Spline Lube explained

[wilcom]

I am forwarding a response by Tom Cutter addressing the How and mostly WHY we need to grease the Transmission input splines on our Airheads. It's the best explanation I have read to date about a procedure that we have to do on our bikes. This response was posted to the "Airhead List".  Tom was a BMW factory guy when our Airheads were new and now has a shop in Pennsylvania servicing BMW's. His response follows......................

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In all honesty, I wish that BMW had gotten the input splines right so that
we could ignore them like all other vehicle owners seem able to do. But,
alas, they did not. they do wear excessively and they do fail. I like to
think that by vigilance and arduous efforts to disseminate the information,
we have managed to greatly reduce the number of Airheads that suffer this
extremely costly failure. Twenty five years ago, spline failures and
attendant shifting problems were legion. Now there are a few, but that is
because people are attending to the service as it is needed.

Cleaning the spline is more important than lube, though that is certainly
also important. The "rust" on splines is not corrosion from environmental
conditions, it is oxidation caused by high pressure and the metal splines
sliding against one another. the condition is called "fretting corrosion"
and the cure is three-fold:

First one needs to remove the by-products of previous corrosion, so that
the do not contribute to future wear.

Second, an agent* needs to be added to both lubricate (this reduces the
peak temperatures caused by the high pressure) and also to reduce the
exposure to the oxygen necessary to allow the oxidation to proceed.

Third, it is important to reduce the sliding component of the assembly by
controlling the end play in both the crankshaft (and the attached clutch
assembly, and the end-float of the transmission input shaft, Both of these
factors are controllable by proper shimming of the respective components.

*After buying virtually every snake oil product foisted upon the dealer
network by BMW, I finally accepted Oak Okleshen's suggestion that the best
product for the job did not say "BMW" on the label; instead it says
"Honda," that being Honda Moly 60 Paste.

Unfortunately, Honda Motor Corp has discontinued the packaging and
distribution of this fine product. They suggest in its place to use their
new product "Honda M77 Paste." It is a decent substitute, and I bought a
few dozen tubes to sell when clients order the Honda product. As the name
implies, it is the same product as Dow Corning MolyKote M77 Paste, which is
available in a small container that can last for many spline lubes. I
suggest using a trimmed acid brush for the job, and I supply a brush with
each tube of lube I sell.

The Dow Corning product MSDS is available here:
https://www.dowcorning.com/applications/search/products/Details.aspx?prod=01005103&type=PROD

Tom Cutter
Yardley, PA
www.RubberChickenRacingGarage.com

[montmil]

I'll ration my Honda Moly60. Properly applied, it does not take much to keep splines happily "splining and sliding".

[Bob_Roller]

I've got access to Molykote M77 at work .
I scavenge the remains from the containers .
I mix wheel bearing grease with this, for rear wheel spline lubricant .
It's a bit too thin and gets out of the rear wheel splines and onto the brakes .
.

[georgesgiralt]

In Europe one can stilll find the Molykote BR2 which is what BMW advised for spline lube in 1982.

[nhmaf]

One can also find other premixed sticky greases with high moly content.  One "boutique" brand is called "guard Dog", but I've found some other in general automotive supply stores.

I used to apply just the Honda Moly paste, but found it dried up and fell off fairly quickly.  The molybdenum molecules tend to bind with the surface and do their slippery thing, but there isn't anything to reduce oxidation.  So, I alway mix it in with some "red-n-tacky" tractor and HD equipment grease that sticks well to everything and forms an oxidation barrier, as well as holding the paste in place.

[Justin B.]

Just out of curiosity has anybody tried the spray-on moly coatings that dry to a film?  This kind of stuff (brand name "Black Cat" comes to mind) is pretty popular out in the oil fields...

[georgesgiralt]

Maybe it will work if you have the tranny on the bench. But with the tranny into the frame, I would be afraid to put Moly on the clutch...