Sticky tach

[SFT2]

I wasn't sure if this should go here, being the primary engine instrument, or in the electrical section, being an electric gauge, so I picked one at random.

The tach on my 89 Maxum 1700SR, with a Mercruiser 3 liter/Alpha I, is sticking. It works if you smack the face to free up the needle, then it sticks again at the new setting. Naturally this isn't an ideal situation. Is there any way to disassemble the tach and clean the bearings, jewels, bushings, or whatever it might have?

Alternatively, could a standard automotive tach be put in it's place? From my groping behind the panel I've figured out there are 3 wires that I'm guessing are hot, ground, and signal, and I think there's a 4th wire by itself for the backlight.

Any ideas?

 

[Don S]

Re: Sticky tach

Moving to Electrics, Electronics and Trolling Motors (not engine)

 

[Texasmark]

Re: Sticky tach

I tried that once and a tach is liken to a speedometer and is not easily cleaned because of the way the needle circuit is made to respond to the varying pulses caused by rpm changes. Merc has them for $88 in Quicksilver brand and usually match your other instruments.

My experience with them and speedometers is that when it starts doing that you have worn out the bearings.

Mark

 

[SFT2]

Re: Sticky tach

That's what I figured. I'm going to give a fairly cheap ($50) car tach a shot since I hate ordering things unless I absolutely have to.

 

[SFT2]

Re: Sticky tach

At least this part of the project has a good ending. I stopped and picked up a Teleflex tach at the boat stuff store today, climbed in, and pulled out the old tach. When I was setting it down I noticed the needle twitch, so I fiddled with it a bit and the needle bounced around freely. Hmm. So I plugged it back in, fired up the motor, and there it sat at 800 RPM. So now it's back in the panel and the new tach is going back. $60 saved

 

[wire2]

Re: Sticky tach

I believe one of the movement pivots came out of the ruby bearing cup. You may have jostled it just enough to get to go back in when you removed it from the dash.
It may be a bit loose, and pop out again on a solid wave next time out, keep 2 fingers crossed.

 

[SFT2]

Re: Sticky tach

Could very well be what happened, but I didn't knock it around much until I saw it was moving again, then I gave it a couple of half decent smacks to see what it would do. It has a plastic housing, so I'm thinking that it might have been tightened a bit too much and distorted something just enough to make it bind. But since I won't have a chance to take the new one back until next week, and I'm hoping to get to the lake twice this weekend, I'll have a chance to beat on it some.

 

[Texasmark]

Re: Sticky tach

If something went whacko there was a cause. If you got it working again, gotta ask yourself, what caused the problem in the first place and did I eliminate that problem or just temporarily rearrange it.

Course if it works whopee. If it does it again, you know what to do. Seems reasonable.

Mark

 

[SFT2]

Re: Sticky tach

If something went whacko there was a cause. If you got it working again, gotta ask yourself, what caused the problem in the first place and did I eliminate that problem or just temporarily rearrange it.

Course if it works whopee. If it does it again, you know what to do. Seems reasonable.

Mark

I'm fairly sure it was just screwed in unevenly and the plastic housing deflected enough to throw something out of alignment. With the insane little bearings air core instruments have it doesn't take much. Look at it funny and it'll get it's feelings hurt and go pout in the bow for the rest of the day

I'm halfway considering trying to find a set of digital gauges for that 80's Knight Rider look, but being notoriously cheap... well, there's not a lot of chance for that happening. Maybe if I have a few hundred left over after the deck, interior, props, and trailer get overhauled.