MG Car Repair: MG Slow to turn over, starter solenoid, earth connection

Question
QUESTION: Hi
I've a 73 MGB which I have been restoring for (a while). When I bought it I did get the engine going once before I stripped the car down.
My problem is that, I've rebuilt the car, and its ready to start, however, the engine turns over reaaaallly slow. Not enough to start. I've replaced the starter, cleaned the earth from the engine to the chassis, cleaned the earth connection from the battery to the car. The engine will turn easily by hand. I've tried jumping it from my ford to see if its the battery - still no joy. Right now, there is no ignition switch, so I'm Turning the little black fitting from the back of the ignition with a screw driver, but I don't think that is the problem.
Any ideas?
Andy

ANSWER: Hi Andy,
Even though the engine turned over easily by hand it can still be a starter problem. But first you need to do a few tests with a volt meter. Even though you cleaned a few connections that don't test the system. You need to do "voltage drop" tests of the (+) and (-) cables.

First test the battery voltage. (12+v) (always test at the posts not the cable ends) Then turn the starter switch to "Start" and read the volt meter again. A low voltage reading is either a very high amp draw or a battery problem. (low meaning below 10v)

Write that reading down and do the "Voltage Drop" tests. Put the (+) test lead on the (+) POST of the battery and the negative test lead on the (+) POST of the starter solenoid. And put the volt meter on a low volt scale.
Turn the switch to "Start" and read the volt meter. (It should read less than .5v) (Write down the readings)

Now put the (-) test lead on the (-) POST of the battery and the (+) test lead on the engine block or head and turn the switch to "Start" and read the voltage. Again it must read less than .5v. Write it down and let me know what the readings are.

Howard

---------- FOLLOW-UP ----------

QUESTION: Hi
Thanks for the quick response.
So I did the tests:
1. Battery Voltage:- 14V (as it was boosted from my ford whilst running)
2. Battery voltage when turned to start:- 4.9V
3. Drop test from +ve battery to starter when turned to start:- 2.9V
4 Drop test from -ve battery to engine when turned to start:- 1.9V

I dont understand the big voltage draw. I just bought the starter last week (it was a reconditioned one).
Andy

ANSWER: Hi Andy,
You have several issues to work on. None of you voltage readings are acceptable. First you need to put a good battery in the car and then remove the spark plugs and run all three tests again with no external jumper. With the plugs out it should spin fast and show 11 to 12v at the battery while spinning the engine with the plugs out. This will also make the voltage drop tests on pos and neg show a good ways below .5v also.

Two batteries connected in parallel and one that is low upsets all the tests. You can't disconnect the in car battery and use jumpers from the other car because now you have added in the factor of the jumper cables.

Any engine trying to start needs to have above 9v at the battery for most any ignition to fire.

If the engine still don't spin fast with the plugs out you need to remove the starter and look at the bendix gear on the starter to see if there is any signs that it is the wrong gear for that ring gear. If it looks ok, you need to take the starter to most any auto parts store and have it tested as they will usually do it free.

You can't condemn the cables yet because of the extreme drag on the starter. This makes the readings on the cables go up due to the high amp draw. The higher reading on the pos. cable just may be due to the longer cable. But neither should be over .5v under load.

Let me know.
Howard

---------- FOLLOW-UP ----------

QUESTION: Sorry - I wasnt thinking when I wrote this (Been a long day). The readings for 3 and 4 were incorrect. The actual readings are:
1. Battery Voltage:- 14V
2. Battery voltage when turned to start:- 4.9V
3. Drop test from +ve battery to starter when turned to start:- 0.29V
4 Drop test from -ve battery to engine when turned to start:- 0.19V

Sorry again.
Andy

Answer
That's good on the cables. You still need to take the low or bad battery out of the picture. Then run the battery under load voltage test and if it is below 9v then pull the plugs to see if it spins fast and note if the starter sounds unusually noisy. Then if it is still slow, take the starter to an auto parts store that has a alt/starter tester and get it checked. Don't forget to look closely at the teeth of the bendix gear for signs that there is a mismatch with the ring gear.
Let me know,
Howard