Yamaha TX750 Restoration: Peace and inner balance.

After getting the clutch assembly out of the clutch basket in the last post I was faced with another dilemma. To remove the clutch basket, I have to have a Yamaha special tool. I know where to get one, but I also know that I will need a bunch more stuff from the same supplier by the time this is all done. Since I want to make one big order to save on the shipping and handling, I had to find other things to strip away from the rapidly lightening lump of motive power hanging off of my engine stand.

Here is where the trouble started for the TX750 line. The two dark copper colored metal chunks in the center of the pic above are the counter weights for the "Omni Phase Balance Assembly" that Yamaha used to make this parallel twin engine run as smooth as the Honda CB750 inline four that was the TX's competition back in the day. These are run off of a chain on the crank shaft and rotate in opposite directions from the crank assembly to smooth out the inherit vibey nature of the parallel twin engine configuration. The inner balance created by the careful timing of theses weights was noted in the reviews of the bike when it first came out in the magazines of the time.

The problems started when the first iteration of the weights had issues with the chain stretching causing the weights to get out of time. The vibrations from this made the bike unrideable. There was no adjustment built into the system and Yamaha engineered a fix for that. Then as people started to get rev happy with the motor, the lower quality motor oils of the 70's as compared to our modern oils would get frothed like latte foam in the cavity you see above that is in the center of the engine sump cover plate from the bottom of the engine. The engine is a dry sump system and when the oil got foamy, the suction pump lost suction causing havoc in the forced oil lubrication system vital to keep the engine alive resulting in blown engines. Yamaha made a fix for that too in the form of a deep sump to move the oil pickup away from the flinging weights. All of this was to no avail. Dealers were fed up with all of the warranty work that doesn't make them any money and customers knew the bike had a bad rap. 1974 models languished on showroom floors and the line was canceled. Todays modern oil with all of the engineering fixes Yamaha made in the 70's means that good running examples operate outstanding and are a joy to ride if you can find one.

Off comes the stator and into the bag it goes. I will need to do something with the wiring as the wires from the stator are older cloth covered ones and the color coding is hard to decipher. I also need to find the rotor lock bolt that seems to have gone missing from when I took it off a year ago.

Here is a pricey little item that made it possible for me to get the bike running. It is an electronic ignition trigger for the electronic ignition module I got from Germany. The bike had a much better reputation in Europe as the Europeans used the bikes for canyon touring instead of stoplight-to-stoplight drag racing that caused all the ruckus for the TX here in the states. There is a big following in several European countries for this bike which is why I was able to plop down $350 for this unit. Once I got it installed the bike fired right up. It mounts in the same location as the stock points, but need to no maintenance once set up unlike breaker points do.

The ignition system runs off the same shaft that drove the breaker points. It uses a hall effect (magnetic field) sensor to trigger both spark plugs at the same time in what is called a "lost spark" system. This makes it really easy to set up. The system came with a circuit box the size of a pack of cards that I hid under the tank when I did the wiring. It come preprogrammed with eight different advance curves so that I can play with how the engine runs. Its not a cool, tune by laptop engine ECUs we have on modern bikes, but it does bring the bike partly into the modern age.

Keep coming back as I slowly strip away at the engine. I also have a movie to edit from a recent track day at the kart track with the Ninja. I will be saying goodbye to the KTM soon and there just may be some end of summer changes coming to the bikes in the Motorbike Obsessions stable. See you soon!

Blue