I went to change my valve seals today in my LS3 GS vette. I was removing the spark plugs and pumping air into the cylinder to keep the valve up. When I got to the 3rd spark plug on the passenger side air sounded like it was going straight through the crank case. I did a crank compression that registered 150 psi and did a leak down test that came back good. So I went to put air back into the cylinder to keep the valves up and again it sounded like air was blowing right through the engine. I have the tool that allows me to change the valve springs without removing the head and every time I compress the spring even with the air going into the cylinder the valve goes down with the spring not allowing me to get the separation to remove the keepers. does this mean that I have a bad head or valve. Is there anyone out there that has had this problem

 

Piston at TDC?

 

not sure, I have so much crap in the way of the crank I may have to pull the fuel and ignition coils and turn it over until I hit TDC. I thought it didn't matter if I put air in the cylinder

 

It really doesn't matter if TDC, but might want to move the piston up or down and re-check to see if that makes a difference. When you did a compression test on the #6 did you check to see if the pressure held for a bit? I assume you still have one of the valves in the cylinder still installed.

 

If you have good compression, I doubt there is anything wrong with your heads or piston rings. Not really sure what the problem could be.

I would recommend NOT using compressed air to hold up the valves however. Still too high possibility of dropping a valve and for what ever reason this is not working for you.

I would use the TDC method. With this method you turn the crank until a cylinder is at TDC (which will put another cylinder also at TDC) and you change the valves 2 cylinders at a time. Then you rotate the crank 90 degrees and do two more, etc.

You turn your motor using a large socket or wrench until one piston (usually #1) is at TDC (piston all the way to the top). Verify that the piston is indeed at the top by inserting a wooden dowl into the sparkplug hole. At TDC the dowl won't go in very far. Now you change the valves on #1 cylinder and #6 and the valves can't drop no matter what. Then you rotate the crank 90 degrees and change 8 & 5, rotate 90, 7 & 4, rotate 90, 3 & 2. Just make sure you verify that which ever cylinder you are working on is at TDC by inserting the dowl in that cylinders sparkplug hole. Make sure the dowl is long enough so that if the cylinder is not at TDC, the dowl can't fall in the cylinder.

Just do a search for the proceedure as I may have left out some details (going by memory here).

 

If cylinder has acceptable leakdown head, rings, piston, valves ....etc are ok.