simon metcalfe Posted August 12, 2017 Share Posted August 12, 2017 How hot should the coil get in a crossflow? It's running the Lucas electronic ignition supplied by Caterham in 1987.Was out for a blat last weekend and the engine cut out without warning. Engine would not restart at all so towed home.. I traced the fault to the coil, which has run well for the past 2 years. When I fitted an old coil (possibly not the correct spec to run with the electronic ignition) the engine started immediately and ran well for 20 miles - when there was a loss of power and misfiring etc - the engine would not rev above 3000 rpm but fortunately I was able to drive it home like this. The coil was too hot to touch.I have just fitted a Lucas DLB105, which I'm told is the correct one for the ignition. I've just been for a test and it all worked very well - however, again the coil gets very hot, perhaps not quite as hot as before but still too hot to touch really.Are these temperatures normal? I'm concerned that there may be a fault which is causing damage / overheating to the coil. I've been careful to reconnect the +ve and -ve as before and checked the plugs and leads and distributor cap, all of which look ok.The new coil seems to work perfectly, the engine running as it should but I don't want to risk going too far if the overheating is likely to cause it to fail again.Any thoughts much appreciated.Simon Link to comment Share on other sites More sharing options...
Member Jonathan Kay Posted August 12, 2017 Member Share Posted August 12, 2017 I don't know how to tell if it's too hot.I've been careful to reconnect the +ve and -ve as before and checked the plugs and leads and distributor cap, all of which look ok.The new coil seems to work perfectly, the engine running as it should...That's good news. Next step is to test the internal resistance. You need the values specified for your particular coil, which might be here, but it would be nice to find something official. Jonathan Link to comment Share on other sites More sharing options...
Area Representative Piers300 Posted August 12, 2017 Area Representative Share Posted August 12, 2017 Hi SimonTrust all well. If the coil is getting very hot, I would look at the earth connection and the + connection and make sure it is good. It could be that a bad contact could increase current and resistance and this may be the reason for it getting so hot. I don't recall my Super Sprint coil getting that hot.By the way, Charles has been in contact with a long email.regards Piers Link to comment Share on other sites More sharing options...
Area Representative Piers300 Posted August 12, 2017 Area Representative Share Posted August 12, 2017 Hi SimonI've been thinking about your coil. If the voltage is being reduced by a bad connection, then the current increases. So for example, a 12 volt system pulling say 6 amps, if you halve the voltage to 6 volts, you double the current to 12 amps. Your 7 is unlikely to go as low as 6 volts, but you get the point. So check every connection and make sure everyone is good.regardsPiers Link to comment Share on other sites More sharing options...
elie boone Posted August 13, 2017 Share Posted August 13, 2017 If you have the plastic rotor that would be your first port of call, they know to fail. unfortunantly the only cure is a new dizzy and you will have to ditch the old Lucas electronic ign too but the new dizzy could have everything inside it. Link to comment Share on other sites More sharing options...
Area Representative Piers300 Posted August 13, 2017 Area Representative Share Posted August 13, 2017 Elie - please can you explain how does the rotor make the coil hot. Is it high resistance contacts inside the distributor cap ?I would expect that Simon is still on his original distributor and the shaft and bearings in the distributor may have worn out, causing bad contacts within the cap. Is this causing the issue ? Piers Link to comment Share on other sites More sharing options...
elie boone Posted August 13, 2017 Share Posted August 13, 2017 I also guess that it's the original ign system with big Lucas box. when a coil is to hot to touch that is not right and the reason is in the electronic box witch is triggered by the rotor in the dizzy. For these systems there are no replacement parts aldo I think I still have that electronic box somewhere lying around. Bottom line is that when there is any problem with the Lucas system replace the whole ign system. Link to comment Share on other sites More sharing options...
anthonym Posted August 13, 2017 Share Posted August 13, 2017 I have two of those boxes somewhere... though finding them might be an issue. Link to comment Share on other sites More sharing options...
OliverSedlacek Posted August 13, 2017 Share Posted August 13, 2017 Old school coils do run pretty hot as they are designed for 'fixed dwell' points. The inductance of the coil stores energy in a magnetic field, which is released as the HT spark. The inductance sets the rate at which the magnetic field is charged up when the points are closed, but after a few milliseconds the coil is magnetically fully charged and more electrical power just gets turned into heat. This is actually more of a problem at low revs, where the points are closed for longer. In extremis, leaving the ignition on with the engine stopped and the points closed will make the coil pop!Modern ignition systems are 'constant energy' systems, where the electronics works backwards from the spark point to decide when to start charging the coil. The modern coil doesn't have to be designed to withstand overcharging as it relies on the electronics to protect it. Fitting a modern to coil to an old school system can lead to problems.Having said all that, I would say that a coil shouldn't get hotter than 70C, which still feels pretty hot. Link to comment Share on other sites More sharing options...
simon metcalfe Posted August 14, 2017 Author Share Posted August 14, 2017 Thanks to all for your advice.Jonathan - is the internal resistance measurement in order to check if the coil has been damaged?Piers - yes I will check all the connections - I can obviously check the connections at the coil end but where else should I be looking? Are there any connections inside the distributor? I wouldn't be surprised if there are some poor earths etc as it's all 27 years old now... It was excellent to meet up at Goodwood on the Caterham stand! and I'm pleased Charles has been in contact with you - great news.Elie - yes the rotor is partially plastic - it has a slotted metal component which passes the copper terminals on the cap. I've cleaned all the terminals and the metal surface which connects to the central terminal also. all looks ok. Yes, I've read about the "new" electronic ignition being part of the distributor now.Thanks again to you all and I will let you know how I get on...Simon. Link to comment Share on other sites More sharing options...
