modok wrote: ↑Tue Jun 18, 2019 7:24 pm
Ah thank you. I have done so, that's actually when I started wondering about it about 15 year ago.
As far as the topic of the thread, sorry for over complicating it, but the point I was headed for is that those of us who have been carefully running near to bind as we dare, have not found the limit of how tight is too tight. If being near coil bind is good, (and IMO it almost alway is) then next the logical question is.... what is the low limit?
And...I don't know, all I can say is it's tighter than generally thought.
If the spring company or a peer says you can run .070" from bind on a given spring, that may be a conservative estimate, not a HARD minimum as you might expect. But EVERYTHING has tolerances.
And this is a case where you have a large tolerance stack.
What interests me is how many cycles a spring can run under controlled conditions ie with no surge. The manufacturers should be able to give a cycle count as they should know the stress at max lift and at installed height to. Then using the S-N curve for the material a life estimate can be established. Running close to bind means running high stress even at idle and the accumulation of fatigue damage will get you eventually. This is probably more an issue on a hot street car that sees alot of controlled cycles and fewer poorly controlled ones.
How do they know the weights of the valve train? How do they know the amount of oil>> cooling.
The only thing they know is the spring in the worst environment.
modok wrote: ↑Tue Jun 18, 2019 7:24 pm
Ah thank you. I have done so, that's actually when I started wondering about it about 15 year ago.
As far as the topic of the thread, sorry for over complicating it, but the point I was headed for is that those of us who have been carefully running near to bind as we dare, have not found the limit of how tight is too tight. If being near coil bind is good, (and IMO it almost alway is) then next the logical question is.... what is the low limit?
And...I don't know, all I can say is it's tighter than generally thought.
If the spring company or a peer says you can run .070" from bind on a given spring, that may be a conservative estimate, not a HARD minimum as you might expect. But EVERYTHING has tolerances.
And this is a case where you have a large tolerance stack.
What interests me is how many cycles a spring can run under controlled conditions ie with no surge. The manufacturers should be able to give a cycle count as they should know the stress at max lift and at installed height to. Then using the S-N curve for the material a life estimate can be established. Running close to bind means running high stress even at idle and the accumulation of fatigue damage will get you eventually. This is probably more an issue on a hot street car that sees alot of controlled cycles and fewer poorly controlled ones.
How do they know the weights of the valve train? How do they know the amount of oil>> cooling.
The only thing they know is the spring in the worst environment.
I'm talking about stress just due to the spring deflection not dynamic effects I.e. essentially what you get at low rpm. At 0.060" from coil bind even rotating by hand the stresses are enormous rotate it enough it'll break within a finite period if it's a performance spring . This gives you an indication how stressed it is.
That spring mike said did 1200miles let's call it ave speed 120 so 10hrs at 5000rpm ave cam rpm so 3 million cycles.
If the engine idled for a period of time with equivalent number of cycles how far would it have been from fatiguing out? Would it last 10 million?
That would tell you how much damage is due to dynamics and how much due to compression between installed and max lift
There is a maximum cyclical stress limit for steel alloys (the endurance limit) below which the cycle life is infinite. Don't know where typical (or extraordinary) performance springs lie on the curve.
Also, Lunati (and, AIR Comp) shows a minimum coil to coil clearance of 0.060" to 0.100"! https://www.lunatipower.com/valve-spring-tech
Why would they build additional travel into the spring?
perhaps for those always wanting to TEST the limits, but a lot of these springs are at least "implied" to replace production parts.
Go through the SBI catalog and look at every spring for every car on teh road, open height and bind are listed. They run tight.
MadBill wrote: ↑Tue Jun 18, 2019 10:34 pm
There is a maximum cyclical stress limit for steel alloys (the endurance limit) below which the cycle life is infinite. Don't know where typical (or extraordinary) performance springs lie on the curve.
Also, Lunati (and, AIR Comp) shows a minimum coil to coil clearance of 0.060" to 0.100"! https://www.lunatipower.com/valve-spring-tech
Classically yes there is a fatigue limit but the reality is different though especially for real parts vs a lab specimen. Some industries classify 10 million as infinite but a valve spring may do 100's of millions. I don't think the average high performance aftermarket spring will have "infinite" life which is why I'm curios
The valve spring does not know what it's coil bind dimension is, unless it is actually compressed into coil bind. Therefore there is no detrimental affect to the spring by running it "close" to coil bind. However, with this said, a valve spring will last longer if it is run in conjunction with a valve that has extended stem length. For instance a valve lift of .800" with stock valve stem length, versus the same valve lift with .100" longer stems.
