motometer tacho

[Ageing Rotarian]

Dear all, I have had a motometer tacho rebuilt with modern electronics and still have a fluctuating reading. I have changed the wire from the ignition unit and I am now using a wire from the coil, is there anything wrong with wiring it up in this way and any thoughts on what could cause the issue?The repairer has suggested checking the signal wire with an oscilloscope (which I can do) but other than this I am at a bit of a loss due to the fact the bike seems to rev freely and not apparent misfire. I have checked previous posts and there is a lot of good information (most condemning the motometer unit) but with a rebuild and new components I thought it would be ok. just for information I have a veglia unit on the bike but this is erratic in operation also, but this is triggered off the alternator.As a side issue I am looking at having some classic rear lenses cast as I can't seem to get hold of any, is there anyone who would be interested if they work out ok?all the best Roy

[Interpol2471]

yes I would be interested if you get some rear lens made. Cheers Paul

[Ageing Rotarian]

Paul, I will keep you posted. It may take a while, as we are looking at a product called alumilite resin, which can produce very high quality reproduction lenses from a silicon mold. it is an American product and only certain types are available in the u.k, but I have a supplier who may be able to help. I have a le perie rear lens (stop light) so will try and replicate that first and if successfull, will then try the rest. I contacted the original supplier who are still going and very local to me in Suffolk, but although they have records going back to the fifties, could not find reference to my lens so may have been such a small run that they did treat it as a normal job? Can anyone confirm if the stop light and indicator lens on a classic are the same size? If not I may be looking for a donor to make a mold from, this would not harm the lens as the rubber is completly removed It.Let you know if It works outAll the best Roy

[Interpol2471]

Out of Interest did you call Startrights as they have some lens listed on their website but this of course could be out of date?

[Ageing Rotarian]

I did contact Graham and he said that they had gone a little while ago so the website Is a little out of date. As I may have said Paul, I only have a red rear lens so will start with that but I don't know whether the indicator lens is the same size. I will keep digging and hopefully someone can advise If they are the same size or I may be able to have a look at a classic to have a measure up. I am also trying to get to grips with the tacho issue which looks like more of mountain to climb but I like a challenge.RegardsRoy

[Richard Negus]

Hi Roy,The red and yellow lenses are the same size, but originally had different reference numbers moulded in.There were two different red ones, one was supposed to be the centre, tail, light and the other two were the stop/tail lights.Allegedly, the 'red' was not the same for these two, but it didn't matter too much then and doesn't matter at all now.Neither do the reference numbers matter now.Your tacho problem is a puzzle!The Motometer takes its signal from either coil signal wire (black/white or black yellow) so it doesn't matter whether the connection is at the ignition unit end or the coil end. The two nine-pin connectors under the instrument binnacle are always a source of concern so, as changing the tacho guts hasn't cured the fault, it may be an intermittent bad connection there. An external wire between ignition unit signal and tacho might confirm this, as would a separate wire between battery -ve and tacho black. Try a wire direct from battery +ve too. If you still have the original Boyer ignition, it may have a dodgy signal too slight to be felt in the drive.I'm afraid the Veglia symptom is very much a case of "Yes Sir, they often do that".

[Ageing Rotarian]

Thanks for the confirmation Richard, is the indicator lens configuration the same as the stop light ( the stop light lens I have has a continuous ribbed profile on the inside)?I have checked a few things out on the coils and I have a continuous 12v onto the six volt coils (regardless If the ignition turned on or not). I presume the ballast resistor should be regulating this to 6v, Just wondering, if the ballast resistor has 'Gone south' then this may effect the signal to the tacho? The bike doesn't seem to misfire and starts easily but maybe you give me your thoughts?All the best Roy

[Richard Negus]

