CBR 600F2 1991 - 1994 CBR 600F2

First Failure for 26 Year Old Bike - A Tach?

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Old 12-13-2017, 03:35 PM
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Default First Failure for 26 Year Old Bike - A Tach?

Eh...other than dirty and neglected carbs, my trusty '91 has been bombproof. Until two days ago, that is.

Headed home from a short ride, I looked down and the tach was sitting at 7K whilst at a stoplight. Say wha? Revved the engine and it went to 10K and fell back to 4K, with a few hesitations inbetween.

Bike is in the garage now, with the tach sitting at 4K. While the bike has been kept immaculately clean through the years, obviously some bit of crud has managed to work its way into the gap between the magnets & coil on the tach. Now, I know of several companies that specialize in the repair of such meters, but the low end cost is probably around $100 or so.

I'm sure a lot of guys would use this as an excuse to swap in a new digital cluster, but I happen to really like the look of the stock setup. So...anyone tackle such a repair (cleaning the magnet gap)?

There's also a lot of guys who have swapped out the stock cluster for digital ones. If ya happen to read this and still have your old gauges, man, I'd love to hear from ya.
 
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Old 12-13-2017, 03:58 PM
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I would open it up and have a look-see.
 
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Old 12-13-2017, 05:36 PM
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Yeah, that's the plan. But my day job is restoring vintage audio gear, and I'm well familiar with flaky analog gauges, and debris in the magnet gap is the most common issue, and I'm all but certain that that is the issue here. The gap is narrow (<0.010") and it seems that nearly always whatever gets stuck in there is magnetic, which means finding and removing it is a real exercise in micro-surgery.
 
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Old 12-14-2017, 11:00 AM
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Perhaps it would be possible to transplant the rev counter from a used instrument cluster?

I never actually took my cluster apart when I had one, so I'm not sure what would be possible, but that way you'd keep the originality of the bike.
 
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Old 12-14-2017, 11:47 AM
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I can't speak concerning a f2, but I've had my f3 cluster apart. It was easy. Getting the cluster removed from the bike was the hardest part, and that wasn't a chore.
It might be something as simple as pulling the indicator needle and placing it in the proper position.
 
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Old 12-14-2017, 03:31 PM
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The tach can be removed on its own...I've seen them selling from time to time. Moving the needle won't accomplish much except making the situation worse by having a sticky needle AND an inaccurate one.

The analog tach on these bikes is nothing more than a leaky voltmeter. The input from the ignition module is rectified and filtered and presented to the analog gauge, which shows a voltage. More revs = higher voltage. I believe there's an adjustment for rise and fall time on these tachs, but I'll have to wait till I pull this one apart to see. I'll try to reverse engineer the electronics when I have it apart, just 'cause I like to do that stuff.

Anyway, 99% certain that crud in the magnet gap is the root issue, and clever though I may be with this stuff, it's still probably the kind of thing that a professional who does this type of thing daily will have to tackle. Cheapest fix is replacement, if a working one can be found.
 
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Old 12-14-2017, 03:42 PM
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I've pulled a set apart on my 900 and rebuilt them into a new case (they had been damaged in an accident by the previous owner) just make sure you take plenty of photos and draw a wiring diagram.

 
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Old 12-14-2017, 03:52 PM
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Looks like fun.

There's an off chance (small one) that I might be able to repair the one that's on the bike now, but I'd like to have a replacement sitting here so I don't have to pull the thing apart half a dozen times in case that I cannot.
 
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Old 01-28-2018, 11:38 PM
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Got a replacement tach from eBay for a really cheap price, but I wanted to see if the old gauge could be fixed. Pulled it apart since I had to fool with the lamps for the nth time anyway, and carefully blasted the gauge innards with compressed air. Amazingly enough, that seemed to take care of it!

Sometimes, chit just works out. For me, not that often, but even a busted clock is right twice a day.
 
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Old 01-29-2018, 09:49 AM
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Probably just a bit of debris and you blew it out with the air.

Glad the replacement was cheap.
 

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