Rotax 582 faulty tacho

[sandman]

There e are 2 parts to this question 1. When I do a ignition check there were small variances in the drop in revs between the two ignition modules, now when I switch off the left ignition I get a drop of about 1000rpm on the tacho but not in the engine. 2. When increasing to WOT the tacho won't go past 4800rpm but the engine is doing more revs than that, I'm hoping it is not a faulty generator but maybe an earth trouble or ignition switch. The tacho appears to work fine at idle power correctly but not ignition checks or past 4800 rpm.

 

 

[sandman]

just to add a little to this, the engine runs fine and battery is fully charged during flight and the electric starter shows no sign of reduced power.

 

 

[thommo]

I have new tach in stock if you need one.

 

 

[sandman]

Hey Thommo, I may need it, is it one with the colour band around it and is it the aviasport one, could you send a photo of it please.

 

 

[thommo]

Attached is pictures

 

 

 

 

[Jabiru7252]

Does anybody know how this tacho works. Is it a 'diode pump' (fairly simple way to make a tacho) or some fancy digital nightmare? Just curious.

 

 

[cscotthendry]

Jab:

 

The Aviasport tachos are the digital nightmare sort. They use a microcontroller to count pulses. If you have one of these the rotax tacho coils can sometimes overload the input. There is another thread here about rotax tacho issues. Essentially you sometimes need to put a small resistor across the signal and ground pins of the tacho. But do check your ground connections carefully first, especially if this is a new problem and nothing else has changed in your aircraft.

 

 

[Keith W]

I have a problem with the VDO tacho in my gazelle, it wasn't reading at low revs now it doesn't work at all, I've had the taco checked and its ok checked the wiring and connections all ok, 238 ohms resistance across the trigger unit, the only thing I can think of is the air gap so can somebody tell me how to measure and adjust it in a 912 and also what the air gap should be thanks Keith.

 

 

[Guest T2 6199]

There e are 2 parts to this question 1. When I do a ignition check there were small variances in the drop in revs between the two ignition modules, now when I switch off the left ignition I get a drop of about 1000rpm on the tacho but not in the engine. 2. When increasing to WOT the tacho won't go past 4800rpm but the engine is doing more revs than that, I'm hoping it is not a faulty generator but maybe an earth trouble or ignition switch. The tacho appears to work fine at idle power correctly but not ignition checks or past 4800 rpm.

Hey Sandman . I hope you had some luck with your faulty tacho because I'm having the same problem . I'm thinking its a faulty stator . Could you please let me know what you discovered . Regards . Kevin .

 

 

[Blueadventures]

Hey Sandman . I hope you had some luck with your faulty tacho because I'm having the same problem . I'm thinking its a faulty stator . Could you please let me know what you discovered . Regards . Kevin .

Hi Kevin

 

Always worth checking that the female connection from the pulse line (engine sender to guage) that connects onto the pin on the back of the guage is not broken inside its heat srink. They can break and be held in partial contact by the heat srink causing an intermitant fault and be hidden from view. I have had this intermitant tacho problem in the past. At first thought it was a ground connection problem then discovered the connection end broken.

 

Regards

 

Mike

 

 

[Mountain Flyer]

Hey Sandman . I hope you had some luck with your faulty tacho because I'm having the same problem . I'm thinking its a faulty stator . Could you please let me know what you discovered . Regards . Kevin .

Hey Kevin and Sandman. Same problem with the tacho for the 582 in my Lightwing. Good at low revs but no good at high revs. I am wondering if anyone has a more detailed fix such as resistor size etc. As I recall, mine was OK for a few hours when installed then fell over. Pete

 

 

[sandman]

I fixed my tacho by snipping off a cable zip tie that came out if the stator. At first I thought the stator but the ohm reading was 38ohms right in the middle limits for a blue head, ( 35-40 ). I did a process of elimination so check the wiring, with a spare tacho I had wired up the grey tacho wire directly to the tacho ( I had to use a hell of a lot of electrical tape to the rear seat belt so I could see the tacho from start ). The problem still existed so the wiring in the aircraft is ok, I was thinking its gotta be that dam stator but the ohms are reading good what can it be. At this stage I was going to insure it then burn it..... just jokin!, At this stage I thought stator is ok wiring from the harness in the aeroplane is ok, so the wiring between the stator and the harness had a zip tie just out from the housing so I snipped that off then went out to fly thinking if it's not this I'm stuffed if I know, well I'll be buggered it's all good and linear now. I did get a little help from Glen Shaw at Dalby Air Maintenance.