Head work
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i take it from that ^ that you agree with erik,s findings then dave (thats a refreshing change)
So you agree with Erik's dial gauges then?
frank
Club Member
i dont agree that he has increased the poundage of the spring by over 20%, no.
i do agree that he has increased the preload that holds the valve onto its seat when closed, yes (there,s about 8mm of stock preload, and he,s added another 1mm).
the effort/force required to open the valve still stays the same, but you and paul were stating that the poundage had been increased, thats the only thing i dont agree with
pollyp
Club Member
basically at the springs natural unloaded stable length we would zero the force gauge
#heres the science# cos we assume that the two ends of the spring object is in equalibrium exerting zero force towards/away from each other to maintain a steady stable length (newtons 1st law).
as you pull the lever to displace the two ends of the spring, for every mm increase of displacement you apply from the natural unloaded origin length, the spring produces a value of reaction force in the opposite direction (newtons 3rd law).
plot the force reading per mm of travel on a graph to analyse the type (linear or progressive) and rate (amount of force required to move between each unit of displacement) of the spring.
(e.g. for a linear 10kg/mm compression spring: 0mm displacement = 0kg, 1mm = 10kg, 2mm = 20kg, 3mm = 30kg etc)
now when you pull and hold the lever down to compress the 10kg/mm linear spring by say 2mm and it reads say 20kg, you've preloaded the spring by 20kg (ur now acting like a fixed preload strap or fully extended damper or valve head resting against the seat).
for another person (representing external force of the road or cams) to move that lever/squeeze the spring further beyond that 2mm, they'd first have to apply the same 20kg force on the lever as you did to get the spring to that point (and so relieve you from duty i.e. preload strap is slack or valve seat pressure is zero)
and then apply a further 10kg (30kg total applied force) to squeeze the spring 3mm from it's natural length.
and then a further 10kg (40kg total applied force) to reach 4mm from natural length. etc etc
pollyp
Club Member
oh ur talking bout eriks gauge.
example: lets say a stock cam with 10mm lift squeezes a 1kg/mm spring between 10mm and 20mm from its natural length and gives force readings of 10kg and 20kg respectively.
now preloading means we squeezed the spring abit more to begin with before the cam squeezes it further by the same physical 10mm lift.
so the preloaded valve would now squeeze the spring between say 15mm and 25mm from its natural length given force readings of 15kg and 25kg respectively.
as a result the force readings (valve shut force, force to crack open valve, force to fully open valve) are all equally raised from increasing the preload on a linear spring.
The spring poundage or rate has never changed. Neither you nor I nor Paul has stated that it has changed. Therefore agreed.
The spring preload is equal to the load at the valve seat in closed position. This has been increased due to the additional shim. Therefore agreed.
Let me know if you agree with the following;
A standard spring has ~8mm preload. Given the 1kg/mm spring rate, we have ~8mm x 1kg/mm = ~8kgs initial seat load.
With an additional 1mm shim, the preload is now ~9mm. Given the identical spring rate, this is ~9mm x 1kg/mm = ~9kgs initial seat load.
pollyp
Club Member
thats the bit i dont agree with paul, it does,nt matter how many washers you fit, it always takes 10kg to compress the spring/open the valve 10mm
ur ignoring the "from it's natural rest length" bit
frank
Club Member
yes i agree, and my shimless preload was 7kgs
frank
Club Member
nah, if erik had measured the force to compress it from its free length (40mm) to its fitted length (32mm) and then the 32mm value with the washer added would measure 1/8th more pressure.
that would have given an accurate value for the valvebounce calculation (the fully compressed measurement wont)
Erik's values are at ~8mm lift Frank, (~24mm compressed height).
OP
OP
pollyp
Club Member
fitted length is the distance from the base of the spring to retainer cap with the valves closed yeah?
are the washers placed between the retainer top and the spring to squeeze/preload it further? (if the washer was between the valve and the cam bucket thats a different issue)
and assuming during zero lift stage of the cam lobe the bucket isn't touching the cam.
the spring would be squeezed further from 32mm by the thickness off the washers (say 2mm). so spring would actually be compressed from 40mm free length down to 30mm fitted length with washer spacer (10mm displacement) as oppose to 40-32mm (8mm displacement) without a washer spacer.
to calculate what the absolute force would be, you need to plot a force/mm graph of the spring with the spring force gauge tool and then find what force the graph says for that particular amount of displacement.
where'd you get 1/8th extra pressure from or is it a guess?
are the washers placed between the retainer top and the spring to squeeze/preload it further? (if the washer was between the valve and the cam bucket thats a different issue)
and assuming during zero lift stage of the cam lobe the bucket isn't touching the cam.
