The uprated camshaft will give 1.5mm extra valve lift.
The max rpm will stay the same at 6500rpm.

I have three choices:
1) stick with a new set of oem (£10 x 16 = £160)
2) schrick springs that also require extra retainer and new valves (Approx £700-800)
3) or some cheaper alternative after market ones with one less coil (maybe catcams springs) (Approx £200)

Picture of the schrick vs oem:


First of all the schrick is wider and has an extra retainer for the lower end which stops wobble 100%
Second thing I notice is the schrick one has one less coil which I am guessing it made for high lift cams so that the coil does not bind. but the cost of new spring, cotters, valves, retainers will be around £800!!!

The camshafts I am using are street mild cams 264/264 which will push the valves further down by 1.5mm (total of 10mm lift)

Is it wise to find a spring same height & width as the oem one but with one less coil? There are a few who has used this cam and they don't change the springs but just the hydraulic followers so probably worrying for nothing but always good to aim for better.

[Edited on 12/12/15 by bikecarbfred]

[Edited on 12/12/15 by bikecarbfred]

Bit of vital info needed
WHAT ENGINE?

1.4 16 AFH - I thought the principle would be same for all engines. =i.e valve lift, rpm and bhp.
i'll be running 150bhp

Time for some measuring and maths.....

You need to work out the retainer to spring seat distance with the valve closed and opened. Opened can be calculated from closed + lash - lift. Then you need a spring that will give you much the same pressure on the seat when closed but will not bind when opened - with an allowance for "floating" although you will not get much of that at 6500rpm,

The bottom of the retainer is, or can be, a spacer to adjust seat pressure when the valve is closed.

I suspect you would be fine with the standard springs. Cheap test - fit standard springs and cam see now big a shim it can tolerate without binding.

I have a manual for my engine that has a great explanation for setting up springs designed to run at 11,000 - its a rather large pdf but if you are interested I will try and post the relevant pages as photos

schrick
42mm: length of spring
20.51mm: spring fully compressed in vice
NET SPRING compression = 21.5mm
24mm: fully compressed with 2 retainers on

3.65mm thickness


oem
40.66mm: length of spring
23.55mm: spring full compressed in vice
NET SPRING compression = 17mm before binding
26.3mm: fully compressed with retainer pm

3.13mm thickness



Now I'm ASSUMING there's about a approx 2mm extra allowance before binding with the schricks. (with the retainers on!)

this extra 2mm allowance must be for the extra lift you get with the uprated camshafts
264's give you 1.5mm extra lift so i am guessing the 268's and on must give you 2mm extra lift or more.

so the question is.... can you get away with the standard spring. very interesting.
Also had to take into account there is an initial spring compressiong when installing the springs and fitting the retainer on. This is around 5mm. It's so difficult to measure that.


I also found this from hotrod.com

"Thinking has evolved on how much safety margin is needed. About 0.060 inch (1.5mm)used to be the textbook minimum, with more OK and even desirable. That's still an acceptable standard for everyday performance use, anything more than 0.150 inch (3.8mm) can cause spring surge, which can greatly reduce the available spring load needed to close the valve."

It is easy to work out lift. Measure across the cam and tip to toe - subtract one from the other to get lift. A different cam may or may not have more lift - much is in the timing - that is the 264 /284 figure

You should be able to measure the installed height (seat to retainer) try putting in a stack of washers around a valve then using feeler gauges.

I have just checked and the manual for my engine specifies a clearance of 0.035" before coil binding .....not a lot! That is for 10,500rpm but with titanium valves (less momentum). If you have 0.060" you should be safe as houses.

quote:

---

Originally posted by Theshed
I have just checked and the manual for my engine specifies a clearance of 0.035" before coil binding .....not a lot! That is for 10,500rpm but with titanium valves (less momentum). If you have 0.060" you should be safe as houses.

---

Well what's interesting is, from my measurements the oem might produce better performance :/

It is 10 grams lighter to begin with and there is around 1.5mm clearance before binding which is 0.060 inches!

" About 0.060 inch (1.5mm)used to be the textbook minimum, with more OK and even desirable. That's still an acceptable standard for everyday performance use," Hotrods


The schrick clearance before binding is around 2.99mm which is 0.114 inches. So this could give float? Does float happen more at higher rpm's? So at 6500 rpm is the shrick the best option to go with because it does not go anywhere near the binding zone?

" anything more than 0.150 inch (3.8mm) can cause spring surge, which can greatly reduce the available spring load needed to close the valve." hotrods



[Edited on 14/12/15 by bikecarbfred]

Have you tried asking the cam manufacturer?

These engine are made of cheese at the best of times, you don't want to put unnecessary strain on the cam gear by putting too heavy a spring on.

The cam manufacturer who supplied me with the cam are shrick. the shop say it's not required but recommended the shrick springs. they would say that as they want business.

i would not bother if they say they are not needed but are recommended