Fieuw things to know about big valves

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jseng1 said:
See the comparison of springs with recommended installation height specs for the street. Chart below shows .350" lobe lift (stock is approx .330").

Fieuw things to know about big valves


Its important that the peak pressures are not greater than stock if you want to avoid excessive wear on the street. For race cams - thicker bottom shims and higher pressures are used.

I deleted my previous chart because it showed lift up to .450" and was misleading.
Click to expand...
Thought it might interest some to see a plot of force vs displacement for the valve spring data JSM provided. The beehive spring exhibits a slightly non-linear change in rate with compression as would be expected. The conical spring appears to have a very linear response to compression as does the stock spring. However, the stock spring has one outlier data point that occurs at the highest compression (shortest length – 0.900”) and is possibly due to the closed-end coils beginning to contact adjacent coils, thereby reducing the spring’s number of active coils and resulting in an increase in spring rate.
Fieuw things to know about big valves
 
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splatt said:
A clever man would allow for a good quality oring between the guide and head to help seal oil migration, the lower edges of the spring seats must get very thin when the ports get to large.
Click to expand...

Perhaps we weren't so clever in the '70s!
 
Hi there,
I am just back from my friend Eddy van Engelen and we make the mesurments from the spring tension at 1.400'' and here are the results:
Two springs at 106 pounds
Two springs at 115 pounds
I don't think I must change anything, I plan to use the two 115 pounds at the intake valves.
Thanks Steve, I will try to use the seats with integtal oil seals also
Feel free to give your opinion, keep in mind that I use a JS 2 camshaft and never run more as 6.200 RPM
Yves
 
For
yves norton seeley said:
Hi there,
I am just back from my friend Eddy van Engelen and we make the mesurments from the spring tension at 1.400'' and here are the results:
Two springs at 106 pounds
Two springs at 115 pounds
I don't think I must change anything, I plan to use the two 115 pounds at the intake valves.
Thanks Steve, I will try to use the seats with integtal oil seals also
Feel free to give your opinion, keep in mind that I use a JS 2 camshaft and never run more as 6.200 RPM
Yves
Click to expand...
My street instructions say you should shoot for 1.450" (1.4" minimum). You can lower the pressure to 1.450" height for 90+ lbs installed height and you will still be fine on the street.
 
Jim describes a logical way forward for the street user, i.e. many of his customers, where specific pressure can be compromised slightly. i.e. use a fitted length that will give a seat pressure in the range of acceptable pressures. Jim seems to give lengths that will give a minimum pressure. This is a reasonable compromise and covers the case where you don't have access to a spring guage and don't want to buy one for occasional or one off use.

Or you can employ the lengthier process using a spring guage, which is surely only really necessary for motors stressed to maximum rpm regularly (race bikes).

This involves checking each spring to the required specific seat pressure (you decide based on use and expert advice). Simply measure the compressed length of each individual spring at that pressure, and shim each individual spring installed height to set the exact pressure required. In truth, due to available shim sizes you will compromise here, but the tolerance is much smaller.

So, where Yves and his friend set the spring compressed length to 1.4" and recorded pressures, you would set the spring to say 100lb pressure and measure the length. Though due to the nature of springs and simple guages, I have found it worth a moment to compress, measure, over compress, return to pressure, measure, reduce pressure and repeat a few times to establish a median and record that.

Once you have bought a pressure guage you will always do it this way! But sometimes (e.g. when it is not a race motor), just because you can.
 
SteveA said:
Jim describes a logical way forward for the street user, i.e. many of his customers, where specific pressure can be compromised slightly. i.e. use a fitted length that will give a seat pressure in the range of acceptable pressures. Jim seems to give lengths that will give a minimum pressure. This is a reasonable compromise and covers the case where you don't have access to a spring guage and don't want to buy one for occasional or one off use.

Or you can employ the lengthier process using a spring guage, which is surely only really necessary for motors stressed to maximum rpm regularly (race bikes).

This involves checking each spring to the required specific seat pressure (you decide based on use and expert advice). Simply measure the compressed length of each individual spring at that pressure, and shim each individual spring installed height to set the exact pressure required. In truth, due to available shim sizes you will compromise here, but the tolerance is much smaller.

So, where Yves and his friend set the spring compressed length to 1.4" and recorded pressures, you would set the spring to say 100lb pressure and measure the length. Though due to the nature of springs and simple guages, I have found it worth a moment to compress, measure, over compress, return to pressure, measure, reduce pressure and repeat a few times to establish a median and record that.