the spring would be squeezed further from 32mm by the thickness off the washers (say 2mm). so spring would actually be compressed from 40mm free length down to 30mm fitted length with washer spacer (10mm displacement) as oppose to 40-32mm (8mm displacement) without a washer spacer.
to calculate what the absolute force would be, you need to plot a force/mm graph of the spring with the spring force gauge tool and then find what force the graph says for that particular amount of displacement.
where'd you get 1/8th extra pressure from or is it a guess?
pollyp
Club Member
my brain is hurting lol
i know, this is turning into a physics revision class lol
frank
Club Member
adding the 1mm washer to the 8mm preload paul (40mm free length and 32mm fitted length)
pollyp
Club Member
adding the 1mm washer to the 8mm preload paul (40mm free length and 32mm fitted length)
so the spring is compressed from 40 free length to 31mm (40 - 8 - 1 = 31mm) = 9mm displacement
you know what the spring rate is?
frank
Club Member
erik,s gauge is reading 50 lbs fully compressed i think mate
pollyp
Club Member
and fully compressed length is?
think it's best to plot the force per mm throughout the springs travel and calculate the spring rate within its linear working range cos as it approaches coil bind, the force reading begins to rise exponentially before it's fully coil bound/compressed.
so trying to calc spring rate from a single force & displacement reading and assuming it's linear might be mis-leading
frank
Club Member
23mm mate
i had to remove my washer to fit the 10mm lift cams, so the stock fitted length must be close to 33mm
pollyp
Club Member
ok very rough calc ignoring ring binding suggests
10mm lift cams
40mm free length
50lbs(22.68kg) at 23mm (17mm displacement) = 1.3341kg/mm springrate
valve seating force with stock 8mm preload = 1.3341 x 8 = 10.67kg
peak valve lift force = 1.3341 x (8 + 10) = 24.01kg
valve seating force with stock 8mm preload & 1mm spacer washer = 1.3341 x (8 + 1) = 12.01kg
peak valve lift force with 1mm spacer washer = 1.3341 x (8 + 1 + 10) = 25.35kg
overall the spring exerts 1.34kg more force between valve fully closed (12.56% increase) and valve fully open (5.58% increase) with the 1mm spacer washer
10mm lift cams
40mm free length
50lbs(22.68kg) at 23mm (17mm displacement) = 1.3341kg/mm springrate
valve seating force with stock 8mm preload = 1.3341 x 8 = 10.67kg
peak valve lift force = 1.3341 x (8 + 10) = 24.01kg
valve seating force with stock 8mm preload & 1mm spacer washer = 1.3341 x (8 + 1) = 12.01kg
peak valve lift force with 1mm spacer washer = 1.3341 x (8 + 1 + 10) = 25.35kg
overall the spring exerts 1.34kg more force between valve fully closed (12.56% increase) and valve fully open (5.58% increase) with the 1mm spacer washer
pollyp
Club Member
it's displacing the spring a further 10mm (or 9.75) from the 8mm preload beforehand
frank
Club Member
yes, and because the springrate is the same regardless of preload, then the force needed to displace it 9.75mm remains the same (washer or no washer)
if you were opening the valve from the free length, then the washer would increase the load needed (41mm displacement, as opposed to 40mm)
pollyp
Club Member
huh um no
the difference between the highest & lowest force are the same with/without preload washer yes, and that's determined by the spring rate.
but the peak force required to push a more preloaded valve is higher cos spring force is not the same at any 2 displacements
(i.e. if ur body weight can compress/displace a susp coil 1/2way, preload the spring to the same 1/2way point with spring-compressors and see if the same weight can now compress the spring by the same amount till its fully compressed? nope)
(another i.e. if the cam can only exert 24kg max to reach full valve lift, once you add a 1mm preload washer on the spring the cam can't push the valves all the way cos it requires 25kg)
i think the issue is ur imagining as though the spring is always under zero preload whenever the valves closed when in fact there's 8mm (or 9mm with that extra washer) of preload to overcome first.
the difference between the highest & lowest force are the same with/without preload washer yes, and that's determined by the spring rate.
but the peak force required to push a more preloaded valve is higher cos spring force is not the same at any 2 displacements
(i.e. if ur body weight can compress/displace a susp coil 1/2way, preload the spring to the same 1/2way point with spring-compressors and see if the same weight can now compress the spring by the same amount till its fully compressed? nope)
(another i.e. if the cam can only exert 24kg max to reach full valve lift, once you add a 1mm preload washer on the spring the cam can't push the valves all the way cos it requires 25kg)
i think the issue is ur imagining as though the spring is always under zero preload whenever the valves closed when in fact there's 8mm (or 9mm with that extra washer) of preload to overcome first.
My brain is hurting from all this physics......
All i know is that putting in the extra washer did the trick for me!
