Install a used head gasket and the cylinder head.  Torque the head nuts.  Turn the engine through several rotations, then take the head off and measure the thickness of the lead wire.  In my case, the thickness of the lead wire and feeler.  I got .038”.  Pretty darned close to the target.  Good enough.

Armed with a bunch of data, we can go to the RB Racing website and use their calculator to see what the actual static compression ratio will be.  The magic number is 10.42:1.  That’s pretty high.  Hope the local refinery can keep me out of the detonation zone.

Make sure the ring is square in the bore when you check the gap.  The edges of the butt should be parallel.

I mentioned earlier that the piston does not have an orientation arrow.  You must measure the valve reliefs to determine which side is for the intake valves and which side is for the exhaust valves.  The intake relief is 63mm wide.

This piston runs very close to the head, about .150” closer than the stock piston.  It is mandatory that valve-to-piston clearance be checked.  Web specifies a minimum clearance of .080” for the exhaust valves and .050” for the intakes.  Other experts are more conservative, .100” for the exhaust and .080” for intake.
 
I am running the Web 340b cam in this engine.  It has more TDC lift than any of the other readily available cams (.143” Int/.092” Exh).  I found that the combination is unforgiving.  To meet the minimum clearance specs the cam timing had to be exact.  The slightest bit of advance or retard resulted in the clearance dropping below minimum.  Advancing resulted in the intake valve getting too close, retarding resulted in the exhaust valve getting too close.  It had to be spot on to meet the minimum clearance spec.  No playing around with cam timing on this combination.  I ended up with .06” on the intake and .08” on the exhaust.

You can check the valve to piston clearance with modeling clay.  Install the piston and cylinder with the correct thickness base gasket.  Degrease the top of the piston and apply modeling clay in way of each valve.

Now install the forward cam chain guide and cylinder head with a used head gasket.  Properly torque all the head nuts.  Install the cam, cam sprocket, cam chain, rear chain guide and tensioner.  Set the cam timing.  Make sure the factory marks line up perfectly.   Rotate the engine through several turns and make sure the factory timing marks align perfectly each time you stop at top dead center.

Once you are confident that the cam timing is just right, install the head cover with rocker arms.  Adjust all four valves to .004”.  Now carefully rotate the engine in the normal direction of rotation (clockwise viewed from the right side).  If you feel anything that might be contact between valve and piston, STOP.  Figure out what’s wrong before you continue to rotate the engine.  If it rotates normally with no indication of contact, continue to rotate at least four revolutions.  Then remove the cylinder head to inspect the clay impressions.

Use a small knife to cut through the center of the clay impressions.  Dip the blade in water to keep the clay from sticking.  Use light pressure so as not to mar the top of the piston.

Here is what the intake impression looked like after cutting through the clay.  It gives a clear picture of how close the valve comes to the piston.

A small drill bit with a short section of plastic spray tube from an aerosol product works good for measuring the thickness of the clay.

You also want to check the radial clearance between the valve OD and the piston relief.  I don’t have a spec but .05” seems reasonable to me.