CONNECTING RODS (early MGA Twin Cam)

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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