MG-Cars.info

Welcome to our Site for MG, Triumph and Austin-Healey Car Information.

Parts

MG parts spares and accessories are available for MG T Series (TA, MG TB, MG TC, MG TD, MG TF), Magnette, MGA, Twin cam, MGB, MGBGT, MGC, MGC GT, MG Midget, Sprite and other MG models from British car spares company LBCarCo.

MG MGB Technical - Like the Old VW Days

Hi All,

During my teens and 20s in southern California (won't say when that was!), I owned a succession of VW Bugs and vans. They ALL had starter solenoid problems. Not such a big deal, but you had to slide under the rear of the car, and beat on the solenoid from below - then they would start.

In April 2009, I replaced the starter in my '63 B with a High Torque starter from Moss, Part # 541-545 (see attached screenshot). I replaced the starter because the original was engaging a worn spot on the rear of the ring gear and the replacement engages the unworn front of the gear. This starter has its own solenoid and bypasses the wheel-well-mounted push-button solenoid.

Not long after installation, sometimes when I tried to start the car, the solenoid would click but the starter would not spin and engage. It has gotten worse, and it's about a 50/50 proposition whether the starter works. But, if I zap the battery with the charger, the solenoid kicks in and the starter cranks over.

I have been been having voltage regulator "issues" for a couple of years and lately I've been monitoring the battery voltage carefully before installing a solid state voltage regulator conversion by Bob Jeffers at Wilton Auto Electric. Tonight, I routinely checked the voltage before starting and it was about 12.6 V. When I turned the key, the solenoid clicked and the starter didn't spin or engage.

Then, following up on the old VW days, I took a 1.75-inch wooden dowel, placed the lower end on the solenoid (from above - standing!), and whacked it with a hammer. Then the starter function properly.

So, I'm thinking I've got a sticking solenoid, just like in my old VW days. Is this some bad karma? Or are there issues out there with sticking solenoids on these starters. Are these starters sensitive to battery voltage (do I need 12.8 or 13 volts as opposed to 12.6?)?

As always, I would appreciate the excellent input from you all.

Cheers,
Greg

Greg Van Hook

Greg - How long has your MGB sat without being driven? If it sits for periods of two weeks or more, it is a candidate for a battery conditioner being plugged into the battery every time it sits without use (I installed a plug in our TD and always plug it in when it is parked). The battery conditioner (also called a battery tender, battery manager, etc.) trickle charges the battery to about 13.6 volts, then shuts off and lets the battery discharge down to a preset low voltage and then goes back into a charge state. By cycling the battery this way, it keeps it from sulphating or being boiled dry as a plain trickle charger does. This usually take care of starting problems. Cheers - Dave
David DuBois

It could be that, like arteries in old people, the wiring is not conducting as well as it did some 50 years ago.

One solution may be to place a relay in the starter circuit so that full battery voltage gets to the starter motor.

Cheers,
John
J Tait

Greg -
The real problem is high resistance connections in the main battery-starter circuit, but the same conditions generally mean other electrical gremlins. Like maybe your "regulator" problem. When you ask the electrons to pass the bad connection(s), they are insulted and refuse to go, unless forced by lots of volts. And bad connections eat volts!

The VW was especially prone to this because
A) it was 6V, therefore requiring lots of amps; and
B) the main wiring connections were buried up in the works and were ALWAYS BAD.
I couldn't tell you how many VWs dripping snow I had to go under to fix the damned wiring.

The starter solenoids stick very rarely if ever. The starter drives stick because they get engaged by the feeble electricity, which then can't turn the engine.

12.6 is normal voltage for a fully charged battery that has been resting for a few hours; they may go as high as 13.5 just off the charger, but will drop quickly. In your case, the extra half volt or so makes the difference.
Measure Batt V across the Batt posts, say it is 12.6V. While an accomplice cranks the car, measure it again - it should be about 1-1.5V less under load, say 11V. If so the battery is good. If it is down 2V+, the battery is probably bad, have it tested with a heavy discharge tester.
Now, while cranking, measure V at the solenoid post to block. It should be within .5 of Batt V, say no lower than 10.5 in this example. The .5 is the total circuit drop. and .5V is the max; should be more like .25V. This drop includes both hot and ground sides of the circuit. Measure loaded V from Batt hot to solenoid, should be near zero, .25V max. Measure from Batt ground to starter case, again should be near zero, .25V max. These are the loaded V drops, and added together should be less than the acceptable .5V total. If either or both are significantly higher, find the bad cable or bad connections.
(We used to find the VWs with only 2.5-3.0V across the starters!)
In fixing this, you will have also fixed the main parts of the charging circuit, which may cure that problem, as well. You check the other circuits the same way - voltage drop under loaded operating conditions. both hot and ground sides.

Look in the archives for GG Ginty's saga of starters. I just kicked up the last installment, but there are about two years to this story in archives.

If you want more, send me an email, ask for "Electrobabble".

FRM
FR Millmore

Hi Dave, No I don't have a Battery Tender, but I have a reminder on my calendar to start the cars the first of every month. I'm guessing that's not adequate.

Thanks FRM. Just want to confirm a couple of things.

My car is still positive ground.

