Bad Ticker

I can’t say I’m surprised that my aging VT700 project bike has a bad ticker. Specifically, one if the two pulse generators it’s testing bad. The pulse generators are basically the pace maker of the bike. As the pistons move up and down, they turn a sprocket with an arrow-shaped piece of metal on. As the sprocket rotates, the tip of the arrow passes two magnets, each positioned I about 70 degrees apart.

As the arrow passes the magnet, the magnet zaps an electrical signal up to the ignition computer, which then zaps a signal to the ignition coils, which causes the spark plugs to spark, which if nights the air and fuel mixture, which moves the cylinder, which pushes the pistons, which turns the sprocket, which moves the arrow. The circle of life is complete.

Each pulse generator signals one cylinder to fire, and they are positioned so that each signal fires in the optimum sequence for power (and Federal emissions standards). When on pulse generator fails, only one cylinder works, and the other is just dead weight.

So, the the Honda shop manual says that the pulse generators should have a continuity between leads of 480 OHMs, plus or minus ten percent.

One of my pulse generators tests at 430, which is close enough. The other doesn’t read at all.

The connectors and wiring are good on the failed pulse generator, so the problem is likely a break in the mile or so of thin copper wire wrapped up around a magnetic post inside the pulse generator.

Like everything else in this bike the pulse generator assembly is discontinued at Honda, and there us no aftermarket option. After a week of hunting online, I purchased a used replacement assembly off of eBay, but it’s fails exactly the sameway. My theory is that the lower pulse generator, because it is immersed in oil all the time, is exposed to greater heating and cooling variations compared to the top pulse generator, which does not always sit in an oil bath.

So now my plan is to scavenge the good pulse generators from the two bad ones and try to makes a working assembly.

I have had to remove the clutch assembly to get to where I can work on the pulse generator, so it looks like I’m rebuilding the clutch, too.

The excitement never stops!

 

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