swingarm

[JamesW]

I could very well be wrong but I think BMW began using the single sided swingarm on the 1979 R80GS.

 

It also seems to me that the final drive failures didn't become an issue until much later with the oilhead bikes.  I can't find any mention of final drive failures on the airhead bikes single sided swing arm or double sided so I wonder what changed when oilhead production began to cause issues with the final drives?  I've always believed that by switching to the single sided swingarm which eliminates the rear axle was the root cause of all the final drive failures.  Maybe this isn't the case.

[dirtrider]

1 hour ago, JamesW said:

I could very well be wrong but I think BMW began using the single sided swingarm on the 1979 R80GS.

 

It also seems to me that the final drive failures didn't become an issue until much later with the oilhead bikes.  I can't find any mention of final drive failures on the airhead bikes single sided swing arm or double sided so I wonder what changed when oilhead production began to cause issues with the final drives?  I've always believed that by switching to the single sided swingarm which eliminates the rear axle was the root cause of all the final drive failures.  Maybe this isn't the case.

 

Evening James

 

Pinning down the oilhead final drive failures to one thing or to one area is going to be a difficult task.

 

Right from the get-go there were random crown bearing failures on the oilhead bikes.

 

A lot of speculation early on  that  the rear brake rotor heat migrating into the bearing (1100 had the  brake rotor mounted to the axle spool) was causing the bearing failures (maybe something to that as BMW moved the brake rotor to be mounted on the wheel  for the 1150 bikes. But 1150 still had some crown bearing failures.

 

Then you have the ever popular crown bearing shimming (or improper factory shimming as the cause)-- might be something to this also but  if a simple shimming improvement would  have cured the failure then BMW would have corrected this as years went by & they figured this out  (not a doubt in my mind the BMW looked into the shimming as a possible failure  cause & addressed this at assembly inspection &  better assembly set-up procedures). In fact BMW removed the shimming requirement for crown bearing  preload on the 1200 bikes as they went to a floating spool with a crown  bearing designed to not need shimming.  (still failed a few 1200 crown bearings but the ones I have seen failed were for a different reason)

 

Then you have the ever popular grit entry through the top vent -- I know for  a fact that the vent allowed water & dirt in as I could see the sand/dirt trail on the baffle inside the final drive on some that I took apart (In fact I added a remote vent to my 1100 & 1150 bikes by remote venting the final drive to the air cleaner box). I'm not sure that was the end-all  cure for bearing failure but it kept the dirt & water out of the final drive anyhow. BMW must have thought the same thing as the (hexhead) 1200 bikes final drives were designed &  built  without any  vent (that then brought on other issues like seal leaks & bearing chamber gear oil ingress). Solve one problem but add another?

 

BMW did play with the number of balls in the crown bearing over the 1100/1150 run by going back & forth between 19 & 17 balls.  The 17 ball allowed a thicker more robust ball separator to be used  (ball separator failure was the usual cause of full bearing failure) but the 17 balls carried more load per ball & that added to bearing stress. The 19 ball bearing handled ball loading better but required a thinner less robust ball separator. (neither seemed to be the answer to stopping all the  bearing failures).

 

Then you have my personal suspicion of using tires with no carbon reducing static bands that allowed a build up of static electricity in the tire, to the wheel, then arcing across the bearing balls to the final drive assembly pitting the bearings slightly, then the rough bearing wearing the ball separator & allowing it to come apart.

 

Might be one or more of the above, or might a stack-up of the above, or might be none of the above, might be that the final drive just wasn't designed with a large enough crown bearing to handle the loading, might be a switch from bias to radial tires,  who knows but they definitely had a number of bearing failures through the 1100/1150 era.

 

I would also imagine that some 1100/1150 crown bearings were slightly brinelled by improper trailering the bike as without the wheel rotating the bearing balls sat in the same place in the races as the bike bounced along for hours on a rough riding trailer. 

