'77 B - Ignition Problems

[JoshP]

A few days ago, I received my rebuilt 25D distributor from Advanced Distributors. Quite the showpiece; only bad thing is, it makes the rest of my engine bay look bad . The car in question is a 1977 MGB, 25D distributor with points, twin SU HS4s.

Anyhoo, I confirmed points gap of .015 and installed the distributor. I turned the engine over to have number 1 at 10 degrees before TDC. Luckily, the rotor pointed to 2 o clock where it usually does for number 1, so I didn't have to fiddle with repositioning. I went to static time the engine with my test light; lo and behold, my test light would only light up intermittently on the LT post. It started out OK when I first plugged the light up; when I started to turn the distributor clockwise, the light went out as it should. However, when I turned back the opposite way, the light didn't come back on at all. I rocked the rotor a bit and it came back, but started blinking and finally went back out again. As such, I wasn't really able to get a good time on the engine with the light.

I did a visual timing by watching the points open and close as I turned the distributor, stopping it at the point where the points just start to open and locking it down at that point. I know it isn't nearly as good as what a test light or timing light would give, but I thought of it as acting on the same principle as what the test light shows.

Not surprisingly, the engine would not start. Oddly enough, when I first tried to start the engine, I heard something snap and crackle from under the hood after one crank, and the ignition light died out. I disconnected the battery and took a look under hood to find nothing appearing amiss. No smoke or loose wires. I reconnected the battery and tried again; it cranked and cranked, but no start. I recently had to replace the fuel pump and I can confirm fuel flow to the carbs.

I watched the John Twist video on static timing and did as he did, connecting the test light between the LT connection on the distributor (lead disconnected) and fuse #1 on the fuse box; I've read also that it can be done by connecting the test light to the white/black at the coil and ground. Should I have done it this way instead?

Help?

 

[testaj]

Was the car running before you pulled the distributor for a rebuild?

 

[JoshP]

It's one of those typical "ran when parked" scenarios. I'd put the car in storage late last year and have been reviving it lately; stepping through Tony's list. When I first started out, the fuel pump was DOA, so I replaced it with an electronic SU pump. Fuel flow is confirmed OK; charged up the battery, put in some fresh gas and attempted a start with no go.

I pulled the distributor cap and found that the points weren't opening and closing; they seemed to be seized together. I pulled the distributor and separated the points and also found the shaft had a lot of slop. I sent it off to Advanced Distributors and had it rebuilt. That brings us up to the present dilemma.

 

[Deleted member 8987]

The flickering almost sounds like you have some lubricant on the point faces.
Rotate the engine until points are closed, take a small liece of cardboard or even business card, open the points manually, insert the cardboard, let go the points.
Drag the cradboard out and inspect cardboard.
You may see some oily residue.

Sometimes, to keep from splashing Brakleen into the bowels of the bowl, I soak said cardboard in Brakleen AWAY from your car, insert that, and drag it out.
Then try it.

Just a thought, and it's cheap.

 

[JoshP]

Update: just now, I replaced the points and condenser with a new spare set that I had; same results. I took a piece of sandpaper and cleaned the points up nice and shiny, then let the points open and close a couple of times on a strip of clean paper. No residue to be found. I popped the distributor back into the car and attempted to time it. No light on the test light at all; the test light is confirmed good on a battery.

With the previous points/condenser set, I was able to confirm spark to the cylinders on cranking, albeit a yellow spark; I think this may be due to the power draw causing the spark to be a little on the weak side though. It's hard to tell from this standpoint, and I'm as stumped as a fallen tree.

 

[Deleted member 8987]

Not sandpaper........
That was the quick and dirty test.
If the cardboard had come out clean with no residue, we go elsewhere.

Internal grounding wire intact?
Coil fried?
Full 12V at the feed side of the coil?

Points closed (or distributor side of primary grounded), ignition "on", what is the voltage at the hot side of the coil primary?

Ignition off.
Un-ground distributor side of coil.

Do you have a test lead with alligator clips?
If so, connect to the points or condensor grounding screws, ground wire to block, try your light now.

If it works, try (with cap and rotor off, coil wire out of top of cap) cranking it with ignition "on" and see what kind of spark you get.

If that is good, and it goes back to zip with the grounding wire removed, most likely the internal grounding wire it broken.

USUALLY, my experience is on Lucas, that a broken ground just makes them idle like crap, not create a no-start condition, as the springs that rub the breaker plate to the base plate generally provide SOME contact.

Coil is probably the culprit is all other tests (including full 12V at coil) are okay.

The "snap crackle pop" may have been the secondaries of the coil arcing over internally.

What made me want you to check for oil residue on the point faces was A) newly rebuilt, and B) the test light flickering.

Odd.

 

[JoshP]

I'll check those things out tonight and see what I make of it. Unfortunately, I don't have a spare coil laying around; if it turns out to be the coil, I'll have to pop for a new one. Thanks!

 

[JoshP]

I'm getting 12V to the coil; I tested the ground wire on the distributor body with a meter and it checked out good. The ground wire is a new piece, soldered to the base plate on one end and screwed down clean on the distributor body. To reduce the number of variables in play, I swapped the points/condenser/rotor back to the set that the rebuild came with.