Roy,The brown/white wire comes from the fusebox to the ballast resistor and then on to the + terminal of both coils; it's a direct, fused, lead which, as you say, is live at all times. There is also a brown/white wire from the ignition unit which connects to the coils side of the ballast resistor.The black/yellow and black/white wires from ignition unit to coils are the signal wires which are alternately connected, when the ignition unit is live, to ground to produce the spark. When the ignition unit is not live, neither signal wire is connected to ground and the battery cannot discharge, as some on here have suggested.There is an orange wire from the motor side of the starter solenoid to the ignition unit. When you press the button, that orange lead is energized at 12v (or whatever the battery voltage is when the motor is working) and puts 12v into the ignition unit and, now the Boyer 'fudge', comes out as the brown white without connecting to any other items inside the black box. Result is that the coils get full battery voltage whilst the button is pressed, rather than a reduced voltage whilst being fed via the ballast resistor when the button is released. Typically around 9 volts, the result is an excellent spark from the 6 volt coils when the engine is running normally. The original Lucas ballast resistor has only one main fault, that of internal corrosion increasing its resistance and reducing the normal running voltage. In extreme cases, the resistance is so high that it is effectively open circuit and there is no supply to the coils. Press the button and the engine starts normally, release it and the engine stops. The simplest fault to diagnose on a rotary! If you still have a Lucas item, I suggest you replace it straight away with one of the similar ones off that well-known on-line auction site. They have a much better way of attaching the resistance wire to the terminals and don't hide it all under a gobbit of moisture-attracting clay. I haven't seen a single old Lucas resistor that, when you look at the underside, doesn't have signs of rust in the clay.I can't imagine a way that a faulty resistor could influence the tacho signal.I believe the basic lens moulding is the same for both yellow and red, just the numbers on the outside are different (and unnecessary now anyway).Apologies for the ramble - it's still a bit cold to go out to the shed yet.R.

[Ageing Rotarian]

Richard, thanks for the ramble and as usual, you have made things very clear so will check the circuit out and see what's what. After the explanation I agree, can't see the resister causing the issue and maybe just clutching at straws. I have an oscilloscope on loan for the weekend so hopefully this may show some irregularities in the signal. Only thing after that is what to do to cure it but that's another matter.Have a good weekend and thanks for the input.Roy

[Richard Negus]

Roy,This may not be relevant, but I've been static running a rebuilt Classic today and noticed that, although the engine is idling smoothly at about 600, flicking the side stand down causes the tacho needle to rise and fall by over 500 rpm with no change in engine speed.I expected the engine to stop and the stand warning light to come on with the stand down, but neither happened so there's obviously something amiss somewhere in the system, more than just a blown bulb perhaps.All Motometer tachos give a flick of the needle when the ignition is first turned on; all the problems may be the result of a momentary spike in the circuit voltage. Voltage regulator fault perhaps?The owner doesn't want me to do (or him pay for) any more than the agreed engine work, so I'll probably just disconnect the switch to be on the safe side.R.

[Ageing Rotarian]

Interesting Richard, I have tried all the suggestions so far and no real difference. I have tried the oscilloscope and found a reliable trace but a bit noisy one compared to my A65 ( the wave form not quite as well defined but regular) which has a boyer system and boyer twin output coil. The only thing i haven't tried is powering the Tacho from a completely separate supply (12v battery) to see if this changes things at all which might mean there is too much variance in the supply voltage.With regards to the side stand isolator switch, it has already been dispensed with on my bike so I am assuming this will probably have no effect.The tacho has been returned to the refurbisher for checking and cosmetic work and will I will resume mission when it returns. In the mean time all I can do is send the recording of the trace to boyer and see what they think but I guess, because the bike does not seem to misfire, that the will suspect the gauge (the saga continues).Does anyone know of a source of holy water?All the best Roy

[Richard Negus]

[quote="Richard Negus"]Roy, without connecting to any other items inside the black box.Sorry folks, I've just realised that that statement was rubbish! There must be a blocking diode in there to stop the brown/white feeding back into the orange and trying to run the starter motor. Instant harness toast, or at least a blown fuse.Roy,It's the way of the world; the ignition man will says it's a wiring or tacho fault, and vice versa. As is often the case, the tacho needle drops to zero yet the engine runs normally - so not an ignition fault. An external wire from the coil signal wire will tell you if it's a fault in the yellow wire from coil to tacho. But since so many IP2 and Classic tachos exhibit the same, or similar faults, I feel sure it's something in the tacho which your instrument man hasn't eliminated.The later Commander uses exactly the same ignition system, with a higher rev limiter, and has a Yamaha XJ900 instrument console (Nippon Seiki, I think). No problems with tacho flutter there. Same with the F1, NS instruments again.I wonder if I can fit the Commander 'works' inside my Motometer tacho? Not that I look at my tacho that often - rev 'til it stutters and change up!R.

[Richard Negus]

Turns out my tacho is an original Veglia and working well.The ND 'works' will fit inside a Veglia/Motometer case but I'm loathe to butcher mine.Anyone got a duff tacho for me to modify?R.

