Technical Starter Motor Bench Test Wiring Problem

[Strada Bianche]

Hi,im a newbie to Fiats, Restoration and Forums so please forgive my ignorance, experience spelling etc!
I am rebuilding my 1970 500F from and am starting to bench test my rebuilt 126/650cc engine stage by stage, starter motor first.
I have mounted my new 126 (Pull lever) starter in the bell housing (minus engine) to test with the following circuit.
The 12V battery's positive terminal connected in series to a 16 amp fuse, then to the ignition key then to the hot terminal on the starter, and a ground wire from the bell housing to the negative terminal on the battery.
With the ignition key on, when I pull the starter forward to the end of its travel the fuse blows.
Knowing that starters take a large current I have tried various fuses up to 35 Amp rating but they all blow.
I am now suspecting that I'm being thick and in need of help and guidance!

 

[g8rpi]

Hi,
You should not connect the starter in series with the ignition switch, you will damage it. Just connect the starter directly to the battery. It will turn when you pull the lever. Don't run it too long without the engine as it may overspeed and be damaged. If you want to use a fuse it should be a 70 or 100A bolt in type, but there isn't one in the car as standard.

HTH,
Robert G8RPI.

 

[Strada Bianche]

Hi,
Thanks for the speedy response, I shall take your advice and give it a go in the morning
happy new year

 

[fiat500]

If you're testing it on a working engine but it is out of the car you need the proper, heavy-duty battery cable direct from the positive of the battery to the large terminal on the starter.
Then the same sort of cable from the negative terminal on the battery and secured under a significant nut or bolt on the engine. Obviously you will need to source some appropriate cable with the correct battery and ring terminals, (some people would use a set of jump leads).
The ignition coil needs to be earthed so it should be bolted to some part of the engine that is away from moving parts and where you can connect cables and leads to it without fouling anything...particularly the exhaust.
You connect the HT leads to the distributor/ sparking-plugs as normal.
A low tension wire connects from the appropriate terminal on the coil to the distributor.
Finally the positive side of the coil is connected to the positive of the battery. This needn't be a fancy connection (Ijust nipped the bare end under the ring clamp) although you could put a switch in that circuit because once connected, although the engine won't start, the coil is energised and will start to heat up.
Once connected like this not only will the starter turn over when you pull the lever, but the engine should also fire if everything else is correct.
By pulling the feed to the coil from the battery positive the engine will be stopped.
No fuse is strictly needed in the ignition circuit for this and a normal fuse would last milliseconds in the starter feed circuit.
All of this carries plenty of potential danger of the electrical, mechanical and incendiary variety, so only do it if you are really confident and have taken a lot of care and thought over it. Don't rush and remember to disconnect everything, particularly the feed to the coil which shouldn't be left connected with the engine stationary for more than a minute or so.

 

[Strada Bianche]

Hi, The test was to check the starter in isolation before I run the rebuilt engine for the first time, you have magically answered my next set of questions before I have even asked them! (As always I have a rubber mat, fire extinguisher and assistant by my side) Starter worked fine with your set up, I used some high amp rated domestic oven cable by the way, so many thanks. I will be using a '123 ignition' distributor which hopefully will make things easier.
happy new year !

 

[F123C]

I've always just used car battery jumper cables to test a starter motor. There isn't even any need on small starter motors to clamp them in a vise. Some people just place them on the ground and place a foot on them. They're not going to go ballistic on you.

On starter motors fitted with a solenoid, some people just short between the main live terminal and the small solenoid terminal using an old screwdriver,to make the motor operate.
I,of course, have never done such a thing.

Al.

 

[phoenix1]

You are up early (6.15} posting on here.
I read yours at 7.15 so we both need somthing else to occupy our time .Bryan