Ever wanted to see what your valves are doing?

[steve_t]

OK, so it might not be your valves but the valves of a BMW S1000RR. Pretty amazing our bikes can rev so frickin high - and this is 'only' to 14k RPM

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Oh, and when I was looking to see if I was reposting, I found this thread which is pretty frickin cool too if you haven't already seen it

http://www.kiwibiker.co.nz/forums/showthread.php/58164-In-cylinder-video-footage

[schrodingers cat]

That is cool! Interesting watching the valves rotate as well

[peasea]

That's pretty cool.

I saw a test bed for fuel systems in operation once with a pump and injectors off a supercharged, injected, alcohol burning big block Chevy going hard out. It fed into a perspex box and you would have been astounded at the volume of fuel that puppy ate. They talk in gallons per minute and even though a 1/4mile run might only take six seconds or thereabouts with a good alcohol deal (some are faster) that might equate to 18-20 gallons per run, or 90 litres, that's in 6secs-ish. (Rough figures, and nitromethane powered vehicles get through even more!)

[peasea]

That is cool! Interesting watching the valves rotate as well

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.

[onearmedbandit]

That's pretty cool.

I saw a test bed for fuel systems in operation once with a pump and injectors off a supercharged, injected, alcohol burning big block Chevy going hard out. It fed into a perspex box and you would have been astounded at the volume of fuel that puppy ate. They talk in gallons per minute and even though a 1/4mile run might only take six seconds or thereabouts with a good alcohol deal (some are faster) that might equate to 18-20 gallons per run, or 90 litres, that's in 6secs-ish. (Rough figures, and nitromethane powered vehicles get through even more!)

Mighty impressive alright, but you also have to account for idling, staging and burn-out. But still that's gulping a heck load of fuel.

[peasea]

Mighty impressive alright, but you also have to account for idling, staging and burn-out. But still that's gulping a heck load of fuel.

Ahhh, burnouts.
Hard launches are cool too.
Our wee thing had a 0-60ft time of .9 something.

[peasea]

Check the slick distortion, not bad for a 355ci small block eh?

[onearmedbandit]

Very impressive. What pressure would you run on average in the back hoops?

[bogan]

Ever wanted to see what your valves are doing?

well I'm still wondering, cos I'm pretty sure my valves don't go that fast :bleh: cool vid though

[Katman]

At 6000 RPM a piston is moving up and down 100 times per second.

I've been a mechanic for 30 years and it still blows me away that things can happen that fast.

[peasea]

Very impressive. What pressure would you run on average in the back hoops?

Shit, you got me there, I was the engine man. I think it might'a been 3.5 or 4 lbs, sfa.

[peasea]

At 6000 RPM a piston is moving up and down 100 times per second.

I've been a mechanic for 30 years and it still blows me away that things can happen that fast.

Actually, the crank goes round at 100 times per second, the pistons go up, then down, for that one revolution.
Not long into my engine building years I put together a single four-barrel small block Chev, 302ci, roller cam thing that went through the traps at 9,000rpm. 150 rps. That's where ring surface speed enters the equation.

[peasea]

well I'm still wondering, cos I'm pretty sure my valves don't go that fast :bleh: cool vid though

What's your bikes red line?

[Katman]

Actually, the crank goes round at 100 times per second, the pistons go up, then down, for that one revolution.
Not long into my engine building years I put together a single four-barrel small block Chev, 302ci, roller cam thing that went through the traps at 9,000rpm. 150 rps. That's where ring surface speed enters the equation.

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.

[bogan]

What's your bikes red line?

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

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fucking brutal

[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 :laugh:

[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

[dipshit]

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

I heard one of the hardest things on conrods and pistons is slamming the throttle shut suddenly from high rpm. Especially on V-twins with relatively bigger and heavier pistons. The piston coming up no longer has a air/fuel mix to compress and cushion itself against at the top of the stroke... instead there is now a vacuum in the combustion chamber and no cushion. This is when a conrod can stretch fractional more than usual and damage the piston.

[bogan]

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

hmmm, peak acceleration is when the velocity is zero so get dV/dTheta then:

V = RPM / 60 * 2 * sin(Theta) * Stroke(in m) /2

dV/dTheta = RPM / 60 * 2 *cos(Theta) * stroke(in m) /2

so peak acceleration is same number as peak velocity, just 90 degrees later, and g force is that figure over 9.818

[Pixie]

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

A high value for an F1 engine: at 19,000 rpm, the maximum piston acceleration in a BMW P83 of formula 1 is 10'000 g .

But road engines are more like 1000 g

[peasea]

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?

To the best of my knowledge (coz OHC engines were never really my thing) it's flat. The outer face of the bucket that contacts the cam lobe should be convex though so that it rotates.

Sure, valve springs rotate (which is what I meant by 'doing the whatoosie) but it's a by-product not an intent. If the springs are kept under control then, yes, they are (or should be) in contact with the retainer and cylinder head/shim.

What I find interesting in modern, high rpm engines is the ability of the valve springs to survive as long as they do. Springs will exert a given force at a given length when new but there's always an initial 'fall-off' and in racing circumstances the springs need to be shimmed to regain that initial seat pressure. So many of today's engines run for ages without that need and can still attain giddy rpm limits.

Things have moved on from Morrie Minors and AJS single-bangers.

[peasea]

I heard one of the hardest things on conrods and pistons is slamming the throttle shut suddenly from high rpm. Especially on V-twins with relatively bigger and heavier pistons. The piston coming up no longer has a air/fuel mix to compress and cushion itself against at the top of the stroke... instead there is now a vacuum in the combustion chamber and no cushion. This is when a conrod can stretch fractional more than usual and damage the piston.

Quite right. In class racing, where we had to run a flat-top piston, the deck height was machined to a bare minimum. We dyno'd the engine and got what wanted etc, with no apparent difficulty in the piston-cylinder head department. However, in the real world, when the car went through the traps and the throttle was released rapidly (unlike the gentle wind-down on the dyno) the pistons started slapping the heads, only just, but they did.

Easy fix in the lathe, just a lesson learnt.

[peasea]

hmmm, peak acceleration is when the velocity is zero so get dV/dTheta then:

V = RPM / 60 * 2 * sin(Theta) * Stroke(in m) /2

dV/dTheta = RPM / 60 * 2 *cos(Theta) * stroke(in m) /2

so peak acceleration is same number as peak velocity, just 90 degrees later, and g force is that figure over 9.818

Are you a dentist?

[bogan]

A high value for an F1 engine: at 19,000 rpm, the maximum piston acceleration in a BMW P83 of formula 1 is 10'000 g .

But road engines are more like 1000 g

how did you get 1000g? I only got 3.

[Madmax]

try rotary valves