sbc valve measurement help?

Question

When I measure  the change in my valve spring height from closed to open it says it's much less than the cam advertised lift, I am using a digital caliper and measuring from the top edge of the spring to the seat at both heights.  What could cause this, or am I just doing it wrong? 
The cam is in good shape, no flat lobes it measured correct when installed.  All of the springs are measuring like this, could it be my pushrods or rocker arms?? 
Thanks in advance

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Measure the pushrod side if you can.  That should reflect the cam lift better than the springs.  Still way too short?  I am assuming you are finishing up a rebuild and maybe the lifters are not pumped up yet.  You should be able to pump up the lifters by cranking the engine with a full oil pan.  Even a few dozen turns should make a change in the lift height.  You don't say if you have hydraulic or solid lifters or even a roller cam so it is hard to make a good judgement.  Wrong push rods will show up quickly as improper wear on the rocker arm.

? · Answer

You have two different measurements going on here.  Lobe lift, then you have to factor in the rocker arm ratio which could be one and a half times more, or 1.6 times more.
Up date:  Do not crank engine just to get a measurement.  If this is a new cam you will wipe the lobes.

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It's because you're depressing the plunger in the lifter body. AS Bob said, use a solid lifter for this type of measuring. A solid flat-tappet doesn't have the plunger mechanism.

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Yes, it could be your rocker arms or your pushrods.  It sounds to me like you are doing something wrong.  It is very, very hard to believe that each and every cam lobe measures the same amount of lift loss.

? · Answer

It is your hydraulic lifters, they need oil pressure in them to work properly. use a solid lifter for measurments

sbc valve measurement help?

5 Answers