Sunday, February 26, 2012

Motorcycle Wheel Alignment

I just aligned the wheels on a new old motorcycle I just acquired. This is one of those activities that is an arcane procedure.
I dug up an old post I made to the ducati mailing list in the mid 1990's about this.

The "Thread Method"
I've always aligned my wheels the way I saw Rich Oliver do it on his TZ250 years ago. I think this way is standard "racer" practice. Put bike on service stand. Take about 15 feet of string (elastic thread works best!). Tape center of string to back of the rear wheel about 4" off the ground. Bring the ends of the string to the front of the bike. Tie the ends of the string to some movable objects (I use a pair of jack stands), at the same height (4"). The idea is to set the strings so they are parallel and "just" in contact to the front edge rear tire by moving the jack stands. With the strings taped to the back of the rear tire, and "just" touching the front edge of the rear tire, they should make two parallel lines that run forward, passing along either side of the front tire. Now the alignment of the front and rear wheels can be easily observed by examining the clearance of the front wheel and the string on either side. Adjust the chain adjuster appropriately if necessary, and then recheck. It's a pain to do the first time, but then it gets easy. Use the thinnest, elastic thread you can find. Also, try rotating the rear wheel to several points to make sure you aren't just adjusting for uneven tire manufacture. And make sure the thread isn't on some bump of "mold seam" rubber or in a tread at the edge of the tire. This would screw up everything. Obviously, this method ignores how the chain and sprockets are aligned, and focuses on how the wheels and tires are aligned. I can imagine that having the sprockets and wheels aligned simultaneously may not be possible, and I'd rather have the wheels lined up. When using this procedure on my '92 750SS, a quarter turn of one of the chain adjusters is quite significant. When complete, the adjusters appear to be at even marks at either side of the bike, indicating adequate manufacturing. However, a quarter turns seams to effect the alignment significantly, but is just about invisible in relation to the adjuster marks.

The "ProAligner"
There is a relatively new gizmo available to help riders to align there wheels, its called the ProAligner. What I quickly found, is that I had trouble using the ProAligner on my oldest vintage bikes. The tires are very narrow (2.50" or 2.75"  by 19) and have the same size front and rear. One might say that you could in theory just sight down the tires even without the ProAligner, but I have trouble with that. I ended up doing those old bikes with my old and reliable thread method.

Today, I aligned the wheels on my newly aquired 1981 GPz 550. It came to me with the tires visibly way out of alignment. Investigation showed that the plastic chain guard had warped so it hit the tire, and some previous owner had "fixed" this problem by tweaking the chain adjusters until the tire was clear of the guard!
The GPz has a 3.25 x 19 front and a 3.75 x 19 rear. I quickly tried out the Proaligner and saw how it would work, but this time had a bit of trouble with my vision sighting down the tires. It occured to me that the bigger the difference in tire size, the easier the aligner would be to use. Frankly, I again went back to my old thread method.  Having done it that way for 30 years, I'm just very comfortable with that. After getting the wheels spot on with the thread, I pulled the ProAligner back out and tried it again. Lo and behold, the ProAligner also showed the wheels perfectly aligned.
(A note here, with the wheels aligned, I note that the hash marks on the chain adjusters are not even on both sides. This is typical, especially on older bikes. That's why some of us don't trust the chain adjuster marks.)

My thoughts? The ProAligner is a great gadget, especially for those with laser vision, no experience with thread, and tires that differ significantly in size from front to rear. Its certainly easy to see when the tires are way out of alignment. But if the tires are similar in size, it is delicate, and requires a really sharp eyeball to tell the small differences between each side of the tire. The ProAligner web site claims accuracy to "less than 0.1 inch (2.5mm)". That's possible, but, well I'd have trouble getting it that close. It's not just about being able to sight down the ires, you also have to adjust your focus from the front tire to the rear tire, and not move when you do that. I'd say getting to within 5mm or 3/16" would be pretty do-able with good vision.

For me, an engineer and long time rider and thread aligner, I don't see the ProAligner as much more (or any more) accurate than the thread method. But I don't think it's any less accurate either! With the thread, you really have to be very careful to get it to just touch/miss the front edge of the rear tire and to not "bend" the thread. With the Pro Aligner, you have to sight down the tire just right, adjust your focus carefully, and really see the hash marks.

