OK you said the D21T has a machined piston from billet is the billet forged billet? The reason I ask is being a motorcycle mechanic and machinist for over 35 years I know the forged expands more then cast. When I bore a cylinder for forged pistons I have to fit them up looser then cast. Never had a STS D21T but do have the STS D21B and the 28, which I have not even taken out of the box, yet as I am so tied up racing my buggy. To start a D21T for the first time must have to hook two car batteries in series to get 24 volts to get the start box to turn it over. After over 3 gallons on my D21B with a chrome top Ofan 12 volt with the one big electric motor have to loosen the glow plug to get it to turn over when cold I would hate to think what it takes to turn the D21T over. [X(]