At 535 grams, the flat-top is 35 grams heavier than the stock piston.

The flat-top uses Wiseco ring set 3819XS.  No wire guide in the oil ring expander.

The bigger bore requires a special head gasket.  The stock gasket hangs over the edge of the 97mm cylinder.  I don’t recommend trying to use a stock gasket.  Copper Gaskets Unlimited (CGU) in Phoenix, AZ can provide the correct head gasket for the 97mm bore, and they also have a variety of thicknesses.  Lani at CGU gets these gaskets out quick.  Please don’t try and use a stock head gasket with these 97mm pistons (especially the flat-top).

The copper head gasket is not nearly as forgiving as the stock multi-layer steel gasket.  The head and deck surfaces must be perfectly flat.  On the 97mm pop-top build I wasted a lot of time resolving oil leaks.  Take a look at the Big Bore Engine Project Part 6.  It provides a lot of details on my gasket fiasco.  On this flat-top installation, I had zero problems with oil leaks.

For the flat top piston, deck height is critical.  I suggest you try and adjust the cylinder height using the base gasket.  Shoot for “zero”  deck, meaning that the piston is exactly flush with the top of the cylinder at TDC.  Adjust the thickness of the cylinder base gasket to achieve “zero” deck, and then use a .042” thick cylinder head gasket.  That will set your quench clearance right at .042”.  Mockup your engine, take some measurements, and then order the appropriate thickness gaskets.  Just shoot Lani an eMail at coppergasketsunlimited@yahoo.com.

Once the cylinder is in place with the correct thickness base gasket (for “zero” deck), apply modeling clay on the valve reliefs in the piston.

Granted, my intakes are 1mm larger than stock (34mm vs 33mm), but that’s only 0.5mm (.020”) on the radius.  Even with the stock valves, there would not have been enough clearance.

I addressed the clearance problem by increasing the radii on the intake valve reliefs.   I’ll go through the process I used, but keep in mind there’s more than one way to skin a cat.

You can use a 17/64” transfer punch through the valve guides to mark the top of the piston.

Now you have punch marks exactly on the centerline of each valve.

Set up the piston in a drill press or mill.  Adjust the angle of the piston top to the appropriate angle (117° for the intake valves, or 63°depending on how you look at it).

Raise the mill/drill head and install the flycutter.  Then slowly and carefully plunge into the piston top with the flycutter until you reach the depth you want.  In this case, there was more than enough depth, the problem was on the radius, so I just plunged in until I reached the depth of the existing relief.