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MG MGB Technical - Awakening my 1978 MGB - No Results
|Having driven the 1969 MGC to shows, rallyes, etc, since 1999...I put the 1978 into storage at that time...Kind of forgot about her. |
Last night I looked at her...and decided to wake her up.
Put in a new battery...pulled the coil wire...shot some oil into the cylinders...spun the starter.
fuel pump worked immediately...oil pressure gained almost immediately.
This car has a points distributor, NOT an electronic ignition.
Put the coil wire back on and spun her over again....no fire.
Gave her a shot of starting fluid....no fire.
Pulled the coil wire from the distributor and held it near the block, spun the starter...no spark.
Checked coil for voltage...almost 13v on the ignition side.
Checked the black/white leads to the distributor for resistance...wires good.
Pulled the distributor cap and spun the engine (with the coil wire reattached) - no spark.
Put in a new coil...no difference.
Checked the points for resistance...no resistance when they are open OR closed...so the problem appears to lie within the distributor.
There is voltage from the coil to the distributor.
There is no spark when the points open.
So...I'm taking the MGC to the Champagne British Car Festival tomorrow....
Tomorrow upon my return home, I'll change the points and see if that remedies anything...but if it does NOT...where should I look? Can a condensor go bad just sitting in storage?
|Try a new distributor cap Rick, a neighbour had a similar problem with his B after a lay-up. Everything tested good but no spark was delivered to the plugs. Although the old cap apparently gave no problems before the lay-up, replacing it did the trick.|
Check the condenser. A DVM should gradually rise on the ohms setting from zero to infinity. Reversing the leads should discharge it.
|Rick - Either replace the points or scrub the contacts of the existing points to clean off the film that has built up over the years the car has not been run. the same thing is going to be needed for the points in the fuel pump. Cheers - Dave|
|Cleaning the points is on the to-do list for this afternoon. (I just got back from the 19th annual ChampagneBritish Car Festival, held this year in Bloomington, IL).|
The fuel pump is fine, delivering (skanky, old) fuel at a good rate.
Thanks, all...I'll keep you posted.
|Try swapping the rotor. Some have had problems with shorting|
through the insulation to the distributor shaft.
|Buy a point file at your local NAPA store. They still stock them. It sounds like your points have filmed over, as Dave mentioned. A quick pass with the points file should have you on your way. I've gotten countless older cars started this way, and a ton of motorcycles. RAY|
Take this from someone who has awakened at least 20 old cars/motorcyles/scooters/mopeds: apart from no spark, the engine will NOT start on the old fuel. All the lighter particles will have evaporated, leaving a very "heavy" fuel that is very hard to ignite.
USE FRESH FUEL! (and first get a spark...)
|Willem vd Veer|
|Swap swap swap? Oh dear me no. |
Fist step should always be to clip a timing light onto the coil lead and each plug lead in turn. Flashing on the coil leads indicates bad plugs or no fuel, remove the plugs and sniff them. If there is no fuel smell there is no fuel. If they are wet it is flooded, but you should be able to smell that anyway. They should have a strong fuel smell but not be wet.
If flashing on the coil lead but not the plug leads then either the rotor is shorting to earth (no plug leads flashing) or the cap is breaking down (one or more plugs flashing but not all.
If the coil lead isn't flashing, then if you can check you have 13v on the white side of the coil, probably dropping to about 10v when cranking, then you can check the voltage on the points side as well. As the engine is turned manually this should change between 13v and 0v as the points open and close respectively. If it stays at 13v then the circuit through the points and distributor ground wire is open-circuit, quite possibly points oxydised. If it stays at 0v then remove the points wire. If it still stays at 0v then the coil is open-circuit (coil change noted) but if it jumps up to 13v then the points are short-circuit, either through having no gap or the condenser is short-circuit.
|Paul Hunt 2010|
|thanks, Paul. I was hoping you would jump in here.|
I havde some time today and will be playing with this problem.
"Pulled the distributor cap and spun the engine (with the coil wire reattached) - no spark"
This would indicate a problem with the points or the ground to the distributor body. Check that the points hooked up correctly--the wire from the coil and the wire from the condenser need to be insulated from the center post and in contact with the spring arm. Check that the small wire from the points plate to the distributor body is firmly connected at each point and in good condition.
"Checked the points for resistance...no resistance when they are open OR closed...so the problem appears to lie within the distributor." This, too, indicates a points problem with the points being grounded (spring arm to points plate) internally, hence, no infinite resistance when the points are open.
It sounds like your points or condenser have an internal short which is causing the coil voltage to short to ground.
A test light or analog voltmeter can be hooked up to the distributor terminal of the coil and be observed while the engine is being turned over. The light should blink on and off or the voltmeter should cycle between about 8V and 0 if the points are operating properly.
|Had a similar situation once and tried everything before a seemingly insignificant part came to mind. If you had the distributor cap off, did you check to see that the diode didn't fall out? I think that's what it's called. It attaches to a spring and is inserted into the distributor cap. Without it, your coil wire doesn't complete the circuit to the rotor. I've had it fall out and spent hours of frustration before I thought to check for it.|
|No diode in a distributor, you probably mean the carbon contact that touches the top of the rotor. A friend lost one of those and it did run as the spring stayed in place, for a while at least until that burnt/wore out.|
|Paul Hunt 2010|
|Paul, it was late last night when I made that suggestion to look for and seemed that "diode" came to mind in some schematic. It's commonly called the "carbon button" and only sold as part of the distributor cap from what I can tell. The spring's coil tension holds it in the distributor cap, although it is minimal. It can be pulled out of the cap with little effort and can fall out easily from an aged distributor cap. The carbon button has shoulders on one end and usually stays attached to the spring. I've had them fall out more than once over the years and can create a lot of frustration since they're a less than obvious part to check when ignition problems arise.|
|Rick. A good idea. I, too, have seen a bad carbon bushing in the distributor cap. But, this is at least step three in the process. As I noted in my post, the fact that Rick notes that he gets no spark with the distributor cap off (i.e. when the cap is removed to allow you to see the points opening and closing and the coil is tested for spark on the lead going to the central terminal of the distributor cap) indicates a low tension circuit problem. This problem needs to be found and corrected before any trouble shooting of the high tension system can be effectively undertaken.|
|I'm not sure why the discussion is focussing on high tension and fuel - if there is no spark across the points when they open then that certainly narrows the field to begin with!|
I've had odd problems with new points recently - gave them a good clean with solvent before fitting, they ran fine for 2 days and then left me by the roadside. A cleanup with a file got me going.
A local mechanic who is a highly-regarded British car expert told me that he has struck this a few times as well.
|Cleaning points by drawing a piece of paper through them can leave fibres behind, especially if a torn edge is pulled through, and these can burn and become an insulator. I do use paper to clean my points after initial setting with a feeler gauge, but stop pulling before the edge reaches them and open them instead. This is to clean oil/grease off of course, but paradoxically the last set I took off had the contacts covered with an oil or grease 'bubble' and had been running perfectly well, and had no spike or pit when wiped.|
|Paul Hunt 2010|
|Rick, no progress reports ? I guess you must have remembered where you installed that anti theft immobiliser switch back in '98. I can't make it to the V8 meet this year,but I hope it's as good as usual. Barrie E|
This thread was discussed between 06/06/2010 and 16/06/2010
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