The reason for this is that a coil spring is actually a small torsion bar that has been wound into a circular shape. Every time the spring is compressed the whole spring wire material twists very slightly. Therefore a taller spring will have less twist motion that the shorter spring does - assuming that both springs are manufactured with the same wire material thickness, materials, etc.
Bill
Perfect Circle Doctor of Motors certification
SAE Member (30 years)
ASE Master Certified Engine Machinist (+ two otherASE Master Certifications)
AERA Certified Professional Engine Machinist
Running an engine with it's valve springs compressed near to coil bind is bad for spring life.
I know this for sure because there are (were) no aftermarket valve spring kits for my favorite engine; American Motor's '56-'67 Rambler V8.
Since I was building a comparatively low budget 443 CID stroker Rambler V8 and the heads and stock valvetrain would need improvements to flow more air, I began to investigate my best bang for the buck higher performance valve spring set up.
According to info I read on one particular valve spring manufacturer's website (an industrial supplier -for nearly all types of springs) the general rule for maximum spring life is 25-30% of the spring's full compression from it's manufacturer's specified installed height to coil bind.
Then I discovered this is exactly how the stock Rambler V8 springs are set up from the factory.
I know I should furnish the actual numbers to verify this statement, but it's true, and very likely many other factory built engines use this same engineering guideline.
Make a long story shorter, where the stock valve lift was .375" what I ended up doing was increasing the install height of the stock spring by .1" in order to get a safer, approximate .475" lift. (install height from stock 1.81" to modded 1.91")
From there, I did tons of research to find a second inner spring, to get my final 'closed' and 'open' spring seat pressures.
Judging by what I've learned, the better dual spring set ups will feature opposite wound outer and inner springs with closer to equal value spring rates because they tend to turn the valve retainer when they're compressed -whereas opposite wound outer and inner springs tend to control valve rotation ...way better than any type of single coil spring.
In any case, the stronger spring will have more influence on valve rotation (rotating the retainer, the locks and the valve stem, as an assembly -common sense)
Based upon Physics, valve train weights are also important to valve spring durability; the valve spring must apply more opposite force as those weights become heavier -where force is 'energy', doing 'work', which requires heat ...so the 'energy' stored in the spring will be doing less work, and run cooler, with lighter valve train components.
The more 'control' the spring has, the less undesirable movement there will be in the associated components. IE: If the spring fits sloppy loose on the retainer, there will be more movement between the spring and retainer, more rubbing friction, more heat, and more wear (of all associated components) (Another cornerstone rule of Physics: without control, the experiment will always lead to failure)
The general rule for minimum valve spring clearance between coils is .010".
This of course varies among springs, as do the amount of windings.
EG: if the coil has six full windings, allow .060" clearance before coil bind, if five, allow .050" before coil bind etc.
-The .010" clearance between coils is done to help avoid coil to coil contact, which could increase coil spring 'surging' (by impact and reactionary forces) and lead to a broken spring, dropped valve etc.
A polished valve spring will demonstrate greater durability than an unpolished spring by having reduced stress risers on it's surface texture. For this reason also, if not polished, a higher performance spring should have some type of corrosion proof coating to help prevent oxidation -from 'blow by' air containing moisture/humidity. This is why one might notice GM higher performance LS V8 valve springs painted blue.
amcenthusiast wrote: ↑Sat Aug 10, 2019 2:31 amAccording to info I read on one particular valve spring manufacturer's website (an industrial supplier -for nearly all types of springs) the general rule for maximum spring life is 25-30% of the spring's full compression from it's manufacturer's specified installed height to coil bind.
Then I discovered this is exactly how the stock Rambler V8 springs are set up from the factory.
I know I should furnish the actual numbers to verify this statement, but it's true, and very likely many other factory built engines use this same engineering guideline.
