Article [11] ST1100 - O-rings in the final drive (rear wheel)

[CYYJ]

Much has been written about the importance of properly lubricating the final drive with moly paste whenever the rear wheel is removed.

Not so much has been written about the importance of ensuring that the three O-rings in the final drive are checked to ensure that they are in good condition, this to enable the three O-rings to keep the moly paste inside where it belongs, and to prevent dirt from entering into the area where the moly paste is and causing excessive wear of the final drive.

I get about 8,000 km (5,000 miles) out of a rear tire on my ST 1100. Every second rear tire change - in other words, every 10,000 miles - I replace the three O-rings in the final drive area. They are inexpensive (less than $10 for the set of three), and I believe that replacing them before they wear out is cheap insurance against having to spend well over $1,000 to replace the final drive assembly.

Two of the O-rings are relatively easy to find: they are located on the rear wheel assembly and you can see them on the wheel assembly when you remove the rear wheel. The third O-ring is often overlooked, because it resides in the final drive itself, and the final drive remains attached to the motorcycle when you remove the rear wheel.

Below are parts diagrams that illustrate the three O-rings, and pictures showing where to find these three O-rings. The parts diagrams and part numbers given are for my 2001 ST 1100, but I believe that the part numbers are the same for all ST 1100s.

Parts Diagram for the two O-rings that are attached to the wheel:

A picture of the most obvious O-Ring (#23 in the diagram above):
The O-ring is covered in moly paste, sorry about that


A picture of the other O-Ring in the above parts diagram, which you will see once you remove the "spider" shown in the photo above:
For unknown reasons, there are two part numbers that can be used for the same part


Parts Diagram for the O-ring on the final drive:
This is the O-ring that most people fail to inspect and/or replace. It is difficult to see unless you know where to look for it.


A photo of where to find the above-mentioned O-Ring:
The O-ring is missing in this photo, but you can see the groove it fits into at the tip of the red crayon


What happens if the third O-Ring (91356-MG9-004 in the picture above) is missing:
Back in the winter of 2008, an apprentice at my dealer in Zurich replaced the rear tire on my moto. He removed the three O-rings to replace them, but the youngster forgot to install the O-ring inside the final drive (photo directly above). The next time I went in for a rear tire change, 9,000 km (6,000 miles) later, the master mechanic did the work, and he was horrified to find that the final drive assembly (the spider, and the matching gear in the final drive) were almost destroyed. Some investigation determined that the apprentice had forgot to install the third O-ring at the previous tire change.

The damage you see in the picture below happened in just 6,000 miles of riding, much of which was in rainy weather. Water and dirt got into the final drive and caused excessive wear on the gears. The dealer was honourable and replaced all the components at their expense - but it was awfully expensive for them to do this.

Moral of the story: Carefully check the condition of these three O-rings every time you change the rear tire, and consider replacing the three O-rings on a regular schedule, before they fail and let dirt get into the final drive.

 

[DeanR]

Good reminder Michael.
My o-rings always look great at tire change time. As a result, I've skipped using new ones a few times, since the old ones look new. Perhaps not the best idea though, and I rethink it each time.

 

[Big-E]

Great post. Saved to my "servicing file" for future reference! Thanks.

 

[Upt' North]

Thank you Michael, good reminder.
Like you said I think weather makes a massive difference in wear and the importance of changing the 'o' rings seals. If you're a sunny day man you'll probably get away with it if lubed regularly but not in the wet/salt/dust/crud etc.?
Upt'North.

 

[Techman]

Excellent pictures and post.

 

[dwalby]

My o-rings always look great at tire change time. As a result, I've skipped using new ones a few times, since the old ones look new. Perhaps not the best idea though, and I rethink it each time.

my bike is 21 years old, 112k miles, and I've never changed any of those 3 O-rings. It might help that I rarely ride in the rain. Not necessarily recommending this maintenance plan, but it hasn't caused me any issues.

 

[ReSTored]

I've taken a more conservative approach and change all 3 o-rings at every tire change, which for me is every 8,000 - 10,000 km. This costs me $10 a year and is dirt cheap insurance IMO.

 

[Bush]

my bike is 21 years old, 112k miles, and I've never changed any of those 3 O-rings. It might help that I rarely ride in the rain. Not necessarily recommending this maintenance plan, but it hasn't caused me any issues.

I've taken a more conservative approach and change all 3 o-rings at every tire change, which for me is every 8,000 - 10,000 km. This costs me $10 a year and is dirt cheap insurance IMO.

Ha Ha! Here we have the extremes of dealing with this little maintenance item, but it isn't rocket science really. You just have to look at the damned things and see if they are worn or not.

The only one that I find wears noticeably over time - and not every tire change - is the thin one that sits in the groove on the hub.

 

[W0QNX]

I'm still using these.

http://www.carolinabikeandtrike.com/ORings.htm

 

[ReSTored]

Really,

Ha Ha! Here we have the extremes of dealing with this little maintenance item, but it isn't rocket science really. You just have to look at the damned things and see if they are worn or not.

The only one that I find wears noticeably over time - and not every tire change - is the thin one that sits in the groove on the hub.

Given the huge amount of press on o-ring / Moly 60 related issues over the years on this forum and the enormous cost and inconvenience of failure there is no value to me spending any amount of time pondering a $10 a year cost. I've better things to do and consider it a PM issue just like oil and filters. Imagine thinking "ya, they still look good" and then at next tire change seeing splines that look like the OP's because one or more of them had failed.

