Oil cooler is an old issue that is basically a non issue in Nortons of about any sort.
Alan Goldwaite was the one who put thermo probes in various places including the oil from exhaust side of head down push rod tunnels. The oil there got over 400'F. Jim Comstock has a probe inserted deep between the jug and finds over 500'F there. His temp probe in the front of head gets up to 400'F.
http://www.nortonclub.com/docs/OilTemp.pdf
There is about only 2 conditions that can over heat, one a ridden Commando in about dry- no humidity air going up hill loaded in top gear in same direction and speed as the wind. The other would be about WOT for quite some time with engine totally covered up. This of course assumes good tune condition & timing.
I've done my own measures and heat is almost a one to one relation to how much throttle/fuel is being fed, almost regardless of air flow. I can grantee that you can not even get a Commando to 2/3'ds its hi way temps by long idle near 1000 rpm in 100'F full sun on radiating heated cement is sheltered from wind area. I left Peel idling outside my office window about 5 ft from my eyes to watch its meters for over 30 min and it would not get hotter than 250'F CHT or 900'F EGT, mostly settled to 220'F CHT and 800'sF EGT. Oil temp leaving bottom of tank only read 125-135'F. Skin of 99+% of people feel 143'F is about hottest shower they like for comparison.
Of all the places to put an oil cooler I'd have to say only the flow to head.
There has not been a completely thorough oil thread coverage on lists yet to fully cover what matters most. What matters most are the corrosive acids from reaction with moisture that come from combustion and cool down condensation.
This takes close to boiling temps 212'F to cook off water. Also the protective zinc and phosphorous metals don't become effective to bind to surfaces until at operating temps over 150'F - below that they accelerate friction wear, such as idle when there's not oil pressure to get much/any hydrodynamic pressure layer separation so metal to metal contact occurring the most but w/o the protective additives ain't sticking around to do their job. The higher Zn/P levels over 1000 ppm degrade parts life even in old flat tappet engines. So too much of a good thing is too much. Chevy Corvair experts know the score here and then some.
They know to let engine get full temp before leaving or loading it much. Best Manx owner blip throttle for 10-15 min sitting still - every now and then feeling the fins. Partly to stablize thermal parts clearances but also to get the tappet protective metal package working too.
In Ms Peel prime it took 30+ min of near red line in low gear sports bike spanking games to get the max oil tank temp to 195' F. Then when turning to go home 60 miles away in lazy relaxed 80-90 mph cruise in twisting hwy, oil temp dropped in under a min to below 165'F in summer heat over 95'F. Just running at 120 mph for half mile long opens only got oil temp to 170'F. Peel was still eager to pull another 15 mph w/o much delay ok. Max I ever got - EGT 1375'F and CHT 425'F.
Old school was to just cut vents in TS tank cover. Some like Alan G. made an space age looking finned plate cooler that was part of the cover itself for most compact attractive effective radiator. I can't remember seeing oil coolers on vintage racers of all makes, but may have over looked that somehow. i expect to have to insulate spinal oil tank but sure thinking about a head oil only cooler in boosted Peel, but not a worry to even put a meter on plain Trixie Combat after seeing what it took to even get Peel to moisture cooking temps. Inside exhaust side of head is whole another issue but at conflict with rest of the engine needs.
Main oil factor in our bikes is to let it get hot enough to cook off moisture and then change it often as can afford. Another thread is needed to cover the couple dozen oil varieties chart we and other air cooled road craft should select from.
Picture a cover with 3 inch strip of Al fins running length of the cover and sticking out proud a bit in the air flow. I've the pdf file to share private but can't covert or copy the image to display here.
Oil Coolers for the Norton Commando motorcycle
Prices: primer finish $99.95
painted, with decal $129.95
please specify black, silver, red or primer
and 750, 850 or MkIII decal
Available from:
Magic Devices
1780 Chanticleer Avenue
Santa Cruz, CA 95062
(408) 475-7505
• Replaces stock side cover, using original bolts
• Solid-state design - no hoses or fittings to leak oil