Scooter Final Drive GL-3 80W-90

[GuyB]

I have a Piaggio BV250 scooter and the final drive gear reduction spec is for a GL-3 80W-90 gear oil. I am running Amsoil severe gear 75-90 now, which is certainly overkill but is significantly less draggy than what was in their previously. I would like to run a lighter oil than that to eke out additional performance, but am not sure if there is any risk to that.

The reduction drive is all helical cut gears supported by ball bearings and there are no shock loads because it is a centrifugal clutch CVT tranny. The oil will not be much hotter than ambient so the relevant viscosity would be close to the 40C spec.

I have some M-1 ATF on the shelf and am tempted to try that, but is there any reason to think more viscosity is needed? Would something like Redline MTL be better?

Thanks,
Guy

 

[Brybo86]

I would stick with a 90w gear oil in there.
Most new 50cc scooters recommend 75/80w90 gear oil in trans
Most new scooters over 50cc recommend 75w140.
I'm surprised the 250cc scooter recommends a 90weight and not a 140

Stick with what you have for gear oil Amsoil is the best.

 

[DoubleWasp]

Don't get things confused. Those things will burn up if treated incorrectly.

 

[beanoil]

Aprilia SportCity, basically the same scoot as you.
Redline Shockproof Heavy.
I have trouble believing your butt dyno can tell the difference between factory and AmSoil.
If you want more performance, go for the 300cc big bore kit.

 

[barryh]

Don't know about your scooter specifically but consider that for reduced losses, car manual gearboxes have moved to some very thin oils. Mine uses a 75W with a KV of 40.8 @40C. So there should be plenty of choice out there in GL4 spec. If there are only helical cut gears involved I can't see why GL5 would be needed. Like I say I don't know the bike but the thought of it needing a 140 oil sounds bizarre.

I have a motorcycle with shaft final drive and experiments with slightly thinner oils in the gearbox and final drive leaves me in no doubt that you can distinguish differences in oil drag just by spinning the wheel by hand.

 

[toneydoc]

If you are really wanting to "eke out additional performance" trade it in at the Harley dealership. You can treat yourself to a little get up and go there

 

[MolaKule]

I would recommend something like this Redline:


https://www.redlineoil.com/product.aspx?pid=140&pcid=7

 

[GuyB]

Molakule is the winner!!! I found another spec for the same drivetrain calling for a GL-4 75W-85 as he recommends.

Now, I have a theoretical question, if manual transmissions last essentially forever at an operating temp of 75 degree C using 75W-90 oil with an operational viscosity of 30 cSt, and front drive automatic transaxles last a long time at the same operating temp on DEX VI with an operational viscosity of 10 cSt, then why does the scooter hub operating at 40 degree C require 75W-85 with an operational viscosity of 64 cSt?

For reference, if I were to run DEX VI in the hub at 40 degrees C it would have the same operational viscosity of 30 cSt as the manual transmission with 75W-90 at 75 C.

Thanks,
Guy