Ever wanted to see what your valves are doing?

[peasea]

Yeah, but a crank spinning at 100 times per second isn't as mindblowing as a piston moving from stopped to warp speed to stopped at 100 times per second.

And back again. You're right, it does your head in.
I also used to have trouble fathoming how all that torque went through such a small trans input shaft then on to an equally small driveshaft uni'.

[peasea]

bout 8k, has 66mm stroke though, which is bit longer than most high reving bikes I think, so higher piston speed. Which actually gives a max piston speed of about 27.6m/s which is just a fraction under 100kmhr. This sort of speed translates to oh fuck that hurt, when a piston flys through the head and smacks you on the elbow
fucking brutal

I saw that vid, ouch.
Your bike's valves are still doin' it though. 8k is getting there. Mine's out of puff at 5.5, crackup.
I wonder which one is stressed less?
(And therefore will last longer...)

[bogan]

I saw that vid, ouch.
Your bike's valves are still doin' it though. 8k is getting there. Mine's out of puff at 5.5, crackup.
I wonder which one is stressed less?
(And therefore will last longer...)

I thought the SS reved to 14k? but yeh mine do same, just not as quick. And as for the longest lasting, the one made by honda of course

[scooute]

bout 8k, has 66mm stroke though, which is bit longer than most high reving bikes I think, so higher piston speed. Which actually gives a max piston speed of about 27.6m/s which is just a fraction under 100kmhr. This sort of speed translates to oh fuck that hurt, when a piston flys through the head and smacks you on the elbow

fucking brutal

Owwwwww thats deff. not a funny bone moment...

[schrodingers cat]

And so they should, if they don't they can burn.
The tip of the valve (the end you can't see there) should be slightly convex to induce this rotation. From memory I think we ground the valve tips to 1.5 degrees.

So the rotation isn't induced by the action of the coil spring? Surely it must be as all the valves rotate in the same direction.
(I don't doubt the tip grinding is also linked, just doubt it is the sole influence)

[trailblazer]

fuck thats got to hurt. I bet he shit himself.

[peasea]

So the rotation isn't induced by the action of the coil spring? Surely it must be as all the valves rotate in the same direction.
(I don't doubt the tip grinding is also linked, just doubt it is the sole influence)

Seriously? I was never (in 30+ years) told any different. I can understand your question but while I can see valve springs doing the whatoosie here and there, their motion is removed somewhat from the valve stem. You have a valve/retainer/collet connection that may (may) remain intact through interference/friction, but the valve spring is, for want of a better analogy, in 'free' motion between the aforementioned assembly. The valve spring is free to rotate, sure, but nothing governs its direction and similarly nothing dictates that it should rotate. It operates on flat surfaces. The valve's surface at the tip is convex, as I say, and therefore is driven into a certain motion.

[Pixie]

Yeah, but a crank spinning at 100 times per second isn't as mindblowing as a piston moving from stopped to warp speed to stopped and back to warp speed at 100 times per second.

Well ,warp speed is a bit of a stretch - mean piston speed in a bike engine is in the order of 25 metres per second

As for the cause of the valve rotation - the piston rings also rotate.
It's magic

[schrodingers cat]

Seriously? I was never (in 30+ years) told any different. I can understand your question but while I can see valve springs doing the whatoosie here and there, their motion is removed somewhat from the valve stem. You have a valve/retainer/collet connection that may (may) remain intact through interference/friction, but the valve spring is, for want of a better analogy, in 'free' motion between the aforementioned assembly. The valve spring is free to rotate, sure, but nothing governs its direction and similarly nothing dictates that it should rotate. It operates on flat surfaces. The valve's surface at the tip is convex, as I say, and therefore is driven into a certain motion.

As a spring compresses one of the seating faces rotates relative to the other (tip - fit a thrust washer underneath one end of your shock spring to reduce stiction). The wind direction of the coil dictates which way it twists. I see what you are saying about the valve spring being a 'free' object but invariably there is some friction and the tiny force would add to the rottional force. The tip grinding alone couldn't cause ALL of the valves to rotate in the same direction. Does the mating face inside the bucket have any shape or is it flat?

[Katman]

Well ,warp speed is a bit of a stretch - mean piston speed in a bike engine is in the order of 25 metres per second

Yes, I have been known to exaggerate sometimes.

25 metres per second mean piston speed only equates to 90 kph. But that figure is where the redline is generally set. So an engine running at a redline setting of 10,000 RPM has pistions going up and down 166 times per second.

Peak piston speed is generally in the region of 1.5 times faster than mean piston speed.

Therefore the piston is accelerating from a standstill up to a speed of about 140 KPH and than decelerating to a standstill then accelerating again to 140 KPH before coming to a standstill again - all at 166 times per second.

Pretty impressive.

[schrodingers cat]

Due to the action of the conrod the piston has a controlled rate of acceleration and decelleration. Does anyone know a ballpark g figure?

[bogan]

As a spring compresses one of the seating faces rotates relative to the other (tip - fit a thrust washer underneath one end of your shock spring to reduce stiction). The wind direction of the coil dictates which way it twists. I see what you are saying about the valve spring being a 'free' object but invariably there is some friction and the tiny force would add to the rottional force. The tip grinding alone couldn't cause ALL of the valves to rotate in the same direction. Does the mating face inside the bucket have any shape or is it flat?

but when the spring comes back up, a friction linked assembly would un-rotate again.

[schrodingers cat]

but when the spring comes back up, a friction linked assembly would un-rotate again.

The friction isn't constant. Notice at low revs the valve behaves as you say. As the assembly goes through phases of resonant sympathy the rotation starts. The differing componant mass and rates of elongation etc mean the relationship can't be constNT FROM 1 - 14,000 RPM

[bogan]

Yes, I have been known to exaggerate sometimes.

25 metres per second mean piston speed only equates to 90 kph. But that figure is where the redline is generally set. So an engine running at a redline setting of 10,000 RPM has pistions going up and down 166 times per second.

Peak piston speed is generally in the region of 1.5 times faster than mean piston speed.

Therefore the piston is accelerating from a standstill up to a speed of about 140 KPH and than decelerating to a standstill then accelerating again to 140 KPH before coming to a standstill again - all at 166 times per second.

Pretty impressive.

its all dependant on the stroke, the peak figure is easy as to calculate. RPM / 60 * 2 * PI * Stroke(in m) /2 and the mean speed is RPM / 60 * 2 * Stroke(in m). So yeh peak speed is 1.571 * average (PI/2)

[bogan]

The friction isn't constant. Notice at low revs the valve behaves as you say. As the assembly goes through phases of resonant sympathy the rotation starts. The differing componant mass and rates of elongation etc mean the relationship can't be constNT FROM 1 - 14,000 RPM

tbh peaseas explanation sounds better