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Discussion Starter · #1 ·
For the techos of the forum, Curtis and the like, I have researched some information from the SKF Catalogue and put together a document which may help when checking and assembling the 61917 C3 Bearing on the bevel gear trunnion and in the FD housing. Hope this is useful, Dennis.
 

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K100Dennis said:
For the techos of the forum, Curtis and the like, I have researched some information from the SKF Catalogue and put together a document which may help when checking and assembling the 61917 C3 Bearing on the bevel gear trunnion and in the FD housing. Hope this is useful, Dennis.
Dennis, Thanks for posting this.
 

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Thanks Dennis! Printed, and added to my book of K12 Maintenance!
 

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Dennis - Awesome job... Cheers mate!

I reformatted spacing and margins slightly to fit US Letter size paper, and added footnote to indicate revised version. I hope you do not mind.
 

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I suggest one additional decimal point be added to the .pdf inch dimensions to accommodate those of us that still have only inch micrometers.

These numbers are from SKF for a standard application, where we have aluminum hub and housing Maybe we can eventually add some actual readings (including measurement temperatures since we are dealing with aluminum) from the FD rebuild gurus?

Aluminum expands about 11x10^6 microinches/inch per degF.
 

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niel_petersen said:
I suggest one additional decimal point be added to the .pdf inch dimensions to accommodate those of us that still have only inch micrometers.

These numbers are from SKF for a standard application, where we have aluminum hub and housing Maybe we can eventually add some actual readings (including measurement temperatures since we are dealing with aluminum) from the FD rebuild gurus?

Aluminum expands about 11x10^6 microinches/inch per degF.
Hi Niel,
You are still stuck on calling the hub aluminum. I know you corrected yourself before, but you're still stuck on that "brain fart". ;)
Aluminum housing, check.
Aluminum cover, check.
Crowngear assembly tapered roller bearing end- Aluminum, check
Crowngear assembly, crownwheel bearing end (the hub the rear wheel bolts up to) - Carbon steel, not aluminum. This is the trunion that the inner race of the crown wheel bearing is pressed onto.

The interference fit of the inner race of the crownwheel bearing onto this hub is pretty tight. Having pulled off more than 50 of them with a bearing puller, they are on there pretty good.

There was speculation quite some time ago that too tight a fit might be contributing to premature bearing failure by causing bearing impingement. But I think that the looseness of the C3 bearing gives some latitude here. It is the preload on the bearing that is the issue. The more I learn, and the more I think about this, I'm increasingly convinced that it is excess preload shim thickness that is the primary cause of the "classic" crownwheel bearing failure.

Thanks again to you and all those who have contributed to our increasing understanding of the problem. :thumb:

Addendum: as far as getting measurements, I still haven't purchased the needed measuring instruments. The frequency of FD rebuilds in my shop is slowing down, so I'm not sure I'll buy those tools; and I'd have little other use for calipers and micrometers that big. So don't hold your breath. ;)
 

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niel_petersen said:
Yr right (as usual)! BF from just three days ago recognized (again!) :histerica
Right after seniority comes senility.... :D

Problem is, I never had seniority.
 

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Discussion Starter · #9 ·
Niel, point taken on going to the fourth decimal for the imperial measurements. I rounded it, but as you know, just divide the metric number by 25.4 and use as many decimal points as you like. On the housing fit, I had to make some assumptions as SKF don't provide a table for aluminium housings. Some accurate bore diameters from a good housing would be great so I can close the loop on that one.

Curtis, just a point, the inner bearing raceway should never be "pressed" onto the trunnion. I think you would know this. Heat the bearing (to maximum 110 degrees C) using hot oil (an old deep fryer works well), then slip it onto the trunnion (which can also be pre-chilled). Take care to keep it snugged down to the shoulder or abutment during cooling as the bearing has also expanded in width during heating. To do the set-up for the preload calcs I would advise that the housing should be heated up to around 60 degrees C and chill the bearing & bevel gear in a freezer. The bearing can then be inserted into the housing without degrading the fit interface. Let the assembly normalise before proceeding with measurements etc. One other thing - I would really like to get my hands on an old FD housing, so if anyone in Australia knows of one please let me know. Best regards, Dennis.
 

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K100Dennis said:
......the inner bearing raceway should never be "pressed" onto the trunnion. ..... Heat the bearing (to maximum 110 degrees C) using hot oil (an old deep fryer works well), then slip it onto the trunnion (which can also be pre-chilled).
We speculated in the past that improper bearing installation might be playing a role in premature crownwheel bearing failure, but I think that would be unlikely at the factory. Installation pressure applied on one race, through the balls, onto the other race would be damaging. However, nothing I have read tells me that pressing directly on the race that is being seated would damage the the bearing as long as parallelism is maintained.

Temperature guidelines for heating/chilling components are found in the BMW Service Manual. I suspect that the Clymer's manual has the same data but I'd have to confirm that.
 

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Discussion Starter · #11 ·
BMW Service Manual,........... I'd like to get hold of a copy of one Curtis. Where are they available ? I think my Clymers is more generic in this area, or they often state "refer to an authorised BMW dealer" etc. One can never have enough technical publications, maybe I need to get a life !
 

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K100Dennis said:
BMW Service Manual,........... I'd like to get hold of a copy of one Curtis. Where are they available ? I think my Clymers is more generic in this area, or they often state "refer to an authorised BMW dealer" etc. One can never have enough technical publications, maybe I need to get a life !
I bought mine, a printed copy, from a BMW dealer. I understand the manual has been available on CD for sometime. (Some enterprising individuals sell pirated CDs and manual downloads on the net).
 
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