Another point though to the OP, if you are going to all this hassle then take the time to measure you valve spring free length against the specs. I stripped a head about a month ago and found that all the springs were 1-1.5 mm out of spec, this would make a big difference in a high revving engine. i am sure new ones are available but i just stripped another low mileage head and used them.
All i know is that putting in the extra washer did the trick for me!
Another point though to the OP, if you are going to all this hassle then take the time to measure you valve spring free length against the specs. I stripped a head about a month ago and found that all the springs were 1-1.5 mm out of spec, this would make a big difference in a high revving engine. i am sure new ones are available but i just stripped another low mileage head and used them.
frank
Club Member
hmmm, so you,re saying that adding a 1mm washer has increased the strength of the spring by 12.5% when its half pressed, and 5.5% when its fully pressed then paul ?
that sounds odd to me and contradicts the "same springrate" regardless of preload rule tho eh.
if you add a 1mm washer to a 40mm spring and then preload it to 39mm, you will have double the preload of a 40mm spring @39mm (2mm of preload instead of 1mm of preload) so thats an increase of preload of 100%.
and when compressed to zero cam lift that may be your 12.5% figure and full cam lift your 5.5% figure ?
but thats an increase of preload not strength tho eh paul ?.
i think erik has in fact increased the poundage/strength of the spring, because he has compressed a 41mm spring down to 24mm (a stock setup would compresses a 40mm spring down to 24mm eh)
but that is only an increase of 2%ish tho
No, Erik hasn't done that. Standard 40mm spring would be compressed to 24mm with no shim, i.e. 16mm compression, (40-16=24). With a 1mm shim the standard 40mm spring will have actually been compressed to 23mm, i.e. 17mm due to the 1mm shim (40-17=23). It's still having to remain within the same 24mm space. This is shown in Erik's photos that you keep referencing
Similarly a standard 40mm spring with 5mm of shims would be a 40mm spring compressed to 19mm, (40-5-16=19). Still within the 24mm space.
We already agreed previously that the spring has the same rate.
We also agreed that there was a load holding the valve closed that was equal to the spring preload.
In order to open the valve we must first counteract the force holding the valve closed, i.e. acting against us before it can open.
This is also supported by Paul's calculations where you can see the required force to compress the spring by 10mm remains unchanged, as agreed. i.e. the spring rate is not changed. However, both the closed load and the total force when open has increased as a result of the increase in preload.
valve seating force with stock 8mm preload = 1.3341 x 8 = 10.67kg
peak valve lift force = 1.3341 x (8 + 10) = 24.01kg
valve seating force with stock 8mm preload & 1mm spacer washer = 1.3341 x (8 + 1) = 12.01kg
peak valve lift force with 1mm spacer washer = 1.3341 x (8 + 1 + 10) = 25.35kg
Force required to move valve 10mm with 8mm preload - 24.01 - 10.67 = 13.34kg
Force required to move valve 10mm with 9mm preload - 25.35 - 12.01 = 13.34kg - the same
If the required force when fully open remained the same as you state at 24.01kgs, with an increased preload of 12.01kgs due to the additional 1mm shim, the required load needed to open the valve to peak lift would be as follows;
valve seating force with stock 8mm preload & 1mm spacer washer = 1.3341 x (8 + 1) = 12.01kg
original peak valve lift force = 24.01kg
Force required to move valve 10mm - 24.01 - 12.01 = 12kgs
As you can see, the load required to fully open the valve has now decreased. The only way for this to happen would be to change the spring rate, which we have already agreed does not happen.
The below website may help you understand the relationship between preload and spring rate, (i.e. preload does not effect spring rate). Especially so since you were referencing coilover suspension systems. Bare in mind though that the valve has to move by a fixed amount dictated by the cam, unlike a coilover unit, which will only move as a result of the weight applied. If you set coilover preload to more than the vehicle corner weight, (which would be the same as the valve spring scenario), it will not compress in a static state and make for an utterly horrid drive!
http://www.zoomsquared.com/resources/technical-information/coilover-spring-preload-explained
frank
Club Member
ok so can we conclude from this tortuous discussion
that the extra washer increases the preload (and the extra force needed to initially open the valve) by about 12.5% (which is relevant in regard to valvebounce)
the load on the top of the cam lobe is increased by about 5.5% (which is relevant to valvetrain wear)
and that for a 1.0 screamer the mod is effective (borne out by lord lucan,s experience )
so can we conclude from this tortuous discussion that the extra washer increases the preload (and the extra force needed to initially open the valve) by about 12.5% (which is relevant in regard to valvebounce)
the load on the top of the cam lobe is increased by about 5.5% (which is relevant to valvetrain wear)
and that for a 1.0 screamer the mod is effective (borne out by lord lucan,s experience )
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