bstark Posted June 22, 2014 Share Posted June 22, 2014 This is slowly doing my head in ... The car is a sixties Fiat 500 running a dynamo, separate regulator, points and wasted spark ignition. All was well until a few weeks back the ignition light came on at speed on the motorway. Car drove fine but at anything above about 2500rpm the ignition light came on. Have since had the dynamo checked out and apparently brushes, springs and bearings are all good. Have fitted new regulator. Tested in garage and light goes out once started and stays out even when revved hard - hooray! Go for a drive and almost immediately the light comes on when revved - pretty much only goes out at idle or at less than 55km/h in top (guessing about 2400rpm), so presumably load related? Electrics are not my thing and short of spending time and a chunk of cash replacing the apparently sound dynamo with a new one to see if it works I'm at a loss. Is this something that could be caused outside of the dynamo and regulator, eg. The wiring between or the battery or something? Help appreciated! Bob Link to comment Share on other sites More sharing options...
Member Jonathan Kay Posted June 22, 2014 Member Share Posted June 22, 2014 Can you think of anything that's different between the conditions in the garage and on the road? Lights, radio, fans? Do you have a standard cooling system? Check fan belt. How to test the dynamo, voltage and current regulators. Jonathan Edited by - Jonathan Kay on 22 Jun 2014 12:18:58 Link to comment Share on other sites More sharing options...
bstark Posted June 22, 2014 Author Share Posted June 22, 2014 Hi Jonathan, I've seen that link before and it's useful, although some of the tests aren't very practical given the location of the regulator (which I replaced with no change to the symptoms). Fan belt is tight. Other than engine load there is no difference in conditions. The cooling system is the standard fan arrangement. Link to comment Share on other sites More sharing options...
bstark Posted June 22, 2014 Author Share Posted June 22, 2014 Just to make absolutely sure I've just tried tightening the fan belt to the point of over-tight and it's actually made the problem worse. In garage, light went out, as soon as I drove forwards the light went on, and then stayed on even at idle. Link to comment Share on other sites More sharing options...
alan7 Posted June 22, 2014 Share Posted June 22, 2014 Dynamo pulley spinning on the shaft? Al Edited by - alan7 on 22 Jun 2014 18:38:41 Link to comment Share on other sites More sharing options...
bstark Posted June 22, 2014 Author Share Posted June 22, 2014 That's an interesting thought... The pulley is held on by three triangulated bolts rather than a central bolt so unless something is loose inside (which I'd have hoped the dynamo expert would have picked up on) I can't see how it could. Link to comment Share on other sites More sharing options...
elie boone Posted June 23, 2014 Share Posted June 23, 2014 It's possible that the carbon bushes start to float at higher rpm due to ovality of the copper core on the dynamo. if it's have it turned down and do not forget to remove the resin in between the copper. Link to comment Share on other sites More sharing options...
Member Jonathan Kay Posted June 23, 2014 Member Share Posted June 23, 2014 Assuming it doesn't have a garage sensor then engine speed and temperature somewhere are possible differences. What happens if you do the test as possible: * Induce the fault, noting the engine speed * Back in the garage asap, and run through those engine speeds again. It doesn't sound like a problem with the warning light but it might be worth checking the dynamo output voltage with a meter to check that it isn't. Jonathan Link to comment Share on other sites More sharing options...
bstark Posted June 23, 2014 Author Share Posted June 23, 2014 Elie - that's kind of what I've been wondering about. It's a pain to pull the dynamo on these so didn't want to speculatively pull it out yet again if there could be an easier wiring issue elsewhere. I'm guessing the brush springs losing strength could have a similar affect? Jonathan - I think it is heat related, but we are only talking long enough for it to have warmed up a little (couple of minutes running time from stone cold) for the effect to happen. No rev counter so guessing at engine speed (easier to do in top gear). The initial problem was certainly being seen at the battery end where the voltage would climb to just over 15V then immediately fall off to 12.3V or so at the same time the light came on as you slowly built the revs. Link to comment Share on other sites More sharing options...
redlight Posted June 23, 2014 Share Posted June 23, 2014 No body has mentioned an earth fault, is this a possibility? A poor earth can cause all sorts of problems. May be worth a look. Link to comment Share on other sites More sharing options...
bstark Posted June 24, 2014 Author Share Posted June 24, 2014 No body has mentioned an earth fault, is this a possibility? Funnily enough someone on Pistonheads has just suggested the earth strap. This one may have legs as I can imagine a situation with this that matches all the symptoms. The engine mounting on the 500 is very soft and positioned centrally at the back, allowing a lot of torsional movement of the engine under load. The earth strap goes from underneath the dynamo mounting on the far left of the engine (middle of cooling fan) to the far left of the engine bay (one of the rear panel mounting bolts). If engine movement under load is pulling the strap and breaking the connection that would explain the repeatability under load, and why it could be initially fine at high revs but no load in the garage after refitting the dynamo. The problem first showed itself under high load cornering hard which would also fit. Heading to garage as soon as I get home to check! Bob Link to comment Share on other sites More sharing options...
