|
|
Post by dave1800 on Dec 4, 2012 4:47:44 GMT
It's been a bit quiet here recently I guess because of the cold weather in the UK so here is a new thread that may be helpful to those of you who venture out to try and start their cars. Often the emphasis quite rightly is on the importance of replacing high tension ignition components, plugs, leads, distributor caps etc. But I see less written on basic wiring checks that are quick and easy to perform. If you look at the standard Lucas HA12 or equivalent coil it's primary resistance is in the range of 3.1 - 3.5 ohms. If the resistance of the combination of the wiring, connectors, ignition switch and contact breaker taking the power to the coil should approach this figure through corrosion, wear and deterioration then the power from the coil would be reduced by 50%!!! A loose fitting or corroded Lucar connector on the coil can be sufficient to prevent cold starting or cause misfiring. Examine the wire and connectors to the coil carefully for any signs of deterioration. In practice there will be power losses that can easily be checked with a voltmeter and ammeter - preferably an analogue type to avoid damage to the meter from voltages fed back from the coil known as back EMF. With the ignition switched on and the contact breaker closed there should be no more than 0.5 volts measured between the coil + terminal - (not the wire) and the chassis (ground). If the figure is higher it could be a bad connector or the ignition switch itself worn. If you now measure across the contact breaker the voltmeter it should read no more than around 0.3 volts. If it is higher then the contact breaker is suspect or the distributor ground (not so likely). Taken together 0.5V + 0.3 V = 0.8V of unprevantable loss or around 6% of the ignition power. The next check I suggest is to measure the current with the ignition on, contact breaker closed and the engine not running. The current should fall in the range of 3.5 - 4.0amps with a cold coil. Finally repeat the last test with the engine running. Usually the reading is lower than expected as the meter pointer is trying to average the current as the contact breaker opens and closes and it settles around 1.8-2.0 amps. Any views? regards David Attachments:
|
|
|
|
Post by tommydp on Dec 4, 2012 20:43:47 GMT
Hi Dave! A great write up and schematics,very useful to all owners I believe!
It's a bit quiet here at the time, so contributions are very welcome! Personally, I tend to post most more when I'm working on/ driving the cars. With minus 20 degrees Celsius and the cars hibernating I'm not that active I'm afraid! I'll try to post more often though, it's important to keep the forum alive!
Back to the ignition circuit, I'll compare my two crabs later on. I've done it before on the blue one, and didn't find anything peculiar then. Thinking of all the running issues I've had with it, it amazes me it has never failed to start. It starts first time everytime, and when hot it fires immediately. Even now in very cold weather it will burst into life after a few rotations, with full choke of course.
I'm rather curious to find out what heats the coil beyond normal. What on earth can it be if amperes to the coil are ok, as well as ignition components/ distributor?
Let's "pretend" the cam timing is off.. This will disturb the firing point, right? Even if I set the timing correct according to the crank mark and pointers, static or dynamic, the spark will be off related to the pistons as the distributor is driven by the cam.
Now, if the ignition timing is off, even on an engine with correct cam timing, the coil could overheat as far as I've found.... Just a thought. I remember I found the dimples were in line on cylinder 1, but not spot on on cylinder 4. I also found both the static and dynamic setting different on these cylinders. This was also evident on the new distributor...
Well! Time will hopefully show!
