The 300U cold water start project 5/16

Nice day to work on this. Went down in the 30's last night and was still in the 40's when I got out there. So we are working with a freshly charged battery today and just a reminder it is a 12v conversion with a 12v coil.

First thing I did was run a jumper from the ignition side of the battery to the battery side of the coil. There was no noticeable attempt to start when cranked a few times.

Second I grounded the wire from the coil to the distributor (at the distributor) and, with a meter on the battery side of coil gave it a few cranks. Before cranking there was 12v, this dropped to 5v when cranked. Not even close to the 10v +/- I was looking for.

Third I inspected the wires and the knife switch that is "in line" on the battery positive side and found a couple of connections that MIGHT be an issue but probably not. I took the starter side of the switch off and took it directly to the battery, no change.

Lastly, I put my meter on the battery itself and gave a couple of cranks. 12v went down to 5v when cranking.

I have some ideas, but if I knew anything the tractor would be running already. I am interested in YOUR ideas and opinions. Any and all appreciated!

seems to me if the engine cranks over that would rule out the starter side of things, that leaves you with ignition circuit, if you have no spark (pull a plug, put plug wire on it and ground it to bare metal, crank engine)then go through John T's elecitrcal checklist (should be in archives). If you have a nice blue spark then you are not getting fuel.

Even a miracle will not allow it to fire on 5 volts. The battery voltage you ingicated was on the posts of the battery I assume. If on the cable terminals, they might still be the issue. If i=on the posts, it is a bad battery even if it cranks. A 6v starter will spin it like s gyroscope. the battery voltage while cranking needs to be 10 or above!.. Jim

My thinking also. Taking it for testing tomorrow. I still have the issue of the switch and one connection heating too.

Use a different battery, or jump start it. If you charged the battery, and it cranks, it could also be a dragging starter, but things would get hot in a hurry.

What is starter drag? What causes it?

Essentially,starter drag is a bad starter:it draws too many amps,because of defective windings.And if you put your hand on the starter motor,it would feel warm or very warm,or even too hot to touch,yet it might still crank,although slowly.A good starter,or any connections,won't get warm while cranking,unless you crank for along time,like 5 minutes.This assumes good battery and cables,of course.
Right now you need a good battery-it's probably only cranking because you probably still have the 6v starter on the tractor.
I have a 300u with 7500+ hrs on it,and it is still 6v.Dad and my uncle bought it with 75 hrs on it the year I was born.It has always cranked slow,but it has always started within a few revolutions.When you get everything right it'll start right up.Mark

Many things bad bushings and bearings bad brushes worn Bendix. I would get the starter refreshed then maybe new cables if either end gets warm when cranking but its nice to make sure the starter is in good condition first remember its over 50yrs old