Hi Fellas   Trying to save this std bore 312. Bought this and 4 or 5 others in early 80s. Was looking for a std bore 312 for my 56 TB. Most of them were freeze broke. Finally found one with wrist pin gouge that I used. I saved this one, has a dent in deck (web area) where push rod go thru, 4 missing caps and number 2 main threads stripped. I check for cracks when I took it out of hot tank. Any body have opinion for thread fix or just let it go. Bill  Oregon

Hi Guys  Thanks for advice. My first thought was a insert of some type. My main cocern was oversizing boring bolt hole for 1/2 inch insert would weaken the block where cap seats. Ted, did you suggest using a 7/16 insert and bolt? Thanks

Keep it original; ½ -13 thread size for the Helicoil insert.  The Helicoil inserts are available in different lengths so use longer when possible just for additional thread retention.  Because this is a 312 and not a 292, I’ll suggest using a Helicoil insert rather than a Tyme insert as less material will be removed from the block in which to install the insert.  The amount of material at the edge of the main bolt hole on a 312 is marginal so minimizing the amount of material removed for a thread repair is recommended.
 
The Tyme insert will require an 11/16” drilled hole before tapping to the required ¾-16 outer thread size.  The Helicoil requires a much smaller 17/32” drilled hole before tapping the hole with the supplied Helicoil tap.

Lorena, Texas (South of Waco)