The BSA A7-A10 Forum
Technical (Descriptive Topic Titles - Stay on Topic) => Frame => Topic started by: duncan32bsa on 06.07. 2010 19:42
-
Hi all,
I have now rendered my 1960 Golden Flash to largish lumps prior to rebuilding it...
I thought I'd check the frame dimensions, particularly as the front seat mount looked like it had been welded in place by someone on a work experience scheme.
I had assumed that the 1954 swinging arm frame drawings commonly available were consistent through the subsequent years, so imagine my surprise when I found that not only were they not consistent, they were several inches out.
e.g steering tube to tank mount approx 12" rather than 14.031". Tank mount to seat mount approx 10" compared to 8 13/32" and tank mount to top rear bracket about 26" rather than 23.781".
So, are they meant to be different and if so, do SA frame drawings for 1955 on exist anyway?
Of course, I could just ignore it and out it all back together but I'd rather know!
Thanks for any help offered.
Gary
-
Measuring along the top tube my 55 and 57 frames both have the same dimensions. Seat mount to tank mount is just over 10''
Regards
Mark
-
Mark,
Thanks for that. It's a relief anyway. It does seem that the SA frame changed in '55 - or the frame drawings posted everywhere are wrong...
Gary
-
Gary -
The first swing arm frames were introduced in 1954 and carried over to 1955, and are stamped CA7. The swing arm pivot was a solid shaft.
In 1956, the frame was changed to EA7 and incorporated a hollow pivot shaft plus other changes to adapt the Ariel-type brakes. Then came the FA7 and GA7 frames in 1958 and 1960, respectively.
That there is no dimensional similarity between the 1954 and 1960 frames is not surprising.
David
-
Wow, here I am, many years after your original post, wrangling with the same frustration!
After starting with likely the same 1954 drawing I was confused -- were the dimensions on the drawing in code, what the heck is going on? Then it dawned on me that just maybe that a 1954 frame is not quite the same as the 1960 frame in my garage. A quick search brought me to this thread and the answer to my question! Thank you!
I'm creating a 2D model of the 1960 frame in a graphics program, to help with creating engine plates, since my 1960 A10 frame is getting a 1969 Triumph T120R unit engine. Converta plates were made for this pairing at one point, but I can't find any and the consistent recommendation from forums is to make your own.
I've attached a cleaned up, transparent background, version of the 1954 frame drawing in case anyone wants it. If my 1960 version turns out I'll post it too.
Thanks again!
Matt
Nova Scotia
-
G'day Matt, *welcome* to the fold.
That was a popular conversion back in the day. A mate down here has a Tribsa. Not sure if it has BSA or Trihard box.
A quick search found this https://tinyurl.com/j6ukrc48
Please go over to Intros and give us your story https://www.a7a10.net/forum/index.php?board=13.0
Cheers
-
Hi Muskrat,
Thanks, it's good to be here! :)
Those are the exact brand of plates I need, except they are for the pre-unit Triumph (more on that in my Intro!).
I'll do my Intro later today.
Cheers,
Matt
-
Except it's not an A10 frame but a B series, judging by that kink in the bottom rail.
-
The original drawing file said it covered "A group, B group, and Gold Star". So could the dotted lines be for the A series, and the kinked solid lines for B? Using that assumption would make sense as the general layout is the same as my frame. However, if the B series was a little more compact than the A, it would certainly explain the mismatch in dimensions.
Matt
-
The basic diagram is for both 1954 season on singles and twins, as well as showing the singles oil pump kink and twin straight tube (dotted) it also shows the different head steady brackets on the top tube - tube for twin and plate for single.
I do not think there is any significant difference in dimensions of the A series frame from introduction in late 1953 until end of production in 1963. There are, of course some structural differences over the years - front engine mounting lugs, steering lock plate, brake rod/brake cable mounting, sidecar lug, stand mountings both centre and prop, steering head brace and no doubt a few more.