I will be doing a cam swap very soon, almost all the parts are here. I had just a general question when doing the spring swap.

http://www.thunderracing.com/catalog/summaries/s105.jpg

I know you put it inbetween the the cylinder head and put the retainer on top of it. But do we really need the check the height?? I dont want to buy un-needed tools. Can any of you cam installing experts give me some insight.

Also should I go through buy a push rod length checker tool? The heads have been worked over and decked. But the pushrods in it now have been fine with the hotcam, but now im going to a bigger cam and i was wondering if this is needed too.

I understand most things but im a little clueless about this.

 

You should know the installed height before installing the springs. You don't need to buy that tool, I have a couple of those you pictured, but never use them, I use snap guages and a calipers. You can get a thousandths steel ruler for less than $5 that will eye-ball you withen .030". Get the installed height, then calculate based on spring rate your seat pressure and open pressure, look for 115-130# seat, 295-320# open.

Your stock pushrods will be fine as long as you have not changed cam base circle, head castings, or valve length.

 

If your valves are stock ya got a 1.750 installed height + whatever the valve job gave ya maybe .010-.015

 

So is the purpous of this guage is to make sure your spings are all correct, and matching? I guess thats more to the point of the question.

 

I'm a fan of the barrel mics for checking installed height since it's going to give you the closest reading to what the springs will actually be installed on the heads. You can do it the way MachinistOne suggested if you have those tools.

A lot of this depends on how accurate you want to be.... I set heads up to have the installed height within .010" of each other, so that later on if I have to swap a set of springs in the heads I don't have to remove the seals and recheck installed heights.

The installed height can easily vary valve to valve due to spring pad heights and VJ depths. A really good valve job will have the valves all within .001 or less. This leaves only the spring pad as a variable and on aftermarket heads it's rarely a problem.

As for the PR length checker.... This is also a good idea. I just noticed on HP TV today that they just put in a +.100 longer pushrod because their valves were +.100 longer.... just blows my mind. Forget that the increased lift of the cam will make the base circle smaller, or the rocker arms can change the PR length, or heads etc....

All depends on how accurate you want to be, and if you want to know that it's right or always wonder if that's a issue with your setup?

Yes, to make sure you have them installed at the proper height.

Bret