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    Reply

    Recommend Message 2 of 7 in Discussion
    From: MSN Nicknamestillstanding462 Sent: 1/18/2008 10:59 AM
    I'll probably get flamed for this, but I always use a tight .002 on these bikes.
    I don't think.0012 is even achievable for most of us, and a tight .002 seems to yield no more noise or wear.

    bill

    Reply

    Recommend Message 3 of 7 in Discussion
    From: MSN Nicknameoldcycle Sent: 1/19/2008 2:17 AM
    0.03mm Starrett feeler gage is available at the link below for about $4.00.

    http://www.use-enco.com/CGI/INSRIT?PMAKA=990-2365

    Reply

    Recommend Message 4 of 7 in Discussion
    From: MSN Nicknameelvis__evans Sent: 1/20/2008 11:44 AM
    I've always used 0.0015". It's close enough. Elvis

    Reply

    Recommend Message 5 of 7 in Discussion
    From: aries_58 Sent: 2/7/2008 9:20 PM
    Don't know if this will help at all. Wish I could say I have tried it but my bike started acting funny so I never got the chance. I found this on a website and it sound like it might work.


    The old Honda 350 and 450cc twins had what are called eccentric rocker arm shafts. That is, the center of the shaft is ground off center so that as you turn it, the rocker arm that rides on it, moves back and forth. This increases and decreases the valve clearance. If you adjust the valves on these engines the regular way with a feeler gauge you will be ok But, there is a better way.

    Start and warm the engine up enough so that it idles good. Loosen each valve adjuster lock nut and turn the adjuster shaft with a screw driver. The valve will get noisy and the engine RPM will go up. You want the highest engine RPM with the lowest tappet noise. Do this on each valve. You will notice that the engine RPMs go way up. Sometimes as much as 1000 to 1500 RPM gain. Now back the idle down with the throttle stop screws and do it again. We want the highest RPMs and the least tappet noise, with the emphasis on the RPM. Yes, they will be noisy but, where do you think that RPM is coming from ? Stock clearance too tight ? I learned this trick from a factory mechanic when I worked in a Honda shop in 1968. I have never heard of it from any other source. It works though. I've used it on a lot of 350s/450s with no ill effects.

    Reply

    Recommend Message 6 of 7 in Discussion
    From: MSN Nicknamestillstanding462 Sent: 2/7/2008 10:07 PM
    I'm sorry, but never, EVER do this on a 450.
    Works OK with a 350, but not a 450 - you'll toast your followers and cams.
    We did it on 350's all the time back in The Day, but I've seen the results on a 450, not pretty.

    In point of fact, tight intakes on a 450 will cause uncontrollable reving - I've seen it more than once.

    bill

    Reply

    Recommend Message 7 of 7 in Discussion
    From: MSN Nicknamehonda3370 Sent: 2/8/2008 12:14 AM
    I agree with Bill Lane, his suggestion is valid,when you give the rocker & cam lobe more room, there is MUCH better oil flow between the too. I have been using 004 on the intakes and 005 on the exhaust, for 14 years now, always trying to get better oil flow thru these motors, and if you think the motor is making noise, you can always tighten them up, nothing will be hurt by trying it. I never have been able to figure out why Honda made the clearance so tight ( that would be a good subject of discussion on the site ). maybe someone out there knows for sure ...with out guessing.
    And from the hondatwins.net posting I found all of this in, Bill Lane weighs in on the 'time it by ear method on the 450, and his quick valve adjustment walkthrough:

    Never, EVER, use the "set the valves by ear" method on a 450.
    It's only acceptable on a 350, and only then if you're very experienced.

    Do it with a stone cold engine.
    First set the cam chain adjuster, as outlined in the manual.

    Bring the left side to TDC compression stroke, line up the "LT" mark and hold it there (kind of a feat in itself).
    Adjust both left side valves to 0.002". Adjusters should make the valves tighter when rotated away from the head (meaning turned towards the front on the exhaust, or towards the rear on the intakes).

    Do not attempt to set them to 0.0012" like the book says, you'll never make it and there's a real danger of getting them too tight. Tight intake valves will cause an uncontollable high idle, and tight valves in general will toast your top end parts.

    Turn the engine 180 degrees to TDC compression stroke on the right side, line up the "T" mark, and set the right side valves to 0.002".

    The adjusters may try to move on you when you tighten the nut down, so double-check after locking them down.

    That's all there is to it.
    Well, they do give you 0.0012" feelers in the little Honda tool kit that comes with the bike.
    They're like tinfoil, they last about one or two valves - and that gap is totally unreasonable for normal humans to achieve. I've done it a zillion times, and I'm not comfortable with it.
    I just use 0.002", no noticable increase in noise or wear. I use precision "shim stock", I get it in 25' rolls, because even 0.002" feelers don't last long. I just cut off a new piece whenever I need to. I get it in 0.002", 0.003", and 0.004" to do most Hondas out there.
    Like Terry mentioned, he regularly goes to 4 or 5 thousandths on his 450's.
    Last but not least, 450roo here suggests the following as an emergency fix:

