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Old 06-10-2013, 02:43 PM   #83
Gnarly Adventurer
Joined: Mar 2006
Location: Mid-California
Oddometer: 264
I read up on the stem issue on the other thread. It looks like the old nut from KTM had 20mm of threads and then used a ~3mm washer leaving ~17mm of engagement. The replacement nut has 12mm of thread height but only 8mm of engagement because of the wide thread relief at the bottom. Either one is fine for a KTM, but apparently the different bearing taper of the BMW bearings requires significantly more torque than the KTM stem/nut were designed to take.

I don't know if this is really a huge problem, as I could only find one instance of it happening. Never-the-less, it seems like a good idea to address the issue at this time. I have cancelled the order for the KTM stems and have placed an order for 7075 stock to machine them from scratch. I will maximize the thread engagement on both the nut and the stem.

Since the parts are being machined from scratch, maybe it would be a good idea to copy the thread pitch of the BMW stem bolt so torque values would remain the same for the BMW bearings? This might eliminate some confusion regarding setup. Does anyone know offhand what the thread pitch is on the BMW P/N 31 42 1457859 "Screw" used on the '87-'91 R100GS?
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