Non starter??

[commemorative74]

Firstly I hope all have had a good Christmas and wish everyone a prosperous New Year.
I am still battling on with my total rebuild 1973 roadster. A couple of weeks ago I managed to get her running but was not happy with how difficult she was to start. The original Lucas starter motor seemed very sluggish so I decided to take it off and have it rebuilt which was a nightmare as the car has a full Haywood and Scott exhaust system including manifolds which has been fabricated in a way that once the starting motor has been unbolted it "caged in" and cannot be removed.
.... A week later after stripping most of the car down again to remove it there was no way I was going to install an original Lucas MG45 so I opted for a high torque, gear reduction starting motor purchased from Norman Motors.
Everything was re installed, turned the car over with no sign of engine firing. I checked the plugs for spark - nothing. Then checked few reading with the multi meter and seemed very low so I exchanged the whole ignition system (distributor, amplifier, coil, ballast resistor etc ) for a new one I had that was destined for another car. Everything fitted, turned the car over - no spark!
Decided to check all ignition feeds with multi meter and compared them with another V12 roadster I have with the same Barrett Opus ignition kit.

Basically after a whole day checking wires when the car is cranked over the battery voltage goes down to 4.82 volts. This is also reflected on the taco side of the ballast resistor where the middle white wire that is connected to the ignition starter and the bottom blue and white wire, which is connected to the C1 terminal at the starter solenoid are both also 4.82 volts.
However the readings on my other car are around 10 volts. - By the way both batteries on both cars are reading just under 13 volts.
So it is quite clear it is being robbed of power - but from where??
Another interested find, still with the ballast resistor - the top wire, which is white with a blue spiral, that is connected to the taco, when the car is cranked this shows a voltage of 5.3. This is not correct- when testing the other roadster it shows a reading of .75 volts Stood there for a while scratching my head and done a few more checks which included cranking the engine over and attaching the volt meter to the back of the dash onto the choke cables which highlighted about 5 volts. This was also evident on other earthing points. Mmmmm ok - quite clear there is a massive short somewhere so again I am scratching my head trying to work out where the problem is.
I connected the multi meter to an earth point on the engine touched the probe onto the starter solenoid spade, which alerted me with a bleep that this was going straight to earth. Looking at the instructions supplied with the starter motor it states " If necessary remove the link wire fitted on the Powerlite unit that is fitted between the stud and spade (or small stud) terminals"
so I am now thinking should I have dis-connected the link wire prior to fitting the starting motor?? - How do I know "if necessary"... can anyone advise?
If the starter motor is not the problem can anyone can up with any other suggestions as I am quickly now running out of patience. The engine is earth bonded and I attached another earth bond to the engine and frame just to make sure and the massive voltage drop is only under engine cranking, not when the ignition is just turned on, where the voltage remains at about 12.5.
Any suggestions very welcome..

Alex

[andrewh]

I feel for you, these sort of problems are a real marathon but when you find the issue all will be happiness and light. Keep the faith.

It certainly sounds like you have found the problem area, in that your voltage is not as it should be to start the car. I suppose you could rig a separate supply from another source to the ignition and that will prove the point. I am sorry I have no idea why the link may need to be removed as i have not used a Powerlite but I am sure someone here will know or else a call to their factory next week should solve the conundrum .

Edit. Did you fit a new loom?

[MarekH]

Firstly, don't flog the battery down to 5v - it isn't going to start even a torch at that voltage and you'll just toast your wiring. If you can turn the engine over (presumably faster than before as it is a gear reduction motor) then you are not being robbed of power - this is the lion's share of the electrical load.

Basically, it should be turning over faster and easier than before. If you are failing to start, then remember that you are probably also flooding the engine and making it harder to start next time.

I'd start by looking at the continuity of the wiring (and importantly - negligible resistance) between all of the parts along the chain.

I'd then clean the plugs as they ought to be soaking wet and briefly run it without plugs to clean the petrol out of the cylinders also.

There is nothing wrong with a standard starter motor, especially if it has just been rebuilt. It only has to get about three cylinders to catch and the reaction becomes a runaway train which needs to be throttled.

Some starter motors have a spade for the bendix whire/red 12v from the starter relay and some have a screw fitting - this is of no consequence in the scheme of things as your starter runs.

kind regards
Marek