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Engine Serial Number

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I have two Ossa engines, one frame that I believe to be 1972 250 MARs. There is no number on the frame, but the engines numbers are: M-345710 and M-343770. The limited information I can find anywhere show only numbers beginning with the letter B. Any information anyone has would be helpful for when trying to find parts. Thanks.

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Thanks, Mick. Am I correct in assuming that when new, the motor number and frame number matched? If so, that clears up the confusion on my end. Thanks again.

34 sequence is a MK1 MAR from 72/73 and as Mick mentioned M prefix = motor, B= frame.  The MK1 didn't have the number stamped on the frame, just a sticker on the headstock which is usually long gone. From the factory the engine and frame numbers matched so if the engines are original to the bikes, they will date your bikes. The MK1 had plain hubs, flat bottom forks, shorter swingarm with shock mounting right over the snail cam stop

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