Misaligned wheels

[BSA Bob]

Some bad news now I've stringlined the rolling chassis of my R26. The wheels are out of alignment.
With the string on the left hand side of the bike, it touches the wheels at 3 points. It touches both points of the front wheel. It touches the rear point of the rear wheel. The front point of the rear wheel is 3-4mm to the right. Meaning of course that the rear wheel points slightly to the right.
I've repeatedly checked this, I've swapped the wheels round & tried a spare swingarm & get the same results every time. I'm wondering about my next move. What do people think?

[BSA Bob]

[Kees]

Zieht er nach rechts? Beim fahren?

[BSA Bob]

Hi Kees
No, this is only the frame, forks & wheels together. I can't tell what it would be like on the road.

[4Taktix]

Spare swingarm on the rear or in the front ?
Several possible rootcauses:
- Fork bent/damaged ( string left + right parralel to steering head + compare distance )
- Frame bent/damaged
- Wrong spacers front
- wrong parts or assembly of bearings/spacers/shims in the front hub.
- one or both wheel-spokes assembled off centerline

just my first quick ideas.

Regards,
Sascha

[Kees]

I wouldn't worry about 3-4 mm's.

[cwf]

If you've ever had a chain-driven bike, you'll know there are rear wheel adjusters that help to keep the wheels in line. Many people don't know and their rear wheels point in a slightly different direction to the front and they don't notice.

If the frame or swing arm are bent, I've used Motoliner in Maidstone, who have done a good job.

Charlie.

[Jollyjester]

I have heard good reports on Motoliner.

Some years ago, 4-5-6, a Gentleman came to me having restored very well a Pre 1940 BMW. He wished me to 'sort' the ' Official Registration and confirm the R xxx was actually an R xxx from 1939, in my Official Role.

However, what had been over looked was discovered when they found the drive shaft would not fit.

The frame was bent!!!

Motoliner have skills to correct this, which they did successfully. No idea of the cost, but it was that or nothing

[rolf]

I wouldn't worry about 3-4 mm's.

I THINK THE SAME

[BSA Bob]

Thanks for this input folks. I'll put up more information so we all know what we're talking about.
As I said, the string on the left touches the front wheel at its front & rear points. It touches the rear wheel at only the rear point. The front point of the rear wheel is about 3mm to the right, meaning the wheel is skewed to the right.
On the right of the rear wheel, with the string touching at both its points there's about a 10 mm gap between the string & the front tyre.
Sorry to ask the question again but what do people think?

[Kees]

You could check a few other things too.
- are the wheels vertically parallel?
- is the too frame tube still straight? After an accident this tube easilly buckles upwards. The infamous Katzenbuckel.
- are the two front lower frameloops still straight? Easy to check with a flat wooden panel.
- straightness of the frontfork. Axle parallel with swingarm pivot and square to stearinghead tube.

[Kees]

Have a look here too: https://forum.2-ventiler.de/vbboard/showthread.php?84734-Rahmenlehre-Allianz-f%FCr-BMW-wer-kennt-die-Bedienungsanleitung

Especially answer #6 shows how the old fashioned BMW frame meassuring jig worked and the allowable misaligment with this jig. With a bit of trigonometrics you could calculate how skewed your frame could be before it falls outside of factory specs.

[cwf]

By the way, what size are your tyres? Because only if they are the same size can you hope for a string to touch at all four places.

Charlie.

[Kees]

Remember when you use Duane Ausherman's test with strings on both sides (https://w6rec.com/tests-for-a-bent-frame/), he does this on a /5 which has a 4" rear tire and a 3.25" front tire. So he projects the "box" of the reartire around the front tire with the two strings which is possible because the rear is wider then the front. On the R26 both tires are probably the same so you run into troubles with this same test. You could make your rear tire a bit wider for the test with a few 2x4's and a bunch of gaffer tape.

[Kurt in S.A.]

Remember when you use Duane Ausherman's test with strings on both sides

Kurt

[BSA Bob]

Thanks for all this.
Both tyres are the same size, cwf. So using the Ausherman idea, running lines from the rear wheel the right string clears the front tyre by about 10mm. The left string of course runs into the front tyre 10mm in.
I think the rear wheel has a slight vertical twist to the right at the top, not sure. And there's a different measurement between the top motor mounts & the swingarm pivots. Left 483mm   Right486mm.
Kees, I wish I had one of those jigs.
Kurt, you've seen my post on the VBMWOA. I'm trying to change the username to the one I use here, no luck so far.
So the bottom line is, how do you all think this will affect the bike? An R26 wheelbase is 975mm. With a difference of 10mm at the front, this means there's difference of about 1mm in 10.
Rolf, if you're reading, I'd like your ideas. And anyone else.

[Kurt in S.A.]

Kurt, you've seen my post on the VBMWOA. I'm trying to change the username to the one I use here, no luck so far.

I will check to see how that can be done.

Kurt

[cwf]

Have you tried these people? https://blueprintengineering.com.au/ (motorcycle frame straighteners in Adelaide)

Charlie.

