From what i have seen over the years the higher spec oils seem to have greater % of Zinc/Phosphorus in them as an anti-wear additive. It is also apparent that the so called "longer life" oils have greater amounts of detergent and because of that lower levels of Zinc. Good oil tech guys, i.e. Penrite,Joe Gibbs Driven recon Zinc in motorcycle specific oils need to be at 1200 parts per million minimum, Joe Gibbs for example have 1700ppm in their XP7 semi syn dirt bike oil, Penrite in their HPR10 GAS are at 1200ppm etc. From personal experience there is a MARKED difference in top end wear and easier gear changing with "higher levels" of Zinc/Phos. Some companies reckon Zinc will cause clutch slippage, this i have not experienced. I currently run an oil with 2500ppm in a modified 1100cc 4cyl engine, this engine sees oil temps consistently over 100 deg c. (air cooled) I have found even higher levels Zinc (Zddp) can have some effect on plug colour/fouling, but generally think around 1700-2000ppm on a run-in engine to work well. Water cooled single cylinder with 4 valve cyl head would have much weaker valve springs and less valve lift so might not see a need for high zinc (1700-2000ppm) but i am led to believe oils like Hondas generic brand and Yamahas brand are both around 1700ppm as is Joe Gibbs etc.
Interesting subject for sure. Zinc,ZDDP,ZDTP,Phosphorus (all same/similar for our purposes?) are STILL heavily added to industrial,aircraft,highload machinery etc, oils used purely for competion engines also use a lot of Zinc, most of the engines and machinery using this type of oil is generally old school stuff, not the multi valve F1 inspired (of some years ago!) type engines, so maybe the Zinc is not needed or at least replaced by something doing a similar job in the oils we use these days in later types of engines,however when speaking to various oil "techs" both here and in the u.s.a over the last few years about half of them agreed that Zinc in various forms is still a very useful additive so long as was not an oil with high detergent levels, detergent apparently keeps a percentage of the Zinc suspended in "suspension" and doesnt allow it to do its intended job. Further they say some os the zinc has been replaced with other things (calcium!) being one. When i say half these techs i mean about 4 of the eight i have spoken with, spoke to them on phone (Aust) and email U.S.A., kept record of times and dates and names, when you keep going back to the same guys they get friendlier and coff up more and better info. From what i have learned i would say most if not all oils are good enough so long as you pick something designed for the purpose you will use it for, you need to know what engine oil temps will be for a start, I would suggest never using straight mineral oil if its going to work at all hard (any dirt bike works hard) by hard i mean heat build up, i'd suggest from the info Disco and others have listed that Penrites HPR GAS 10 or the "Everyday syn" 10w/40 or 5w/50 would be the minimum specs for single cylinder dirt bikes (4st), it doesnt have to be Penrite, just have a look at the Penrite specs and use them as a minimum OR simply stick to the big name dirt bike or sports bike specific oils ALL will do the job so long as changed before too contaminated. Personally I use 300v Motul in my 450 Kato, I am using Joe Gibbs XP7 in my Z900, and anything semi synthetic in my Zrx. If i can add zinc reliably to the HPR GAS 10 or Everyday Syn 5w/50 I WILL be switching all of them over, i'll add the Zinc to the Z900 only for insurance in the Z900 as it has high lift cams,big valves and F..KING HARD valve springs! I checked today on Penrites price...$48.70 for FIVE LITRES at Supercheap...and to think i have been paying $100 for 4 litres of 300v....no wonder i worked saturdays for 30 years! Sorry for the long winded babbling Gents but the more info out there/here the more others will learn and prosper with! BY THE WAY, the Joe Gibbs oil is $16 per quart (950ml) bottle, reasonable for dirt bike specific oil.
