Hi, as can be read in another thread, I blew a rod bearing crossing the high bridge part of Great Belt bridge at relatively high speed (55 - 60 km/h - 35 - 40 mph). Now I have opened the bottom of the engine and identified it is cylinder #3. But what I have also revealed is, that there is no hole drilled in the bottom of the rod bearings and neither dippers. I am aware of that both is something done and installed later, but probably a good idea when you sometimes have to drive your model T at high way speeds (the Great Belt Bridge is in reality the only way to cross from east Denmark to west Denmark and is a highway).
Now how big a hole would you drill in the lower part of the rod bearings? 3 mm/0,12"? 4 mm/0,16"? Larger? Smaller?
I do my rebuilds at 5mm.
I drilled mine 5mm and fluted that hole slightly in the bearing surface. I also drilled a 3mm hole on top the bearing curve in the rod web area and fluted that hole on the flywheel side of the rod.
I was going to post 4mm, but I agree 5 would be ok too. I have drilled them 1/16 inch. I don't know how that compares to 4 or 5 mm.
If you're going to use 30 weight roofing tar instead of 5-30 or 10-30 motor oil you'd be better off to drill the oil holes in the caps to a quarter inch.
Ok, 1/8 inch.
I always add the dippers on a rebuild. I put a flat washer under each end of the dippers to make them set better against the rod caps.
3 mm I think is approx 3/32 or 1/8 for us stateside boys
The rods we have built we use 3/16 on each side of the web, like the Model A.
The T caps have to have at least 3/16, and 1/4 would not hurt.
Model A caps have a 1/4 hole in the dipper.
The Chevy 4 has a 3/16 hole in the cap. and a 1/4 inch hole on each side of the web.
A 216 Chevy has a 5/16 hole in the cap, and 5/32 in one side of the web.
A Model T engine oils well and will run 35-40 mph for extended periods just fine. If something fails it is usually the crankshaft. That has been my experience. I suspect your rod failed because of poor fit due to looseness or a twisted rod. Adding holes and dippers may improve things but I don't think your #3 rod failed because it did not have them.