[rolf]

first, THE tyres had to be parallel (?)
not very necessary to be in one line.....ok, it is better..but not so important
Look at the people who has a bigger rear wheel, and so the respoke (?) the rearwheel out of the middle....no problem to go 10-20mm off the line
Enough pidgin english ....if you don`t understand some parts of my pidgin....ask
Relly....the only important thing is that the wheels are parallel

[Kees]

Let's do some theory. Basic trigonometrics.

Your bike is like my first drawing. I pressume you meassured the 10 mm at the front of the frontwheel. So, distance between the middle of the rearwheel and the front of the frontwheel is about 1430 mm. That makes a misalignment of 0.4 degrees.

Second picture is the BMW jig for post '70 bikes. Presume that the tolerance is the same for earlier bikes. I guess the jig is 500 mm wide. The allowed misaligment is the checkered circle. I conservatively guess from this picture it is 10mm diameter, 5mm radius.

Third picture is a drawing of the jig in a skewed frame. Angle a = angle b. Angle is arcsin (5/250) = 1.14 degrees misalignment allowed.

There is still a length issue in here. the jig is about 110cm long while your wheel base is 140cm. But still, 0.4 deg is a lot less then 1.14 deg. I think you are safe and your frame is straight enough.

Of course I just did this quickly and could be wrong. If someone wants to blow holes in my theory: please, be my guest! We can all learn from this example.

[rolf]

don`t forget
Parallel is the only thing that counts

[Kees]

Ja parallel waere schoen. Aber dievon Bob ist nicht parallel. Daher habe ich versucht aus zu rechnen wieviel unparallel die raeder sein koennen.

[BSA Bob]

Once again thanks for this.
cwf, I've looked up frame straighteners here & this lot have a very impressive website. My mechanic knows another firm.
kees, thanks for all those drawings. I see the calculation for the first drawing, 0.4 degrees out doesn't seem much putting it that way.
I understand the drawing of the jig but not the calculation. Wouldn't the 10mm distance need to be considered? I'm probably not getting this right, no head for maths.
It's easy to turn the forks to get the wheels parallel as Rolf suggests. Doing this, the wheels are of course not following in the same track. The rear wheel track is 9mm to the right of the front.
My mechanic says the bike will be quite rideable like this, it's up to me whether I'm satisfied with it.
There's a slight & short downhill in front of my house, but it's a dirt road. I tried the chassis, not very fast (20-30 km/h? I don't know) & it felt OK but this isn't much of a test.

[Kees]

Hi Bob,

The last drawing is the jig in a twisted frame. It's not so easy to imagine your case where the wheels are twisted in a horizontal direction, it is much more obvious in the vertical direction, like when your wheels are tracking properly behind each other at ground level but they are leaning over in different directions. So, I think my drawing is kind of correct, but I am not 100% sure. It sure doesn't need the 10mm of your misaligment, because this allready represents a jig in a twisted frame.

[rolf]

Ja parallel waere schoen. Aber dievon Bob ist nicht parallel. Daher habe ich versucht aus zu rechnen wieviel unparallel die raeder sein koennen.

das kann man aber schön am Rahmen hinbiegen
ein Bekannter hat so seine R 75 und KS sen eingestellt ( 8 sTÜCK NANNTE ER SEIN EIGEN)....Räder rein....dann am Rahmen gebogen (beim Starrrahmen geht es einfach) bis sie zumindest parallel liefen...fertig

[Kees]

Meinst du vertikal parallel? Weil im Fahrrichtung parallel konnte man einfach der Lenker ein bischen drehen.

Immer schwierig diese Dinge nur im Schrift ein ander zu erklären.

[BSA Bob]

Kees, yes it's hard to get your message across sometimes. When I said I could get the wheels parallel I meant in a horizontal direction.  As the bike travels down the road the wheel tracks would be parallel but the rear track would be 10mm further to the right than the front.
There's a small vertical misalignment too, I'm trying to work out how to measure it with the stuff I've got.
I did some more measuring, I ran lines between the  front motor mount bolt & a rod I placed between the swingarm pivot points on the left & right of the frame.
It definitely shows a twist with the right swingarm pivot a couple of mm above the left. I can't measure the amount, by eye it looks about 2-3mm. I   measured the distance between these points & they seem equidistant, I couldn't get the measurements exact.

[Kees]

I don't think they need to be 100%, but it is now up to you to decide.

Mine isn't 100% either but I decided to leave it like this: https://bmw-einzylinder.de/forum/index.php?topic=21276.msg321785#msg321785

[BSA Bob]

Kees thanks for that thread, I'll examine it carefully.
Thanks to all who helped here and yes,  now it's up to me to decide. Any work's a few months off so I've got time to think (obsess?) about it.

[BSA Bob]

I'd better add that I've found one problem. Running rods through the top motor mounts & swingarm pivots, they aren't parallel.
The left pivot point measures about 3mm forward of & below the right. Eyeing the frame, I think it's the left side that's out.