question GMC CCKW , upgrade to 12 volt.

Before I steam in and purchase one of the conversion kits available , I though I would use the power of the forum to ask those that have moved from 6 to 12 volt their opinion .

Sorry to purists , but Starting reliability and better lights push my decision.

So , is it worth the purchase of a kit or can with the adjustment of the regulator and replacement of the dynamo to 12 v with battery and Bulbs do the job ?

Love to know good / bad experiences and comments, thank you.

My WC54 is six volt. Keep the starter connections clean and tight, and I fitted one of Frank Jolleys electronic ignitions, no problems starting. Biggest problem is if they have been left the carb dries out and you wind forever to pump the fuel up. I've found that that tipping about 250 ml of petrol into the carb before starting and both the 12 volt WC51 and the 6 Volt WC54 start up easily enough.

If you are going 12 volt, why not jsut fit an alternator? No regulator required.

I have had several six volt military vehicles over the years and still have a Ford GPW and Cadillac Staff Car. Both are still 6v, in most cases poor starting and lighting is purely down to either bad earthing or the wrong earth cables/battery. My GPW was a sluggish starter and I considered the 12v route but then discovered an American website which explained the above causes. I hadn't realised that 6v earth leads are virtually twice the thickness of 12v ones and sometime in its life my jeep had had modern 12v earths fitted. I changed the leads to proper 6v ones and my jeep actually starts better than virtually all my friends running 12v. Most cannot believe mine is 6v. Again the Caddy is 6v and it is a 5.7 litre flathead V8 no problems at all, both have good lighting and start virtually instantly. As long as your battery is the correct amperage your starter is in good condition and your leads are both correct 6v items and earthed properly there really is nothing to be gained by going to 12v. As they said if 6v was good enough when they were being shot at they are good enough now. Try checking your system from top to bottom especially the items mentioned first you may save yourself a few quid :-D

I did fit an extra earth cable to muy WC54, from a BMW of all things! It was there and had connection eyes in all the right palces.

Though I've had 12 volt earth problems as well. My WC51 once drove out of her shed, I switched her off and she then refused to do anything. Problem was the main earth strap, it looked clean and was tight, but being unable to think of anything else, I took it off cleaned and reattached, away she went as usual. :nut:

The wriggly experts claim you only have to adjust regulator only as the dynamo will put out enough voltage. Starter fine, I always think a fuel pump with priming handle to be essential unless very regularly started, especially if cranking over original 6v starter on 12v just tho get petrol up.

Lazy way and also probably better reliability is an alternator kit, I have one of the side-splitting Mr. J's waiting to go on a jeep. By the time I've begged a freebie scrap alternator (Landrover ones are right pattern for GMC) and exchanged it as core unit for a rebuild from local auto electrical factor and sorted pulley, it's cheaper and simpler to order a full kit.

I'm hearing very mixed reviews of electronic ignition kit reliability which gives me cause to consider retaining the old points system (I guess I'd need another condenser or will they do either voltage?) - don't know which way to go now as I have an electronic kit here ready.......

I have had several six volt military vehicles over the years and still have a Ford GPW and Cadillac Staff Car. Both are still 6v, in most cases poor starting and lighting is purely down to either bad earthing or the wrong earth cables/battery. My GPW was a sluggish starter and I considered the 12v route but then discovered an American website which explained the above causes. I hadn't realised that 6v earth leads are virtually twice the thickness of 12v ones and sometime in its life my jeep had had modern 12v earths fitted. I changed the leads to proper 6v ones and my jeep actually starts better than virtually all my friends running 12v. Most cannot believe mine is 6v. Again the Caddy is 6v and it is a 5.7 litre flathead V8 no problems at all, both have good lighting and start virtually instantly. As long as your battery is the correct amperage your starter is in good condition and your leads are both correct 6v items and earthed properly there really is nothing to be gained by going to 12v. As they said if 6v was good enough when they were being shot at they are good enough now. Try checking your system from top to bottom especially the items mentioned first you may save yourself a few quid :-D

Thanks for that - I know it's been put on here before but easy to forget something as simple.

Might give that a look before messing with MB.

I've had Franks ignition on the WC51 for about 14 years now and the WC54 for about 5, never a problem with either.

Great hints and tips thanks, I always follow the Tony tip of fuel in the carb top from standing , as you say this saves loads of cranking, but have forgotten to check earths , and did not know that 6v should be a greater core , so will check:thanx:

For a 6 volt system you need '0' or better still '00' gauge battery to earth and battery to starter cable the cable and fittings are available via the web from several vintage vehicle electrical suppliers sold by the meter make them up with soldered fittings and star washers where appropriate.

A 12 volt conversion will produce a higher cranking speed however with regard to the lighting issue modern 6 volt Halogen or LED bulbs are more than adequate......... at the end of the day the choice is yours.

The only comment I would make is to repeat the advice that has already been given namely 12 volts will not improve bad earths, bad wiring or tired electrical and/or mechanical components.

Pete

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Great hints and tips thanks, I always follow the Tony tip of fuel in the carb top from standing , as you say this saves loads of cranking, but have forgotten to check earths , and did not know that 6v should be a greater core , so will check:thanx:

A lot of heartbreacking problems solved by clean earths! DC current runs IN a Wire AC runs ON it.The amount of current AMPS is mulitiplied by the 'Pressure ' of the curent VOLTS to give you the amount of power WATTS. So as 6 volt is half 12 volt it needs twice the amount AMPS for the same WATTS. So you need a thicker cable to push it through. Very basic but enough to understand why you need thicker cable. There are plenty of graphs on the web to sort what gauge of cable you need.

