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Yes, the Biturbo is an interference design. Heads off, rebuild top end of engine. Not cheap, or fun. Setting tappets using valve stem shims ( tiny cups of various thicknesses) is an art. If you get it wrong. the noise will cause the computer to dump boost, and the car runs like crap.
Edit: very interesting design with 2 intake valves, one small, one large, actuated by a single cam lobe.
Last hijack, I promise... My very first car was a 1972 Fiat 124 Sport Coupé... which had "shim over bucket" valve clearance compensation. The BiTurbo obviously has, per Oishi, shim under bucket design, like DOHC 4 cyl Alfa's do. The shim under bucket Alfa design, well the one on the intakes of the sohc Busso V6, are very slow to get 'outa adjustment. But the sheer brilliance with that design on the Busso is that the timing belt/sprocket does not have to be disturbed, with removal of the intake cam, {to effect a change of shim (s)}.
 
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