 

[Bush]

O-rings don't fail, they wear. Next time you take them out, put them beside your new ones and see if you can discern any noticeable difference. Put a micrometer on them, if you have one, for positive verification. If worn, replace them. As I said, not rocket science, just mechanical aptitude and knowledge.

EDIT: Over 23 years of 1100 ownership, I have replaced the thin hub o-ring maybe 6 times, the one inside the final drive never and the one on the spider once, I believe. Failure to keep the rubber dampers and inserts in the wheel in good condition is a major reason for wear on the o-rings.

 

[dwalby]

O-rings don't fail, they wear. Next time you take them out, put them beside your new ones and see if you can discern any noticeable difference. Put a micrometer on them, if you have one, for positive verification. If worn, replace them. As I said, not rocket science, just mechanical aptitude and knowledge.

EDIT: Over 23 years of 1100 ownership, I have replaced the thin hub o-ring maybe 6 times, the one inside the final drive never and the one on the spider once, I believe. Failure to keep the rubber dampers and inserts in the wheel in good condition is a major reason for wear on the o-rings.

I think this makes a lot of sense considering the one at the base of the wheel splines never has any movement that would cause it to wear, the two splined surfaces it contacts with rotate as a unit. Not sure about the one inside the pumpkin, does that round part that holds the O-ring rotate along with the splines???

The one on the hub would be more prone to wear because I think the cush drives in the wheel will allow some small amount of rotational movement between the two metal parts in contact with that O-ring.

 

[ChriSTian_64]

O-rings don't fail, they wear. Next time you take them out, put them beside your new ones and see if you can discern any noticeable difference. Put a micrometer on them, if you have one, for positive verification. If worn, replace them. As I said, not rocket science, just mechanical aptitude and knowledge.

Just replaced my three O-rings.

Visually, the old ones all looked fine. But the micrometer shown a bit of wear.
91358-MG9-003 had 2 mils,
91302-MA6-003 had 1 mils,
91356-MG9-003 had 1 mils.

Bike is 21 years old. No idea when they were last replaced, hence I ordered new ones.

It is not easy to measure a rubber O-ring with a micrometer.
The way I did it (I just wanted to see if there was a difference between new and old), I just pinched them, just enough so that the micrometer could hold the O-ring between its jaw.
Then, I very slowly re-opened the micrometer, until the O-ring fell on my desk, then looked at the value.
I repeated this a few times for each, to make sure the reading was constant.
This method doesn't give me the exact diameter value, but nevertheless, I could see and measure the differences between the new ones and old ones.

 

[Andrew Shadow]

This method doesn't give me the exact diameter value, but nevertheless, I could see and measure the differences between the new ones and old ones.

If you are concerned about compressing the O-ring and not getting an accurate cross-sectional measurement, subtract the O-ring inside diameter from the outside diameter. Divide the result by two. This equals the O-ring cross-sectional measurement.

 

[Bush]

Or get a ratcheting type of micrometer that stops closing down on the subject when both surfaces are contacted. Similar to a click type torque wrench.

 

[George]

Another reason for failure of the o-rings is failure to realign the final drive after it has been removed for any reason. Simple procedure: fully install and tighten the rear axle without the wheel in place before tightening and turning the 4 pumpkin nuts. Repeat any time the pumpkin is removed.

(Note to self: I need to do this myself on STerling as I don't know if it's been done on her.)

 

[George]

Rob Parker used to provide new o-rings for the cost of postage. Don't believe he's still around.

Quick search returns this site as a potential source. https://orangeseal.us/collections/o-rings?gclid=Cj0KCQjwna2FBhDPARIsACAEc_VTC69ZzE6LidmAkH3DMWELLJVbQP6r1f0FZSR4rU3RQdtyujaL5p0aAtSrEALw_wcB

 

[CYYJ]

O-rings don't fail, they wear.

That is mostly true, in the sense that O-rings will usually wear flat on the outside edge before they fail (failure in this sense being breaking apart), but keep in mind that any rubber part is also at risk of perishing (deteriorating) over time, losing elasticity, or stretching.

Personally, I consider O-rings in general - not just these ones - to be calendar time-limited components, not mileage-limited components.

Michael

 

[Andrew Shadow]

Or get a ratcheting type of micrometer that stops closing down on the subject when both surfaces are contacted. Similar to a click type torque wrench.

Depends on the accuracy desired. Every micrometer that I have ever tried to measure an o-ring with will compress the rubber noticeably before the resistance is great enough to overcome the friction drive of the micrometer's thimble. Is the amount of compression an issue? Overwhelmingly it is not. Sometimes it can be. I have sometimes found that there are two O-rings available that are so close in dimensions that I couldn't tell which one matched the one that I was measuring. This is more of a problem with O-rings that have a very small cross section because the amount of compression represents a larger percentage of the total dimension. It is less critical with larger cross-sections. I only mention it as an F.Y.I. to anyone measuring an O-ring with a very small cross-section and where they need or want accuracy.

 

[Andrew Shadow]

Personally, I consider O-rings in general - not just these ones - to be calendar time-limited components, not mileage-limited components.

Interestingly enough, shelf-life of O-rings seems to be less and less of a concern with the materials they are made of now. Most O-rings I have experience with used to have a shelf-life of five years. Many years ago the shelf-life was increased to ten years on O-rings used in the same applications. Now many of these same O-rings have no shelf-life specified at all. They are considered to good as long as the package has remained sealed.

Shelf-life is not an indicator of how long an O-ring can remain in service of course, but I find it interesting how the progression of materials has improved the quality so much that age related deteriration is no longer an issue.