Author Topic: Shaky tachometer on 1975 Honda 550/4 (Read 3744 times)

43and countiing · « **on:** June 05, 2018, 02:14:09 PM »

55,000 miles, and the needle was jumping all over. I replaced the cable, to no avail. Bought 3 used off EBAY, 2 had basically same results, and the current one works up to about 50mph and then sometimes gets into a jumping needle mode, and other times not. There appears to be no way to get these apart, and the one I did manage showed no internal damage or broken parts (unfortunately, I also see no way of getting the ring back on to seal it together). I can only guess that it is the internal gears. So, it would appear to be relatively easy to take the tank off and replace the tach gearbox, but all I've seen on line is a single gear shaft. My concern is that there must be another gear in the engine that could be worn?
Strictly a limited person from going into an engine, although I did once change the head gaskets, Any ideas on this problem? I've owned the bike for 43 years and this drives me nuts (embarrassingly, my old ears don't always register what gear I'm in by sound). If consensus here is that the internal gear is the problem, and suggestion on where to get one?

carnivorous chicken · « **Reply #1 on:** June 05, 2018, 02:19:14 PM »

This definitely could be the drive gear. Very easy to have a look -- single bolt to mount it to the engine, holding the cable in place. Unscrew the bolt, pull off the cable, and the drive gear will just pull out with a slight rotation. I've had drive gear shafts break but stay together and it may cause these symptoms. Regardless, easy to check to cross it off the list of possible suspects.

calj737 · « **Reply #2 on:** June 05, 2018, 02:55:00 PM »

If you need a tack gear, send me your address via PM and I’ll happily throw one in the mail to you.

thep1pe · « **Reply #3 on:** June 05, 2018, 03:15:02 PM »

It usually is the damper in the tack gauge. After 40 odd years the oil/grease in the damper dries up and allows the needle to bounce about. Usually a instrument technicians job to fix.

Tews19 · « **Reply #4 on:** June 06, 2018, 05:57:11 AM »

My current 550 has low miles. Gauges look brand new. Unfortunately they are slow to respond. No matter how fast I go they never go above 5k. Then upon descent, the needle may sticks at times. No fluttering though

Deltarider · « **Reply #5 on:** June 06, 2018, 07:29:04 AM »

I didn't read you lubed the inner cable with lithium grease. Not saying that's the cause. 35 years ago both my speedo- and tachometer behaved badly. Pulled the inner cables, cleaned them and lubed them with lithium grease. Never had the problem reoccur. Tacho stable up to 10.000 rpm, speedo up to 180 km/h

Tews19 · « **Reply #6 on:** June 06, 2018, 09:44:23 AM »

Quote from: Deltarider on June 06, 2018, 07:29:04 AM

I didn't read you lubed the inner cable with lithium grease. Not saying that's the cause. 35 years ago both my speedo- and tachometer behaved badly. Pulled the inner cables, cleaned them and lubed them with lithium grease. Never had the problem reoccur. Tacho stable up to 10.000 rpm, speedo up to 180 km/h

White lithium grease?

Deltarider · « **Reply #7 on:** June 06, 2018, 10:55:13 AM »

Duckhams's transmission something. Sorry have to go to the basement to check.

Deltarider · « **Reply #8 on:** June 06, 2018, 11:56:34 AM »

It's Duckhams Keenol Grease My 35 year old can is still half full. But I'm sure other brands have similar.

jakec · « **Reply #9 on:** June 06, 2018, 12:13:10 PM »

I was having both my needles jump around wildly whenever I went over 60. Turns out I was missing the spaces that make the gauges loose in the rubber shock mounts. Since there was no vibration damping it was causing the needles to go crazy

43and countiing · « **Reply #10 on:** June 06, 2018, 01:48:57 PM »

Thank you...I'll get to it this weekend and let you know either way

RAFster122s · « **Reply #11 on:** June 11, 2018, 02:36:22 PM »

There is a thread on the site showing the dashpot to drill a tiny hole into and fill with silicone shock oil from the rc cars at the hobby shop. 35000 weight if I recall correctly. Then you seal the hole and reassemble. The crimp rings can be reused but you need to make a holder for pressing the front down against the edge while you recrimp the back. The thread covers this.
Marcel in the Netherlands rebuilds them and does a very nice job on them...

43and countiing · « **Reply #12 on:** June 17, 2018, 04:33:52 AM »

Once again thank you...I haven't had a chance to get at this task yet, but I appreciate the feedback and offer. I will let you know.

43and countiing · « **Reply #13 on:** August 28, 2018, 04:20:22 AM »

So with nothing to lose as the tach needle went crazy at about 50mph/5000 rpm, I pulled the gear and lathered it in lithium grease my dad used to use for grease fittings. For the life of me, I cannot understand why adding grease to a gear that is normally soaked in hot engine oil solves the problem, but fingers crossed that it lasts because that needle is now more steady than my old fart hands.
Thanks for the tip!

