21A rods set up on a 4" Merc crank

[Bored&Stroked]

I sent you an message response . . . it should help with your questions.

One thing to note is that the bearing MUST float - easily. This requires that you "tune" the bearings to match the crank/rods. You'll want a total clearance of at least .002 . . . up to .0025. With a good oil pump, it is better to be loose than tight. As noted, you need to measure the bearing thickness in order to compute the total clearance.

I'm sure you've seen my Youtube video on the manual procedure to tune/polish the bearings so they float.

My preferred bearings for a 4 1/8 stroker are the Cadmium-Silver variations . . . usually titled "Truck and Bus" from Ford. They are a much softer material than the harder bronze ones and don't wear the rod journals as much as the more common bronze variants.