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'72 Honda CB450. Doing a complete teardown and rebuild of the motor. Got the heads off and am trying to strip them.... except I can't figure out how to remove the torsion bars..... I've taken the camshafts out, opening rockers and pivots are out, the bolts that hold the torsion bars in (on the little levers) are out.... but I can't the torsion bars to come out... what am I doing wrong?
I'm not sure if this is the right way to do it, but this is how I have removed them on two different heads and it seemed to work fine. Did one tonight actually.
What I didn't realize at first is that there is a knock pin where that bolt was, keeping the spring from relieving the tension. Think of it as a small piece of tubing that was around that bolt. It is still in there, sticking out of the head. You have to push the spring out past that pin to get it to relieve. It is actually really easy.
I take a sharp flat head screwdriver or dull chisel and put it in the little crack where the two torsion bars meet in the middle. I then take something and gently tap the screwdriver, driving it in between them. One of the bars will start to get pushed out. I then turn the screwdriver prying it out more until it clears the knock pin. Then just pull it out. As you slide it out, the valve lifter will try to bind so I found it best to apply a little pressure with your finger to the top of it towards the center of the head as you slide the spring out. You then should be able to figure out the rest.
The actual torsion bar part is thinner than a pencil and is inside the larger tube that you see so don't worry too much about damaging it until you actually get it out of the head.
If this doesn't make any sense, I can try to get some pics.
What I didn't realize at first is that there is a knock pin where that bolt was, keeping the spring from relieving the tension. Think of it as a small piece of tubing that was around that bolt. It is still in there, sticking out of the head. You have to push the spring out past that pin to get it to relieve. It is actually really easy.
The actual torsion bar part is thinner than a pencil and is inside the larger tube that you see so don't worry too much about damaging it until you actually get it out of the head.
AHHHH ok. That wasn't clear in the Clymer book... just a warning not to damage, nick, or scratch the torsion bar. I didn't know the torsion bars were inside those tubes... thought those tubes WERE the torsion bars.
FYI, just in case you didn't know already, make sure you keep track of where each torsion bar came from. It makes a huge difference. I learned the hard way.
Why not? Why would they lose their stiffness when standard springs don't? Do you know some facts we don't or are you repeating something someone told you?
So it is standard practice to replace valve springs? At what mileage is this typically done? I have only rebuilt one engine so I will admit my ignorance, but as an aerospace structural engineer I have never heard of metals losing there stiffness unless pushed into the plastic strain region or they are overheated, changing their temper.
The only engine I rebuilt was my 450 and I didn't even consider replacing my valve springs unless they were damaged since new ones are nonexistent and nos ones are as rare as unicorn tears.
Valve springs are checked for uncompressed height and subjected to a load (usually by means of a hydraulic press) to check if they are still "good" for use in a motor. Specs are in most all shop manuals.
Your latter statement is specifically the reason why a lot of the time the old ones go back in. That isn't to say the old ones aren't ok to use; as long as they are in spec then your fine. It's only worn springs that can lead to issues, including valve float at high rpm (mostly an issue due to the springs having less strength then they used to as a result of being tempered) and valves not closing all the way (if the springs uncompressed height is below a point where it can be shimmed then valves wont close all the way).
Valid point on the metal stiffness not changing unless pushed into the plastic strain region (I'm studying to be a mechanical engineer myself) but what we've all witnessed with our own eyes tells us that theres something more. Combination of age and varying conditions (including load changes, temperature changes, etc) have a serious effect on the metal.
Also, if metal never lost its hardness (or in this case, elasticity, though they are related) then we would never have to change out worn shocks and springs!
'72 Honda CB450. Doing a complete teardown and rebuild of the motor. Got the heads off and am trying to strip them.... except I can't figure out how to remove the torsion bars..... I've taken the camshafts out, opening rockers and pivots are out, the bolts that hold the torsion bars in (on the little levers) are out.... but I can't the torsion bars to come out... what am I doing wrong?
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