Why Some PCMOs Are No Longer Suitable Fore Motorcycles

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JAG

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“WHY SOME PASSENGER CAR MOTOR OILS ARE NO LONGER SUITABLE FOR MOTORCYCLES: GEAR PITTING ISSUES”
Starts on page 12.

https://hrcak.srce.hr/file/9883

“SUMMARY
While there is a constant push to develop more fuel efficient oils for passenger car applications, these same oils become less suitable for motorcycle applications. It is known that highly friction modified oils developed to enhance fuel economy in passenger car engines can cause clutch slippage. It is also known that oils of viscosity grades lower than 10W-30 can cause gear pitting issues when used in motorcycles. This paper demonstrates that even 10W-30 oils developed for passenger car applications may cause gear pitting issues when motorcycles are run under heavy load severe service conditions. Today’s 10W-30 engine oils formulated for passenger car applications are typically formulated with non-shear stable viscosity modifiers. In motorcycle engines, however, shear thinning of the viscosity modifier combined with low viscosity and low phosphorus oils may lead to gear pitting issues under severe service conditions as demonstrated in this paper.”
 
I know Honda has asked for 30 weights in shared sumps for a while. No way I'd run them.
40 weight minimum, and likely at least spiked with a 50 weight in a shared sump if I'm doing it. If it says energy conseving on the donut, it's not in a shared (shred as I say) sump.
I don't agree that the VM's in MC oils are different or more shear stable than VM in auto oils, although reading most of the labels on MC oils you would think they had a genetically modified unicorn that gives shear proof VM's in the form of tears.
 
The reduction of ZDDP in post-SG PCMOs makes them problematic for use in flat-tappet engines like my middle-aged BMW airhead.
 
Originally Posted By: beanoil

I don't agree that the VM's in MC oils are different or more shear stable than VM in auto oils, although reading most of the labels on MC oils you would think they had a genetically modified unicorn that gives shear proof VM's in the form of tears.

I will say that any formulator worth their weight in salt is going to use a different VM for a PCMO and a MC engine oil formula, and yes, the MC one should be more shear stable.
 
It's been a known thing in some models regardless of oil type. The Yamaha XT600 was renowned for chewing out 5th gear, all sorts of oils were tried, and the consensus was to just not lug them in 5th. I have pulled 3 of them down, and all 5th gears were good.I used to have a Yamaha DT230 (2 stroke) and whenever I changed the gearbox oil, a lot of metalflake came out. I was changing the oil every ride, using 30 weight engine oil, motorcycle gear oils, ATF, all with the same result. When I finally pulled it down I was expecting to find a flogged ball bearing...but it was 6th gear, it was really mangled, and blue. Overheated I thought, but when I got the new 6th gears, they were both blue too. A bit strange.
 
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