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MG MGA - Engine cranking/starting anomaly
| Car - 1961 MKI standard engine, standard starter etc. Anomaly - Ignition switched to off, engine spins over at "high" revs. Ignition switched to on, engine hardly spins over and is very difficult to start? After engine is warmed up, re-starting is not a problem. Any ideas? John |
| J Harle |
| check to see if your static valve timing is advanced too far? also do a dry/wet compression test. |
| Fred H |
| John, You say the starter spins the engine quickly with the ignition switch off and very slowly with the ignition switch on. If this is even before the engine starts it is not an engine problem. There must be a large voltage drop when you turn the ignition key on. Can you check the voltage at the starter switch with the key in both positions? If you do not have a voltmeter try the key in both positions with the headlights on. Is there any change in brightness? Mick |
| Mick Anderson |
| John. Mick is on the right track. The first thing I would check for would be a voltage drop at the starter solenoid when cranking with the ignition on. As to starting properly when warm, it takes less power to turn the starter over on a warm engine than a cold engine. Valve timing would have nothing to do with such a difference. Whether an overly advanced ignition timing could create a starting problem seems to be ruled out because it starts properly when warm. I would also expect the engine to be pinging all the time if the ignition timing were sufficiently over advanced to cause the cranking speed to be affected. Ignition timing, however, would be good to check even if just to rule it out of the troubleshooting process. Les |
| Les Bengtson |
| Les--MGA's don't have a solenoid. |
| R. L Carleen |
| I don't think anything at all connected to the ignition switch could pull enough current to slow the starter. Think about it. The starter circuit is like 1 or 2 gauge wire, and the starter is pulling hundreds of amps. The additional 20 or so amps you could draw thru the small wiring to the ignition switch would not be noticed by the starter. It has to be timing related. You could test this out just by removing the high tension wire from the coil to the distributor. |
| Jeff Schultz |
| I recently changed my ignition switch (the hot/cold key thread) because it seemed to be malfunctioning (leaking to earth). Leccie will take the path of least resistance, so if there is an earth leakage on the live side of the switch the starter motor is unlikely to be able to draw its full power requirements. Two major items come into play when the ignition is switched on: the coil and the fuel pump. Faults in either of these could also be a contributory factor. Steve |
| Steve Gyles |
| Jeff's on the right lines - nothing to do with current or leakage on other circuits which would only be a minimal percentage of the starter current which could be 400 amps. The most likely cause is the static ignition timing which if significantly too far advanced will almost stop the engine from cranking beyond TDC. Hot cranking and starting will be easier because the rotating mass will have less frictional forces acting on it and so will carry on after TDC and start more easily. Check the timing carefully otherwise you risk serious engine damage. |
| Iain MacKintosh |
| Thanks for all your suggestions. I shall try the timing first as this is the easiest to check / adjust. Then the possibllity of a volts drop at ignition. I will remove the HT lead from the coil and crank it over with the ignition sw on. Will post the results. John |
| J Harle |
| John, By any chance have you set the static timing on the trailing edge of the cam as opposed to the leading edge?? Check the timing at idle with a strobe to disprove this first. It's worth doing before you check anything else and will take all of two minutes. |
| Iain MacKintosh |
| Iain, I don't understand your reference to leading and trailing edge of the cam. Could you explain? Thanks, Gerry |
| G T Foster |
| I may too have misunderstood but I think Iain means the cam in th dizzy and thus is asking if the timing has been set as the points are closing instead of opening? maybe |
| Bob (robert) |
| Hello Ian, I am going to check the timing with a strobe - but as I know there were no published dynamic timing degree values at production of the MGA - timing lights were rare and $$$ then! Do you have a dynamic timing value? John |
| J Harle |
| R.L. You are completely correct. Technically, a solenoid is an electrically operated heavy duty switch rather than a mechanically operated heavy duty switch. However, everyone I know, including professional MG mechanics, refer to the starter switch as "the solenoid". Thus, the vernacular is incorrect, but, being the vernacular, in common usage. As to the cam Iain mentions. The points cam has a leading edge and a trailing edge on the pointed section. The spark is induced when the leading edge opens the points. The distributor shaft and points cam are rotating counter clockwise (anti-clockwise) while the base plate is in a relatively fixed location on the body. (The points base plate is moved by the vacuum advance, but that does not come into play here.) The proper way to set the static timing is to set the engine at 7 degrees before top dead center on the compression stroke of number one cylinder. The distributor body is then rotated counter clock wise until the points are closed. The body is then rotated in a clockwise direction until the points just begin to open or the test light illumimates. This sets the timing so that the firing impulse is taking place on the leading edge of the points cam. Note, it is also possible to do everything exactly the opposite and time the engine, incorrectly, on the trailing edge of the cam, throughing the timing greatly off and, perhaps, resulting in a problem such as John is having. My workshop manual does not give a distributor curve for the MGA distributor. We do know the static timing is seven degrees. Thus, a dynamic timing of ten degrees before top dead center at about 1,000 rpm will be somewhere in the ball park with the exact timing requirement to be determined by testing. However, if John is showing significantly more than 15 degrees at idle, we would know that excessive timing is part of the problem. I would, however, expect his engine to be pinging/pinking were that the case. Les |
