Double Valve Springs

[petert1345402284 0]

After a fair amount of researching, I've finally found a set of double springs and retainers that are excellent value for money. Co-incidently, the Kawasaki Z900/Z1000 has 7mm valves and 7 degree collets, the same as the XU9J4/XU10J4. I had been looking at the APE's VSP500 double springs. Unfortunately these required a lower installed height of approx. 36mm, rather than 39mm like the Mi16. Then I discovered the VSP520 spring. They're designed for up to 0.520" lift, has 65 lbs. at 39mm and 200 lbs at 28.5mm. Judging by the surface condition, they appear to be a quality spring. And if they can withstand 9500+ rpm in drag bike racing, 8000+ should be a walk in the park. A pair weigh the same as an Mi16 single spring. When used with APE's titanium retainer, you save 8g. I also use the APE single groove collets with custom valves, but they'll work fine with the std. Mi16 collets. The only snag is that you'll need to get the spring base area of the head machined and fit hardened spring bases, the same as for any double spring installation. Check out the prices on the APE website, http://www.kzzone.com/cams.html, but you can do better from other suppliers. I'm going to write a program to churn out the spring bases. So if you want some let me know.