I think if the tires (front and rear) are close to the same in size, or if I want to align the tires very, very close to perfect, the thread works better for me.

But, I'd say, that if you are double checking an alignment that was already done (assuming differing front and rear tire sizes) the ProAligner is quicker and easier. I'd also say, that if the tires are way out of alignment, the ProAligner would be quicker to get the wheels somewhat aligned, as there is no hassle with thread.

And if you have sharp vision, and no experience with the thread, the ProAligner might be the way to go. If you can "see" it, it's pretty foolproof. The thread system takes some time to learn. Then again, if you have trouble with it, don't hesitate to try the thread method.


Tuesday, February 7, 2012

The legacy of the DKW RT-125, the origins of an industry?

I've been amused by all the bikes that were derivatives of the DKW RT-125. Most recently Yamaha produced a concept bike, the Y125. This is an imitation of their first motorcycle, the YA-1. And that was a copy of the legendary DKW RT-125.
Just compare these pics:

The 2011 Yamaha Y125 Concept bike

The original 1955 Yamaha YA-1
The 1954 DKW RT-125

And the ORIGINAL 1939 DKW RT 125

For the record, the 1939 DKW RT 125 was a great design by Hermann Weber.

It appears that after WW2, the design of the DKW 125RT was open to anyone who wanted it. Some manufacturers aded it to their product portfolio, but other companies were started with that very bike as the first product.

From Wikipedia:
The RT 125' is a German two-stroke motorcycle made by DKW in Zschopau in the 1930s, IFA and MZ in the 1950s and early 1960s, and DKW in Ingolstadt in the 1950s and 1960s. "RT" stands for "Reichstyp" or "National Model".
In the 1930s DKW pioneered the Schnürle two-stroke loop scavenging process to dispense with the use of a deflector piston and improve efficiency of the combustion chamber. DKW also developed a highly efficient arrangement of transfer ports. These two features were included in the RT 125 to great commercial advantage. Competitor companies such as Adler and TWN copied the adoption of flat-topped pistons and strove to develop equally transfer port arrangements without infringing DKW's patent.
The RT 125 is probably the most copied motorcycle of all time. After World War II the Soviet Union took plans, tooling and even several dozen personnel as war reparations to MMZin Moscow (later transferred to MMVZ and SMZ) and to a factory in Kovrov, and produced copies of the RT125 as the M1A Moskva and K-125 respectively. WFM of Poland made a modified version of the RT125 (under SHL 125 and Sokół 125 brands), developed into 125/175 cc family motorcycles, produced until 1985. RT 125 plans were also taken to the United Kingdom where they became the basis of the BSA Bantam, and to the USA where they formed the basis of the Harley-Davidson "Hummer". Later Yamaha in Japan copied the RT 125 as the basis of the Yamaha YA-1.

Here is an array of shots some of these copies.

An American 1948 Harley Hummer

The English 1948 BSA Bantam

The Soviet 1946 Moskva M1A

An Italian 1950 MiVal 125T

A German 1941 NSU 125 ZDB

An Italian 1954 Maserati L/125/T2  (Italmoto). Its hard to see in this shot, but the Maserati engine is just like all the others. The frame is a bit more modern.

The first Italian Moto Morini, the 125 Turismo. Thile the top end is the same, the gearbox appears to have a different from the DKW.

The first Italian MV Agusta, the 98 Turismo. Looks like a DKW top end but again with a different gearbox.

An Italian 1948 Sterzi 125 Turismo

The first Japanese Kawasaki Motorcycle, 1955 Kawasaki (Meihatsu) 125

A Norwegian 1954 Tempo

The Czech 1949 Jawa 125

The Hungarian Csepel 125

There are lots more, google these up if you want to see more bikes closely related to the DKW RT 125.

Peugeot 55
Motoconfort 125
Triumph BDG125
James Comet 125
Sokół WSK M01, M06
SHL M02, M03, M04
Royal Enfield WD/RE Flying Flea