OK, I have some data on the long-term effects of Lucas Semi-Synthetic 2-Cycle Oil, rated TC in Trabants Fuel used: Pump gas available in the Chicago area, generally American rating 87 (R+M÷2) octane, with 10% alcohol. Strong preference for Citgo brand. Fuel/Oil ratio: 50:1 Distance travelled: approximately 65,000km on Lucas oil Engine condition at start of test: Assembled with worn second handed crank with good bearings and new piston rings, broken in with Pennzoil Air-Cooled 2-cycle oil. Driving conditions during test: Mostly high-speed, full power, year round at temperatures from -15ºC to +35ºC. Average trip is around 50km. Test ended when installing a K&N air filter drove the jetting too lean, which combined with a cracked #2 cylinder base gasket, lead to seizure of #2 lower con rod bearing (melted needle retainer) at high speed and mid throttle (downhill at 110-115km/h), 67,000 km since overhaul Dissection of the motor reveled the following: With the exception of molten debris from #2 con rod lower aluminum bearing needle retainer, inside of motor was clean. main bearings and #1 con rod bearings OK Excellent oil film strength on undamaged #1 cylinder and related parts, oil impossible to wipe off without solvent No obvious excessive wear or deterioration of rubber flywheel side crankshaft seal No obvious wear of pulley-side metal crankshaft seal (piston ring type) All 6 piston rings free to move, no sticking at all. All 6 piston rings worn out, with evidence of blow-by. Note: some 2-cycle synthetic oils are known for glazing cylinder walls and rings and causing blow-by with unworn rings. Piston ring end gap: 0km: .25mm 67,000km: 1.4-1.6mm Wear found on the rotary valve mounting holes and the locating dowel pins 2 decarbonizing services were performed Preliminary conclusions: A non-standard motorcycle carburetor combined with "low restriction" K&N air filter cause a generally lean condition, made excessively so on #2 by a cracked "new old stock" graphited cylinder base gasket. This lead to overheating the #2 crankpin at high RPM (4500-5000) and low throttle, which melted the needle bearing retainer. This is unlikely to be the fault of the oil. As #2 cylinder was likely to have been lean for some time, I am ignoring wear and damage to it, attributing it to the base gasket fault. Cylinder #1 is a more valid test. The lean condition existed for a few days only. There is a strong oil film coating all parts. The oil film is resistant to wiping off. This film should offer good protection from wear and corrosion. The general wear is about the same as #2. The rotary valve holes are considerably elongated, and the locating dowels heavily slotted. #1 piston rings are slightly less worn, but still extremely worn at 1.4mm gap. They should have been replaced at no later than 30,00okm under these conditions. The tachometer had been acting very strangely for a few thousand km before the Bad Hair Day. As the points are on the #2 side of the crank, it was prbobably related to the impending failure. With both the hastily kludged together crank and the trabantwelt-supplied one, the tach behaves itself.