Deltarider · « **Reply #14 on:** August 28, 2018, 04:27:41 AM »

Quote from: 43and countiing on August 28, 2018, 04:20:22 AM

So with nothing to lose as the tach needle went crazy at about 50mph/5000 rpm, I pulled the gear and lathered it in lithium grease my dad used to use for grease fittings. For the life of me, I cannot understand why adding grease to a gear that is normally soaked in hot engine oil solves the problem, but fingers crossed that it lasts because that needle is now more steady than my old fart hands.
Thanks for the tip!

But... normally it is not soaked in hot engine oil. Decades ago I pulled mine, cleaned them and greased them with lithium grease. So far no need to do it again.

43and countiing · « **Reply #15 on:** August 29, 2018, 08:11:33 AM »

Unfortunately, after taking it for a short ride at 50MPH, it went back to it's normal shaky self. The gear was not damaged in any way, My question: is there an interior bevel gear in the engine that may be worn out? I can't find it in any schematic. I really want this thing fixed! This is the 4th tach I've tried, and it had low miles on it. Any ideas on how I can test it? Ie, If I hook an electric drill on the end, will it turn fast enough so that I can rule out the tach and internal gears??

TwoTired · « **Reply #16 on:** August 29, 2018, 09:28:46 AM »

Are there any kinks or dents in the cable? Any sharp bends in the cable run along its length?
Does the cable fully seat "home" at each end? Both square end and flat end?

Has the cable been lubed with graphite lube?

Do you still have the original cable to inspect?

The tach gear is driven off the camshaft. Turning speed variations are unlikely to source at that point. Particularly if you have removed it and examined the engagement teeth.

Cheers,

Little_Phil · « **Reply #17 on:** August 30, 2018, 10:42:18 AM »

I think I'd start the bike, hold the revs at say 5000rpm for 5 seconds. Is it steady? If yes, re-mount the tacho in a bed of cotton wool and take a ride. But I think them becoming more sensitive to bumps/rattles is a sign of a problem with the internal dashpot.

43and countiing · « **Reply #18 on:** August 30, 2018, 04:43:51 PM »

Thanks for the insights. No kinks or dents...I recently replaced the cable itself. It fully seats. I will have to pull the cable out to fully lube it, but it is almost a new cable so I'm not holding out much hope there. The standard rubber mounts are in place to absorb vibrations, but I will also try adding a little foam or sheepskin inside, as much as the space allows.
I am still in the dark however , about where the tach gear, which appears to be in good shape, matches up to an internal gear. You say the camshaft, but doesn't there have to be a bevel gear on that also? I cannot even see any indication of it on the engine diagrams I have seen.
Thus far, the only place I've seen that can repair it is in the Netherlands (pretty crappy statement about restorations in the US??) Would be big bucks to send it there, and before I did that, I'd really like to eliminate all other possibilities.
One other thing. One of the tachs I have tried was a "reproduction", brand new, never used etc. Said it was for a 550, but when I hooked it up, the dial barely moved at all, which confused me even more.

calj737 · « **Reply #19 on:** August 30, 2018, 04:55:21 PM »

The tach gear feeds into the valve cover then aligns with a gear on the camshaft. The diagrams don't depict that too well.

If you remove yours, snap a picture of it. I have a couple of spares if yours is damaged.

TwoTired · « **Reply #20 on:** August 30, 2018, 05:02:51 PM »

It's more a worm gear than a bevel type.
The cam part is metal. The driven part is nylon, I think, and withdraws along with the holder from the cam/cylinder cover. Held in with a cross point screw.

Cheers,

dave500 · « **Reply #21 on:** August 31, 2018, 02:46:58 AM »

the tach gear in the rocker cover is steel,these were never a real steady guage anyway,why not watch the road more than the shaky tacho?you cant over rev these things anyway.

43and countiing · « **Reply #22 on:** September 03, 2018, 10:56:37 AM »

Dave500, thanks for the insight on how to ride. But FYI, I am one of those who wants mechanical things correct. Period. I don't rely on it, never approach red line. I just want it to work. For 43 years I have kept this machine running better than new, looking great, and mechanically sound.
Man, what a novel idea. Keeping my eyes on the road. And yes, they were steady. My original tach was rock solid steady for the first 45,000 miles. Honda would never put out a piece of crap that bounced around out of the box.

dave500 · « **Reply #23 on:** September 03, 2018, 11:54:34 PM »

yes I guess a shaky tacho can ruin the riding experience for some.

calj737 · « **Reply #24 on:** September 04, 2018, 03:42:32 AM »

I think I would pursue getting it corrected too. Having an instrument misbehave always causes me distractions while riding, and as the OP said, why shouldn't it be steady? Fix it so its right as it was from the factory for EVERY bike.

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Author Topic: Shaky tachometer on 1975 Honda 550/4 (Read 3744 times)