Frame Repairs ... Egads !!

Well the last couple of weeks I have been looking very closely at my frame. While pulling the bike apart I started to notice some gravel rash here and there and a few panels that didn't quite line up. The fairing appears to be pushed to the right, see pic, which I think is just the bracket it is bolted to, and the rear lighting is also pushed a little sideways, which seems to be just a bent bracket also, all easy to fix.

Of greater concern is the repair I found to the chassis, see the second pic, which is of a couple of bolt shanks welded on the inside under the seat. My theory is that the bike had a back rack on it and regularly carried a lot of weight. This caused the frame to fatigue just behind the last weld behind the seat brackets, where the repair has been done.

I also found the rear light mount bracket to be offset a little but this seems to have been put together like this at the factory, see the third pic.

My first question:

How good/bad are these frames toleranced from the factory? I've heard the manufacturing tolerances were pretty ordinary and they were often not straight as built.

Second question:

This bike has been dropped, on both sides. Perhaps just cosmetic, perhaps something more sinister. Before I go spending a whole bunch of time and money on it, is there a straightforward way to check the alignment of the wheels? Is there any adjustment available besides the setup of the triples on the forks?

By the way it's acually a 900 frame with a 750 engine, it was built that way, but it should be basically the same as any other shaftie.

Cheers, Ian

 

Ok, no takers ... I'm thinking the place to start is the squareness of the swing arm axis to the neck bearing axis. If those two axes are not at exactly 90 degrees nothing else can compensate. So I'm going to shelve this problem until the frame is completely stripped and see if I can come up with a simple jig for checking this. Any ideas welcome ...

 

I honestly don't know a whole lot about this topic but since no one else is helping out I figured I throw in my two cents. Have you been able to notice anything feeling strange while riding? Like not riding straight, or tires wearing badly? What would be the tell-tale signs of a frame bent out of alignment? It seems to me if there aren't any noticeable detriments to the frame other than cosmetic, then it's probably not going to crumble beneath you or anything, and you could just keep a close eye on it.

 

A biker-turned-blindman invented (while blind!!) a way to check the squareness of bikes. It involved a length of extruded aluminum channel that is exactly straight, then a method of measuring and aligning along both the front and rear rims. If you use spacers and clamp the aluminum channel to your rear rim, you then measure to the front, and repeat for the other side, and everything should add up - -I think??

 

Hi Ian
I have a 750 & 3x 900s & the all have the fatigue cracks under the back of the seat.
see my thread ..

http://xjbikes.com/Forums/viewtopic/t=26352.html

 

Ride through water onto a dry surface (stay straight) check your wheel tracks afterward. The wet rear tyre track should have covered the front one, and looking closely you should be able to see some of the pattern the front tyre made, it should be dead centre. Make the puddle smaller than the wheel diameter so the tracks overlap a bit.


Not a full test, but a handy check. It actually works, so have a play.

 

If you have a 6' aluminum carpenters' level or even a 6' straightedge, it's easy. You lay it across the rear tire, and measure the offset to the front tire. Repeat on the other side. The offsets at the front should match.

You'll need an assistant to hold the bike up so the stand doesn't interfere.

 

This is nice to know. I think the bike I have in korea is massively bent, even though I wont fix that (no time/space/money allocated for that project) but it would be nice to know anyhow.

I'd also like to check my seca when i get back home next spring.

 

Greetings

Google "GMD Computrack." Wheel misalignment can be much more than twist at the steering stem. You would need to bring them a "rolling chassis" . . .wheels, frame, and engine. Unfortunately, there are only four locations in the country. Also, it costs, both for measurement, and then correction, but they will bring your frame and triple trees into blueprint alignment, way obetter than factory tolerances. Good Luck.

 

This is the trade accepted method over here - Any straight edge aligned with the rear wheel (not the tyre or tyer), and measure the front against it.
If you clamp both wheels to the straight edge using spacers, you then know that the wheels are aligned and can begin to measure the frame/bars at various points. It worked for me - I discovered that my GS had been broadsided - which is why it went beautifully around lefthand bends, and around righthanders like a schizophrenic shopping trolley.

 

With all due respects to Jay-Dub, I would acknowledge that using the rear wheel rim as the base referent is an expeditious way to see if the front and rear wheels are, to use an American expression, "in the ballpark." Using this procedure is not a guarantee that all parts of the chassis are in correct relational alignment. This procedure may detect gross deformities to be corrected and the bike will certainly be "rideable." However, it also does presuppose certain assumptions that should be stated.

So here goes: First, were both the front and rear axles checked for run-out? What if either axle was out of true, Consequently the rims will not rotate in a common plane. Next - was the rear wheel rim checked for run-out around it's circumference before using the straightedge? Was the front wheel rim checked for run-out around it's circumference before using the straightedge? Consider several possibilities: The possibility that the rear rim was out of true axially when the straightedge was clamped to it and measurements taken at the front wheel (which we'll assume is axially in true). The measurement shows that the two wheels are out of a "alignment." Where is the problem? Front Wheel? (No) Rear wheel? (yes) How do you know? (you don't).

Another possibility: Both the rear rim and front rim are out of true axially and, just fortuitously, where the straight edge was clamped to the rear wheel and where the measurements were taken at the front rim, the misalighnments cancelled each other and the wheels were "found" to be in alighment. Problems, problems. If you don't know where your are, and you don't know where you're going, you may end up somewhere else . . . and not even know it.

The correct way to do this is to use the swing arm pivots as the base referent. Then, check the axles for run out. Then check rims for run-out. Correct any problems found here and then begin a measurement process that will detect problems. Now, is the rear axle parallel to the swing arm pivots in the vertical plane? (Most problematic in chain driven bikes with left and right adjusters) In the horizontal plane? (Swing arm twist) Is the steering stem perpendicular to the swing arm pivots. (frame twist) Is the front axle parallel to the swing arm pivots in the vertical plane? (fork issues - bent/twist) In the horizontal plane? (Springs, triple trees) Finally, are the front and rear wheels in alignment in a common radial plane. (wheel spacers).

If you do any kind of high performance riding, entering turns "hot", heavy trail braking to drop the bike onto line, holding the line while on throttle, or changing line under braking (collapsing radius turns) or under increasing throttle (widening radius turns) using heavy throttle to bring the bike up out of the turn, and finally, not apexing left hand turns, chassis alignment and suspension determine whether the rider and bike perform smoothly as one at speed.

I'm just sayin'

 

Agreed, this applies to any method of this type where the wheels are assumed to be on the same axis and both wheel spindles are true, I was aiming at shaft driven bikes and back street mechanics, or the average work with what you have guy - who does not want to "go spending a whole bunch of time and money on it"
If anyone wants to measure a frame with so much precision then they would surely take the machine to a specialist.