I have had a few emails regarding this subject so I thought I would talk
about it a little and list the ARP number.
Rod bolts in Austins and Bantams are really soft, like a grade 2 or worse. My experience has been you look through a box of rod bolts and select the best ones. You start to torque the bolts and they just feel kind of soft and stretchy so you try and ease it together. This doesn’t work. A 5/16 (.3125") rod bolt should be able to torque to 20- 25 ft lb. If you have stock bolts you will be lucky to get 15-18 ft lb. without stripping or stretching them. I would recommend changing them out and use an 8 mm (.31496") ARP rod bolts that fits Honda 1.2 to 1.6 liter. ARP # 208-6001. You can easily torque these to 26 ft lb. You have to ream the rods and caps to 8 mm (just .0024" over) but it’s worth it. I wouldn’t use a stock Austin or Bantam rod bolt in my lawn mower. I think it's worth the time to change them; I have done over a dozen engines and I am very pleased with them. A good machine shop should be able to install them without messing up the babbitt. If you’re going to send them to someone I would recommend J & M Machine in Massachusetts. They do great work. Click here for their web site.
Note: On some engines the ARP rod bolt head can come in contact with the cam shaft. This can be remedied by grinding off (the rod bolt) a small area in which the contact occurs. I recommend that you have all rotating parts of your engine dynamically balanced before assembly. I have only seen this happen on 1940 3 main engines. This is probably due to the longer stroke on a 3 main engine.
Places to find ARP rod bolts
No Limit Motorsports