Frame Swap, frame shims, alignment and the like...

[552255]

Collision damage to K1100LT--

Fishing for some opinions and thoughts on the frame shims i found while swapping out a bad twisted frame.  I noted where they were located for replacement...

My question:  are these just to snug fit/fill the gap to engine, tranny etc.  So you don't bend/tweak the frame upon tightening the bolts?
I see a number of thicknesses available on the MAXBMW site, ie. they vary by .25mm's.

Or, is there something to do with alignment?  Seemingly you could project(stringline) the rear tire planes forward, and possibly adjust the front tire, by shimming the frame either way to get the best centered track alignment?

Sorry for no pictures (have taken many) but havn't had time to download and figure the posting procedure yet...

and, read once where BMW lower tree doesn't bend...mine was very slightly, used a press to fix, fork tubes rolled ok on flat surface (so that was great news) whew...

thanks for all the good advice found here!

Eric,
Lincoln, NE

[johnny]

if it were me...

1... score a new to me moto and retire this 63mm offset tweaked frame moto as a parts donor moto...

j o

[Scott_]

Here's a page from the BMW service manual on installing the frame to the engine.

[552255]

Clarify, clarify...

I have a new(used) straight frame ready in place to bolt down, just getting wiring etc. figured out.  The bike has 25k.

Have the manual diagram printed out already...it just looks like they're may be some adjustment possible in the design of the engine/tranny acting as the lower chord of a frame, and possibly a factor to which alignment is 'set' per se...

or that the shims are just that, spacers between the engine and frame, to take up any space between, so the frame doesn't "bend" in with tightening.


...why the large array of shim thickness's off the MaxBmw fiche?

[Rick G]

BMW say that the shims are to take up any clearance so the frame doesn't get stressed when the bolt is tight. apparently it prevents cracks. I have seen several K frames crack just in front of the rear shock mount and same place on the other side but I am not sure if it was related to not having shims.
I have not had one crack on my but its heaps of fun riding a big lump of jello, bit like a Z900 Kawasaki

[Dalderton]

Bmw frames can be a bit odd. In a former life I straightened Motorcycle frames for a living and the earlier boxer frames before the single sided swing arms I found that some of them must have been out of alignment from the factory as there was no logic to the alignment problem. Normally when a frame is bent or twisted there will be a twist causing the out of alignment where in some cases the alignment was wrong but the steering head was not twisted. For this to happen either the swing arm pivots would have to be bent or the front downtubes would have to be moved sideways without twisting. Does not happen. I spoke to a knowledgeable bloke who actually saw the frames being built at the factory and he said that as they tack welded the frame in a jig then removed the frame to finish weld it and that could have been the cause. Actually this would be unlikely to happen with a K series frame as the angles of the tubes in the critical areas are  much better design and form triangles rather than squares.
 From my experience the shims would be only for spacing in between the frame and bearings.
  Assuming that the wheels are running true to each other ( put a bar with tapered mandrels through the steering head  then with the back mudguard off pull a string from the top of the bar over the centre of the back wheel  and pull another string from the bottom of the bar under the centre of the back wheel and if they meet at the back of the bike then the vertical alignment is QK. Then put a straight edge either side of the back wheel out to the bar through the steering head and measure the distance from the straight edge to the bar on both sides. If this is with 5 to 10 mm  it should ride OK.
  Hope this helps. Regards Dennis.

[552255]

Thank you gents for the excellent timely advice.  I will first shim/tighten according to the manual while checking for gaps between frame mounts and then check the wheel alignment.  Hopefully it will not need any other spacers than the previous frame used... 

thanks for the good write up method for checking alignment, i kinda figured the shims were mostly to take up the space, but could have some bearing on alignment.  As long as the frame is straight (enough) "extra shim adjustment" shouldn't be needed...ha! famous last words.

Hot as hell in central U.S.,  corn and beef prices going up...

Regards, Eric