Burnt rear axle?

[Entoptic]

Decided to clean and lube the back stack and found a ton of dirty grease (expected) but what I did not intend to see was burnt/browning on the axle. As I am not a mechanic I'm not certain this is even something to worry about but thought I'd reach out cause I know you folks are pro.

Please let me know how I can fix this if it's even needed. Thoughts were fine grit sandpaper or 00 steel wool. I've attached a photo of a new one for reference.

Any help would be great.

 

[ctwo]

Looks well seasoned. I'd polish the seal surface in the lathe with fine emery or scotch-brite.

 

[Entoptic]

Looks well seasoned. I'd polish the seal surface in the lathe with fine emery or scotch-brite.

Thanks man.40k miles on the MV and it's still purring along. When you say seal surface I assume you mean the axle surface?

 

[ctwo]

If there is a rubber seal to keep the dirt out and grease in, that's the spot that would matter.

Note, I do see the o-ring marked on the new one so not sure if there are any other seals.

 

[Entoptic]

If there is a rubber seal to keep the dirt out and grease in, that's the spot that would matter.

Note, I do see the o-ring marked on the new one so not sure if there are any other seals.

Gotcha ty for the info. Really appreciate it

 

[Busy Little Shop]

Your axle is not burnt rather its stained... I offer my method to clean both the axle and bearing...

Once you have the bearing removed you employ a two jewelers screw
drivers and carefully lift each roller from the cage...

Give the rollers and cage a bath in gasoline... you be surprised at
all the dirty deposits hidden in the old grease and every nook and
cranny... you're looking at the deposits after only 10K miles of
normal operation...

Once the bearing are really clean lay them out and inspect each roller
for scoring...

Dirt mixed with the old grease will leave a trail of deposits on the
axle at point B...

Spun in a Lathe... it's easy to remove the deposits employing a gray
micro fine 3M pad... it's soft enough that it does *not* remove any
precious metal...

What you'll end up with is an axle with the deposits remove plus
giving the metal a nice luster...

With the bearing cleaned and axle shinning you're ready for grease...

 

[Entoptic]

Your axle is not burnt rather its stained... I offer my method to clean both the axle and bearing...

Once you have the bearing removed you employ a two jewelers screw
drivers and carefully lift each roller from the cage...

Give the rollers and cage a bath in gasoline... you be surprised at
all the dirty deposits hidden in the old grease and every nook and
cranny... you're looking at the deposits after only 10K miles of
normal operation...

Once the bearing are really clean lay them out and inspect each roller
for scoring...

Dirt mixed with the old grease will leave a trail of deposits on the
axle at point B...

Spun in a Lathe... it's easy to remove the deposits employing a gray
micro fine 3M pad... it's soft enough that it does *not* remove any
precious metal...

What you'll end up with is an axle with the deposits remove plus
giving the metal a nice luster...

With the bearing cleaned and axle shinning you're ready for grease...

This is why I love barf. Thank you for the walk through and pictures.

 

[Busy Little Shop]

This is why I love barf. Thank you for the walk through and pictures.

You're welcome...

 

[Tally Whacker]

Larry, you make me wish I had a Honda v-4 just so I could have an excuse to stop by your Sactown shop.

 

[ST Guy]

If you want to make it last longer, when it's clean with no grease on it, get some tungsten disulfide powder and coat the wear surfaces with it. Burnish it in real good with a clean cloth. This includes all rubbing surfaces including individual bearings.

Then use a high quality full synthetic grease and you will have done the best job possible.

 

[quicksparks]

OP I’m not familiar with your particular bike but based on the picture i’m guessing there’s a sleeve/collar/spacer that covers the smooth portion of the shaft next to the splines.

To me that looks like fretting corrosion. Super common where you have two metal surfaces in close contact and a high number of stress reversals like what happens during vibration or a rotating shaft. Micro-movements cause abrasion and tiny particles build up in the joint. This happens despite having what you think is a rigid joint because stresses are so high. Oxygen gets to the particles, turning them into oxides which are harder than the base metal, causing more abrasion and the cycle repeats. It mostly happens with ferrous parts but it even happens to copper which is why you should use dielectric grease on electrical connectors. The grease cuts of access to oxygen, preventing corrosion. Greasing this shaft before reassembly and servicing it frequently should reduce/prevent this problem.

 

[DannoXYZ]

Where does this stuff come from?

 

[ST Guy]

OP I’m not familiar with your particular bike but based on the picture i’m guessing there’s a sleeve/collar/spacer that covers the smooth portion of the shaft next to the splines.

To me that looks like fretting corrosion. Super common where you have two metal surfaces in close contact and a high number of stress reversals like what happens during vibration or a rotating shaft. Micro-movements cause abrasion and tiny particles build up in the joint. This happens despite having what you think is a rigid joint because stresses are so high. Oxygen gets to the particles, turning them into oxides which are harder than the base metal, causing more abrasion and the cycle repeats. It mostly happens with ferrous parts but it even happens to copper which is why you should use dielectric grease on electrical connectors. The grease cuts of access to oxygen, preventing corrosion. Greasing this shaft before reassembly and servicing it frequently should reduce/prevent this problem.

If it's a fretting problem, then tungsten disulfide is an excellent cure along with a quality grease.

 

[Busy Little Shop]

Where does this stuff come from?

Mean old Mr.Dirt never sleeps... he tenaciously builds up on your air cleaner and in your axle grease...

 

[quicksparks]

If it's a fretting problem, then tungsten disulfide is an excellent cure along with a quality grease.

I never heard of tungsten disulfide until now. Looks like there is an industrial process for coating metal with it but what you’re talking about is using it in powder form as a dry lubricant. Seems like it can’t hurt but that dry powder alone won’t cut off oxygen, you need grease (which you also recommended) to do that.

 

[ST Guy]

I never heard of tungsten disulfide until now. Looks like there is an industrial process for coating metal with it but what you’re talking about is using it in powder form as a dry lubricant. Seems like it can’t hurt but that dry powder alone won’t cut off oxygen, you need grease (which you also recommended) to do that.

I'm sure you've heard of molybdenum disulfide, or moly. Once upon a time, when the properties of these two materials was discovered, molybdenum disulfide was much less expensive than tungsten disulfide, so moly was used in greases, oils, etc. Everyone became aware of it and it's still widely used in many applications. Oils, greases, and assembly lubes, for instance.

However, tungsten disulfide is even better and in the intervening years, many new sources of tungsten disulfide have been discovered, bringing the price down in line with moly. I have both, but prefer the tungsten version now. Heck, you can buy the stuff on Amazon.

Both are microscopic powders that are inert and can handle pressures and temperatures way beyond even the best synthetic greases. And there are commercial products now that use tungsten instead of moly. However, since they are dry lubricants, they must be blasted into or burnished into the materials they are to be used on. And, of course, many applications require grease as well.

What I do is start with a clean component. Then I apply the dry powder (straght powder or a powder spray). After it's burnished into the surface of the material, I then use an appropriate grease or oil per normal.

It makes an excellent anti seize. And a high content paste (with grease) makes an excellent lube for grease seals. Heck, the stuff is even used on artificial joints like hip and knees for humans.

Search Amazon for tungsten disulfide.