1. Keri

    Keri Leader

    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.
    Last edited: Aug 11, 2015
  2. radioman

    radioman Premium Member Forum Donor

    Regarding piston ring wear,did it run 67,000km on a new set of rings or were they part worn when you rebuilt the crank
    I'm using fully synthetic at 50 to 1 as I only done 300 or so km so far plugs look a chocolate brown on the insulators & both same color
    Thanks
  3. Keri

    Keri Leader

    The rings were new at the beginning, "0km" of the test period. The ring gaps were set to .25mm or slightly less.

    Running the motor at high rpm and full load on a continual basis is what lead to these results.
    When at less than full load, I generally kept quite rpm high so as to reduce the force on the conrod bearings.
    This was bound to be hard on the rings, and was intended to be relatively easy on an old, worn crank.
    Apparently it was, as #1 conrod bearings seemed about as worn as the day I put the crank in, 67,000 km previously
  4. VADOC

    VADOC Premium Member Forum Donor

    I am using Lucas also ( 40:1) and this is encouraging , not smoking unless under heavy load or after sitting for some tine
  5. turbofiat124

    turbofiat124 Loyal Comrade

    Are you saying running a K&N air cleaner will cause the engine to run too lean? I've been running a K&N ever since I got mine. Although I have only put no more than 5000 KM on my engine.
  6. Keri

    Keri Leader

    I am saying that a motor that had many thousands of kilometers under the same conditions (oko carb, worn crank and rings, cracked base gasket) seized within a week of switching to K&N.
    The filter did make a change to the driveability. Apparently the lower air restriction leaned the midrange to the point where the side with the air leak seized.
    Probably if the base gasket was intact, it would not have seized.

    It's also possible that either the K&N was not filtering well or that the oil it is impregnated with reacted badly with Lucas Semi.

    And of course, it's possible that the crank finally wore to the point where failure was inevitable. This typically happens on #2, which is the side that failed.

    As #1 was still pretty good or at least sorta OK upon disassembly, I suspect the lean out theory.

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