...measure V at the solenoid post to block... you mean negative voltmeter lead on the solenoid and positive voltmeter lead on the engine block, right?

...measure loaded V from Batt hot to solenoid... I'm not sure where you mean - aren't they both negative?

...measure from Batt ground to starter case... here they're both positive?

I expect my converted voltage regulator back from Bob Jeffers in today's or tomorrow's mail. I'm hoping that will solve my problems. I noticed that with the stock voltage regulator (actually, the Moss non-Lucas replacement), with the engine running the voltage reads about 14.6, but when I turn on the headlights it drops to 13.something. So, obviously the voltage regulator is not working properly.

Cheers,
Greg
Greg Van Hook

Greg-
"My car is still positive ground.

...measure V at the solenoid post to block... you mean negative voltmeter lead on the solenoid and positive voltmeter lead on the engine block, right?"
>>>Yes since it is still positive grd, but it doesn't matter, assuming you have a digital meter. You only care about the magnitude, not the sign of the reading. Analogue meter must be hooked up the right way round as it only reads one way.
'

"...measure loaded V from Batt hot to solenoid... I'm not sure where you mean - aren't they both negative?"
>>> As above. You want the number not the sign. One end of any wire with current flowing is positive and one is negative relative to each other; it is the difference you want. These "should" be small readings .01V to .5V, bigger they are the worser things is.

"...measure from Batt ground to starter case... here they're both positive?"
>>> Same

"I expect my converted voltage regulator back from Bob Jeffers in today's or tomorrow's mail. I'm hoping that will solve my problems."
>>>Doubtful to zero chance

"I noticed that with the stock voltage regulator (actually, the Moss non-Lucas replacement), with the engine running the voltage reads about 14.6, but when I turn on the headlights it drops to 13.something. So, obviously the voltage regulator is not working properly."
>>> Not obviously and probably incorrect. Exactly where are you measuring this? It matters! You have voltage drops throughout the system,which is why you have problems. The regulator can only work with the readings it sees at its location, but these are squirrely, so the results follow.
The 14.6V is about perfect for 3000rpm, and indicates that the regulator is correct. If the voltage drops below that when loaded, either the generator is not working correctly, or you are measuring at some point downstream of bad connections.
Assuming the problem(s) is all sections of the system involved in both starting and lights:
If the light load of about 15A pulls the voltage down 1.6V, by Ohm's law V/A = R or 1.6/15 = 0.11 Ohm total resistance under those conditions.
Again by Ohm, V(drop across bad connection)= A(starter draw =150A)x 0.11 Ohm = 16.5V. This is clearly impossible; the effects are non linear but it gives you a rough approximation and pretty clearly tells you why your 12.6V battery won't start your car!

The new regulator was probably not necessary and will not solve your problems, unless you happen to fix part of the bad connections in the circuit while changing it. Some of the voltage drops may be in those connections, but most of the starter problems will be in battery cables or connections to the solenoid. You may "fix" some of that if you disconnect the battery in this process, but if not actually corrected it will come back.

Again, send me an email and ask for "Electrobabble". Also, I think I asked this before but where in PA are you? I'm upper left = Titusville, 50 mi S of Erie

FRM
FR Millmore

I'm guessing that this (see attached photo of engine block ground strap) might qualify as a "bad connection". No other connections in the circuit even approach the hideous nature of this. I would never have thought of even looking here.

We're pretty much diagonally opposed! About 50 miles north of Philadelphia in upper Bucks County by the Delaware River.

Sending our son off to Rochester Institute of Technology this Fall. I've got a feeling we're going to become familiar with the term "lake effect snow".....

Cheers,
Greg

Greg Van Hook

Good possibility, but connections do not have to look bad to be bad. I frequently find ten or more bad things adding up in a circuit. You can tell for sure if you haven't messed with it yet. Measure V from block to frame under load. Should be 0.1V max while cranking, preferably 0.01V. That may also account for your charging problem, since it is the ground side of the charging circuit.
When you put it back, put the frame side tab underneath after cleaning the area with sandpaper; one or two less surfaces to cause trouble. Use OxGard or similar on the joints.
I worked trucking out of Rochester for three winters - yes you will!

FRM
FR Millmore

When I converted my '67 over to a 4 synchro/od trans, I used the later backing plate, flywheel and pre-engaged starter. However, I kept the original fender mounted push button solenoid in the starting circuit. I ran a single heavy cable, from the fender mounted solenoid, down to the starter motor's solenoid. I then made up a small jumper wire to connect the two starter motor solenoid terminals together. Now, when the ignition switch is turned to the start position, power goes to both terminals at the same time, energizing the solenoid's magnetic field, which engages the Bendix drive at the same time that the starter motor begins to turn. I've been using this setup for 30 years with no ill effects, while using the original '68 starter motor that I used for the conversion. I believe that this setup allows for more amperage to reach the starter and prevents the problem that you are encountering. It also allows you the convenience of having the push button solenoid for turning the engine over to adjust the valves. RAY
rjm RAY

This thread was discussed between 13/05/2011 and 14/05/2011

MG MGB Technical index

This thread is from the archives. Join the live MG MGB Technical BBS now