| Les Bengtson |
| I've seen all these posts and you have read the meaning correctly. Les has agreed that the strobe will either prove or disprove this once and for all. His suggestion of 7 degrees at idle (vacuum connected)is fine, so start off at that point. From there you will have to get the best setting by trial and error advancing the timing gradually by the knurled adjuster until pinking can JUST be heard when accellerating hard in 4th gear between 20 and 40 mph. At that point the setting is optimum for your vehicle. Iain |
| Iain MacKintosh |
| Thanks for ALL the input - this sure is a great tool. I will check the timing etc on Saturday and then post my findings. John |
| J Harle |
| Could the mechanical advance mechanism be stuck, or sticking? Ralph |
| Ralph |
| My two cents: Timing that is far enough off to cause turnover problems should show up at idle - hot or cold. The only time I have ever personally experienced this particular type of timing-related problem was when I put the engine back together with one tooth off in the cam sprocket. That causality obviously does not apply in the present situation. I would go back to Les' original suggestion of measuring the voltage drop while cranking. Also, one of the items that no one else has mentioned that has an impact when the ignition is on is the generator. There is more drag when the field is energized. Whether or not this enters into the current problem, and regardless of the stated battery cranking capacity, the cranking voltage should be the first thing measured in a situation such as this - in my opinion. Steve |
| Steve Brandt |
| Steve. I agree with your analysis. I have never had an engine start and run properly with the timing so far off that it was slowing down rotation when starting. I have had bad starter cables and battery clamps which caused a voltage drop at the starter. If the system is marginal, this may be happening. I would expect a short to ground, sufficient to affect the starting circuit when the ignition switch is on, to be severe and hot wires/melted insulation and smoke to be present. But, once again, if the situation is marginal, it may not have progressed quite that far yet. Your comments are timely. The last thing we want to do is get into a "group think" mentality. One of the strengths of this group has always been the multiple suggestions as to what could cause a problem. If we decide what John's problem is, then focus our advise on that "solution", we ignore the fact that, commonly, we never get a full and complete listing of all that is happening when the problem is described. If the individual is competent to understand exactly what is happening and what needs to be written for the rest of us to make an accurate dianosis, he does not need our help. He can solve the problem himself. Hence, your suggestion that we look at several different possible causes is timely not only for John's information, but also reminds us to keep our own minds open to all of the possible causes. Thanks. Les |
| Les Bengtson |
| A simple way to check if advanced timing is the culprit would be to pull the hot lead off from the coil. Then turn the engine over.If all appears well it is the timing that could be causing the problem.I find it hard to believe that the engine runs well after it starts if the timing is that far off. Sandy Sanders Hudson Florida |
| conrad sanders |
| Sandy. Pulling the coil lead, or king lead, from the coil and turning the engine over is a test of the complete low tension circuit and a test of the high tension circuit up to the end of the coil lead. It can tell you nothing about ignition timing as it is not referenced to the crankshaft position. The factory workshop manual does not list the mechanical advance curve for the Lucas DP2P4 distributor, specification 40510, which was used in the MGA. One internet source gives the following: 1.5 deg at 300 rpm 7 deg at 650 rpm 12 deg at 1,500 rpm This information is what you would get when testing a distributor on the distributor test machine. You have to double each of the figures to get the reading at the crankshaft. (Remember, the distributor is turning at one half engine speed.) The workshop manual also tell us that 7 degrees of static advance should be set in. This is set when the mechanical advance is not engaged and, thus, is added to the mechanical advance figures. So, we can interpret this data to indicate that a dynamic reading of about 21 deg BTDC at 1,300 rpm would be a ball park figure for a distributor with a properly working mechanical advance. (Weak springs will allow the advance to come on sooner, giving decreased overall advance when set at in intermediate rpm or excessive advance at intermediate ranges when set at the 31 degrees BTDC at 3,000 rpm which should produce the max overall advance.) I note that this is very similar to the older MGBs which showed 20 degrees advance at 1,500 rpm. Les |
| Les Bengtson |
