Tough To Start... Need some help

I have an 800. It has a 6 volt system although the prior owner stuck an 8 volt battery in it.

Over the last few months, starting it has gotten worse and worse to a point it will not turn over.

I have put a new 6 Volt battery, a new 8 Volt battery, a remanufactured starter and a tune up kit in it and tweaked the timing forward and backward a bit to see if this was the issue. But, still after all that, a 12 volt jump start is what it takes just to turn the engine and even this is very slow and sometimes it just sits there and heats up the jumper cables.

What do you think the issue here is?

I really appreciate your help!
Thanks!
Patrick

Did you measure the terminal voltage at the starter while crankin? Should rule out hi-Z electrical connections. I've found an old fluke min/max voltmeter very handy if you have one.

Thanks for the replies!

I have had no less tha 4 brand new batteries (2 6 Volt, 2 8 Volt), new battery cables of 4 gauge or bigger, 3 starters in all that all work in another tractor at 6V.

You see, I have 6 Fords in all.... I have a lot of working parts to choose from!

But, still, If I hook the starter to a 12 Volt battery only, the engine starts to turn. It will not with 6 or 8 volt.

As an electrical engineer (not mechanical), my training tells me that something mechanical is causing the starter to not have enough electromotive force to turn the fly wheel unless 12 volts is applied directly to the starter. A 6 volt starter will free spin 2 times as fast with 12 Volts as it will with 6 volts. It is a DC Motor. Under load, that energy converts to torque and, thus, it will pull twice the load.

So, what mechanical object in the engine is causing me not to be able to turn the flywheel under a normal configuration with a new starter tested in a different tractor, a spare starter from another tractor and 4 seperate brand new 6V and 8V batteries and.... new 4 guage cables?

Thanks for your help!
Much appreciated!

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