 

The 1200 (hexhead) final drive addressed some of the shortcomings of the 1100/1150 final drives but in typical BMW style the NEW  fix brought on new issues that I call designed to fail. The no vent thing was a bad move but if more air volume was built in it could have worked (BMW finally went back to venting on the camhead 1200 but that venting was done correctly using a membrane that allowed pressure in & out but wouldn't pass dirt & moisture).

  

BMW did change the (hexhead) 1200 crown bearing to be a clean bearing (use it's own grease & not run in the contaminated gear oil (would have been a good move IF the drive was vented so the hot drive didn't suck water & contamination into the bearing as the hot drive was run through cold rain water & the interior cavity went to negative pressure). The basic seal used was designed to keep the grease in not keep stuff out under a negative pressure operation.   

 But to me the BIG disappointment in the 1200 final drive was the crown bearing fit design (designed for failure if you will). That darn 1200 crown bearing was a press fit on BOTH the ID & the OD (stupid design) as that required the spool to be perfectly machined to a very tight tolerance, required the cover bearing bore to be machined to a very tightly controlled tolerance & also required the bearing itself to be perfectly within specifications as well as have perfect C rating so it didn't run too tight or too loose. (The too tight side was the bearing killer)

 

  

   

[JamesW]

Hi DR, I added a remote vent to my RS final drive as well and I know for a fact that water and dirt can and does get into these final drives through the vent as it was originally installed.

 

Still curious as to why FD failures seemed to become more frequent beginning with the oilheads but apparently not with the airhead bikes.

[dirtrider]

9 hours ago, JamesW said:

Hi DR, I added a remote vent to my RS final drive as well and I know for a fact that water and dirt can and does get into these final drives through the vent as it was originally installed.

 

Still curious as to why FD failures seemed to become more frequent beginning with the oilheads but apparently not with the airhead bikes.

 

 

Morning James

 

Maybe it isn't a mechanical thing but more related to the oilhead bikes appearing in the home computer age with dedicated BMW motorcycle  forums where  riders could post their failures. 

 

Or maybe related to awareness-- in the old days if a BMW rider had a failure the dealer told him that it is the first one of those they have ever seen & the rider believed it (one of a kind random failure). BMW dealers still say the same thing (first failure ever seen) but the modern rider knows better due to electronic media available now. 

 

I have lost track of most of my 1100/1150 bikes that I used to own but one rider that bought my 2002 1150rt bike now has over 150,000 miles on it (been to all the states except Hawaii)  & sends me an E-Mail once in a while (showing a new state & bike packed sky high with camping gear)

That bike failed a crown bearing on me at about 17,000 miles-- I rebuilt the drive with a new  17 ball crown bearing, properly shimmed, & added a remote vent,  afaik- that bike is still gong strong on that same final drive since then.  

 

 

[JamesW]

You know...I just can't get too excited about a possible future FD problem.  I pay attention to my FD and do the rear wheel shake test regularly and if it fails I'll just fix it and hopefully catch the problem early enough to avoid finding a new drive.

 

You're most likely correct about airhead issue drive failures in that there just wasn't the communications back then anything like today.  Probably not that many early R80GS bikes around to fail for that matter.

[Paul De]

Wild speculation here but going from airhead through the various iterations of the boxer motor included dealing with running more power through the drive train with each generation.  Maybe to keep unsprung weight down BMW was always designing the final drive without any added margin for the loads it could see.

[LittleBriar]

I'm a first time BMW owner so don't know much of the history of the FD failures. I understand the problems have pretty much been fixed on the wet heads. Is that correct? If so what was the fix?

[Paul De]

The Wethead is pretty new but after 6 years the anecdotal information is this iteration of FD is a reliable design.  Shiftcam I think uses the same FD and you could include their FD issues in the group as time goes by.   I would say in any system reliability discussion you should keep the perspective of total units in service VS noted failures and in that light all the FD versions would be considered reliable.  That said, if you owned one of the minority of machines with a FD failure you care little of the thousands of others who have had no issues. Naturally, with a shaft drive system that is supposed to last the life of a machine capable of a few hundred thousand  miles of service and is costly to repair, it will get a lot of notice of even a few failures occur.