1982 GS450L Tachometer Slow/Incorrect

[Guest]

Hi all - my tach has been killing me, it's never worked correctly, the needle goes up and down, but very slowly and never over 3000. I've replaced everything - tach gear, seals, cable, and even the tachometer itself with a tested good unit. I'm not sure where to look next, any suggestions? Thanks!

[John Park]

It's possible to damage the gear on the camshaft itself if you install the cam with the driven gear in place; always good practice to remove it first and reinstall. Next time you're in there, rotate the engine and inspect the cam gear all the way around.

Because the tach cable rotates so slowly and has no real load, a munched worm gear on the cam may not damage anything but just fail to deliver. I'm currently running a cam with a somewhat munched gear - it's been cleaned up with a file - but it's engaging well enough and has worked fine for 10k miles.

You might be able to pull the tach drive and see down the hole.....

[Gorminrider]

but very slowly and never over 3000. I've replaced everything - tach gear, seals, cable, and even the tachometer itself with a tested good unit

this comes up a lot. Given you swapped tachs out I'd guess the speedo's magnet has lost its oomph.
Read link below here: hope is not entirely lost, but nearly...you might try an instrument rebuilder if you are really needing this oem tach in place, because it can be hard to find a second hand one exactly the same without the same problem.

https://www.thegsresources.com/_forum/showthread.php?250702-Help-with-tach-mechanism&p=2456681#post2456681

[John Park]

this comes up a lot. Given you swapped tachs out I'd guess the speedo's magnet has lost its oomph.
Read link below here: hope is not entirely lost, but nearly...you might try an instrument rebuilder if you are really needing this oem tach in place, because it can be hard to find a second hand one exactly the same without the same problem.
https://www.thegsresources.com/_foru...81#post2456681

According to the OP he swapped the tach for a 'known good' unit and the problem persisted.

Maybe it's the desert air, but 35-40 year old speedos and tachs round here still read accurately- when they still work.

[Gorminrider]

yes but the OP didn't say whether the replacement tach worked correctly or not. The symptoms are so familiar too.
Maybe I've somehow blundered into creating an accidental "de-gausser" in my shed but I've had two of suzuki tachs tire out in 5 years without any issueI can find at the bearings, rebound spring, or cable drive. (ie: swapped tachs work fine while swapping the bad tach to a known good bike is a fail etc..etc..)

failed magnets are merely a theory I have, seeing as the ones in these instruments do seem to be just magnetized steel and I know these can be demagnetized over time or with a tool...like a screwdriver or cassette player head
But I'd love to be wrong and someone come up with a useful doable fix! It's a "forum", after all.
Speedos -no problems yet .

[John Park]

yes but the OP didn't say whether the replacement tach worked correctly or not. The symptoms are so familiar too.
Maybe I've somehow blundered into creating an accidental "de-gausser" in my shed but I've had two of suzuki tachs tire out in 5 years without any issueI can find at the bearings, rebound spring, or cable drive. (ie: swapped tachs work fine while swapping the bad tach to a known good bike is a fail etc..etc..)

failed magnets are merely a theory I have, seeing as the ones in these instruments do seem to be just magnetized steel and I know these can be demagnetized over time or with a tool...like a screwdriver or cassette player head
But I'd love to be wrong and someone come up with a useful doable fix! It's a "forum", after all.
Speedos -no problems yet .

He said 'tested good'; that was all I had to go by. Presumably he borrow a friend's good tach and it did the same thing on his bike.

I have no theory on magnets. But I find the good ones attractive.

[tarheel]

Sorry for the slow response, been busy with work all week. The replacement unit came from a local bike shop that I trust. I never personally saw it work properly, but I'm friends with the mechanics over there and they're always willing to help out. I'd have them take a look at it but honestly it's not a deal breaker and I like to work on my bike myself. I'll pull off the valve cover and do a more thorough inspection in there. I did a valve adjustment just a few months ago and it didn't appear to be too hosed up. I have a couple of pictures but can't really tell if the grooves on the exhaust cam are damaged. This is probably the best picture I have of it:

[Gorminrider]

be aware that the thickness of the valve-cover gasket is important to the tach driving gears. Perhaps that's how some these gears get "munched up"in the first place...

[John Park]

be aware that the thickness of the valve-cover gasket is important to the tach driving gears. Perhaps that's how some these gears get "munched up"in the first place...

Given that the driven gear is in the head, the cover and gasket are irrelevant.

They get munched when you drop the cam in and tighten down the caps before ensuring that the gears are meshed. I'd rather not talk about how I found out.

[Gorminrider]

oh-that's right! - it's not a gsx 400..(that has the gear on the valve cover)

[John Park]

oh-that's right! - it's not a gsx 400..(that has the gear on the valve cover)

Probably a better idea, but I think available space might have been the motive. Given that the shoe for the cam chain is also on the cover, using silicone instead of a gasket is a really - REALLY - bad idea. No doubt been attempted tho.