Sun Parkes

Dating early Sun Parkes machines from SNs is explained here:
Not sure where I found it online, but thanks to the original poster.

Dating Sun Cycles from frame numbers.

Pre 1934 a frame number only code was used, found either at the lower front of the head tube or nearside of the seat lug. Sun factory records being destroyed this code is not yet positively broken at the time of writing. To date all verified Suns carry either an eight, six or five figure number. However, from earliest days, Brown Brothers, who were the largest wholesalers of Sun fittings, produced frames and complete cycles indistinguishable from factory originals (compare 1902 Brown Brothers and 1905 Sun frame illustrations) except fot the frame numbers. As Sun also sold complete frames and cycles to small shops to affix their own transfers up to the early 30s identifying early period Suns without transfers can be difficult.

From 1930 a rolling letter code similar to their motorcycle system was adopted whereby the first letter of the code refers to the financial year running from 1^st April to 31^st March the following year. This is set out here:

A1934/5 B35/36 C36/37 D36/37 E38/39 F39/40

G40/41 H41/42 J42/43 K43/44 L44/45 `M45/46

N46/47 O47/48 P48/49 Q49/50 R50/51 S51/52

T52/53 U53/54 V54/55 W55/56 X56/57 Y57/58

Z58/59

Second (or last if there are three) letters refer to frame building shops and appear as one of the following: C/D/E/F/H or P/R/S/T/V/W. Parkes lightweights usually carry I or L.

Letters are sometimes missed or transposed but this usually takes the model so far out of known production period as to make it apparent. (EG HV 1562 on a Sid Patterson only available in 1952/54 and which therefore cannot be 1941) In three letter groupings, mostly found post 1940 the middle letter, often S or W, may have been used to distinguish Super Vitesse and Wasp models from similar framesets as the code is most often found on these models. Different letters and numbers sometimes found on both seat lug and rear dropout and in this case it is usually the latter which bears the correct one.

Tandems 1927/1958

As Sun were major suppliers of tandem fittings to both large and small manufacturers tandems which show only number codes without original transfers and letter codes without original badges are rarely actually Suns.

1959 onwards.

It is not yet certain whether the code restarted from A in 1959/60 but some Z and B codes, albeit with three letters, are found on models only in production late 1959/62. This gives us the following codes:

A64/65 B65/66 C66/67 D67/68 E68/69 F69/70

G70/71 H71/72 J72/73 K73/74 L74/75 M75/76

N76/77 O79/80 P78/79 P78/79 Q79/80 R80/81 S81/82

T82/83 U83/84 V84/85 W85/86 X86/87

Following careful matching with catalogues, transfer styles and specifications no models have yet been found which do not fit this dating list. However some Worksop Suns adopted long number only codes (EG 156202 - 32270) which are at present still mysteries.

Later Worksop frame numbers are more often found on the bottom bracket shell or at the top of the seat tube, sometimes with the year code letter as a separate offset stamping. 

A useful starting point for vintage Sun/Parkes fans?? 

Here is one of mine...

...during refinish. A Sun. Lovely vintage machine eventually.