[Ageing Rotarian]

Evening Richard, my Tacho has been tested this morning and with twelve volts, the tacho performed fine but I asked the repairer to try different voltages to see what reaction he obtained. Increased voltage to 13 volts and the needle started to slow down and stall, increased to 14 volts and the needle exhibited exactly the same charitaristics as when it as on the bike so we seem to have struck on why it played up as the engine speed ( and charge ) increases. We have been discussing how to install a voltage regulator/ stabiliser and think we have a plan but does the bike not have anything to control the voltage to the instruments or should the tacho look after itself?Will let you know what we come up with and how the unit performs after installation. All the best Roy

[Richard Negus]

Roy,For the generator to charge the battery, voltage output from the regulator must be higher than battery voltage.With ignition off or engine stopped, battery voltage is usually around 12.00 - 12.7 volts. With the engine running, battery voltage measured at the terminals is almost always higher, typically around 13.5 - 14.5 volts. This applies to most vehicles, not just Classics. If the measured voltage is over 15.0 volts at around 3000 rpm, it usually indicates a fault, either in the regulator itself or its ground connection.I suggest you check all the black wire terminals for corrosion or breaking wires which might give a high resistance and confuse the regulator.The Kokusan generator and Boyer regulator are not known to give problems.I'm surprised there isn't a voltage stabilisation circuit already in the tacho. Motometer are a well-known manufacturer of automotive equipment and must know that vehicle circuit voltage can vary.

[Ageing Rotarian]

Richard, the regulator was changed when I got the bike as it wasn't charging and the output is as you suggested 14v ( the same for most vehicles). The problem is manifesting itself when bench tested so the tacho does not seem to be able to cope with anything more than 12v. There may still be a fault on the tacho, as you suggest, these devices should able to cope with voltages above 12v whether it be internally or through an external voltage stabiliser. I'm sure we wil get to the bottom of it sooner or later.RegardsRoy

[johnbirchjar]

I would! as a "just in case" 'cos like you say,I would emagine they are a bit hard to find now (ex Morris Marina I think some one once told me )J.B.

[Ageing Rotarian]

Gents to give you an update:1) have added a voltage regulator which limits the supply to the Tacho to no more than 12v. Affect was that the tacho operation was smoother with it but the needle still fell dramatically over 4000 rpm (seemed worse on one coil than the other for some reason)2) on the advice of the gentleman who builds the ignition boxes for Graham, I added a 10k resistor to the tacho signal wire (at the coil) and added a 0.1uf capacitor in line at the tacho end (grounded to the tach earth supply) and now have a fully functioning tacho . Tacho movement is very smooth right through the Rev range and the only flicker is when I turn the lights on but it is only momentary and the tacho returns to read correctly afterwards.I will have to have a word with the refurbisher and ask whether there is something on the existing tacho circuit which should be doing this function and whether he has missed it (I can guess the response). what I also haven't done is to remove the 12v regulator and run the tacho to see what happens. Only down side was that when I rode the bike this evening I had an idle issue were the bike refused to idle below 2000 rpm after a high speed run. When I returned I investigated the throttle linkage, tightened the fast idle linkage which was loose and the bike seemed to idle correctly, so will have another ride tomorrow just to make sure ( as if I needed an excuse ).Just a quick question, with regards to calibration, the bike is registering 4500 rpm at 70 does that seem right?Over the last two days I have had two cracking rides locally of over 100 miles each and still think the rotary is a very underrated bike. Mine is only a converted ip2 but runs smooth (when hot), handles well and does everything I want a bike to do and I haven't regretted buyer it (despite the odd dillema).Will keep you posted if I find anything else outAll the best Roy

[Richard Negus]

Roy,As yours is a converted IP2 (as is mine), speedo/tacho relation depends on what final drive sprockets are actually fitted and what rear tyre section you have.Front sprockets can be either 17, usually, or 18 on some early bikes; rear can occasionally be 42, ofter 43, and on late IP2 and Classic, 44.I usually work on 17/43 with a 110/90 or 120/80 rear tyre to give 15.6 mph per 1000 rpm. 4,500 rpm = 70 mph at that ratio.Interesting to read of the mods to make a decent Motometer - I always thought Julian a decent chap!Intriguing that the ND tacho has never, to the best of my knowledge, suffered a similar problem.R.

[johnbirchjar]

I fitted an 18 tooth sprocket on the g/box on mY Classic many thousands of miles ago and 4000rpm is now 75mph,(didn't improve mpg though)J.B.

[Ageing Rotarian]

John, how did the bike react at low speeds to the higher gearing, did you have to slip the clutch etc in traffic? I see that you changed it several thousand miles ago so must be reasonably happy with the set up? I upped the gearing on my old commando as I aways thought it 'sounded busy' at reasonable motorway speeds but regretted when in slow moving traffic. RegardsRoy

[johnbirchjar]

Hi Roy,The Classic's fine in traffic,(have to make an appology,been out on the old girl this evening and noticed the speedo reads 72 at 4000 )Re; your Commando in traffic,I allways thought Commando's were quite high geared anyway,much higher than rotories(or they sound like they are when ever I am riding in their company)J.B.