Member Jonathan Kay Posted August 14, 2017 Member Share Posted August 14, 2017 is the internal resistance measurement in order to check if the coil has been damaged?Yes. they used to go off before they failed. I don't remember them getting hot, but it's certainly plausible... if it's passing the same current (and yours is running well) and the internal resistance is high then there must be extra heat somewhere...Jonathan Link to comment Share on other sites More sharing options...
simon metcalfe Posted August 14, 2017 Author Share Posted August 14, 2017 Thanks Jonathan - I will check the resistance - is this done without the engine running?Apologies to Antonym and Oliver - your posts were only included in this thread when I replied earlier.Piers, you are correct, it is the original distributor and Lucas electronic ignition - I expect you helped fit them!!! Redline have mentioned the newer "in/on" distributor systems to me in the past. Not sure if this is the Aldon type I've heard mentioned? If I do go down the completely new distributor route, are there any recommendations or advantages of one type over another?It's all a bit of a shame as - as mentioned before, the engine really does run perfectly - it's just that the coil gets suspiciously hot and having failed before I'm just not confident to drive it too far..I suspect that each time I drive it may damage it slightly and cause it to fail again!Regards Simon Link to comment Share on other sites More sharing options...
Member Jonathan Kay Posted August 14, 2017 Member Share Posted August 14, 2017 I will check the resistance - is this done without the engine running?Disconnect everything from the coil, then test the two circuits.Jonathan Link to comment Share on other sites More sharing options...
elie boone Posted August 15, 2017 Share Posted August 15, 2017 If you have a Super Sprint and go the Aldon route then you will have a better suited advance curve. Link to comment Share on other sites More sharing options...
Member Jonathan Kay Posted August 17, 2017 Member Share Posted August 17, 2017 Just got the official spec for the DLB 105 coil back from Lucas:Primary resistance is 3.0 ohms Secondary resistance 8.7 k ohmsJonathan Link to comment Share on other sites More sharing options...
DaveMorris Posted August 17, 2017 Share Posted August 17, 2017 Simon,I thought that I had an old Lucas box in the garage - but failed to find it.However I did find a Lucas distributor, marked Aldon with the 29Z-V4 sensor installed, and with 103FXY5 engraved on the side.Found a second Lucas/Aldon distributor with sensor 08Z-V4 label on it, and with 103FXYUL5 engraved o the sidde. This dizzy does not have the magnetic pulse ring slotted over the spindle, nor a rotor arm.Also found 2 dizzy caps and a set of red KV85 Competition magnecor leads.All were used on my x-flow supersprint in the past, but no longer required.Let me know (email) if any of this might be of interest to you, (though sorry I've not a clue what it's worth)regards, Dave Link to comment Share on other sites More sharing options...
elie boone Posted August 17, 2017 Share Posted August 17, 2017 dave, don't say you ditched the X Flow ? Link to comment Share on other sites More sharing options...
DaveMorris Posted August 17, 2017 Share Posted August 17, 2017 I now has an MBE and Jenveys fitted. Hence no need for the dizzies. Dave. Link to comment Share on other sites More sharing options...
simon metcalfe Posted August 17, 2017 Author Share Posted August 17, 2017 Jonathan,thank you so much for taking the trouble to obtain these figures - it's extremely helpful.I have spoken with Redline who advise that it is normal for the coil to get "fairly" warm so I'm going to go for a few tentative drives and test the resistance each time in the hope that all remains constant.Then, I think over the winder I will change the distributor - or certainly switch to the more robust "in distributor) electronic ignition which will hopefully lead to improvements all round.I will keep you updated with the resistance readings!Simon. Link to comment Share on other sites More sharing options...
simon metcalfe Posted August 29, 2017 Author Share Posted August 29, 2017 Hello all, just a quick update on the coil / ignition issue.I've been for several test drives using the new coil now and all seems well - although the coil does still get pretty hot.I have checked the primary resistance which when cold is 3.0 ohms, rising to 3.5 ohms when hot and returning to 3.0 ohms as it cools. Unfortunately I am unable to get a reading for the secondary resistance - it may be my multimeter is not suffiently advanced? But I'm thinking the consistent 3.0 ohm cold reading means this coil is not sustaining any damage so far.Anyway, fingers crossed, I hope things will continue as they are and I will probably change to the Aldon ignition over the winter.Thanks again to you all for your help, Simon Link to comment Share on other sites More sharing options...
Member Jonathan Kay Posted August 29, 2017 Member Share Posted August 29, 2017 Secondary resistance 8.7 k ohmsWhat ranges do you have on the multimeter?Jonathan Link to comment Share on other sites More sharing options...
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