Hi Graham
I would not expect you to do the T/V calcs and post them. Big job!!!!
Ok just to clarify a few points
1 Do you agree that any crankshaft is going to suffer from torsional vibrations irrespective of how well the crank is centripetally balanced due to the nature of the application of the torsional force.

2 I did not say that the T/V was transmitted to the cam shaft, just to the driving medium.IE chain or belt.

3 from the artical I posted from metaldyne I was pointing out that a camshaft also creates a torsional vibration due to it also being twisted due to torque[drive one end] and loads applied to various points along the camshaft [valve springs]. This does create a torsional vibration and the 2 opposing T/V's both act on the drive medium.

4 My comment about the "V" belt was not that it transmitted vibrations to the cam shaft but as the "V" belt is driven by the crankshaft damper so the vibrations from the damper as it's working to dampen the crank vibrations has a flow on effect to the "V" belt. Hence the "V" belt vibrates.

Now my original question was "why are you stuffing around with valve spring rates to take the harmonics away from the camshaft."
All coil springs create " harmonics" and this is going to be transmitted to the camshaft.
Now with the spring load on the camshaft for any 2 opposing forces to cancel each other out IE one opening and one closing they must be both of the same magnitude and on a shaft they must be exactly diametrically opposite and not be influenced by any centripetal out of balance force.. IE the exact point when one force is applied the opposing force must be exactly 180 deg opposite, but a inlet lobe does not start to open precisely when a exhaust is finishing closing and the kenetic energy required to compress the spring is not exactly the same amonut of potential energy in the compressed spring.
This over-lap is when the torsional vibration occurs with the twist of the shaft.

Now you have admitted that your engine has problems with valve train"harmonics" so why not look at the root cause of these "harmonics", the springs.
I would think that the logical answer would be to fit pneumatic valve actuators and do away with the springs. This was my original comment was leading to but it some how got clouded with a lot of irrevelant comments.
As a matter of interest it has been done and I found that they worked extremely well .

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Hi David
One lot of springs that i had made that all the experts said would be the best spring for my application at 7200 rpm they went out of control but changing the crank and a few other fiddles these springs now work, but the funny thing is that they work excellent in the fords, datsun and other 4 and 6 cyl motors but now these springs won't work with new cams i have designed, with one cam the motor would not go past 4000 rpm before the springs lost it, so it was find a better spring to cope with the problem which i have now done,and has led to more torque through the range.
Graham Russell

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"It's better to be not informed than ill-informed"

I'd like to see that!

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Hi Graham
I find this problem that you are talking about very interesting and at the same time confusing.
What actually happened when you state" out of control" and" lost it". All I can guess is that they bounced and broke.
Why would the engine not pull more than 4000 RPM because if the springs were at fault they would have to be bouncing or if they were that stiff as to stop them from compressing to the valve lift then something would bend or break.
Now I know that you do not devulging things but I am curious as to the spring diameter, pitch, spring rate and the UTS of them. I presume that they are a constant pitch spring.
It only requires a couple of simple calcs to see what the peramiters of a spring are and to see if it would be suitable.
Part of our programme maintenance requirements for class on a ship is that the engine componets are required to have regular testing ,so we do valve springs testing/reports all the time for class.

This is the advantage of running pneumatic actuators as there is no problems with frequency changes, compression rates and the load on the valve gear is greatly reduced and is more power effiecient. when you read the engineering reports from the various engine manufacturers there is a very big reduction in T/V which contributes to valve bounce at critical rev ranges.

When you had the crank hardened what UTS did it go to. I hope it was not too hard as it would become very brittle .

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HI GT Mowog
You won't me to prove it no problem, if you ask Greg at Karcraft that when he was visiting Paul Ivy of english fame he had the original drawings from BMC [ he worked there at the time] Gerg thought the hardning went in .080 so they still had nitriding when the crank was ground .080 under size,but then when you don't believe them i have the end piece of crank from the EN40B sprite crank that i had testsd by Steve Hooker who at the time was the metallurgist for Hawker DeHavlin at Bankstown air port he now works for him self as MT and C Engineers, Crack Testing Shot Peening Cryo Treatment and Consulting metalurgest a very cleaver man so if you would like to come and borrow the crank and have it tested you will find the hardning is in .060 tho, or may be you could ring him he may remember or go visit him he's only at silverdale
i use him a lot for various things' he now has a new machine analysing metals with out distroying the metal
Graham Russell

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"It's better to be not informed than ill-informed"

