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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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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

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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

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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

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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.

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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

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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.
 

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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!
 

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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').
 

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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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Re: Proposed 450 Valve Adjustment Sticky

hansleopold said:
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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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 hasn´t 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.....

:?
 

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Discussion Starter · #9 ·
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.
 

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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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Ouch OK - not sure how long they were run like this, kind of abandoned by the PO but I adjusted them back correctly, hopefully no significant damage. Thanks for clarifying.
 

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Couple of questions about this.

When I set LT to the timing mark and checked the cam indicator marks. Both marks were off the mark on the bearing holder by 1/16th of an inch or less. Is that something I should be concerned with? Not being spot on the mark?

Also, since 0.0012" is basically impossible to find in a store. I use .0015" and before tightening down the nut I can slide it out the feeler gauge with minimal effort, then after tightening the nut, I can't get the feeler gauge all the way between the cam & follower. Will that be okay since I'm using .0015"? or should I still set it so I can get the gauge all the way in there with minimal resistance? Since they say the gap will increase with a warm engine, I was thinking that a very tight 0.0015" cold will probably be good once warm, but is this wrong?
 

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Hi, Ive been hearing some valve noise on my 1971 CB450. I just performed the first valve adjustment since bringing it back to life about a year ago. It's been running fine other than the recent valve noise. I took the covers off the engine and before I adjusted the valves I loosened the bolt on the cam chain tensioner. I was able to actually see the chain tighten slightly with the intake side valve cover removed. So THAT works.

The issue is that I adjusted the valves to 0.002" as several people have recommended. Now that the engine is buttoned back up and running it sounds great. Minimal noise. After the engine warms up it wont maintain a proper idle. It revs up to around 3000rpms and wont settle back to idle. Tried adjusting the carbs but this didn't solve the rpm issue.

Any suggestions? Is this high rpm a possible result of tight or loose valve clearance? I rechecked all of the valves before I closed it up but this is the first valve job I've done. The feeler was snug but able to move. The legs of the T-marks on the adjuster screws are facing away from the spark plugs on both sides of the engine both intake and exhaust.
 

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"Tight" valves can cause this, but also any, even miniscule air leak.... Did you remove the carbs when doing the valves?.... Remove carb cables?.....Cracks in Carb "boots"?.....What else did you move or remove for accesss to the valve adjustment?....
 

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Figured it out. It was unrelated as far as I can tell. The screws holding the points base-plate had become loose so my timing was way off. The plate was fairly loose and when I moved it with a screwdriver the idle came right back to normal. Re-timed it and set the points. It's running very nicely with the valve clearance at .002" Pretty quiet too. Thanks for the info on valve clearances, it was very helpful because the recommended clearance from honda at .0012" was freaking me out. Sooooo thin!

Some observations from a first-timer on this 1971 cb450 valve adjustment:

The valves on my bike were set so that the leg of the "T" on the adjustment for 2 of the cam followers was pointed toward the spark plug instead of away from it when I started the valve adjustment. The cam lobes nearest the backwards "T"s had more wear than the others. Coincidental? Probably not. I simply loosened the lock-nut on the outside of the cam follower and was able to turn it around in the proper direction. I went very slowly and felt resistance when I went the wrong direction then turned it the other way and it all went fine. The adjustment could still be made when the "T" was turned around and facing the proper direction. No biggie. Setting the gap took some time to get the knack for tightening the lock-nut while maintaining the proper gap. Trial and error. It helped a lot to have the lock-nut already a little bit snug instead of loose when doing the adjustment because the adjustment kept changing when I tightened the lock-nut. Took the vacuum cylinder and vacuum piston off of the carbs to get better access to the intake-side valve cover but left the carbs on the bike.
 

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I think my scenario falls into this category
I have a cb500t, it has the valve adjusters on the heads. I reinstalled the engine and set the valves at .003 as manual states. but when i started it, it started ticking and shooting air back through one of the carbs. My buddy (harley mechanic) said two things. Adjust the valves and replace carb boots. I got back home and tightened carb boots, and tried to adjust valves while engine was running, but never got the ticking out or the back pressure through the carb, I got it better but not perfect. Also side note I had tow striped bolts where the points are, so i replaced them, and with doing that I also might have put timing in wrong position. Any remedies on repair?
 

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hey guys.
talking about a 75' CB500T here, this post was really helpful for me to understand the task i have in front of me. ive run into a snag tho. so ill try to explain as best as i could. bare with me im very new to bikes its my first!! OK..... took the engine apart thinking i had a blown head gasket, replaced the gasket no problem,was losing power so i figured gasket because of light oil coming out on my fins (still not sure if that was my problem tho, the gastket looked 'ok') but now im stuck. Im looking at my cams and trying to line up the index marks, and the only one that will let me line it up is my inlet cam. when the chain was connected i could rotate my generator and see where the exhaust cam index mark was and when you rotate it to access the master link the cam rotates and wont let me rotate the cam (with out chain) back to line up index mark. i understand that both cams need to me lined up. but the exhaust cam will not allow me to line it up, its on the other side of the cam??? is there a way to rotate the cam with out the chain connected?? any help guys would really be great. one of my buddies mentioned its possible my "shims" went out and thats why i was losing compression/power on my left cylinder.

also, i noticed that my valve adjusting lock nut seems to be froze to the middle adjusting screw, any tip on getting that free? simple lock eaze do the trick?

thanks guys for any help

-scott
 

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I'm having a nightmare of a time trying to set mine. I have set valves on bikes before but never on a CB500t and never really ran into any problems until now.

The bike runs absolutely fine and completed 40 miles last week with no problems, reason I wanted to do a valve set is to make sure I have an accurate compression test.

Main problem is when I set the mark to LT with marker on right cams and then rotate 360 degree, one side has already reached TDC and released way before it reaches the LT marker again. It's had a new cam chain so maybe it wasn't put on spot on?

That and the smallest feeler gauge I have is 0.05mm which is really flimsy, it doesn't fit in between any of the cam and cam followers at any point. Perhaps that is a good indication that the valves are well set?
 

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koolio said:
I'm having a nightmare of a time trying to set mine. I have set valves on bikes before but never on a CB500t and never really ran into any problems until now.

The bike runs absolutely fine and completed 40 miles last week with no problems, reason I wanted to do a valve set is to make sure I have an accurate compression test.

Main problem is when I set the mark to LT with marker on right cams and then rotate 360 degree,...LEFT valves are set at "LT" on LEFT cylinder compression stroke...RIGHT cylinder valves are set (180* rotation) to/at "T" on the RIGHT cylinder compression stroke..... one side has already reached TDC and released way before it reaches the LT marker again. It's had a new cam chain so maybe it wasn't put on spot on?

That and the smallest feeler gauge I have is 0.05mm which is really flimsy, it doesn't fit in between any of the cam and cam followers at any point. Perhaps that is a good indication that the valves are well set?
 
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