| The problem with measuring cranking voltage is that even if you see a large voltage drop, you really haven't proved anything. If the starter is turning very slowly, you will either measure very little voltage drop, in which case the starter is probably bad, or else you will see a large voltage drop and you won't know if that is a symptom of high load on the starter, or of battery or cable problems. If the starter is slowed down by excessive load, the the starter will pull extremely high current, which will cause a high voltage drop even with healthy battery and cables. The only way to tell would be to measure the starter current, and that takes equipment the average home mechanic does not have. Also, there is little to no load on the generator or the electrical system caused by energizing the field coil. The load is put on the generator when the regulator connects it to the battery, and that doesn't happen at cranking speed. |
| Jeff Schultz |
| Conrad has a valid point. He is not suggesting that it is a timing test. If the engine turns over at normal cranking speed with the coil wire disconnected, but turns slower when it is connected, one must assume that the spark timing is affecting the cranking speed. |
| Ed Bell |
| Conrad and ED are spot on. The thread has drifted off the original question till people have lost the plot. Although there has been a lot of good advice read the thread. Denis |
| DENIS |
| Yes it's gone well off track. At no point does John say that once the engine starts it runs OK. It may well do but we don't know, so until then I think we are awaiting feedback from him after the weekend |
| Iain MacKintosh |
| First off, it is my understaqnding that whenever the voltage in the battery drops below the voltage regulator setting, the generator is energized to try to balance the current flow and charge the battery up to full voltage. In the simple MGA charging circuit, if the battery voltage drops below the setting during cranking, the generator will try to charge the battery (under load). This may be related to the output voltage of the generator, which is related to rotation speed, but I'm not sure. The original post states, "After engine is warmed up, re-starting is not a problem." It does not mention how the engine runs, but in this case I think that it is fair to make the assumption that if the engine misfired, or ran rough, the post would note that as part of the information. But that is an assumption just like assuming that the lights are not on during the cranking process, even through that fact is not explicitly stated. The thread has not wandered. There are two distinctly different approaches that have been suggested. Not necessarily mutually exclusive, but certainly different root causes. Do not confuse the cold cranking capacity of a new battery with the current capacity of a worn out cell. The starter probably only draws 50 -80 amps at worst, if the battery is near the end of its life, it can easily be marginal and 5-10 amps from the rest of the circuit might be sufficient to cause a slow turnover. This will show up as a voltage drop below about 7.2V. See questions 13,17, and 21 at: http://www.autoshop101.com/asetest/asetest4.html. Making this measurement does "prove something." It directs the faultfinding attention to a part of the electrics that has little or nothing whatsoever to do with the timing circuit. If the voltage during cranking is low, it is easy to either connect jumper cables or a charger to verify that the batter(y)(ies) is (are) low, or to continue to troubleshoot in the area of the fault, starter, wiring, etc. I don't know if the problem is with the battery, the starter, the generator, the timing or whatever, but to make a case that such a measurement is worthless is contrary to every troubleshooting analysis I have ever known an objective mechanic to make. Steve |
| Steve Brandt |
| I may be off base, but the problem does not sound as if it is an engine problem at all, but rather a battery problem. A bad cell will degrade the performance of the starter circuit such that while cold, the battery hasn't the power to do the job, yet after the engine is warm, the battery also has the juice to do it's job. It is not stated whether you have two 6 volt batteries, one 12 volt battery, or two 12 volt batteries. Check all cables, even the ones between the batteries. Also, if you have period batteries, i.e. the ones with the tar sealed tops, they easily discharge, and you may wish to wash the outside of the batteries, as well as insure that you have rubber insulators between the battery and the battery box. I would first of all clean all electrical terminals, including any engine ground wires, the distributor and coil primary wires, and the starter wire terminals. I would check for a loose wire on the ignition switch, and look also for chafed wires through the fire wall. Take care of the obvious first, and when this is done, it will point to the not so obvious. |
| mike parker |
| What Conrad said was to spin the engine over with the coil lead removed and the ign on,that is not a big job. If it still spins fast its probibly timing, if its slow its a short or at least a big power draw. Denis |
| DENIS |
| Could there some problem with the ground on the engine? When the ignition is off, the ground is adequate, but with the ignition on the ground is not. |
| Ray Ammeter |
