These are the bolts for big end bearing caps on connecting rods for Twin Cam engines. Please review the prior page TC-307C for con-rod weights and balancing.Note that there was a change of design off the con-rods and big end caps to change the method of balancing, changing from matched weight selection to grinding the ends to match weights. This resulted in thicker big end caps requiring longer bolts.

     From the Twin Cam Service Parts List:
	Big End Bolts and Locktabs: 

Part No    Description
  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 -locktab (4) -changed to AEH648 -Com.(E)1343
  AEH648   Washer for bolt -locktab (4) Com.(E)1343 -was 6K881

This issue came up when someone purchased ARP bolts, then discovered they were a size match for the factory later style longer bolts, too long to fit the early style con-rods.

ARP bolt kit

Early and Late big end caps

Late and Early con-rods

Differences of bolts

The early caps are shorter, later caps longer. -- The early bolts have tapered nose, later bolts have flat ends.
The ARP bolts (center in the last picture) are close match to the later bolt dimensions.
When used with early style rods, the ARP bolts bottom out in the tapped holes before coming tight under the head.
To use the ARP bolts with early style con-rods, either grind a taper on the bolt nose, or use a hardened steel flat washer under the bolt head .