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Bonneville T120 -69. Why do the primary oil disappear? Now in the beginning of the driving season I´ve just changed primary oil. Same oil as earlier, Castrol GP 10w-30. As we know it needs 0,35 liters. After one kilometers run almost all has gone out from the breathing tube. Light brown as milk chocolate. Only a half 0,05 liter left. What´s wrong?:confused:
 

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You need to open your engine covers (including timing, primary & transmission), open the sump drain plug, drain the oil tank, drain the transmission from it's drain plug.

Next, thoroughly clean everythjing you can reach under the covers you've removed.

Then, flush EVERYTHING out with solvent, then flush with clean lightweight (10/20) oil.

Lastly, top everything back off with proper lubricants.

Blowing oil / residue out your vent pipe after that may indicate mechanical issues which can include worn rings and broken or missing timed breather disc (requires splitting the main engine cases).
 

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A '69 primary is unvented ... primary and crankcase are wholly separate before '70 ... My guess is either a bad seal somewhere (crank seal ... maybe the engine wet-sumped and blew it out) or just a bad leak. Either way, you seem to be losing it pretty fast ... wish I had more of an answer for you ...
 
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