| It could be as simple as an impending full grounding of the starter's field coils to the case. I'd inspect the brush bracket rivets on the back of the commutator end plate for signs of arcing/burning. You should concentrate on those that are supposed to be insulated from the back plate. It doesn't take long to test for shorting/grounding of those rivets to the back plate. The field coil grounding is more involved. This one really fooled me, as it seemed to turn over fine (while building up oil pressure as it had sat for some time) until I tried to start it. My starter's failure was a little more advanced though at the time. Maintenance is always good if it will need to be performed anyway (soon enough usually). This problem can have or appear to have multiple causes. You will either eliminate the problem or at least some of the probable causes simply by performing some maintenance and tests as you go. I'd still start with inspecting the cables and the grounds. If the battery is failing, I doubt it would hold enough of a charge to get past the hard starting. Too much advance would cause a kickback, no? The mechanical advance adds to the static setting, no? Starting at 7 BTDC and adding the 7 for 650rpm would be ~14 (more like 15 BTDC at 700rpm (dynamic), no? I doubt the timing was too far advanced, but if you've played around with the timing and want to start fresh (sorry to post such long-winded basics): I'd remove the dizzy top plate and inspect the cams. Do they move easily (don't over-stretch) and spring back? If so...probably OK. If not...clean and lube. Refit the plate. Pull the plugs and the valve cover (you may consider setting the gaps at this time, while you're at it). Stuff a small wad of paper towel in the #2 spark plug hole and then bump (small bumps, eh) the engine over till the wad pops out. You're probably close enough now to turn the engine at the crank pulley nut to get her to 7 BTDC. Twist the knurl nut on the dizzy to position slightly more on the retard side as you'll later use this to dial in a best setting thru trial and error. Loosen the dizzy clamp as necessary and use a probe lamp to set the points when they just open on the front of the cam. If you're not sure...rotate the dizzy in the direction that the rotor would turn and go past where it lights and goes off. Then rotate slowly against the direction of rotor rotation until it just lights. Lock her down. Your timing is close enough now. Your choke setup is working correctly too of course. You've inspected the batteries...tested the electrolyte density values and the cells were NOT down below the tops of the plates...right? The batteries were fully charged AND the batteries were then Load-Tested...right? If so, you're ready to test for a voltage drop in the starting system as Steve has listed a few posts above... I love these problems more than a good whodoneit mystery....can't wait to read what happens next...Cheers |
| Jon Bachelor |
| John We are all waiting with baited breath for what you found out this last week end. Don't keep us in suspense for too long! Regards Steve |
| Steve Gyles |
| Sorry guys - I am away on a trip at the moment. Will hopefully be back in Frankfurt this weekend. And will T/S and let you all know... John |
| J Harle |
| Well guys I returned to Frankfurt early - and have performed some T/S on the car. It seems both schools of thought on this anomaly were correct! I discovered two things: 1. The igntion was advanced by some 10 degs beyond the 15 degs dynamic value, at aprox 25+ deg BTDC. I have eletronic ignition fitted so I could not perform the static timing check. As I was setting the timing, my timing light decided to "croak" after 30+ years of faithfull service! So, I was not able to accurately set the timing. I cannot figure out why the timing was set so far in advance - ???? 2. The electrical connector at the starter motor was slightly loose and upon removal I discovered some corrosion on the lead lug. Cleaned and reconnected. I never thought to look for corrosion as my car is garaged, never run in the wet and has only covered less than 10K miles since a FULL restoration! The car "NOW" cranks at the same HIGH cranking speed with the ignition selcted to ON and with it selected to "OFF". Thanks again for all the help and suggestions. John |
| J Harle |
| That's good John and makes a lot of sense. I just had a feeling that the motor was kicking back during cranking and that of course would have put huge loads on the starter circuit and indeed it failed at "the waekest link" Interesting to note though that an additional 10 degrees was enough to tip the balance. |
| Iain MacKintosh |
| Well then...Bravo! I hadn't read that you had electronic ignition fitted before now. If you were running fine before (with it already installed), then perhaps the dizzy had somehow been moved?? Curious...in lieu of using the test lamp for static setting, can't you just set the #1 plug wire end near ground and stop when the spark snaps across? |
| Jon Bachelor |
| <<<Snip>>>First off, it is my understaqnding that whenever the voltage in the battery drops below the voltage regulator setting, the generator is energized to try to balance the current flow and charge the battery up to full voltage. <<<snip>>> But, you've forgotten about the cut out. If the generator's output is less than 12 volts, (due to insufficient RPMS) the field coils are deactivated and the generator is disconnected from the circuit. Thus at cranking speed the field coils of the generator are not energized unless the cut out is malfunctioning. IF the cutout is malfunctioning, then the battery while quite often discharge after several days because the field coils in the dynamo are still on. Blake |
| Bullwinkle |
| Thanks for the information, Blake. You are right, of course. As part of the entire paragraph's context, the last sentence reads: "This may be related to the output voltage of the generator, which is related to rotation speed, but I'm not sure. " My memory of the generator/voltage regulator circuit operation is about 25 years old. The the current rebuild, I am switching over to an alternator. Steve |
| Steve Brandt |
This thread was discussed between 24/01/2005 and 04/02/2005
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