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MG MGB Technical - Hot wiring the engine

My engine compartment is now painted. Depending on space at the body shop I may be ready to install the engine before the shop can do the final body work and paint. I want to start and run the engine before I install it. If there are leaks I will fix them before installing the engine.

This is a 76. My assumption is I need to run a wire from the upper side terminal on the starter to the neagative on the coil and another wire from the positive of the coil to the distributor. Am I wrong?
Kelvin Hawkins

I don't want to seem stupid, but someone has to ask this. How can you run an engine without any exhaust, radiator, fuel supply and how do you bolt it down?

Tony Oliver

I've seen a 4-cylinder engine started and running just sitting on a bench. Wouldn't want to do it myself, but aren't they supposed to be balanced so they don't go jumping all over the place? But for a proper job do as a pal did and bolt it to an engine stand with exhaust, radiator and fuel connected up.

The solenoid stud (which presumably will have the battery connected to it and the block) should be connected to the coil +ve, and the coil -ve to the distributor, but it really doesn't matter which way round the coil goes. The important thing is that a 76 would have used a 6v (1.5 ohm primary) coil with an external ballast resistance contained in the harness. If you use the coil from the car then you must have a 1.5 ohm ballast in series with it, or use a 12v (3 ohm primary) coil instead. The solenoid should have two spades on it, connecting one to the solenoid stud should crank the engine, the other shouldn't do anything. Originally the 'crank' spade would have been normal-sized, and the other one (which is part of the ballast circuit) would be smaller, but rebuilds seem to have them the same size.
PaulH Solihull


Isn't it the negative side of the coil that goes to the distributor and the plus side to the battery? Typically to start an engine on the floor you would put one jumper cable on the block and the other on the large hot terminal on the starter solenoid. With a negative ground, the negative goes to the block. You can run a wire from the hot solenoid terminal to the coil. Then to start it, you touch a small jumper wire from the hot solenoid terminal to the exciter terminal on the starter. To shut it down, pull wire off that you ran to the coil.

You should get a couple ratchet straps or something to strap it to a large board. Otherwise the torque may flip it over if you rev it. You will have to have the crankcase ventilation system hooked up or you may force it to leak oil when it otherwise wouldn't.

Also, to run it long enough to find any oil leaks, you will have to feed it water or you will overheat it. You can connect the radiator or it is possible feed water from a garden hose.

However, I think doing this will only reveal a major oil leak as smaller ones take some time to show up.

C R Huff

Thanks for the replies.

I have the engine on a large dolly made of 3 layers of 1/2 inch plywood with a 2x2 inner frame. I plan on bolting it down with angle iron brackets to a 1 in square steeel tube. I also plan on hooking up the rad and exhaust, I have an accessory fuel pump from another project, I had not thought of the crank case ventilation. Paul thanks for the info on the ballast for the coil. I got it in my head that it was better to have it running before going to the work of installing it in the car. The shop who is doing my paint wants the car as a shell until they finish painting it. The engine compartment, cockpit and trunk (boot) are done. The underside of the hood (bonnet) and trunk lid and mating surfaces of fenders will be done this week. They can't do the door skins for about 3 weeks then the exterior will get painted. So the end of September if all goes to plan and any day after that is when we expect winter. So the more I do now on the other items the better chance of getting it back together.
Kelvin Hawkins

This thread was discussed between 18/08/2010 and 19/08/2010

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