Farmall 450 Resister Bypass

TXZane · Mar 26, 2019

This is a follow up post from yesterday. I need a new coil for sure. The old is badly corroded. My tractor also has an additional button on the dash that activates the resister bypass. So what is best for cold weather starting? Should I just use a 12 volt coil and get rid of the resister and bypass etc? or should I renew the resister bypass system? What would start the best here in Minnesota?

Bob · Mar 26, 2019

For sure a primary resistor with a bypass setup will give a "hotter" spark during cranking than a "true" 12 Volt coil that needs NO primary resistor.

There's more than one way to set up a resistor bypass system, from your manual momentary switch to starter switches and solenoids with an extra "bypass" terminal, or a small relay wired into the circuit.

Another thing not everyone is aware of is that the resistance of one type of primary resistor stays relatively constant even as the resistor warms up in operation, and there's another type that has a "positive temperature coefficient" (PTC)and it's resistance drops rapidly as it warms up over a minute or two.

ASSUMING the engine starts relatively quickly after the ignition is switched "ON", the resistor acts the same as if it were bypassed during starting, then it's resistance rises to limit primary current to a safe level for the breaker points and coil.

If you get deep enough into a good ignition parts catalog, the specifications will show which ignition resistors are "PTC".

John T · Mar 26, 2019

Zane, the 6 volt coil with ballast and ballast by pass has cold weather starting advantages. Many farm tractors and some cars used it.

There are several methods to accomplish that. A Ford type starter solenoid with the extra I terminal,,,,,,,,,Some saddle mount mechanical push switches had the extra terminal to send unballasted voltage to the coil when cranking,,,,,,,,,,Some used a wire to the coil which had low resistance when cold but it increased once warm for the necessary inline ballast resistance when using a 6 volt coil on a 12 volt tractor.

Sure it will work with a full true 12 volt coil no ballast needed but that lacks the advantages above. HOWEVER if the engine is in good shape, good compression, NOT an oil burner and ESPECIALLY if you have a high capacity heavy duty high CCA battery you should be fine even in cold weather.

My choice would be use a 6 volt coil a ballast and a ballast by pass in extreme cold weather

John T

TXZane · Mar 26, 2019

Thanks, I think that im going to do the bypass. My last 400 had a fresh engine and that thing would fire up easy. this 450 must be pretty tired, it needs all the help it can get to start.

Duner Wi · Mar 26, 2019

TSZane, Good choice to leave the bypass.

OldFarmall450 · Mar 27, 2019

(quoted from post at 11:49:40 03/26/19) Thanks, I think that im going to do the bypass. My last 400 had a fresh engine and that thing would fire up easy. this 450 must be pretty tired, it needs all the help it can get to start.

TXZane, I didnt see your previous post, but on my 450 gas it still has the original 6V system but a 12V battery. I was told it was converted to 12V, but it wasnt.

During a massive tuneup I decided to change the coil. Thinking it was a 12V system I bought a 12V coil....and the problems began. It wouldn't start, backfired, smoked, when it did start ran really rough.

It took me over a month to troubleshoot the problem, all i needed to do was put the old 6V coil back on.

I replaced everything i could think of...now she starts with a few spins of the blades...Like she should.

Just thought my experience might be of some help.

Good luck.

Farmall 450 Resister Bypass

TXZane

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Bob

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John T

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TXZane

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Duner Wi

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OldFarmall450

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