I tested the LT lead with ignition on; test light full on. I attempted the timing routine with ignition on, test light grounded to the alternator bolt and connected to the LT post (LT lead connected). This time, the light wouldn't go off at all.

For my next bit of troubleshooting, I'm going to need a young priest, an old priest and a couple of chickens. Up until this point, I considered myself semi-knowledgeable about MGs and old cars in general; I'm as lost as I can be though.

 

[Deleted member 8987]

Ifd it won't go off, the points are not closing.
However (and forvive me, I am not quesioning your spatial ability) you didn't happen to connect your test lead to the "hot" terminal of the alternator, did you?

Okay.
12V to the primary side of the coil.
Points and condensor connected to the other primary leg.

Test light grounded.

Light won't go off.

Now, connect the test light to the primary load side of the coil, and you can disconnect the distributor/points lead for this (NOT the power side).

Now, carefully, probe the moving leg of the points and rotate the distributor body, and see if the light goes on and off as you would suspect it to.

IF you have the distibutor/points pigtail wire not on the correct side of the insulator, the test light in your original procedure will stay on all the time.

Let me know.

Dave

 

[JoshP]

I connected the test light clip to the bolt that holds the alternator to the block; feel free to question all you wish. There's something I've got wrong or am doing wrong here; I just can't seem to put my finger on it.

I watched the Twist video on installing points/condensers again and rechecked my assembly. In order from the base plate, I've got insulator, points arm, condenser lead, LT lead, second part of insulator and small nut. The first time I did a points job (way back when), I always had a problem with the gap changing or closing up on me when I tightened the cheesehead screw, so I leave the feeler in place when I tighten it up. I then turn the rotor over 360 degrees and recheck gap.

The gap stayed OK after this test, so I slid the distributor home into the drive. I can see the gap opening and closing as I turn the engine over by hand.

I'll try the tests above with my test light and report back.

 

[Deleted member 8987]

Sequence of assembly sounds right.
I just wanted to check on the alternator-stranger things have happened.

Testing the point arm will tell you if you are getting power to the points proper.
What you do next is start moving back up the line with the test light if you have nothing at the points.
There is the possibility the pigtail is broken.

The First Rule of Automotive Repair states:

"Just because it's a new part doesn't mean it's a good part".

Dave

 

[JoshP]

When you say the pigtail, are you referring to the lead from the condenser, the lead from the LT to the points or the ground wire? I ask because I just noticed that the lead from the plastic LT bit looks dodgy; the lead itself is a bit tattered (but intact) and the little housing pops off the distributor body so easily that I have to reseat it whenever I remove the cap.

 

[Deleted member 8987]

Pigtail is the US parts term (sorry) for the primary wire from the coil to the points.


I was out working, pondering, and thought of one other thing.
Do you have the hold-down clamp tight on the housing?
Like, tight enough you have to work to turn the distributor body?

If none of the above solves the problem (like, the light works everywhere when used as directed), conect a ground strap with alligator clips from the body of the distributor to a good ground source.

Just maybe this housing is sprayed with "look good" stuff and not grounding, which will also give the symptoms you are experiencing.

Problem is, if I had the car in front of me, I'd find it in short order, but I gotta try to put the synaptic impulses into words on my keyboard, and that takes a little longer!

Bear with me, we'll get it yet.

Dave

 

[JoshP]

Here comes an update and it's a bit of an oddity. I pulled the distributor once again and went over the body with a piece of sandpaper, cleaned and re-gapped the points, then reinstalled. I attempted to static time with the ground clip of the test light to a hot fuse and the probe on the LT post. Same issues as previous; I took a jumper lead and clipped one end to the distributor body and the other to the alternator mounting bolt.

This caused the timing routine to actually go normally; I performed the static time as was for practice (I didn't have the engine turned to 10 degrees BTDC on cylinder 1 yet). When that proved successful, I detached my leads and turned the engine to 10 degrees BTDC. I reattached my leads and timed it for real this time. However, in the middle of timing it, I noticed that my ground lead had popped off of the distributor body. The timing routine worked normally though! I did it twice just to make sure I wasn't seeing things.

I set static timing to 10 degrees, reconnected the distributor cap and LT lead, then tested for spark at each of my plugs. The spark seemed a little on the weak side, but is now present on each of the plugs. However, I still don't have successful startup. Got a bit more work to do, but it seems I'm heading in the right direction nonetheless.

 

[Deleted member 8987]

See?
We're getting somewhere now!

How tight is the distributor hold-down clamp now?

 

[JoshP]

I cinched it down pretty good; to the point that I was afraid one more turn on the nut would potentially crack the housing. I'm not sure I could move that distributor with a truck now.

It seems that I'm getting fire to the plugs, so the coil may not be bad after all; the spark does seem a little weak, but with the cranking action going on and sucking down the amps, that could very well be normal. Now comes the really fun bit: finding out why I've got fuel + spark, but no fire. I drained the tank during my "reviving" period and put a couple gallons of fresh fuel in; I may end up having to drain and clean the float bowls and put a bit of fresh fuel in those.