Once you have bought a pressure guage you will always do it this way! But sometimes (e.g. when it is not a race motor), just because you can.
Click to expand...
Hi Steve, I plan to go back to my friend this evening and put the spring at 93 pressure, record the compressed lenght from individual springs and addapt my shiming, hope this will ne the end of the story
Keep you posted about the results this eve
Yves
 
Back to my friend this evening to set the springs to 93 pounds and see If we are close to the 1.450 recomanded by Jim Schmidt
Spring #1: 1.448
Spring#2: 1.470
Spring#3: 1.424
Spring#4: 1.456
As you can see we are close to the requested 1.450
I will adapt the shims to the lenghts I find for every individual springs to have 93 pounds on every springs
Yves
 
Yves, these springs you are using have done 50,000km is that right? If so, they are remarkably good and consistent IMHO.
 
Fast Eddie said:
Yves, these springs you are using have done 50,000km is that right? If so, they are remarkably good and consistent IMHO.
Click to expand...
Hi,
It is my TTI gearbox that have done 50.000 km, the JS parts including the springs must have 25.000 km, but I was surprised by theyre good shape
Yves
 
yves norton seeley said:
Back to my friend this evening to set the springs to 93 pounds and see If we are close to the 1.450 recomanded by Jim Schmidt
Spring #1: 1.448
Spring#2: 1.470
Spring#3: 1.424
Spring#4: 1.456
As you can see we are close to the requested 1.450
I will adapt the shims to the lenghts I find for every individual springs to have 93 pounds on every springs
Yves
Click to expand...

Its also acceptable to leave your springs at 106 to 115 lbs. Since you have a high lift cam it would give you a safety margin. Race cams usually get a little more pressure. Anywhere between your range of 90+ and 115 would be good. With a 920 you won't be revving it too high so you can go with the lower 90+ pressure. But its better to balance them out so they are all nearly the same.
 
WZ507 said:
Regarding your request for guidance on spring force required to control a large-valve Norton head at high rpm (8500), IMHO the best advice you will find on this subject is to watch the Comnoz spintron videos that include a variety of cams, springs, spring force, etc. As the videos so dramatically show, results are not necessarily intuitive, and adding more spring force is certainly not always the solution and in several cases made things dramatically worse. Due to lack of stiffness in the entire system (cases, cam, pushrods, rockers, etc) adding additional spring can further exacerbate the situation by causing even more elastic deformation, which in turn further hinders the ability of the system to control valve motion.

https://www.accessnorton.com/NortonCommando/about-time-for-the-spintron.18787/

I believe Snotzo has also modeled your subject cam/engine configuration and could give you a very good idea how to achieve the solution you seek. JSM would likewise be aware of these findings and should be able to offer counsel.
Click to expand...

The JS1 and beehive spring combo has never been tested on Comstocks spintron - but it has been tested on the track at 9000 RPM. The initial spintron test of the JS2 is no longer relevant because the JS2 has been superseded by the JS2 smoothramp with longer smoother ramps and an RPM range of over 9000 RPM with beehive springs. I'm not sure if Snotzo has run the new JS2 smoothramp through his software. The new JS2 smoothramp is capable of another 1000+ RPM over the early JS2 which had the same valve action, lift, duration and ramps as the PW3.
 
jseng1 said:
Its also acceptable to leave your springs at 106 to 115 lbs. Since you have a high lift cam it would give you a safety margin. Race cams usually get a little more pressure. Anywhere between your range of 90+ and 115 would be good. With a 920 you won't be revving it too high so you can go with the lower 90+ pressure. But its better to balance them out so they are all nearly the same.
Click to expand...
I shim everithing at 93 pounds and don't want to change anymore
Yves
 
Has the free length of the two springs with the lower tension shrunk any compared to the other two ? wondering if ex port heat is having any effect
 
splatt said:
As you have two different spring pressures , 106 and 115, I was wondering if two springs are also shorter possibly due to heat
Click to expand...
Yes, maybe but this are the pressures taken at 1.400 and it was the wrong way to take the mesurments, in fact if you wish to have 93 pounds you put the spring under a pressure of 93 pounds and then take the lenght of the spring, in that case we turn around 1.450 with small variation, I don't think thet the heat as something to do with that
Yves
 
yves norton seeley said:
Yes, maybe but this are the pressures taken at 1.400 and it was the wrong way to take the mesurments, in fact if you wish to have 93 pounds you put the spring under a pressure of 93 pounds and then take the lenght of the spring, in that case we turn around 1.450 with small variation, I don't think thet the heat as something to do with that
Yves
Click to expand...
To day I receive the valve seats with intergral oil seals, thanks Steve A, spend 4 hours to shim it, but now the job on the head is done.
I wish to thank everybody for the help I receive from the Commando community, it's a wonderfull world!
By the end of the week I will receive the 81mm pistons from Jim Smith and I will keep you posted
Yves
 
yves norton seeley said:
Yes, maybe but this are the pressures taken at 1.400 and it was the wrong way to take the mesurments, in fact if you wish to have 93 pounds you put the spring under a pressure of 93 pounds and then take the lenght of the spring, in that case we turn around 1.450 with small variation, I don't think thet the heat as something to do with that
Yves
Click to expand...

93 lbs is what they are rated at when new at 1.450" length. It doesn't look like they've changed.
 
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