Cam, head change

[dodj]

When changing out your cam and swapping in new heads, what is the proper process for making sure your valves don't hit the pistons? How close is too close? How do I measure it?

[1 Wild R/T]

There are a number of methods that give a good result... Probably the easiest is using light springs in place of the standard valve springs...

change out the valve springs, set up the valve train, use a solid lifter & set it to zero lash, set up a degree wheel, (zero TDC) so you can keep a close eye on how much you turn the crank.. Set up a dial indicator so it's straight in line with valve travel then bring the engine up to 10 degrees BTDC & check the valve travel then go to 7 degrees & recheck, again at 4, 2, 0, 2, 4, 7....  Do this for both valves...

A safe rule of thumb is .080-inch for intake valves and .100-inch for exhaust... Plenty of guys run it tighter but you'd better be checking everything on a regular basis...

If your looking at an engine that has higher compression & a big cam which = real tight piston to valve clearance you should check every cylinder... If your running something in the 540 lift or less checking one hole is probably fine...

[dodj]

Hmmm. That's the easiest? First problem I have I guess is non-adjustable rockers and I don't have a solid lifter.
But just so I understand the procedure,
I am checking valve travel with the dial indicator to see if the piston is pushing on it?
Still not clear on how I measure the valve to piston clearance to see if I have the .080 or better. I'm sure I do, the cam is .513 lift and the pistons are stock type TRW 1970 magnum. But I want to learn how to check the clearance anyway.

[734406pk]

Checking the piston to valve clearence can be a little tricky, but it is extremely important do when changing your cam and/or cylinder heads. After you remove both heads, save your old precompressed head gaskets. Measure and record the thickness of both of them. Clean the gasket surfaces on the block and old head gaskets. Install soft test springs on cylinder #1 intake and exh valves. Bring #1 piston to TDC and install the new head with old gasket onto the drivers side of the engine and torque to about 1/2 value ( just to seat the head without compressing the gasket further). Set up a dial indicator on the #1 exhaust valve being careful to have the gauge inline with the valve action then press that valve down by hand until you feel it touch the piston. Record that reading and duplicate the procedure with the intake valve. This is your piston to valve clearence using the current head gasket compressed thickness. The cam manufacturer should post the minimum clearence required. If you are close to minimum, check all cylinders the same way to be safe. You could use a thicker head gasket (maybe)to get in spec but piston notching would be recommended (less loss of compression  ratio). If you can get 2 (int and exh)old rocker arms you can weld some 6" handles to them and use as a tool to press the valves down without using the soft springs. A major timesaver if you want to check multiple cylinders!

[HP_Cuda]

P to V - well there is clay involved, valves, springs and adjustment.

 

[moper]

I clean the pistons (do all four corners - not just one). Stick about 1/8" thick and 3/8" wide strip of clay accross the piston in the valve reliefs, or if flat tops make the strip 1 1/2" wide and lay it accross where the valves go. Hint - it's not accross dead center. Then i clean the chambers and valves and replace the springs with checking springs. Lay the heads on without any gaskets. Snug down a couple head bolts (no need to fully torque). Install the rockers and pushrods. Then slowly turn over the engine at 8 full revolutions. Then remove the heads and cut the clay with a razor to see the cross section and measure. You then add the compressed thickness of your gasket to what you have for measurements.