Chain adjustment using jig and laser

[MGR1 40]

Hi all.

 

Just wanted to share some pics of my chain adjustment jig with laser. The jig is cut out of aluminium from a 2 meter straightedge, from the local building material supplier, and pop rivetted together. The 90-degree brackets are closet wall mounting brackets from IKEA, also the glued-on rulers are IKEA paper rulers. Very inexpensive :-).

 

The laser is a Profi Cat Chain adjustment laser. Cost approx 35 Euros.

 

I found that my chain adjuster at the rear wheel was off by 1.4 mm on one side. This translated to 5 mm on the front wheel, for a total offset of 10 mm. This made the bike to pull slightly to the right with my hands off the handlebar. Now after adjusting it goes straight.

 

I checked the chain adjustment directly on the chain sprocket with the Profi Cat afterwards, and the chain itself also ran straight, which is a good thing. However it was straight before as well, so it seems small discrepancies like 1.4 mm on the adjuster, are not measurable on the chain run, so my conclusion is that the jig is better.

 

 

 

 

 

Edited May 27, 2016 by MGR1

[Trev 18,889]

Did that little lot really only cost 35 euro, if so I better get one quick before we vote out 

[DaveM59 1,610]

Nice bit of kit you have made, but a couple or three questions...

The rulers; are both the zero at the centre point, each increasing outwardly, looking at the offset IKEA labels it looks like it?

How do you know you have the front wheel at dead centre, do you have a jig to set this and fix it too?

How do you get the front wheel into the jig, is there enough space if you rock it back on the stand or do you just ride over it?

[MGR1 40]

Nice bit of kit you have made, but a couple or three questions...

The rulers; are both the zero at the centre point, each increasing outwardly, looking at the offset IKEA labels it looks like it?

How do you know you have the front wheel at dead centre, do you have a jig to set this and fix it too?

How do you get the front wheel into the jig, is there enough space if you rock it back on the stand or do you just ride over it?

 

Yes, the rulers are offset, and zero is at the centerline from both sides. I measured this carefully. The jig itself is tight against the front tyre sides.

 

As you can see there are two sets of rulers, one in front of the weel, one in the rear. When I check with the laser I make sure that both the front and rear ones show the same values. I also check the other side. So when, as in this case, the measurement is 9,5 cm front, 9,5 cm rear, and the same on the other side, the front wheel is straight and in line with the rear wheel.

 

The rear plate bracket is detachable, so I can slide the jig in from the front, and the fasten the rear bracket.

Edited May 27, 2016 by MGR1

[MGR1 40]

Did that little lot really only cost 35 euro, if so I better get one quick before we vote out 

 

The straightedge cost me some 20 GBP, the laser itself was about 35 Euros (in Germany).

[MGR1 40]

Profi Cat also makes a complete wheel alignment set, however this is very expensive. It uses the very same principle, although the laser fixing points are on the rims instead of on the tyres, which should give better accuracy.

 

 

Edited May 27, 2016 by MGR1

[embee 7,288]

Bravo. Good stuff.

 

I do think wheel alignment can be a bit of an art as much as a science. Allowing for production tolerances there's no guarantee that the front and rear wheels are both on the "centre line" of the frame (if there is such a thing), you can then make them parallel to each other but not necessarily parallel to the centre line of the frame. There's no way round this and without very sophisticated measuring equipment it's not possible to measure it. The bottom line is that you get the wheels aligned "near enough for practical purposes", which is the difference between engineering and mathematics.

 

As an example, when I had the swingarm out there was a gap of about 0.8mm between the frame and swingarm bearing stack, so when tightened it flexes the frame to clamp the bearings. Similarly the rear wheel is narrower than the swingarm, so that flexes as you tighten it. Where does all that end up in terms of alignment? Answer is "near enough".

[MGR1 40]

Bravo. Good stuff.

 

I do think wheel alignment can be a bit of an art as much as a science. Allowing for production tolerances there's no guarantee that the front and rear wheels are both on the "centre line" of the frame (if there is such a thing), you can then make them parallel to each other but not necessarily parallel to the centre line of the frame. There's no way round this and without very sophisticated measuring equipment it's not possible to measure it. The bottom line is that you get the wheels aligned "near enough for practical purposes", which is the difference between engineering and mathematics.

 

As an example, when I had the swingarm out there was a gap of about 0.8mm between the frame and swingarm bearing stack, so when tightened it flexes the frame to clamp the bearings. Similarly the rear wheel is narrower than the swingarm, so that flexes as you tighten it. Where does all that end up in terms of alignment? Answer is "near enough".

 

 

Good points. In my experience over 39 years of motorcycling and hundreds of motorcycles tested I can say that very few motorcycles are 'straight' from the factory. I often take the opportunity when there are roadshows or similar at the dealers, to try out new models. A surprisingly high number of these do not go straight, Even high-end bikes from renowned manufacturers. And even shaft drive bikes.

 

I measured the wheel alignement on several of my previous bikes with shaft drive, and all where off by quite a large amount at the front wheel, even though the rear is fixed. 

 

A mechanic I talked to, that had visited the Suzuki factory in the '80s, told that at the end of the production line of the GSX750-series were two men with a very long metal bar that sighted the wheels of each bike using their eyeballs only, then put the long bar inside the steering stem, and heaved on it until the frame (that was fixed to the ground using a jig) gave enough so the wheels where reasonably inline. He was not impressed.

 

I think the problem is not that the rear adjusters are wrong, but that the frames are off by some millimeters at the steering stem or the swingarm fixing points. Everyone that has welded metal knows the power of the electric arc weld seam. When the seam cools, it can easily bend even thick steel, and it takes only a millimeter at the steerings stem and a millimeter off at rear, and the wheels are not inline. It can even take some time after the seam is cold before the metal tubes finally sets. What the manufacturers should do is to control and adjust the frames and swingarms after welding, but I have not read about any manufacturer that does that. They weld them in a jig, and send them off straight to surface treatment. 

 

This boils down to the fact that many bikes have wheels that are not inline, and it is pure luck if you have one that is straight.