Hi David
Thats what they did went out of control they could not follow the profile of the cam launching of the top of the lobe crashing down the back of the lobe and bouncing off the seat but as i said they work very well in other engines to 9000 rpm with out any problems they are now used in a lot of the group N and open wheelers pushrod ford motors, the programe used to design these springs is the programe used to design F1 springs at the time and is still used to day for engines using valve springs but as they said they can not programe in the harmonice of the mini engine.
Also David we have watched the valve springs back in the early days with a strobe light only to see the valve caps and ths springs parting company at various rpm ranges, if only people knew what was going on under their rocker cover, if you wan't the spring info i can give it to you but with out the cam info it makes it very hard to work out what the spring is going to do. if any one is interested in what there valve springs are doing take your rocker cover off put a timing light on the springs and just give the motor a quick blip and watch the springs wobble all over the place as the revs rise and fall Then wash the motor off
Graham Russell

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"It's better to be not informed than ill-informed"

Harmonics? Fatigue?



As found on a race track.

Hi Morris 1100
May be he should have it cracked by Steve.
Graham Russell

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"It's better to be not informed than ill-informed"

Nope. No rings!

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Woops that should be cracked checked by Steve

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"It's better to be not informed than ill-informed"

Thats Art

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Master of the Moggie Army & Founder of Awesomestock2010

It is very expensive art...

(stolen from another forum...)

Same thread contains a broken 998 crank

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Nice pic of the busted 998 crank. Interesting that it broke in the same place as 1275 big journal cranks and 1100 cranks.

Now I will run this by you and we will watch the fur fly.
OK torsional vibration has 2 main factors[irrespective of how well a crank is centripetally balanced]
The 1st factor is the peak pressure IE the force on the piston at ignition.

The 2nd factor in a 4 cylinder engine with a firing order of 1,3,4,2 is the force applied to the crank by the 2 only loads during a 4 stroke cycle. Firing and compression.
Now 1 has just fired and 3 is compressing mixture so there is a imbalance between the 2 cylinders IE one being forced down[firing] and the other has a force also downwards due to compression. This situation creates the highest T/V is a engine so the crank twists between 3 and 1 and the vibration is transmitted to the damper end.
Next is 3 firing and 4 compressing. Same forces but the 2 cylinders are close together and the crank does not twist as much . The vibration travels to the damper and there is not forces with 1&2 so little amount of twisting of the crank in that section.
Next is 4 firing and 2 compressing and again twist over longer distance.
Next is 2 firing and 1 compressing and same loads ,but this sequence is the killer.
Now the crank is supported by the main bearings and there is little crankshaft deflection[bending not twisting] close to the bearings. Evertime the force is applied as the crank twists it is trying to drive the flywheel, but due to the mass of the flywheel the crank twist travels to the end of least resistance. The damper end.

In the situation with 2 firing and 1 compressing the crank between front bearing a center bearing is twisting against to mass of the flywheel and with twist and re-bound over short distance and at the end of the crank with least resistance.

Hence the stresspoint is on the web adjacent to the center main on the damper side. The load side of the webs starts with surface stress cracks that eventually cause the crank to break at that point. The stress crack is a 90deg to the centerline of the crank.

OK it's a clear as mud, but I will post some info from one of my text books that explains it a bit better.
This is what is happening to the crank. Note the comments about the metal particals.

This is the stress the shaft is subjected to and highlights the energy that is tored in the shaft and as the initial load deminishes the sored energy then re-bounds the shaft. This is what causes the "vibrations" in the shaft. Torsional is the force and and the re-bounds are the vibration and the number of times it occurs for a period of time is the frequency.

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Research is the difference between speculation and investment. Anyone who copys some one else will always be second
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Hi Graham
I can assure you that after 40 years of engine design and calculations and working on engines I am very aware of what happens to a valve spring under load.
Now you have refered to the "harmonics" of a mini engine again, and as I said before the T/V generated by a camshaft is the major factor in causing a spring to vibrate over it's normal vibration frequency.
This will explain exactly what happens to a spring. Note the section on a sudden applied force.




Now this is all about spring deflection. What you were refering to as "spring wobble". Yep I know about and can calculate it.




When we study engine design we look at the springs in great detail because with T/V ,power requirements, deflections, spring rates and spring frequency engineers find is that quite often a spring required to do the job is not a big heavy stiff one.IE high spring rate.
So if your spring is causing the cam follower to bounce all over the lobe then there is a BIG problem with the whole set-up. Quite obvious that the spring rate is too high . The video posted on this thread the engineer playing with the spring explained it very well.

Consider why many modern car engines have a progressive rate valve spring. How is it that a engine like a honda cbr can rev to 12 to 13,000 revs and not suffer valve bounce,and have a cam that has a very steep cam profile and 10mm travel on the valves with single progressive rate springs.

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Research is the difference between speculation and investment. Anyone who copys some one else will always be second
www.minisprintgt.com