regards, Tommy
|
|
|
|
Post by dave1800 on Dec 5, 2012 1:55:37 GMT
Hi Tommy Thanks for the kind comments, I do hope the schematics help those great mechanics who hate electrics. Minus 20C doesn't bear thinking about I'm not sure I could ever adapt to that! Your hot coil. Some very simple maths. The heating effect of passing current hrough a wire = (I) x (I) x (R) where R = resistance of coil and I = current through the coil. If coil (a) has a resistance of 4 ohms and coil (b) has a resistance of 2 ohms Battery = 12 volts the current flowing in: coil (a) = 12/4 = 3 amps coil (b) = 12/2 = 6 amps Heating effect coil (a) = (I)x(I)x(R) = 3x3x4 = 36 watts Heating effect coil (b) = (I)x(I)X(R) = 6x6x2 = 72 watts With a 45D4 distributor the dwell (on time) is 50% so the heating effects become coil (a) 36/2 = 18 watts and coil (b) = 72/2 = 36 watts. (In reality the power is reduced by the time it takes for the coil to charge but at idle this effect is a tiny fraction so the above hold true) The accuracy of the ignition timing has NO effect on the coil heating it doesn't matter. You could simulate this by running the didtributor off the car driven by an electric motor or similar. Cam timingIf the cam timing is off you can still set the ignition timing correctly by using the marks on the crankshaft pulley (assuming you have checked these are correct). The plug will still fire at the correct time in relation to the piston position BUT the valves will be opening too early or late. When you say the dimples were correct for No1 but not No4 I assume you are you talking about those on the crank/ cam sprockets? Can you be more specific maybe post a diagram as I am having difficulty trying to get my mind around this. Thanks regards David Hi Dave! A great write up and schematics,very useful to all owners I believe! It's a bit quiet here at the time, so contributions are very welcome! Personally, I tend to post most more when I'm working on/ driving the cars. With minus 20 degrees Celsius and the cars hibernating I'm not that active I'm afraid! I'll try to post more often though, it's important to keep the forum alive! Back to the ignition circuit, I'll compare my two crabs later on. I've done it before on the blue one, and didn't find anything peculiar then. Thinking of all the running issues I've had with it, it amazes me it has never failed to start. It starts first time everytime, and when hot it fires immediately. Even now in very cold weather it will burst into life after a few rotations, with full choke of course. I'm rather curious to find out what heats the coil beyond normal. What on earth can it be if amperes to the coil are ok, as well as ignition components/ distributor? Let's "pretend" the cam timing is off.. This will disturb the firing point, right? Even if I set the timing correct according to the crank mark and pointers, static or dynamic, the spark will be off related to the pistons as the distributor is driven by the cam. Now, if the ignition timing is off, even on an engine with correct cam timing, the coil could overheat as far as I've found.... Just a thought. I remember I found the dimples were in line on cylinder 1, but not spot on on cylinder 4. I also found both the static and dynamic setting different on these cylinders. This was also evident on the new distributor... Well! Time will hopefully show! regards, Tommy |
|
|
|
Post by tommydp on Dec 5, 2012 22:50:22 GMT
Thanks! OK, I just seem to remember someone saying a hot coil could indicate incorrect ignition timing, but I could be wrong of course:-)
I'm a bit enlightened when it comes to the camshaft timing now I believe, so it will only affect valve timing if it's off. I rest my case:-)
Regarding the dimples, I meant at TDC for cylinder 4 firing, the crank and cam wheel dimples and centres of cam and crankshaft were perfectly in line putting a steel ruler across them all. At TDC cylinder 1 firing (sprocket dimples furthest apart), the cam dimple was a bit off the line. I remember I was also a bit amazed by the amount of slack of the (new) timing chain. Of course the tensioner takes this up, but I seem to recall there was wery little slack when putting on a new chain on an 1800 years ago..
Also, I checked the current (analogue meter) at the coil today as you described. Results:
Engine not running:
Voltage at battery: 12,4 V, Current, coil 3,9 A (steady needle)
Engine running at fast idle:
Voltage at battery: 14,2 V, Current, coil 2,5 A (steady needle)
Voltage at coil positive terminal: 13,4 V
Voltage at coil negative terminal: around 5, 8 V
Nothing obviously wrong, I suppose? I agree with Ohms law and P= UxI and of course you feel the heat of a say 21 W bulb too:-)
However, there is no doubt the coil heat of this car is noticeable different to others, even when using the same coils:-) After idling 10 Minutes from stone cold today I could heat my hand on the coil. Eventually it got as hot as the top radiator hose.. After around 20 minutes..
Will be interesting to check out the white one later and compare the results.
