Not to rain on your parade, but you MUST tear down that engine and clear the oil passages and sludge traps in the crankshaft before further running. Don't ignore the advice you have received from numerous other experienced owners. Ignore this and you are almost certain to end up as I did.. I forged ahead based on the P.O.'s assertion that he had rebuilt the engine 10 years ago, but supposedly only 1000 miles of operating. In less than 3 months, I wound up with a broken rod, and ultimately $17,000 US in expenses for engine rebuild expenses. (well beyond what I paid for the complete bike!)
The absolute CHEAPEST thing for you to do at this point (if you don't feel capable of doing this yourself), is to hire a professional to disassemble your engine, clean and enlarge the sludge traps and passages. Failure to do this is almost certain to result in disaster!
Many experts opine that 60% of all Square 4 engines have suffered a catastrophic failure due to oil starvation!
Phil Auldridge Austin, Texas - USA
Visit the North America Ariel forum: http://arielnorthamerica.org/phpBB3/
53 SQ 4 MK II, '72 Norton Commando, '78 BMW R100/7, '79 Honda CBX, 2014 Indian Chief Vintage