Make a long story shorter, where the stock valve lift was .375" what I ended up doing was increasing the install height of the stock spring by .1" in order to get a safer, approximate .475" lift. (install height from stock 1.81" to modded 1.91")
Can you please unpack that for like you would go a smart fifth grader? What is 25-30% of what? There’s free height, the recommended installed height with valve closed, actual installed height with valve closed, compressed height with valve fully open (given cam), height with first set of coils touching, height with all coils binding. How should all these heights relate to each other if one is going for maximum durability, given that the spring resonant frequency is comfortably (many multiples) above the maximum rpm that the engine ever sees.
ptuomov wrote: ↑Sat Aug 10, 2019 7:24 am
Can you please unpack that for like you would go a smart fifth grader? What is 25-30% of what? There’s free height, the recommended installed height with valve closed, actual installed height with valve closed, compressed height with valve fully open (given cam), height with first set of coils touching, height with all coils binding. How should all these heights relate to each other if one is going for maximum durability, given that the spring resonant frequency is comfortably (many multiples) above the maximum rpm that the engine ever sees.
Like suggested it threat you just need to design the spring to have acceptable durability according to its herzian stress.
The particular manufacturer stated 'for max durability, working range should be about 25-30% of the spring's compression from it's recommended installed height.'
One of the keys is to set up the install height for the expected valve lift. This is where the task becomes more difficult because changing install height changes rocker arm geometry.
Example: on Rambler V8 stock springs, the install height is 1.81" and stock valve lift is .375".
.375" x 4 = 1.5" (for the 25% recommendation) -the remaining install height of the six coil spring is to allow for .060" clearance between coils, then about .020" to coil bind... so the stock spring set up would handle .395 max valve lift with no other modifications.
Said another way: '56-'67 Rambler V8 valve lift is limited by the stock spring specifications: 1.812" installed height - 1.356" coil bind spec. = .456" - .060" (for .010" proper clearance spaces on 6 coil spring) = .396" max. 'safe' lift allowed by stock spring for reground cam.
There are several ways to change the install height of a spring. One of the ways I increased my spring's install height was to use + .050" retainers. One may also 'sink' the valve seats, install longer valves, cut the spring seats lower etc. -the end goal is to have ample clearance between coils -to avoid coil to coil contact prior to full coil bind.
It's more tricky when we consider what is called 'spring surge' where the spring is moving around at higher rpm levels by it's own inertia/momentum -such as can be seen by watching slow motion movies (aka 'videos') of valve spring action in a engine running higher rpm levels.
...just using Rambler V8 stock spring set up for one example in this instance...
Another general rule is that a spring wound with more coils will impart less retainer rotation. A spring having fewer coils will impart more retainer rotation. -so, for a given install height, a spring with fewer coils may have more clearance for compression (expected valve lift) but it's going to create more unwanted movement of the retainer, locks and valve stem.
This is because, like the other man stated, a coil spring is like a torsion bar, but wound into coils. -The torsion bar won't compress end to end, so when the coil spring is compressed, it applies it's end to end rigidity to rotate the spring retainer -this is what causes the retainer rotation. Some rotation is good -helps to spread out heat transfer. Too much rotation is bad, causing excessive valve assembly motion -the more control of undesirable motion the better.
For spring durability, for the 25-30% general rule of 'working range', consider how bending a paper clip back and forth prior to breaking it causes the metal to get hot -this is what will be happening to an overworked spring -so springs that are forced to run with more working range will be running hotter and fail from bending fatigue sooner.
Where should the installed height be relative to free height? Where is it usually for typical factory springs?
I’m thinking that the spring itself may not know or even care about the manufacturer’s recommended installed height. But each spring does have a free height, so it make more sense to me to specify things off that.
amcenthusiast wrote: ↑Sat Aug 10, 2019 2:31 am..-The .010" clearance between coils is done to help avoid coil to coil contact, which could increase coil spring 'surging' (by impact and reactionary forces) and lead to a broken spring, dropped valve etc...
Conversely, it has been stated by many that designing a valvetrain to operate close to coil bind reduces surge potential by limiting the maximum excursions (and thus stress increase) in the compressed direction.
amcenthusiast wrote: ↑Sat Aug 10, 2019 2:31 am
Running an engine with it's valve springs compressed near to coil bind is bad for spring life.
EG: if the coil has six full windings, allow .060" clearance before coil bind, if five, allow .050" before coil bind etc.
Have you ever seen engines with 4 valves/ cylinder, or 5v/ cyl. ? These engines have plenty of rpm, year after year.
Theres no room for extra clearance, no way you can have 0.010" clearance/ full windings. If you put in camshaft with 0.030" more lift, it becomes coil bind.
I have a Toyota 2jz engine with aftermarket parts and it has a coil clearance less you can ever imagine.
