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BONNET DESIGN CHANGE -- BD-121

There was a one time design change for the MGA bonnet in mid production. At first glance it is very subtle, but it is easy to spot when you know what it looks like. When the Twin Cam model was introduced in July 1958 the crown height of the bonnet was increased slightly to clear the taller valve covers. This design change was incorporated into the pushrod engine cars as well to use a common bonnet.
bonnet crown early bonnet crown later
Early flatter bonnet above left. -- Later higher crown bonnet above right.
Early bonnet bracing below left. -- Later bonnet bracing below right.

bonnet braces early bonnet braces later
AFH1525 AFH4880
bonnet braces first change
From Car No. YD1 572, body no. 61001,
the first Twin Cam body shell.
Notice: No notch.

Internal bracing was also changed. The first cross brace was moved farther back, and the proprod attachment point was relocated. The early proprod was more centrally located while the later proprod was attached more outboard. The later model also had two different attachment brackets for the proprod, looking from front (photos above) the pushrod engine cars still had the proprod on the left while Twin Cam cars had the proprod on the right.

Also notice two rectangular brace pieces half way along the sides. This was an intermediate addition done some time earlier. They will be about 8-inches rearward from the front cross brace before and after repositioning of the cross brace. Body number 26535 (about Feb 1957) has these pieces. Please report earlier body numbers that may or may not have these pieces.
Bonnet modifications:
CHASSIS NO:      BRACES  CROWN  PROPS  CUT  ORIGINAL  BODY  NOTES
HDE43   11094      no     LC     1P    no     yes           Dec 1955
HDC43   14151      no     LC     1P    no     yes    24047  May 1956
        14408      no     LC     1P    no                   May 1956
HDH5    18126      no     LC     1P    no     yes    28528  Jul 1956 
HDR33   18273      no     LC     1P    no            28205  Jul 1956

HDR43 18640 yes LC 1P no 28563 Aug 1956 HDA43 20686 yes LC 1P no Sep 1956 HMK23 23559 yes LC 1P no yes 32006 Nov 1956 HDK43 26368 yes LC 1P no Feb 1957 HMK43 26535 yes LC 1P no yes Feb 1957 HDR33 36743 yes LC 1P no yes 47166 Aug 1957 HDT43 36897 yes LC 1P no no 47301 Aug 1957 6/38695/191 yes LC 1P no Australian HMT43 48150 yes HC 2P no (no) Feb 1958 HDA43 48239 yes HC 2P no no Feb 1958 HMK43 48280 yes LC 1P no Feb 1958
HDL43 50093 yes HC 2P no yes Mar 1958 YD1 572 yes HC 2P no yes 61001 Jun/Aug 58 HDR43 50979 yes HC 2P no yes 62245 Apr 1958 HDK43 51954 yes HC 2P no yes Jun 1958 HDR43 53557 yes HC 2P no 64090 Jul 1958 HMT43 53731 yes HC 2P yes 54885 Jul 1958 HDK43 54805 yes HC 2P no 65407 Jul 1958 HMR23 61262 yes HC 2P no 68132 Jan 1959 YD1 1085 yes HC 2P no 68780 Jan 1959 YD3 1395 yes HC 2P no yes unknown Feb 20,1959
HDK43 61798 yes HC 2P yes yes 72638 Jan 1959 YM1 1463 yes HC 2P yes yes 61872 Feb 1959 YD3 1684 yes HC 2P yes T.C. Mar 1959 HDK43 65521 yes HC 2P yes 77995 Apr 1959 HDA43 68623 yes HC 2P yes 1630 May 1959 GHN 71514 yes HC 2P yes yes B3476 Jun 1959 GHNL 80156 yes HC 2P yes yes Nov 1959 GHNL 82000 HC 2P no (no) B14179 Nov 1959 GHNL 82709 yes HC 2P yes Dec 1959 YGHN2 8/93404/903 yes HC 2P yes yes Australian GHNL 97930 yes HC 2P yes yes B29798 Mar 1961 GHNL 98156 HC 2P yes B30183 Mar 1961 GHNL 101564 yes HC 2p yes Jun 1961 103069 yes HC 2P yes yes B35036 Aug 1961 103426 yes HC 2P yes B35270 Sep 1961 108146 HC 2P yes yes May 1962 GHNL2 108923 yes HC 2P yes yes B40605 12-16/May'62
The earlier bonnet part number AFH1525 was published in early editions of the Service Parts list prior to introduction of the Twin Cam model. With introduction of the Twin Cam model, Twin Cam parts were published as a supplement to the MGA (1500) SPL. A separate SPL for the Twin Cam was published later. Subsequent editions of all SPL's for all MGA models lost the part number for the early style bonnet. Since the later bonnet will fit earlier cars, the earlier bonnet may have been no longer supplied as a replacement part.
bonnet batten change
There is a wood batten with felt (originally) or cork (restoration work) top layer in the front edge of the bonnet to serve as support for the aluminum skin while closing and latching the bonnet. This piece is thicker with the later bonnet profile.

There is sometimes confusion about the length of the bonnet. The bonnet opening in the front body cowl never changed, and is the same on the Twin Cam as an all other models. The difference is noted if you run a tape measure over the top of the bonnet from back to front to measure the length. The early flatter bonnet is 47-7/8 inches long, where the later high crown bonnet will measure about 48-3/8 inches long over the top of the crown. The early and later bonnets are otherwise physically interchangeable (except the early bonnet cannot be installed over a Twin Cam Engine).

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