The older TT 07 GP engine has bronze bushed bearing with purple anodized head. But the fit between crankshaft and bronze bushing are a bit loose fit as new engine.. Do not affect leakage since the engine get enough oil to seal between crankshaft and bronze bushing.

My engine has cylinder head in steel with contrapiston in steel with O-ring. The purple head are a ring retainer for the cylinder head.

The engine are running well as a diesel engine, much better than running as a glowplug engine.