Topic: 1975 750k Tach Issue

[ViniToo]

Hi all. I'm trying to figure out why tachs not working. Tach gear and drive internals were all good when opened last year. Drive turns when running. New tach cable. I have 3 tachs. Original was not working. Found other 2. One tach sort of works but is 1000-1500 high. The original works if I hold it beside engine and seems quite accurate. As soon s I put it in the tach assembly it stops working. Needle will go up a bit at a time and never come down. I take it out and hold beside and it works well. If I sit it in front of tach assembly and it is crooked to other display it works but if I straighten the orientation it stops working. Is the cable binding some how? Is there something electrical happening? I am baffled. I have tried different routings of the cable but that has made no difference. I like having a tach. Any thoughts? Thanks

[BenelliSEI]

Check the tachs by sticking a wooden match stick it in a high speed drill. Use the match in the back of the tach. Turn the drill BACKWARDS. Hold the tach in the normal position and see which one works the best.

With a new cable, the only other issue can be the drive end or the tach. Is either end worn out in the socket so the cable is turning intermittently?

Also, check that when the inner cable is fully seated in the drive end on the cam cover, there is enough cable sticking out the other end to fully engage in the tach to work properly. I’ve seen “new” cables that were just too short (inner cable) to engage.

[Stev-o]

Is there something electrical happening?

The tach is mechanical, so cannot be electric.  I believe John has you pointed in the right direction, possible cable issue.

[ViniToo]

When cable is  seated on cam cover and set screw is in,  the cable can be pulled or pushed almost 1/2".  When cable is attached to tach I think that cable backs out that 1/2 and then tach doesn't work. Both cables have same amount of movement. There looks to be a seal for that tach spindle in fiches. I had one and put it in but it does nothing to stop the play of cable.

When cable is  seated on cam cover and set screw is in,  the cable can be pulled or pushed almost 1/2".  When cable is attached to tach I think that cable backs out that 1/2 and then tach doesn't work. Both cables have same amount of movement. There looks to be a seal for that tach spindle in fiches. I had one and put it in but it does nothing to stop the play of cable.

Check the tachs by sticking a wooden match stick it in a high speed drill. Use the match in the back of the tach. Turn the drill BACKWARDS. Hold the tach in the normal position and see which one works the best.

With a new cable, the only other issue can be the drive end or the tach. Is either end worn out in the socket so the cable is turning intermittently?

Also, check that when the inner cable is fully seated in the drive end on the cam cover, there is enough cable sticking out the other end to fully engage in the tach to work properly. I’ve seen “new” cables that were just too short (inner cable) to engage.

[BenelliSEI]

When you seat the inner cable fully into the cam cover (with the outer cable in it’s correct mount, locking screw in place), is there enough inner cable sticking out the other end to fully engage the tach? That’s the usual problem with a poorly made cable. One end or the other is so deep into that socket, that the other end does not engage fully…..

[ViniToo]

Well the amount of play there is seems to allow the cable to disengage from the tach. I can pull the tach end out so there is enough to engage the tach but I think it just slips back down inside toward the cam cover end then the tach no longer works. I haven't figured out how to prevent that. I guess I could get another cable but I just started trying to use a new cable from DSS.

When you seat the inner cable fully into the cam cover (with the outer cable in it’s correct mount, locking screw in place), is there enough inner cable sticking out the other end to fully engage the tach? That’s the usual problem with a poorly made cable. One end or the other is so deep into that socket, that the other end does not engage fully…..

[BenelliSEI]

I had the same problem with an aftermarket cable. The inner cable is just too short. There is no fix. Try a Honda part?

Still have the old one?

[ViniToo]

It seems so. Yes I have the old one but it is the same as the new one. So maybe an aftermarket one too. The tach has never really worked since I have owned this bike. I will try to get a Honda part. Thx

I had the same problem with an aftermarket cable. The inner cable is just too short. There is no fix. Try a Honda part?

Still have the old one?

[BenelliSEI]

Before you spend money on another cable, check the tack drive in the valve cover. It’s a nylon gear inside the cam cover, driven off a steel gear on the cam. If it’s damaged it could be a problem. Whittle a short piece of wood (a long wooden matchstick will do) and stick it in the drive socket. Check the gear isn’t stripped. If you start the motor, that stick should turn consistently. If the gear is damaged, the cover needs to come off. Impossible with the engine in the frame…….

[ViniToo]

I had all the internals done by a veteran motorcycle mechanic. All seals, gaskets, rings etc. I talked about the tach drive and it was checked and all was good. The drive socket turns consistently. I have had the tach cable attached to the drive and open on the gauge end and the cable is spinning well with good torque. So I don't think that is the issue. I have wondered if the female socket part on the gauge is worn, especially the outer part. Then when the cable retracts back towards the engine it reaches the worn area and no longer drives the tach. Thought of putting some JB weld on there shaped to the drive of the cable and see if that prevents the latter from happening. Thanks for your thoughts on this.

