Valve Springs

Valve Springs

Q. I am in the process of pulling the valve springs out of my 89 ninja. Is there any better way of determining if the spring is good besides the minimum free length. I would like to find out what the K value (spring rate) is on them originally but I haven’t got a clue as to where to look for that. The shop manual doesn’t list it.

A. Here’s how I do this. I buy a new spring (1) then use this as a test spring. I put this spring on my Rimac machine and measure what it reads in lbs. at two specified measurements. What is known as installed height and open height. Installed height is the amount the spring is compressed when the valve is closed. The exact procedure to do this involved and requires special tools, but it goes like this. You need to know the distance from the spring seat to bottom of the retainer, this is the distance the spring is compressed when valve is closed. Once knowing this, you use a dial indicator to measure the amount of lift on the bucket, and subtract this (OPEN HEIGHT) from the installed height, this is known as open height, the amount of spring length when the valve is fully open.

Alright, the short answer, most Kawasakis installed and open height are pretty close.

I use 35mm for installed height and 25mm for full open height. This gives you on average a cam lift of about 10mm simulated, most Kaws range between 9-10mm actual lift.

I then measure the test spring on my Rimac at both 25mm, a good reading is between 35-40lbs. of pressure at closed(INSTALLED) height, and about 110-112lbs at fully open, height. Unfortunately Rimac machines cost about 695 dollars, not cheap. You would be amazed at the # of springs I find good at installed height but bad at open! Once you know what your new test spring measures out at you then measure all of your old ones. SIMPLE HUH! These figures are published NOWHERE, and you cant trust free length measurements. I have found those that measure good, but fail on the Rimac. Most good machine shops have Rimacs.

Since I have given away a lot of my good tricks on this site so far, here’s one more.

In almost every case, intake cams lift higher than exhaust. SO, after measuring all 16 springs, I put the strongest ones on the exhaust side, WHY? because the exhaust doesn’t open as far as the intake, so it doesn’t have to fight the additional spring tension that gets greater as the lift increases. Doesn’t take the extra power from the crank!! NEAT HUH? And as long as they are all in spec it doesn’t hurt having the weakest ones on the intake, which lift farther, fighting the spring tension.

Obviously it takes a ton of power off the crank to fight these springs, which explains why Ducatis make so much more power than you would think they should. THEY HAVE NO VALVE SPRINGS. Well sorta, they actually do use a small spring to insure the valve seals tightly.

If you’r unsure, just buy all new ones, but get this. I had some one bring me a 1990ZX-11 head with 45,000 miles on to do a valve job and he brought new springs. ALL of the old springs checked good on the Rimac and some exceeded the specs of the new springs! So you just never know, My thinking is Kawasaki later in years decided they could squeeze a few extra ponies out of a later Model ZX11 with weaker valve springs that were still strong enough to do the job. In other words they made them too strong in the beginning, but that’s just like Kawasaki!

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