Chris Cardwell Posted June 24, 2014 Share Posted June 24, 2014 Check engine mounts not broken 🤔 Link to comment Share on other sites More sharing options...
OliverSedlacek Posted June 24, 2014 Share Posted June 24, 2014 I had something similar and it was due to excess resistance in the dynamo to battery connection. The generator has to make more volts to push current through the excess resistance and this extra voltage appears across the ignition warning light. Link to comment Share on other sites More sharing options...
bstark Posted June 25, 2014 Author Share Posted June 25, 2014 Well, checked, cleaned and where needed replaced all the contacts to the dynamo and the earth strap. Several were pretty ropey and the earth strap contact was really poor. Put it all back together and... No change... Check the voltage at the battery and it rises to about 15.4v and then drops straight back as the red light comes on with revs. Same story if you take the voltage from the brush terminal on the dynamo but with a higher voltage. This was all in the garage so no real movement to confuse things. So it all points in my mind to the dynamo itself (despite assurance from the local specialist that all is good) and it is the brushes floating as the rotational speed increases. Grrr... Link to comment Share on other sites More sharing options...
Bricol Posted June 25, 2014 Share Posted June 25, 2014 Earth strap on one of my Lancias had a good clean contact between it and the engine. Problem was the contact between the cable and the lug/cable eye it was crimped into. New cable with new ends and all sorted. Bri Link to comment Share on other sites More sharing options...
bstark Posted June 25, 2014 Author Share Posted June 25, 2014 Yep, tried that - replaced cable ends and tested whilst I was going through the leads... Link to comment Share on other sites More sharing options...
Member Jonathan Kay Posted June 26, 2014 Member Share Posted June 26, 2014 Does whoever checked the dynamo have diagnostic facilities that could investigate that sort of speed-related problem? (Do most autoelectricians have any knowledge of dynamos or does it now need a specialist?) Jonathan Link to comment Share on other sites More sharing options...
bstark Posted June 26, 2014 Author Share Posted June 26, 2014 I'm going to call him to find out but he was adamant it was fine from a basic inspection when I gave him the original (and still the same) symptoms. He's the only specialist in Kent, and I believe he is looking at closing down to retire before long. Link to comment Share on other sites More sharing options...
bstark Posted June 26, 2014 Author Share Posted June 26, 2014 Have just checked regulator earth - fine, all the wiring between regulator and dynamo - fine, and all the fuses - fine... Link to comment Share on other sites More sharing options...
Chris Cardwell Posted June 27, 2014 Share Posted June 27, 2014 I had a problem withan HPC7 when the engine revs were in the range 2500 to 3000. It was eventually traced by Caterham to the connector which joins the wiring looms together. The car was stored in a damp garage . . . It took Caterham a few hours to find the problem. Believe the connector joints were remade and the whole lot wrapped in tape. Link to comment Share on other sites More sharing options...
bstark Posted July 3, 2014 Author Share Posted July 3, 2014 This is maddening! Stripped the dynamo and the springs and brushed indeed look fine. Fitted the new set of both just in case, and also cleaned up the brush runners as one of them was full of slight surface rust. Put the dynamo back together, checked it motored ok (it did) and reinstalled in car. Exactly the same symptoms, only now the light stays on once the increase in revs has set it off, even if you then back down to idle. It did exactly this the last time the dynamo was stripped by the specialist. So, individually everything checks out to the level I can apply. Auto electrician here we come, if I can find one who gets these... Link to comment Share on other sites More sharing options...
elie boone Posted July 5, 2014 Share Posted July 5, 2014 Why didn't you check the roundness of the copper on a lathe where the carbon brushes run on, you had I all apart Link to comment Share on other sites More sharing options...
bstark Posted July 5, 2014 Author Share Posted July 5, 2014 Well mainly because I don't have a lathe... Link to comment Share on other sites More sharing options...
Member Jonathan Kay Posted July 5, 2014 Member Share Posted July 5, 2014 :-) Jonathan Link to comment Share on other sites More sharing options...
Chris Cardwell Posted July 5, 2014 Share Posted July 5, 2014 The car should run at higher revs regardless of the dynamo/alternator provided the battery is fully charged . . . You have put loads of effort into investigating the dyanmo - it does not sound like a dynamo problem. Link to comment Share on other sites More sharing options...
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