Production weight of MGA Twin Cam connecting rods could vary widely. Original weight specification was 1-lb 15-oz 6-drams, or 889.5-gm (a dram being 1/16-oz or 1.772-gm), which is just 2.5% shy of 2-lb. Weight variation possible was +/- 1-oz, or 2-oz total range. This is an unacceptably HUGE variation when it comes to balancing an engine. As such, we must be concerned with weight matching for these parts.

Factory specification for acceptable weight variation was a limit of 3-drams total range (5.316-grams). By modern standards that is still a fairly large variation, but it was deemed acceptable for a production engine, back in the day.

Beginning with (E) 1343, the connecting rod design was changed from all of the AJHxxxx numbers to these two numbers AEH642 and AEH644 to incorporate a boss at the small end and a heavier big end cap to facilitate balancing. In other words, they were then providing the lump of metal at each end intended for grinding down for the weight matching process. This then required only one right hand part and one left hand part to replace all of the prior part numbers (no longer supplied in weight match sets).

Refer to the following Confidential Service Memoranda for complete factory details: MG-231 - MG-236 - MG-252 - MG-262

Also see TC-307C for more engine information.

     From the Twin Cam Service Parts List:
	CONNECTING RODS AND BEARINGS:
Part No  Description
AJH5307  Connecting rod and cap +2 (Nos 2 and 4 cylinder)  -replaces standard +1, +2, +3, +4, +5 -Fin.(E)1342
AJH5313  Connecting rod and cap +2 (Nos 1 and 3 cylinder)  -replaces standard +1, +2, +3, +4, +5 -Fin.(E)1342
AJH5308  Connecting rod and cap +7 (Nos 2 and 4 cylinder)  -replaces +6, +7, +8, +9, +10 -Fin.(E)1342
AJH5314  Connecting rod and cap +7 (Nos 1 and 3 cylinder)  -replaces +6, +7, +8, +9, +10 -Fin.(E)1342
AJH5309  Connecting rod and cap +13 (Nos 2 and 4 cylinder) -replaces +11, +12, +13, +14, +15, +16 -Fin.(E)1342
AJH5315  Connecting rod and cap +13 (Nos 1 and 3 cylinder) -replaces +11, +12, +13, +14, +15, +16 -Fin.(E)1342
AJH5310  Connecting rod and cap 2 (Nos 2 and 4 cylinder)   -replaces 1, 2, 3, 4, 5 -Fin.(E)1342
AJH5316  Connecting rod and cap 2 (Nos 1 and 3 cylinder)   -replaces 1, 2, 3, 4, 5 -Fin.(E)1342
AEJ5311  Connecting rod and cap 7 (Nos 2 and 4 cylinder)   -replaces 6, 7, 8, 9, 10 -Fin.(E)1342
AJH5317  Connecting rod and cap 7 (Nos 1 and 3 cylinder)   -replaces 6, 7, 8, 9, 10 -Fin.(E)1342
AJH5312  Connecting rod and cap 13 (Nos 2 and 4 cylinder)  -replaces 11, 12, 13, 14, 15, 16 -Fin.(E)1342
AJH5318  Connecting rod and cap 13 (Nos 1 and 3 cylinder)  -replaces 11, 12, 13, 14, 15, 16 -Fin.(E)1342
AEH642   Connecting rod and cap (Nos 2 and 4 cylinder) -Com.(E)1343
AEH644   Connecting rod and cap (Nos 1 and 3 cylinder) -Com.(E)1343
  AEH435   Bolt for cap (8) -changed to AEH647 Com.(E)1343
  AEH647   Bolt for cap (8) Com.(E)1343 -was AEH435
  6K881    Washer for bolt (4) -changed to AEH648 -Com.(E)1343
  AEH648   Washer for bolt (4) Com.(E)1343 -was 6K881
  AEC977   Bush -small end (4) -changed to AEC882 -Com.(E)1343
  AEC882   Bush -small end (4) Com.(E)1343 -was AEC977
8G2259   Bearing for connecting rod -big end (standard) (1-set)

On 2/18/2021, Mark Wellard in Australis wrote:
"Just an observation regarding the page above, the list of weights for the Twin Cam seems somewhat limited. The markings on my car are +26, so there must have been many more weight options than shown in the literature". -- Mark

For installation of connecting rods in the Twin Cam engine see TC-307C

Addendum Jan 31, 2022:
Photos at right compliments of Michael Anderson in Australia. Photo at left compliments of Dirk Van Ussel in Antwerp, BE.

Early style (right) and later style (left). Notice the "ears" on the small end extra extension on bottom end allowing extra materinal for grinding down for final balancing before installation.