Question regarding maximum valve clearance at 180° cam follower rotation (CB450 K3)

[Highwayace]

Hi everyone,

I am currently in the process of reassembling a CB450 K3 engine and have run into a technical question regarding the valve adjustment.

Does anyone happen to know what the maximum possible valve clearance should be when the adjusting eccentric (cam follower) is turned exactly 180 degrees from the tightest position?

I asked an AI assistant about this, and it suggested a "free" (maximum?) value of 0.25 mm. However, it also admitted that this figure was sourced from various online discussions rather than official factory specifications, so I cannot fully rely on that information. I know the valve clearance (both factory and those guys in Houston; cannot even measure the factory clearance, cannot find tools for that).

I would highly appreciate it if anyone with factory documentation or deep experience with these K-series twins could verify the correct numbers or share their insights.

Thank you in advance for your help!

Best regards,

Ilkka Nyyssonen, Finland

 

[boddy]

Are you asking about this value because you cannot set the proper valve clearance? If you had the valve seats re-cut, sometimes they are cut too deep and the valve stem sit higher. If this is the case you will need to get the valve stem shaved down a bit.

 

[Highwayace]

Are you asking about this value because you cannot set the proper valve clearance? If you had the valve seats re-cut, sometimes they are cut too deep and the valve stem sit higher. If this is the case you will need to get the valve stem shaved down a bit.

That is the case, but I need to know how much to shave.

 

[RobMan]

Does anyone happen to know what the maximum possible valve clearance should be when the adjusting eccentric (cam follower) is turned exactly 180 degrees from the tightest position?

The FSM states: "The standard clearance between the cam and the cam follower for both the intake and exhaust valves is 0. 03 mm (0. 0012 in)." Unfortunately finding a feeler gauge that thin is almost impossible. I believe the consensuses on the forum is 0.05 mm (0.005 in) is OK but no larger and these sizes are available in most feeler gauge sets.

I use a 0.04 mm (0.0015 in) and a 0.05 mm (0.005 in) feeler gauges as go and a no go set. I try to adjust to where a 0.04 mm will slide in but the 0.05 mm will not and and call it good. Adjusting them is a pain in the rear with a lot of second guessing until you find a process that works for you, Hope this helps.

Sorry! Reread the question so please disregard my answer above.

 

[boddy]

I haven't seen any max value for the cam follower clearance in the factory service manual. I'm not certain but I would think about 0.020 in should be sufficient. Maybe others have a better idea.

 

[ancientdad]

I believe the consensuses on the forum is 0.05 mm (0.005 in) is OK but no larger

0.05mm is actually 0.002" (well, 0.0019685 inches)

 

[ancientdad]

I do not know what the max clearance is at that position because the only thing that is important is having a range of adjustibility that will get the follower to zero clearance and up to probably around .020" as Boddy mentioned. When the seats get cut, or sometimes when you get followers refurbished, minimum clearances can change and tipping the valve stem is the only way to compensate for it. Yes, the factory valve lash spec is 0.0012" but typically we set them at 0.002", not enough added clearance to cause issues.

 

[stl360+450]

Something to at least consider is that the ratio between the follower clearance and the valve tip clearance is approximately 2:1. This is one reason that the specified clearances are so small on this motor. The specified 0.03mm becomes roughly 0.05mm at the valve tip, according to the manual. The following screenshot also comes from the FSM.



You ultimately need 0.05mm clearance at the valve tip, so your AI estimate is suggesting five times as big for max clearance, whereas the mentioned 0.02" is about ten times as big.

You need to hit a sweet spot here, so I would assemble the head on your work bench and try to make an estimate, perhaps with the torsion springs removed. Even knowing the desired maximum, you still need to know whether the current clearance is small, zero, or negative as a reference point.

 

[Highwayace]

Something to at least consider is that the ratio between the follower clearance and the valve tip clearance is approximately 2:1. This is one reason that the specified clearances are so small on this motor. The specified 0.03mm becomes roughly 0.05mm at the valve tip, according to the manual. The following screenshot also comes from the FSM.

View attachment 58826

You ultimately need 0.05mm clearance at the valve tip, so your AI estimate is suggesting five times as big for max clearance, whereas the mentioned 0.02" is about ten times as big.

You need to hit a sweet spot here, so I would assemble the head on your work bench and try to make an estimate, perhaps with the torsion springs removed. Even knowing the desired maximum, you still need to know whether the current clearance is small, zero, or negative as a reference point.

Yes, that is the target clearance that needs to be set. However, what I specifically want to know is what the clearance becomes when the eccentric is turned to the position where the gap is at its absolute maximum.

I need to grind a small amount off the valve stem (or the follower face) to get the valve clearances back into the adjustable range. If this "free" or maximum baseline clearance is too small to begin with, I will run out of adjustment range later on as the valves seat in over time.

 

[ancientdad]

I need to grind a small amount off the valve stem (or the follower face) to get the valve clearances back into the adjustable range. If this "free" or maximum baseline clearance is too small to begin with, I will run out of adjustment range later on as the valves seat in over time.

First, unless you dress down the follower with something that will leave it in a smooth if not almost polished finish, it will cause wear on the cam lobe as it cleans up during running. I personally wouldn't attempt to grind the tip of the valve stem, I'd take the valves that need to be tipped to a machinist to get them done squarely and with a machined finish. I had to do that myself on my 450 restomod after getting the seats cut.

 

[stl360+450]

I have a spare head in my basement. Here's what I found looking at the right exhaust valve adjustment.

1. Exhaust cam alignment. (cam lobe out of the way)




2. Adjuster position for no clearance. Remember that if you turn 180° It will also have no clearance.



3. Adjuster at 90° from no clearance yields 0.3mm between the cam and follower. Snug.



4. Zero clearance again at 180°, roughly.

 

[crazypj]

I haven't had head off one for a very long time but it did seem to have massive clearance on base circle of cam, I do remember checking with cam rotated to about 2:00 o'clock position (bike was owned by a local police detective who would 'pop in for a chat' when I was doing his bike, he seemed to break it quite often?)
Before I read the text I thought it was OP setting clearance ten times too wide with a 0.30mm feeler instead of 0.03mm feeler