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450/500 Valve Adjustment

2263 Views 59 Replies 22 Participants Last post by  sbkaye
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.


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?

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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.



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.


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


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.


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.



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 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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1 - 4 of 60 Posts
koolio said:
Sorry to hijack this thread, I'm setting the valves on the other CB500t, while I'm there is there anyway to check the wear on the cam followers? Difficult to see from the front and the rear. Do the side panels where you adjust the valves safely come off?
The side panels are also the bearing housings. So removing these will cause the cam shaft to be unsupported. Also although it can be done they are not so easy to get back.
The best way to inspect the cam lobes is to turn the engine over slowly by the rotor nut and inspect the lobe surfaces whilst doing this.
The alternative is to remove the head and then the cams, but that does involve a lot more work.
Steve you got me again :lol: :lol: :lol: :lol:
If you are concerned about the cam chain tensioner, take the tensioner off and inspect it.

The push rod should move freely and the wheel toothed. It's worth stripping it down if it feels sticky at all.
When you come to replace it,compress the spring and lock down the shaft with the bolt, Insert it land when you have got a little tension on the front section of the can chain the release the bolt you will hear it snick into place. It will be correctly tensioned now.
Thats a definite sadly but it will be worth it. However before you do that.
Was the throttle and choke wide open?
Was the engine at operating temp
Did the compression change after you put some oil down into the barrel?
If it is a yes to all these then its a top end rebuild. If not your valves may need adjusting. And if that does not cure then you will still need to take off the head to inspect the valves.
Yes that is the usual reason for random high idle revving.
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