McCormick 434 IH 1968

darrylh

Member
Hello,

I have a (new to me) IH 434, which will not start. I get smoke but the glow plugs/pepperpot do not seem to work. I have installed new plugs and wired in series. Since then 2 pots have burnt out (orange/white hot). I have started to look at the wiring but key switch is not original and does not have the 6 terminals as per manual wiring diag. Loom wires are all red/red paint! and can only make out one connected wire Brown/yellow (any id please?). I have also bought a new 4-position key switch (only 5 term though) but now have off/ign/heater/start wired to my satisfaction.

Questions: re plug circuit (as it came wired to me). Plug (4?) nearest fan is ground onto plate with CAV pump attached. Is this effective ground?
Plug (1?) has wire to one term on the pepperpot. Other pot terminal goes to term3 on key switch. Is this right??

Would it be better to bypass pepperpot with 12v plugs. I believe these have 20 secs burn, so while the pot might indicate when to switch on, I am used to counting to 20 same as my Series 2A.

Any suggestions and help would be greatly appreciated. Thanks Darryl
 

darrylh

Member
Many thanks guys. Do the 12v ones self-ground, so no need to ground on the front of the block? And just 1 wire to key switch? (434 wiring diag has 2 wires to the key switch for the orig spec).
 

Mur Huwcun

Member
Livestock Farmer
Location
North West Wales
Many thanks guys. Do the 12v ones self-ground, so no need to ground on the front of the block? And just 1 wire to key switch? (434 wiring diag has 2 wires to the key switch for the orig spec).
Yes wired in parallel not in series, no need to earth but you will need three jumper wires to act as a bus bar from one to another unless you modify the original bus bars to have two tight loops. On mine I just wire them direct to the key switch
 
Many thanks guys. Do the 12v ones self-ground, so no need to ground on the front of the block? And just 1 wire to key switch? (434 wiring diag has 2 wires to the key switch for the orig spec).
Yes self ground to block,
just make 3 short wires with eyes on the end, to go from 1 to 2, 2 to 3, and 3 to 4.
Or as I did, the original copper wire has a small eye and a big eye, make the big eye into a small eye, put the eyes in the press to make them thinner, turning them to do each end in press on opposite way about, this off sets them so they sit nicely, put the bakerlite insulators off original heater plugs onto new plug, then fit the altered copper wires so they are touch each other, and use the original heater plug nuts,
This will give the original look with a new style plug,
Then run a heavy wire to the key. could just use the original that is there now, and just behind the pepper pot there should be 3 wires on to it,, 1 on its own and on other side 2 wires together, this was to aid starting on later tractors, more about that later,
On the side with the 2 wires, 1 will go to the key, and the other to heater plugs, remove the one on its own, and refit it to the other side, ie, so now all 3 wires are together in one terminal, this will mean the new plugs will heat in the heat position , as before, and still heat in start position as before, 5 to 8 seconds of heat will be enough to start it, once started if its missing on 1 cylinder, just hold in heat position till it clears,

More about early and later models of heating,
B250 and early B275 & B414 with leaver start, had a twist heater control separately from the leaver start, on this type wire the new type heater plugs directly to this twist control on opposite side to power feed, and bypass the resistor, on later key start models and the likes of the 276, 434, and onwards do as described above,
Like I said in previous post, the old style heater plugs were 1,5 volt, 4 together = 6 volt, and need something to absorb the excess power to stop them burning out, the dash mounted resistor did 2 jobs, 1 to absorb the power and 2 to give the operator a clue to how hot the plugs were, on early leaver start, they had only 1 wire to each side of resistor, and twist handle could be held to heat, and still held to heat when starting,
On later models this was all done through the key, and a better starting heat to the plugs was achieved by this method,
The key was turned to heat position, power was fed down the single wire on its own to the resistor and through time the heater resistor would glow, , but once turned to the start position the second wire from the key fed power to the other side of resistor directly to the heater plug wire, the pepper pot would go cold , but power was fed directly to heater plugs, yet to stop them burning out the starter motor now displaced the power and did the job of the pepper pot to ensure the plugs did not get full 12 volts, this meant although it was still heating the plugs, a saving of power not going through the pepper pot to aid starting,
Both systems are much the same to average man looking at them,
BUT A WORD OF WARNING, if your doing some work like painting or rewire, make sure the wires from the key are right way around, or the old type plugs are toast
 
I’ve just ordered a set of them, been on the look out for extra sets for a while now as the ones I used to get are no longer available and prices have been creeping up on them.
after trying 1 set the difference in starting was like night and day, it revolutionary changed the tractor starting over night, and best thing is if 1 goes down, the other still keep working, was so impressed I ordered another 10 sets for little money, and will fit them as other tractors give bother, simple fix to aid starting in any of the Bradford built tractors
 

Tonym

Member
Location
Shropshire
I did this mod to my 434 years ago when the pepper pot burnt out. The plugs I used were Cargo 100295 which I think were for a Mercedes of some kind. I put both wires on the one terminal of the pepperpot and left it in the dash just for the original look and wired as above leaving off the earth strap at the front.
The company I bought the plugs from made me the link wires and total cost was around half the cost of a new genuine pepperpot at the time.
Best mod I ever did and even if you forget to heat prior to turning the key it will start in around 5 secs when the plugs heat up. You can use a much smaller battery which leaves room for my sandwiches in the battery box when I am match ploughing which is a bonus!
 

Mur Huwcun

Member
Livestock Farmer
Location
North West Wales
after trying 1 set the difference in starting was like night and day, it revolutionary changed the tractor starting over night, and best thing is if 1 goes down, the other still keep working, was so impressed I ordered another 10 sets for little money, and will fit them as other tractors give bother, simple fix to aid starting in any of the Bradford built tractors
I converted one one of mine well over ten years ago by knocking the centre out of the old plugs and tapping them M12 to accept popular car plugs. Up to about 12 months ago Mercedes plugs were on ebay for about £10 a set which was cheaper than buying them at trade prices. Recently they’ve jumped in price unfortunately and the Febi ones are expensive now.
 

darrylh

Member
Thanks to all for the advice. I have ordered the Vauxhall Blits 12v set. The original? straps I have with the tractor are solid steel, about 2mm. Are these OK or would say 4mm sq copper wire be right (seems to be same gauge as the wire from the last plug to the pot). Regards Darryl
 

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