This seems like pretty good info, thanks! I have a DU XXXX serial number, where do I find out what each individual number means? I bought the bike in 1975 already modified into a chopper, but I'd like to know what model it is, Tiger, TR6 or what. Thanks again for any info. The bike hasn't been on the road since the late '80s and even tho' it was completely trouble-free for the 13 years I rode it, I would like to do a total rebuild before putting it back on the street. Thanks for any help!Here's a site with the numbers for you:
I think you may have a 1969 500cc frame with a 73 motor.
And people say the the Speed Twin engine is little more than two Val Page L2/1 single engines side by side. This would take you back to 1931.The amazing thing is that the "grandfather" of the Bonnie was the '37 Speed Twin which for all intents and purposes, is the SAME engine.
You could also add the Terrier engine by Turner (53?) which gave rise to the Tiger Cub, the BSA C15 and its single cylinder descendents which went through to end of BSA, a span of 20yrs.I only go back to the Speed Twin, because of the arrangement of the cam drive and shape of the timing chest. It's virtually identical to the last '62 pre-unit which then went unit through the '83 spec