Before you spend money on another cable, check the tack drive in the valve cover. It’s a nylon gear inside the cam cover, driven off a steel gear on the cam. If it’s damaged it could be a problem. Whittle a short piece of wood (a long wooden matchstick will do) and stick it in the drive socket. Check the gear isn’t stripped. If you start the motor, that stick should turn consistently. If the gear is damaged, the cover needs to come off. Impossible with the engine in the frame…….

[Don R]

 I know it's a silly question, but you didn't accidentally stack two tach seals in the valve cover did you?

[newday777]

I know it's a silly question, but you didn't accidentally stack two tach seals in the valve cover did you?

Good point Don. That would do it.
But I don't think the screw would go in the slot that holds the cable end to the head cover would it?

[RAFster122s]

It could be forced in with two seals but the screw would be burrowing through one of the seals. Never know what POs do before you.

The CX500/GL500 motors have a cam drive that is part of the camshaft and often sheers with difficult cam swap the only solution. Several years back you couldn’t get one of the seals anymore so often it was a source of an oil leak for the motor. Not a massive one, but an annoying one if you liked a bike to not leak fluids…

If you pull the motor it will be accessible to repaint and cleanup efforts that are difficult to impossible in the frame.
In an engine stand you can run these motors if you are inclined to expend the effort to do so…not that it is a trivial thing to do, requires some ingenuity and work arounds.

Be methodical and you will sort it out, good advise has been given.

[BenelliSEI]

I had all the internals done by a veteran motorcycle mechanic. All seals, gaskets, rings etc. I talked about the tach drive and it was checked and all was good. The drive socket turns consistently. I have had the tach cable attached to the drive and open on the gauge end and the cable is spinning well with good torque. So I don't think that is the issue. I have wondered if the female socket part on the gauge is worn, especially the outer part. Then when the cable retracts back towards the engine it reaches the worn area and no longer drives the tach. Thought of putting some JB weld on there shaped to the drive of the cable and see if that prevents the latter from happening. Thanks for your thoughts on this.

Before you spend money on another cable, check the tack drive in the valve cover. It’s a nylon gear inside the cam cover, driven off a steel gear on the cam. If it’s damaged it could be a problem. Whittle a short piece of wood (a long wooden matchstick will do) and stick it in the drive socket. Check the gear isn’t stripped. If you start the motor, that stick should turn consistently. If the gear is damaged, the cover needs to come off. Impossible with the engine in the frame…….

You are on the right track. If the drive gears on the cam cover are OK and the cable turns, with good and consistent torque, there’s only two possibilities.
1. The cable is not fully engaged with the tach.
2. The tach is NFG.

[BenelliSEI]

P.S. Don’s suggestion of the double stacked seals in the hole on th cam cover is a good one. This would definitely cause the inner cable to be too “deep” in the outer cable to drive the tach. If this is the case, installing the locking screw on the cam cover should be almost impossible?

[robvangulik]

Can't you just shorten the outer cable a bit on both ends?

[newday777]

Can't you just shorten the outer cable a bit on both ends?

Not an easy fix.

[ViniToo]

No.

I know it's a silly question, but you didn't accidentally stack two tach seals in the valve cover did you?

[ViniToo]

Yes it seems its down to those two things. The original tach when it works seems quite accurate. The cable doe snot seem to be fully engaged or it is for a bit then backs out and the default position is to slide =back towards the cam cover. Thx for following along.

I had all the internals done by a veteran motorcycle mechanic. All seals, gaskets, rings etc. I talked about the tach drive and it was checked and all was good. The drive socket turns consistently. I have had the tach cable attached to the drive and open on the gauge end and the cable is spinning well with good torque. So I don't think that is the issue. I have wondered if the female socket part on the gauge is worn, especially the outer part. Then when the cable retracts back towards the engine it reaches the worn area and no longer drives the tach. Thought of putting some JB weld on there shaped to the drive of the cable and see if that prevents the latter from happening. Thanks for your thoughts on this.

Before you spend money on another cable, check the tack drive in the valve cover. It’s a nylon gear inside the cam cover, driven off a steel gear on the cam. If it’s damaged it could be a problem. Whittle a short piece of wood (a long wooden matchstick will do) and stick it in the drive socket. Check the gear isn’t stripped. If you start the motor, that stick should turn consistently. If the gear is damaged, the cover needs to come off. Impossible with the engine in the frame…….

You are on the right track. If the drive gears on the cam cover are OK and the cable turns, with good and consistent torque, there’s only two possibilities.
1. The cable is not fully engaged with the tach.
2. The tach is NFG.

[BenelliSEI]

Clean the tach end of the cable really well and see if you can get a blob of solder to stick to it. Shape it square with a small file. A few extra mm might do the trick!

[ViniToo]

Oh yeah. Thats a good thought. I'll  try that. Thx

Clean the tach end of the cable really well and see if you can get a blob of solder to stick to it. Shape it square with a small file. A few extra mm might do the trick!