How do I go about this. I know I use some sort of clay but is there a guide or post somewhere that I haven't found yet? Yes I used the search button but I was haven't found the actual method yet. Thanks for any help.

 

What are you changing, cam and heads or cam only. This may determine the easiest way to check.

 

I am changing heads & cam, along with multiple other things, but these are the main ones.

 

The short version of using the clay method is you put a small amount of clay/play dough on top of the piston. Put the head back on, secure it with a few bolts, install valve train on that cylinder then SLOWLY turn the engine over clockwise. Take everything back off, cut the clay in half with a razor blade and measure how thick it is with feeler gauges or the back side of a caliper. That's your PTV.

I think most people including myself use regular play dough. If you use the light weight checker springs you can use a regular lifter. If you don't use the light weight springs its best to use a solid lifter or a hydraulic lifter that has been modified to be a solid lifter.

Establish the correct pushrod length first. If your pushrod length is too short or long it will effect your PTV so it's important.

Personally if you are going to use the clay method I perfer to use a head gasket for testing purposes. This is the reason why. Your head gasket will probably be anywhere between .040-.051 thick. Which is going to play a part in your PTV. Remember stock LS1 pistons are "proud" or stick out of the block a little bit. Honestly I don't see how you couldn't use a head gasket on stock pistons because I would think the piston would hit the head but I have heard people do it, maybe they had aftermarket pistons.

If you don't use a head gasket you are automatically going to loose that .040-.051. If you turn the engine over by hand and feel the valve hitting the piston you know you don't have enough. But how much more do you need? There is really no way to know. If the engine does turn all the way over when you measure your clay thickness you will add the thickness of the head gasket to that and that's your PTV.

If you use a degree wheel and checker springs to check PTV you can get away with not using a head gasket because when you pushdown on the valve you can see by the gauge exactly how much you have and can add the head gasket thickness to that.

If you use a degree wheel start checking PTV from 15 degrees BTDC to 15 degrees ATDC in 5 degree increments.

I hope this made sense. In my build thread I think I took pictures when I degreed my cam. I can try to find it if it would be of help. I used a degree wheel and dial indicator.

Jason

 

I was just about to post this question. Thanks Jason for helping me understand the correct way to check PVC.

 

use a light "checking" spring so it won't colapse the lifter plunger. Don't put on too much clay, use fresh clay that is very flexible, and put some light oil on the top of the clay where the valve will hit so the clay doesn't stick to the valve. Or you can just use the indicator