Some time ago I bought, at a local swap meeting, the lower half of a Howard Junior engine, mainly because the big end was in reasonable condition. As far as I can tell these big end bearings are now no longer available.
At home I found that the oil hole leading to the big end through the timing side hollow mainshaft was blocked. Whenever I start work on a Howard engine I first check this by forcing oil from a pressure oil can into the hollow timing mainshaft and see if oil comes out around the conrod big end.
Because of the blockage I dismantled the crankshaft and found that the big end roller bearing had been installed back to front, this blocked the oil way to the big end bearing. Fortunately, the bearing looks OK, still packed with grease. This meant that the engine had only run for a very short time after assembly.
The major problem is that the parts and instruction books I have make no mention about this. Even if you inspect the bearing, it is very difficult to tell which way it must be installed.
A major defect with the Junior, 8Hp and 12Hp Howard engines is the way the oil system is set up. An oil pump forces oil from the oil tank into the big end bearing via the timing side hollow mainshaft. A second oil pump sucks oil from the crankcase bottom and lifts it back to the oil tank via a filter.
This means that whatever is in the oil tank is pumped into the big end bearing - this includes dirt, grit and foreign material. The oil ways are very small and easily blocked which prevents oil reaching the big end bearing.
The only way to clear the blockage is to dismantle the crankshaft and clean out the oil ways, then reassemble and line up the crankshaft.
For a long time I have thought that blocked oil ways was the major cause of most of the Howard engine blow-ups, that were very common when these machines were used commercially.
The big end roller bearing appears to be a standard industrial type specially modified for use by the manufacturer for Howard.
Dismantling and assembly of these crankshafts is a job for specialists who have the right equipment and can line up the crankshaft correctly.
To prevent foreign material blocking the oilways, I fit a car type oil filter between the oil tank and the oil pump that forces oil into the big end. Holden, Ford or Toyota oil filters are cheap and not hard to mount on the rotary hoe frame.