Swing arm preload.

[ME 109]

What is/are the correct methods to set swing arm preload, given that tightening the locknut can/does increase the preload?
I aim for just a small amount of preload, so as not to crush the bearings.

[Ray from Indiana]

Chris Harris uses 10 N-m

http://www.youtube.com/watch?v=qXXnNQf2F_k

I enjoy his videos. We should urge him to do a trans rebuild video, no?

[Kurt in S.A.]

Snowbum describes the method quite well.

Kurt in S.A.

[Deleted User 287]

Snowbum describes the method quite well.

Kurt in S.A.

I looked for it (quite well), and could not find it.

But looking closer now, I did find it. At the bottom of a very long page...

http://bmwmotorcycletech.info/frontforks.htm

11. The rear swing arm must be adjusted correctly. If not, the motorcycle will not behave
properly during your test ride.

NOTE: TWO types of swing arm pivot pins are in use. The very early type was 48 mm
long, and the wrench needed is 6 mm hex, up to production of 09/1980. Thereafter they are
42.5 mm long. The thread has always been 20 x 1.5 mm. Both types will interchange.

To adjust the swing arm, first insert the pivot pins (if not already), and tighten very lightly with an
allen wrench (NOT a torque wrench), and go back and forth between the left and right pivot pins
until the spacing from the swing arm to frame is approximately the same, as seen with your
eyeball, or using a drill shank or small allen wrench as gauges. Approximate is OK for this first
step. This approximately centers the swing arm in the frame. Install the locknuts (if not already)
with your fingers or the modified 27 mm or modified 1-1/16" socket (see below on the socket
modification. The nut should NOT be tightened, but maybe a couple turns loose.

Torque ONE side pivot pin allen (hex hole) clockwise to 15 ftlbs. Back off from the 15 setting
maybe half a turn, then re-torque IN clockwise movement (only) to 7-1/2 ftlbs.

Check the spacing from frame to swing arm. See if it is the same, left and right. If not, back off
one pivot pin & tighten the other. Remember, clockwise movement during the tightening to 7-1/2
ftlbs. When the spacing is the same, then tighten ONE of the locknuts to 72 ftlbs of torque.
Recheck the spacing. If still OK, then torque the other side's nut to 72 ftlbs. If the pivot pin
and nut threads are in good condition, the tightening of this fine threaded nut will NOT cause the
pivot pin to rotate during the 72 ftlb torqueing. If you are worried about that, put a mark on the
pivot pin face and associated frame opening, so you can see if the pivot pin moved after you
tighten the nut.

The final step is to force grease into the hex holes with a rubber tipped grease gun. I prefer to
force enough into the bearing, and out into the area between frame and swing arm, to have to
smooth it into a ring of grease, with my finger tip. This will keep water and dirt out of the bearing.
Grease the same way every now and then.

The socket: You can use a 27 mm or 1-1/16" socket. The socket MUST be modified by grinding
the END so there is no taper on the inside, as the 27 mm nut is thin and you do NOT want to
injure the nut. Grind the OUTside of the socket, and do this squarely!.... where it fits into the
swing arm hole... so that the socket goes past any internal projections and then over the 27
mm nut completely and thoroughly. To explain that further, SOME bikes have a second circular
"ridge" inside the swing arm hole, so the socket must be ground on the outside. The very
nicest way to modify the socket is to chuck it in a three jaw chuck on a lathe. The entire job
can be done very neatly on a lathe in 5 minutes.

[ME 109]

Snowbum describes the method quite well.

Kurt in S.A.

I went to his site Kurt to have a look.

Unfortunately the tour guide went home and wont be back till Monday.

[Duane Ausherman]

Chris Harris uses 10 N-m

http://www.youtube.com/watch?v=qXXnNQf2F_k

I enjoy his videos. We should urge him to do a trans rebuild video, no?

Who is this Chris Harris? Does he post here?

That video is full of errors. Too many to bother starting to describe. It is obvious that he cares, but has been trained by somebody that knows very little.

I highly suggest that you read my page on this procedure. http://w6rec.com/duane/bmw/swingarm/

I must apologize for the typos in my article. One or two might be tolerable, but I made a lot of errors in my use of the English language.

Where did you get the idea that tightening the locking nuts added pre-load? If you secure the pin, then tightening the locking nut may reduce the pre-load because it pulls the pin back away from the bearing.

[SteveD]

Chris Harris uses 10 N-m

http://www.youtube.com/watch?v=qXXnNQf2F_k

I enjoy his videos. We should urge him to do a trans rebuild video, no?

Who is this Chris Harris? Does he post here?

He's a u-toober Duane. He's done a few hundred short videos and is quite the character it seems, in a younger curmudgeon sorta way!

https://www.youtube.com/watch?v=VExx_2kIc9c

[Duane Ausherman]

I just edited my post.

after watching that one video, I wouldn't allow him to change a spark plug on my bike.

I just watched the video on valve adjustment. It might be slightly better than the other video.

He completely ignored the main reason for adjusting the valves. It is a diagnostic procedure to see if the top end is stable.

I am in shock.

[ME 109]

Where did you get the idea that tightening the locking nuts added pre-load? If you secure the pin, then tightening the locking nut may reduce the pre-load because it pulls the pin back away from the bearing.

Haven't looked at your site just yet Duane, but I'll answer your question.
Securing the pin. That is my trouble. Using a socket with a ratchet does not allow me to access the 6mm hex to hold the pin still.

[Duane Ausherman]

The video shows one clever solution to holding the pin with the modified socket. One could just use the tool provided by BMW in the tool kit to do the job. I do not trust using those marks because a tiny change may not be seen by eye and it would be a huge change in the pre-load.

That much torque on the pin is way too much for a solo rig. BMW seems to still think that they are building a bike for sidecar stresses. A solo bike has little side stress on the swing arm and box section. The amount of pre-load on those bearings wears them out quickly. A taper bearing isn't made for that load where it only goes through a very small rotation. They get notched quickly, especially with too much pre-load.

It is also very important to have the pin thread in super smoothly to the frame. Otherwise the torque amount is meaningless. I have seen where pins required a lot of torque just to turn them before they got to pre-load.

The comment was made that it was easy to mess up the threads on the aluminum pin. Really? I have never seen one made out of aluminum. Did they change over to aluminum in later years? All that I have seen were steel. Go test one with a magnet and see for yourself.

I have seen them messed up many times and I don't know how it could happen. I guess a ham fisted mechanic could mess up just about anything.

Because many mechanics don't really know what they are doing, all manufacturers try to set it up to be very simple. The instructions are also simple and nearly always restrict "too much information" because it is confusing to many.

This group is far better and we need/deserve the full explanation.

The concern of the spacing is obsessive and useless. Remember that a different top hat spacer can be used to move the wheel to the left to allow a larger tire? That moves the wheel far more than the swing arm spacing. So, somehow it is important when mounting the swing arm and not important when mounting a wheel with a too large tire? See how stupid it is to be concerned with the swing arm spacing? Adjust it by eye and it is close enough.

I can't tell you how many frames we found where the box section was bent and the driveshaft would rub on the inside of the swing arm tube if the swing arm was centered. Of course the frame is bent and this is one of the indicators of a bent frame. If only the box section is bent, it may well track completely straight. It may have the correct wheel base measurement too, but it won't pass the test with the BMW frame jig.

If someone is making a YouTube video about a procedure, then it is incumbent upon them to know what they are talking about. In this case, once the swing arm is centered, then the driveshaft must be checked for centering. That can only be done with the boot not mounted on the transmission.

This gentleman fastened the boot before centering the swing arm. The final evidence was covered up.