Originally Posted by old 94 gmc
So you think that changeing the spring would be best ?
It's not just a spring problem. It's also a problem with the bottom of the stock retainer contacting the guide seal/guide at lifts exceeding stock.
When choosing springs and retainers for any camshaft other than stock, you have to consider a safety margin. Most cam grinders will suggest 1/16" to 1/8" (0.062" to 0.125") retainer to guide/guide seal clearance at full valve lift and will also recommend a minimum of 0.050" between the spring coils (0.010" minimum measured at the five places between the coils for a total of 0.050") to prevent coil bind at full valve lift. It has been published in several places and evidenced by the figures posted by Cobalt here in this thread that the max valve lift with a stock L31 camshaft is ~0.430".
I think what has happened is that some hot rodders have assembled the L31 heads with valves, keepers and locks without springs and found that the travel before the bottom of the retainer strikes the seal is maybe ~0.480"-0.500". Not taking a safety margin into consideration, they have concluded that you can run up to ~0.500" valve lift with the stock retainer/lock arrangement. This bogus information has, of course, been passed from one enthusiast to another until it has become gospel. Maybe it has even filtered into the ears of a cam grinder tech guy who believes it.
Others have concluded that they can include more lift AND A SAFETY MARGIN by grinding the bottom of the retainers for more clearance between the retainer and seal. This is called a "ghetto grind".
So, it's not just about changing springs, it's also about grinding the existing retainers or using aftermarket retainers that will allow enough clearance retainer to seal at the production installed height.
When mixing and matching retainers and locks, caution must be used to insure that the tip of the valve extends above the top surface of the retainer if you are going to retain use of the rail rockers. If you get your combination together and the sides of the rockers touch the retainers before the middle of the rockers contact the valve stem tip, you are going to be in trouble because the rocker will unload the locks. You have your choice of 3 different configurations of locks.... standard, plus 0.050" or minus 0.050" installed height that will place the retainer where you want it in relation to the valve stem tip. Changing installed height will also, of course, change the installed and operational spring pressure, so you have to work that out to insure that you have correct pressure and also correct retainer/seal clearance for the camshaft profile you're using.
The stock spring is retained laterally by the large O.D. of the guide, so you don't have enough room to run a decent spring in the first place in my opinion. The best fix is to cut the diameter of the guide and the spring seats to allow use of a decent spring. At the same time, I would cut the O.D. of the top of the guides for a PC seal (0.530") and trim the top of the guide to allow proper retainer to seal clearance at full valve lift (0.062"/0.125"). I would also cut the rocker stud pads and tap for screw-in studs and guide plates to get rid of those fosdick rail rockers and use conventional stamped steel rockers or a good aftermarket rocker with roller trunnion.
In closing, L31 heads do flow very well in relation to other production cast iron heads, but they are not without their bad points. If you are not equipped to do these alterations I have outlined and must pay retail to have them done, you may be better off choosing another cylinder head from an aftermarket manufacturer that is set up and ready to go.