I was gonna say this so you dont risk cracking a valve or piston but i prefer compressoranother trick to change valve springs is to feed rope into the spark plug hole when the piston is near the top to hold the valve closed.
What is everyone using for compressors I have an engine on a stand and I have a compressor for heads that are off but it wont work? I saw some ls1 compressors on ebay http://www.ebay.com/itm/LS1-LS2-LS3...Parts_Accessories&hash=item2c6506be1e&vxp=mtr does anyone know if this would work?