    Just to add all the possibilities I will post this --- but hasten to add I have used it only two or three times when in a corner. Usually I use the Honda workshop manual method but with a .0015 feeler.
    With the covers removed tighten the gap till it is no longer possible to move the cam follower from side to side then increase the gap till the follower will slide from side to side freely but with no appreciable up and down movement. Tighten the cam adjustment nut and check to make sure it has not moved and you are done.
    Attached Images Attached Images    
    i got wiring loose inside my head :: my 450 K5 build thread :: my XV920 build thread :: go shop the hondatwins.net store

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  3. #2
    Supporting Member Rich Ard's Avatar
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    Re: Proposed 450 Valve Adjustment Sticky

    I am guessing that the procedure would be identical for the 500 - will tag it as such if confirmed.
    i got wiring loose inside my head :: my 450 K5 build thread :: my XV920 build thread :: go shop the hondatwins.net store

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    Super Moderator frogman79's Avatar
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    Re: Proposed 450 Valve Adjustment Sticky

    I say GO other than maybe suggest at the end of the procedure that there are different gauges to use.

    Good job either way sir!
    Franz >>> 450 build >>>360 Build

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    Super Moderator HerrDeacon's Avatar
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    Re: Proposed 450 Valve Adjustment Sticky

    Very nice work, I've already stickied it, this will be useful to a lot of people. Give it a few days to let everyone weigh in and make any adjustments necessary, then feel free to change the name (i.e. remove 'Proposed').
    Perry

    1972 Honda CB350 / 1982 Honda MB5 / 2009 Suzuki Gladius / 1978 Honda XL250S

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  7. #6
    hansleopold's Avatar
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    Re: Proposed 450 Valve Adjustment Sticky

    I personally stick to the instructions stated once by Honda engineers. Can`t understand why it should be more difficult to set 0.03mm play than 0.05mm play. The clearance is set between the cam and the cam follower and it provides a clearance of 0.05mm between the follower and the valve stem due to the geometry of the system.

    Yes it takes some time to do it, but it is very important to do it properly. The 450 head was very advanced for it`s time and still is. So advanced that it was banned on the race track in UK during the mid sixties.

    Just take your time and don`t forget to check the play when the nut has been tightened. I recheck the clearance with a 0.02 and 0.04 gauge, just to make sure.

    You have to work with a high grade of precision, and perhaps readjust a valve several times before it is correctly set. But precision is what Honda engineering is all about....



    _______________
    Hans

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    Super Moderator Znabb's Avatar
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    Re: Proposed 450 Valve Adjustment Sticky

    Quote Originally Posted by hansleopold
    I personally stick to the instructions stated once by Honda engineers. Can`t understand why it should be more difficult to set 0.03mm play than 0.05mm play. The clearance is set between the cam and the cam follower and it provides a clearance of 0.05mm between the follower and the valve stem due to the geometry of the system.

    Yes it takes some time to do it, but it is very important to do it properly. The 450 head was very advanced for it`s time and still is. So advanced that it was banned on the race track in UK during the mid sixties.

    Just take your time and don`t forget to check the play when the nut has been tightened. I recheck the clearance with a 0.02 and 0.04 gauge, just to make sure.

    You have to work with a high grade of precision, and perhaps readjust a valve several times before it is correctly set. But precision is what Honda engineering is all about....



    _______________
    Hans
    Hans, normally I would follow the Honda workshop manual but in this case I trust the words of HondaTwins gurus Steve and Bill and of course Terry at Team Hansen Honda. They have worked on these bikes since the 60's and seen the results of their adjustments on customer bikes after thousands of miles.

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    hansleopold's Avatar
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    Re: Proposed 450 Valve Adjustment Sticky

    I`ve always followed Honda`s own instruction as this is what the engineers once decided is the best. And as long as Honda hasnīt released a tech bulletin regarding the matter I stick to it.

    The tiny clearance (0.03mm) between the cam lobe and the follower is increased to about 0.05mm at the follower and valve stem due to the geometry of the valve system. A normal value for a d.o.h.c engine.

    The valve train on this motor is very advanced, and you have to give it the time it demands when servicing it. I was surprised when reading of an emergency fix procedure, and adjusting the valves on a running engine.....


  10. #9
    Supporting Member Rich Ard's Avatar
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    Re: Proposed 450 Valve Adjustment Sticky

    The valve train on this motor is very advanced, and you have to give it the time it demands when servicing it. I was surprised when reading of an emergency fix procedure, and adjusting the valves on a running engine.....
    I can only speak for myself in that at this point I will take the suggestions of gents who have been playing with this engine for decades over the ones who wrote the book the first time around.

    As to the 'play it by ear' method - I included it as a cautionary note. Bill Lane advised strongly against doing it that way so I wanted to make sure that was included in case anyone showed up here looking to verify that it was a good method.

    For my part I have now done both sides at .03mm.
    i got wiring loose inside my head :: my 450 K5 build thread :: my XV920 build thread :: go shop the hondatwins.net store

  11. #10
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    Re: 450/500 Valve Adjustment

    Quick question, noticed that in the 500T manual on page 7 it states

    NOTE:
    It is important that the small line at right-angles to the
    screwdriver slot on the rocker shafts face away from the
    cylinder head. If this precaution is not observed incorrect
    valve timing, and damage to valve mechanism will result.

    One of the screws on my 450 K7 is facing inward towards the cylinder. Is this bad?

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