Why HTHS matters in your gearbox

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Shannow

Shannow

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Plenty of data presented by JASO can be found on what they've found regarding gearboxes and pitting with low viscosity oils in shared transmissions.

http://fuelsandlubes.com/digital/fli/201...html/page8.html

Quote:
For motorcycles, tests were conducted using various viscosity grade oils. Yoshinobu presented the results. SAE 5W-30 oils with an HTHS viscosity of 2.7-2.9 caused gear pitting during the tests. In contrast, SAE 10W-30/40 and 20W-40 had no pitting, which were measured using motorcycles from four vendors. The current JASO document specifies a minimum HTHS of 2.9. Given the test results, it may be difficult to lower viscosity substantially in the upcoming revision to JASO T903: 2011, he said
 
My Honda called for 5w-30 motor oil in the 5-speed tranny, so I used Mobil 1 engine oil. I learned that it sheared down quickly and changed to Red Line MTL. There is no more problem with shearing down, now.
 
I solved the problem completely: my transmission does not use oil.
smile.gif
 
Originally Posted By: Joshua_Skinner
Originally Posted By: Inspecktor
Amsoil 10-40 motorcycle has an HTHS of 4.4, their 20-50 is 6.0


Solid. Can I get that for $27/gallon?


As soon as I am done with it.
 
I run 15W50 @ 5.0 HTHS in my Duc.

I tried Amsoil MCT 10W40 once but Blackstone UOA showed it had sheared down to a middle 30 weight (in the 10's).
 
Originally Posted By: LoneRanger
I run 15W50 @ 5.0 HTHS in my Duc.

I tried Amsoil MCT 10W40 once but Blackstone UOA showed it had sheared down to a middle 30 weight (in the 10's).


How many miles were on the oil at the UOA?
 
Makes sense. I wouldn't want to go lower than the dino 10w40 oil that's in mine now... which I suspect is shearing itself close to a HTHS of 3.0.

What's everyone experience with shearing between T6 and dino Rotella T 15w40. I would expect the latter to be more resilient to shearing.
 
What matters is the base-oil viscosity, not the HTHS viscosity, because this is boundary lubrication (gears and ball bearings) as opposed to hydrodynamic lubrication (plain bearings). However, the two are related. A 10W-40 will usually have a higher base-oil viscosity than a 5W-30 in addition to having a higher HTHS viscosity. Likewise, a 20W-50 will have even a higher base-oil viscosity.

Therefore, you probably don't want a 0W-40 or a 5W-40, as they will likely have a lower base-oil viscosity than a 10W-40.
 
Originally Posted by Gokhan
What matters is the base-oil viscosity, not the HTHS viscosity, because this is boundary lubrication (gears and ball bearings) as opposed to hydrodynamic lubrication (plain bearings). However, the two are related. A 10W-40 will usually have a higher base-oil viscosity than a 5W-30 in addition to having a higher HTHS viscosity. Likewise, a 20W-50 will have even a higher base-oil viscosity.

Therefore, you probably don't want a 0W-40 or a 5W-40, as they will likely have a lower base-oil viscosity than a 10W-40.


The article says that gear pitting was found when HTHS was below 2.7 to 2.9 (5W-30 oils), but not with 10W-30/10W-40/20W-40 oils. Also says the additives (anti-wear I assume) is more important than viscosity (for gear wear I assume).

Not sure if JASO specifies a certain level of anti-wear additives, but sounds like the "gear pitting" test they were trying to develop back when the article was written was focused on gear wear requirements.
 
What I see in that article says that all things equal, a lower oil viscosity promotes more pitting in the gearbox. Doesn't seem to be much debate there in that article.

I would seriously think about my gearbox if I was running a 30 weight or under viscosity motor oil made for a car in my motorcycle. Pitting tends to be "larger" debris that the filter will take out but won't get suspended in the oil. Used oil analysis won't show that.
 
Originally Posted by ZeeOSix
Originally Posted by Gokhan
What matters is the base-oil viscosity, not the HTHS viscosity, because this is boundary lubrication (gears and ball bearings) as opposed to hydrodynamic lubrication (plain bearings). However, the two are related. A 10W-40 will usually have a higher base-oil viscosity than a 5W-30 in addition to having a higher HTHS viscosity. Likewise, a 20W-50 will have even a higher base-oil viscosity.

Therefore, you probably don't want a 0W-40 or a 5W-40, as they will likely have a lower base-oil viscosity than a 10W-40.
The article says that gear pitting was found when HTHS was below 2.7 to 2.9 (5W-30 oils), but not with 10W-30/10W-40/20W-40 oils. Also says the additives (anti-wear I assume) is more important than viscosity (for gear wear I assume).

Not sure if JASO specifies a certain level of anti-wear additives, but sounds like the "gear pitting" test they were trying to develop back when the article was written was focused on gear wear requirements.

If pitting occurs for 5W-30 but not for 10W-30, it reinforces my point that it's the base-oil viscosity that matters, not the HTHS viscosity, because 5W-30 and 10W-30 have the same HTHS viscosity but 10W-30 has a higher base-oil viscosity than 5W-30.

Of course, the antiwear additives are crucial, but apparently if the base oil is too thin, you still get pitting.
 
Riding style comes into it too. The Yamaha XT/TT 600 engines were prone to chewing out 5th gear - they would be seriously pitted, flanks of gears flaking off. The engine was in production for a couple of decades, and the consensus of riders over time was - don't lug it in 5th, drop down a gear. I've pulled several of these engines apart and never seen a damaged 5th gear...mind you, one engine I got for parts didn't have a gearset, it had obviously been robbed for parts.

I had a Yamaha DT230, and was getting silver in the gearbox oil. I thought a bearing was going and used all sorts of oils in it, from 30 engine oils, gearbox oils and ATF. After finally pulling it down I found all the bearings good, but 6th gear totaled, severely pitted. I don't know what the previous owner/owners had used...or if they even used oil at all in the gearbox. But like the XT engines, it was top gear. A 2 stroke doesn't have the shock loads on the gear train like a big 4 stroke single though.
 
Quote Blackstone Labs on the Importance of Viscosity...

The viscosity, or thickness of the oil, is not nearly as important
as many people think. Oil retains its nature no matter what thickness
it is.Think about this: automakers are continually recommending
lighter multi-grade oil in new engines. The reason is increased
efficiency. It takes power to pump oil through an engine, and the
lighter the oil, the less power required to pump it. The oil's ability
to act like a solid and protect parts is not related to its thickness.
If that doesn't sound quite right, consider this: The gears in a
heavy duty Allison automatic transmission are doing the same work as
the same machine equipped with an Eaton manual transmission. Due to
the hydraulics of the automatic, it runs on a 10W automatic
transmission oil.But the manual transmission uses a very thick
(sometimes up to 90W)gear lube oil. The gears of both types of
transmissions will have a similar life span. We don't find any
significant differences in wear, regardless of oil thickness.
 
Originally Posted by BusyLittleShop
Quote Blackstone Labs on the Importance of Viscosity.

The oil's ability to act like a solid and protect parts is not related to its thickness.


The oil film thickness between parts certainly is dependant on the oil viscosity. It's that oil film thickness that keeps moving parts separated.

Blackstone needs to study up on tribology.
 
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