Regards, T
|
|
|
|
Post by dave1800 on Dec 6, 2012 3:54:10 GMT
Hi Tommy Nothing exceptional in those voltages and current readings that would account for a coil getting so hot especially in such cold ambient conditions. Next time, when you check the white car it may be worth repeating them when the coil is hot. You would expect the coil current to fall as it heats up. It does appear that there maybe too much slack in the timing chain that you fitted recently but this shouldn't account for the alignment issue you describe as long as the tensioner is capable of taking it all up. I think it best to wait until warmer weather and visually compare the timing chains and dimples on the white and blue cars. Perhaps someone here has some additional thoughts?Look forward to seeing the white car coil readings - there has just got to be a simple explanation but I just can't see it! Regards David Thanks! OK, I just seem to remember someone saying a hot coil could indicate incorrect ignition timing, but I could be wrong of course:-) I'm a bit enlightened when it comes to the camshaft timing now I believe, so it will only affect valve timing if it's off. I rest my case:-) Regarding the dimples, I meant at TDC for cylinder 4 firing, the crank and cam wheel dimples and centres of cam and crankshaft were perfectly in line putting a steel ruler across them all. At TDC cylinder 1 firing (sprocket dimples furthest apart), the cam dimple was a bit off the line. I remember I was also a bit amazed by the amount of slack of the (new) timing chain. Of course the tensioner takes this up, but I seem to recall there was wery little slack when putting on a new chain on an 1800 years ago.. Also, I checked the current (analogue meter) at the coil today as you described. Results: Engine not running: Voltage at battery: 12,4 V, Current, coil 3,9 A (steady needle) Engine running at fast idle: Voltage at battery: 14,2 V, Current, coil 2,5 A (steady needle) Voltage at coil positive terminal: 13,4 V Voltage at coil negative terminal: around 5, 8 V Nothing obviously wrong, I suppose? I agree with Ohms law and P= UxI and of course you feel the heat of a say 21 W bulb too:-) However, there is no doubt the coil heat of this car is noticeable different to others, even when using the same coils:-) After idling 10 Minutes from stone cold today I could heat my hand on the coil. Eventually it got as hot as the top radiator hose.. After around 20 minutes.. Will be interesting to check out the white one later and compare the results. Regards, T |
|
|
|
Post by tommydp on Dec 6, 2012 18:19:22 GMT
Thank you, Dave! I noticed, at the end of the session, that the current went a bit down. It was still a bit above 2 A while running when I shut it off after around 20 minutes, though. Thinking of it, when I used the electronic ignition the coil kept absolutely cold, all the time. perhaps a clue? The symptoms were the same however. Of course, the points dwell of the 25d is rather high, with the points closed almost 70 % of the time.. Still, it gets abnormally hot imo..
It will be interesting to compare it to the other one. Further tests will have to wait, however. So far, this December is the coldest here since 1902.. and according to the forecast it will stay like this during next week too. Oh dear.. One positive thing though, you don't smoke that much:-) (I only smoke outdoors...)
Regards, Tommy.
|
|
|
|
Post by dave1800 on Dec 7, 2012 1:02:51 GMT
Hi Tommy Many elecronic ignitions vary the dwell ie the proportion of the time the coil is switched on. The way the coil works is to store energy and when the points or electronic equivalent open this is released almost instantly. The coil takes a finite time to charge up like a capacitor. For a HA12 coil this takes around 3 to 3.5 milliseconds. At idle, say 750 rpm the time between firings is 40 milliseconds. The 25D4 distributor would switch on the coil for around 24 milliseconds whereas the electronic unit would only switch it on for 3.5 milliseconds - the power dissipated by the coil would therefore only be around 15% with the electronic unit so the coil would stay cool. (Note some electronic units don't offer variable dwell or constant energy). As the rpm rises the difference between the contact breaker dwell and electronic unit dwell diminishes - at around 5,000 rpm they are very similar. At least your coil forms a handy heater for your hands should you dare to venture out for a smoke! regards David Thank you, Dave! I noticed, at the end of the session, that the current went a bit down. It was still a bit above 2 A while running when I shut it off after around 20 minutes, though. Thinking of it, when I used the electronic ignition the coil kept absolutely cold, all the time. perhaps a clue? The symptoms were the same however. Of course, the points dwell of the 25d is rather high, with the points closed almost 70 % of the time.. Still, it gets abnormally hot imo.. It will be interesting to compare it to the other one. Further tests will have to wait, however. So far, this December is the coldest here since 1902.. and according to the forecast it will stay like this during next week too. Oh dear.. One positive thing though, you don't smoke that much:-) (I only smoke outdoors...) Regards, Tommy. |
|
|
|
Post by dave1800 on Dec 8, 2012 7:38:43 GMT
Hi Tommy You may wish to look at the duplex timing chain on this MGB video. Ignoring the fact that he sets it up 180 degrees out as far as the distributor drive goes, you can see there is very little slack in the timing chain as both you and I remember. regards David Regarding the dimples, I meant at TDC for cylinder 4 firing, the crank and cam wheel dimples and centres of cam and crankshaft were perfectly in line putting a steel ruler across them all. At TDC cylinder 1 firing (sprocket dimples furthest apart), the cam dimple was a bit off the line. I remember I was also a bit amazed by the amount of slack of the (new) timing chain. Of course the tensioner takes this up, but I seem to recall there was wery little slack when putting on a new chain on an 1800 years ago.. Regards, T |
|
|
|
Post by tommydp on Dec 9, 2012 8:27:16 GMT
Tanks for your replies Dave! You're a good teacher, I learn a lot here! Perhaps there is no problem with the coil getting this warm.
