double disc question

[steven m]

I've been gathering the parts to double disc my trusty 83 standard R65 and have a couple of questions as even the parts diagrams on MaxBMW and RealOEM aren't clear.  What size bolts should be used to mount the discs, 70 or 100mm?  Both are listed.  100mm is pretty long for what seems to me to be a narrow hub.  And are you all running the large plate washer between both discs and the hub or only on the left side?  The right side of the hub is a flat surface while the left side is cut out.  I guess this is why the different sized sleeves are needed for the caliper mounting bolts?  Seems like a good idea to have the correct hardware BEFORE I take it apart.

Steve

[Bob_Roller]

You need the longer bolts for a dual disc installation .

There were no plate washers on either my '81, and '84 LS bikes, they were factory installation, no one had taken them apart since leaving the factory .

[steven m]

Thanks Bob.  Do the plate washers, meaning the circular plates with five holes in them, go outside of the disc then?

[steven m]

Or do you mean no plate washers at all?  Fine with me either way.  

Steve

[Bob_Roller]

I had no plate washers installed at all on either bike .

[nhmaf]

I'm not 100% certain, but I think that the hub width of the LS wheels is not the same as the snowflakes, so you *might* need some spacer/washer combination with the snowflakes that you don't with the LS front wheel.   I don't have a snowflake for direct comparison, however..
the dual disc brake was a dealer-installed option for the non-LS bikes, so perhaps a dealer would have a "kit" or list for the parts required?

[Bob_Roller]

BMW only had two bolt lengths for the front disc's, the 70 mm was for the single disc, and the 100 mm was for the dual disc application .

I made the mistake of ordering a 70 mm bolt for the LS, and it was way short for the dual disc application .

The '81 model year North American R65's came from the factory with dual discs, it was not a dealer add-on, it was the only year BMW did it for the non-LS bikes .