Swing Arm Installation OMG

[Dave 2]

Hello, I have the swing arm in place with new bearings, oil seals and pivot pins. I have reviewed Snowbum and Duane Ashermans tech articles, Googled, and visited a couple of web forums and I still have the jitters about tightening the pins and lock nuts. Clymer wants the pins screwed all the way in and then to preload the bearing by torquing to 20nm. Asherman gets confusing to me when he talks about using new bearing and pins. Otherwise he wants the pins tightened to the point that there is no sideways play.

This morning I tightened the pins until I had no sideways play, and then went to torque [smiley=wall.gif] I did not get much over 15nm and I started spinning...I removed the pins and observed that the thrust sleeve has pushed the inner race in a bit. the bearing still seems to be aligned and spins freely. Can I just put it back together with only enough tightening for side to side play? Do I need to replace my new bearings???  When will I ever learn about too much tightening? Thanks D2

[Dave 2]

I tried to put it back together again, and the bearings are definitely pooched. So live and slowly learn. D2

[montmil]

Latest issue of Motorcycle Classics magazine has a very nice photo essay DIY swingarm bearing job on a Slash 5 BMW. Some good tips. Mostly correct procedural.

[montmil]

Hey, Dave. Sorry your weekend has tanked. Did you use an Allen wrench to keep the pins from rotating while torquing the lock nuts?

Your local bearing supply house should have the bearings in stock and for less dinero than the Beemer dealer.

[Dave 2]

Did you use an Allen wrench to keep the pins from rotating while torquing the lock nuts?

No...Clymer says to torque the pins before you even thread the lock nut on. Thanks for the Motorcycle Classics reference I'm not sure there is anywhere within 50 miles that will carry the mag. Book stores and magazine/newsstands no longer exist around these parts. But I will start looking just in case. Thanks D2

[Julio A.]

What I did after I replaced my rubber boot way back was tightening the pins until there were just touching the bearings and as soon as sideways play was removed. I did a quick torque wrench check then I just hand-tightened the lock nuts.

The specific torque value stated on the Service Manual was 10-12Nm or 7.3-8.8 lb.ft.
It also stated that: "There must be no play on the bearings as well as no excessive preload."

Snowbum also advices to tighten those pins to 15lb.ft, then backing it off to 7-1/2 lb.ft.

There is a BMW specific tool for the job that permitted you to use an allen to make the pin stay in place while you tighten the lock nuts. As a rusty lock nut (like the one on my bike) would make the inner pin want to spin around with it.

[Barry]

D2,

In principle I don't think you did anything wrong and I'm not clear why the bearings are damaged.

The procedure that I followed is to torque the pins to 15lbft to seat the bearing then back off and torque again to 7.5lbft which is the normal amount of running preload. The trick then is to tighten the locknuts without the pins moving. There's a special spanner but all I did was to carefully mark the position of the pin and check after torquing the lock nut that it hadn't moved.

Normally there is no reason why the bearing pins can't be slackened off and torqued again several times in fact that's usually required to get the swinging arm gaps equal either side.

[Bob_Roller]

Can you post pictures of the bearings .

I don't think the load you applied to the bearings would have damaged them .

[montmil]

What Barry says.

Yes, you do torque the pins to set bearing preload, then back them off about half of the initial torque specs. The nut to crack is preventing the pins from self-tightening while the lock nut is tightened.

BTW, the Motorcycle Classics magazine shows a rather ghetto way of achieving the final results. They show a 27mm socket clamped in a ViseGrip plier. An Allen wrench passes through the socket and is used to hold the pins in their correct setting.

Seems rather tractor-like but it gets the job done.  BMW=Green Acres [smiley=cowsleep.gif]

[Bob_Roller]

I've got what is called an O ratchet, the ratchet drive is hollow to allow you to hold a threaded fastener, while tightening up the nut, or what ever you are trying to tighten up .

I originally got it to tighten up  Mc Pherson struts when installing them in a vehicle .

Does a great job on the swing arm nut .

[Dave 2]

Hi All, Thanks for all the comments. I will post pictures tomorrow...the new pivot pin threads seem to be damaged to some extent as well...Maybe everything is ok, but i've got that gut feeling that is telling me that I screwed up. (no pun intended). I think I need to do some reading on metallurgy as it relates to the issues of nuts, bolts, and torque. Any suggestions?  Thanks again. D2  

[Dave 2]

Here are a couple of pictures of the swingarm bearings in their post torqued state  They don't look serviceable to me. D2

[donbmw]

To me it looks like the bearings and race are not installed right. I looks backwards. The outer race goes in first then the bearing. the pivot pin pushes on the inner race and the tapper bearing is pushed on the outer race then torqued.

[Barry]

Never mind the bearings D2 that's a fantastic paint job on the swinging arm !

I'm with Don, Outer racer in first with the widest part of the taper facing out then the bearing then the inner race (On the left side grease retainer plate goes in first before the outer race). Assembled that way although excess torque on the pivot pins might eventually damage the bearing surfaces no amount of torque would push the bearing in further than it should go.

[Dave 2]

Never mind the bearings D2 that's a fantastic paint job on the swinging arm !

Thanks Barry, it is actually powder coated [smiley=bmw_smiley.gif]  The whole bearing assembly was packaged together. Outer race with tapered bearings, inner bearings and finally the thrust Sleeve. I put the whole bearing assembly in as a unit. Big hammer and a hard block of wood until all was level with the end of the swing arm. I then centered the swing arm on the frame and tightened the pivot pins until I had no sideways play. I could have then set the lock nut, but I was afraid that I had not "preloaded" the bearings, even though I pounded the hell out of them to get them in place. It was at this point that I put the torque to her and she failed. I plan to call the tech support people for my torque wrench to be sure that I'm using it properly. Maybe I put the bearing assemblies in upside down I do that kind of thing more than I would like to admit. I obviously can not do this again until I figure out what happened. Thanks for all your suggestions. D2