At least, I would expect it to be hard to start if there was a major ignition problem. It fires and starts instantly when it's warm and when cold it just takes some revolutions before it starts. The video of the start up is an extreme cold start after 2 weeks, so normal under those conditions imo.
Regarding the timing chain, I have been watching that video and I recall that's how it looked when I installed a new (quality item) one years ago. Hardly no slack. When I installed the chain on the present one, I found lots of slack compared to this. Also I notice in his other video, the tensioner goes out very little to take up the slack. Mine went out quite alot, and you wouldn't expect that on a new chain imo.
Will get into the timing gears again around springtime:-)
Regards, T
I smell bad reproduction parts...
Sorry for my late reply, I have been recovering from the annual Christmas party with the other teachers...
|
|
|
|
Post by Penguin45 on Dec 9, 2012 20:33:43 GMT
If I could just add a couple of minor points. Earths. Bad earths can be responsible for surprising drops in voltage and can culminate in components dropping out all together. Connectors. Those crimp-on red and blue plastic terminals are appalling. It is exceedingly difficult to get full contact for the wire core and offer poor vibration protection to the cable. Also, they are not "authentic" on our vehicles. Some years ago I invested in the proper crimping gear and a range of terminals (Primarily for work purposes) and haven't regretted it. I sourced these from VEHICLE WIRING PRODUCTS. Old Wiring. Old copper wiring deteriorates, fact. All too often, I have trimmed back wiring to fit new connectors and instead of revealing shiny copper, found dull pinky/black strands. This can extend back through the entire length of a cable and causes high resistance. As we all know, electrical resistance equals heat......... As for the chain, Moss do the duplex chain for under £10 which has to be a bargain. Cheers, Chris. |
|
|
|
Post by dave1800 on Dec 10, 2012 2:10:07 GMT
Hi Chris Yes some excellent points here. Bad earths cause even more complex problems with modern ECUs and sensors which can result in expensive components being replaced inappropriately. I use a Picoscope that plugs into my laptop and there are some interesting (for me) automotive diagnostic case studies on their website and a forum. www.picoauto.com/automotive-library.html#casewww.picoauto.com/support/forum48.html Sorry no topic to diagnose exploding diffs (sorry) but for those of you with new cars that suffer electrical /electronic problems a read could point you in the right direction even without an available scope. Your mention of the problem with terminals and the link to the crimping tools and the quality terminals is very helpful. But what do you suggest when you try and repair a bad joint and no matter how far back you go the copper is still black and fragile? When I have tackled this problem I have run a new wire from end to end but this can start to look messy and perhaps the whole loom is affected and that's a really daunting proposition I think you will agree? Regards David If I could just add a couple of minor points. Earths. Bad earths can be responsible for surprising drops in voltage and can culminate in components dropping out all together. Connectors. Those crimp-on red and blue plastic terminals are appalling. Old Wiring. Old copper wiring deteriorates, fact. All too often, I have trimmed back wiring to fit new connectors and instead of revealing shiny copper, found dull pinky/black strands. This can extend back through the entire length of a cable and causes high resistance. As we all know, electrical resistance equals heat......... As for the chain, Moss do the duplex chain for under £10 which has to be a bargain. Cheers, Chris. |
|
