[Dave in MN]

I have assembled upwards of 180 engines with inserted rods supplied by Antique Engine Rebuilding (AER) and of those, I have run about 100 of them on an engine dyno to break them in. What I have learned from this work is that rod clearances need to be between .0015" and .0018" based on the methods I use to check assembly clearances. Much over .0018" and a slight rod knock may start after 2 hours of running/break-in. With over .002" clearance it is most likely to develop a knock during the break-in. I have not tried less than .0015" during assembly and at that clearance, I have not had a bearing failure due to lack of oil clearance at a rod bearing.

The suggested final rod bolt torque is 35# for AER and Snyder's insert bearing rods. If torquing to 45# there is a risk of twisting/distorting the rod cap. This twisted condition may also cause a rod knock.

When checking rod journal diameter during assembly, I find that a mid-range journal size within the rod and bearing manufacturer's stated spec. provides the clearances I am looking for.

For loosening the fit on the tight rods, I suggest taking the crankshaft to a crankshaft grinder and have them polish the journals until you obtain the proper fit. Most shops will have a motor driven abrasive belt polisher to complete this adjustment. I have had this process done a couple times prior to purchasing equipment for my Sunnen precision pin hone to adjust the fit. I hope it all works out well for you.
Good Day!