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CONNECTING RODS, early MGA Twin Cam - AJH5307
BMC part numbers: AJH5307, AJH5308, AJH5309, AJH5310, AJH5311, AJH5312,
AJH5313, AJH5314, AJH5315, AJH5316, AJH5317, AJH5318 -all Fin.(E)1342 Twin Cam
Later replaced by: AEH642, AEH644 -- Com.(E)1343 Twin Cam,
Also used as Special Tuning parts for pushrod engines.

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 (then part 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. Factory parts were provided in weight match sets (within 5-gm). Ordering parts in complete sets, or by ordering a part in the correct weight range, weighing was no longer necessary (unless you wanted to get closer than 5-gm weight range).

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

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 AJH5311 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)

AEH642 and AEH644 can also be used as Special Tuning parts for pushrod engines when full floating wrist pin is desired.

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

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