? That doesn't answer my question. HM is using 20w50 in a fresh rebuild on his SOHC. I'm curious why such a heavy oil in a fresh tight engine when lighter weights would seem to me to give adequate protection and tax the oil pump less, in theory.
The Bel-Ray you bought and used also comes in a 10w40. I'd be tempted personally to use that. 20w50 is going to starve for longer periods of time on startup, for one thing.
I'm not here to make any judgments, I'm really just curious.
Hmm...this sounds a little like inexperience? First thing: Honda's recommendation is 20w50 above 50 degrees F (ambient air) operation, and/or for touring use: check any of the OEM Honda manuals and you will find this spec. They consider commuting on freeways as touring use, too.
In 1973 there was a major boo-boo in the Jinglish translation of the Owner's Manuals that came on the 750 and 550 Fours that did not get 'caught' until the 750F2 came out: it resulted in the mis-translation that became, generically, "use 10w40 oil". This "absolute minimum spec" (that was Honda's stated intent) was also cast onto the oil dipsticks of the 500/550 engines (and many Twins of the era) as Honda's last-stop-hope to prevent riders from using straight 30w or lighter oils. What it MEANT to say, in proper Japanese, was, "[never] use LESS than 10w40 oil". Those of us who, by then, had many tens of thousands of miles on our Fours knew this for the error it was: today most of that tribal knowledge is gone, and the later incarnations of motorcycles with water-cooled cylinders, fuel injection to control engine temps, and better metal alloys have made the later bikes all happy with the lighter oils (and confused newer riders who are just now coming to these older bikes). Your 1960s-designed Four needs 20w50 oil unless you never run over 50 MPH and/or have an oil cooler: then it might survive both with 20w40 oil. For example: I have seen engines from the East Coast (US) with 30k miles on them that barely needed new rings, and those mostly from sitting the last 20+ years: the reason is because the owners live in areas where the highest speed limit is 55 MPH, even today. Those bikes seldom, if ever, needed the protection of the 50w at high engine temps, as the engines never got that loaded. Many used 20w40 oils from Bel-Ray, Castrol, Valvoline, or Havoline with acceptable results, except where their valve guides wore too much and made the engine leak or burn oil. Those who used 20w50 oils fared far better.
Here in the West, I ride 80-90MPH every time I hit the interstate, lest I be run over from behind. When I had my shop, it was in rural Illinois near Missouri, and we seldom rode less than 65 MPH on any road. Between there and here (in Colorado) there is nothing but open roads and high speeds, so anything less than 20w50 will cause issues of oil breakdown in these engines, quickly (i.e., with petroleum-based oils). Modern synthetics do have longer chain molecules that can abide in these temperatures, but that's a different topic and one left for engineering and experimentation to fit to these engines: what we know from experience is that 10w40 petroleum is too light for these engines in summertime. I used to use the old Castrol GTX{L series} motorcycle oils in the 1970s in 10w50 for winter riding (so it would start easier), but that's the only time it worked OK.
As for the startup: if your oil pump's check valve works as it should, chances are the oil light will extinguish well before the engine starts (electric start) or at the end of the first kick (kick starter), anyway. If it doesn't do this, then the check valve is leaking the oil back from the oil galley through the oil filter, and this needs to be fixed. It means you're losing flow and pressure when running, too. The oil galleys to the head stay full all the time, so as soon as the kickstart gear moves, it is a solid fluid column all the way to the cam bearing squirt. When I rebuild engines I connect them to an oil tank and spin it until it fills these galleys, monitoring the progress by leaving the cam cover off as the last assembly step (yep, it can make a mess...). Once full, turning even the big crankshaft nut by the points (with a wrench) by hand will make oil drool out the cam bearings.