Just a further example related to my earlier post. A few years back a group of us Jeep owners were up in Pickering for the NYMR War Weekend. We woke one morning to thick frost everywhere. Peoples sheeted Jeeps were white over and it was bloody freezing :-D My GPW was uncovered with frost on the seats, yet my 6v Jeep started first time and was ready to go before ANY of the 12v or 24v ones had started ! As I said earlier get the 6v system right and you will be fine. I do agree with the earlier post that manually pumping up the fuel after standing saves strain on nerves as well as the battery :-D

My WC63 is still 6 volts and have no problems.

On of the MAJOR things people do is, run down to a Auto parts house and buy a new battery cable with 6-volt systems is that the cables are often replaced with 12-volt cables. Since 6 volts is half of 12 volts the wires must be twice the size to carry sufficient current to get the job done. Also, the longer the cable, the lower its capacity.

The old six volt systems require 1 gauge cables. When everything converted to 12 volts the cables were changed to 2 gauge. If someone installs modern cables in the old systems, they (the new 2 gauge type) cannot supply adequate current to the starter and it will spin slowly. Find the original type 1 gauge cables and it works fine, just as it did when it was new

There were THOUSANDS of tractors, trucks, cars built in 6 volt that worked, and still work fine.

The reason that the mfg went to 12 vt is not that it did not work, but as always.... MONEY. They could use smaller/cheaper wiring.

Originally, a lot of vehicles were also radio-suppressed, which among others meant they got extra grounding straps. I'm sure there is information to be found where these extra straps were placed on a GMC, and they're pretty simple and cheap to make yourself. Maybe that's an option?

Here's some good info on how to make them yourself: http://g503.com/forums/viewtopic.php?f=4&t=265682

John, you have a PM.

Before I steam in and purchase one of the conversion kits available , I though I would use the power of the forum to ask those that have moved from 6 to 12 volt their opinion .

Sorry to purists , but Starting reliability and better lights push my decision.

So , is it worth the purchase of a kit or can with the adjustment of the regulator and replacement of the dynamo to 12 v with battery and Bulbs do the job ?

Love to know good / bad experiences and comments, thank you.

Hi John, when I converted my gmc I used a Ford sierra alternator and used the original dynamo pully of the original dynamo, pulled it off and pushed it on the ford alternator fitted a treat, jammy wasnt in it :shocked:

As many have said leave the starter as it is, at 12 volts it turns quick but for much less time than winding it over on 6 volts.

The ignition issue I decided to steer clear of electronic as if it plays up its harder to sort out in the field and a coil and point have been used for years and years. I used a 4.2 Ltr Jag coil as it is a very close match to the gmc engine spec ie ( 4.2 ltrs and a straight 6 so the refresh time for the coil to recover from one discharge to a spark plug would be about the same ) also used the jag condenser in the distributor, never ever had any starting issues, but remember to prime the fuel system before starting.

As others have said connections and rough cables dont help, when my truck was 6 volts I had all new battery cables and when cranking was only getting about 3 volts at the coil connection so not much of a spark this turned out to be a high resistance connection inside the ignition switch on the dash !!!

The battery cables I used were 50mm csa from a welding supplier, much cheaper than the vehicle wiring suppliers, vasaline on all connections and good earth straps battery to chassis and engine / gearbox to chassis dont forget to earth the cab as well it all helps.

This is all incidental to me now as I think mine would now still start even it it was under water :cool2:

Good luck

I have had several six volt military vehicles over the years and still have a Ford GPW and Cadillac Staff Car. Both are still 6v, in most cases poor starting and lighting is purely down to either bad earthing or the wrong earth cables/battery. My GPW was a sluggish starter and I considered the 12v route but then discovered an American website which explained the above causes. I hadn't realised that 6v earth leads are virtually twice the thickness of 12v ones and sometime in its life my jeep had had modern 12v earths fitted. I changed the leads to proper 6v ones and my jeep actually starts better than virtually all my friends running 12v. Most cannot believe mine is 6v. Again the Caddy is 6v and it is a 5.7 litre flathead V8 no problems at all, both have good lighting and start virtually instantly. As long as your battery is the correct amperage your starter is in good condition and your leads are both correct 6v items and earthed properly there really is nothing to be gained by going to 12v. As they said if 6v was good enough when they were being shot at they are good enough now. Try checking your system from top to bottom especially the items mentioned first you may save yourself a few quid :-D

Just an addition to all this, dont forget there are two separate parts to starting.

(1) the circuit from the battery to the starter motor which has the big cables.

(2) the wiring from the starter to the ammeter through the ignition switch to the connection on the coil, this is probably more important than the starter circuit as this feeds the coil and you need all the volts you can get when cranking the engine over try measuring the volts when someone else is cranking the engine over you will be quite surprised how much is lost.

Great hints and tips thanks, I always follow the Tony tip of fuel in the carb top from standing , as you say this saves loads of cranking, but have forgotten to check earths , and did not know that 6v should be a greater core , so will check:thanx:

Try to remember John, that the earth straps are just the return path of the supply cables so should be the same size as the battery cables, ie big.

Hi John,

Sorry we got cut off the other day when we were talking about this.

Mr Jolley's alternator kit is probably the most cost effective way of doing the alternator conversion.

Notwithstanding other peoples' experiences we have had nothing but problems with (his and others') electronic conversion kits and I wouldn't bother with them any more.

I would also fit an electric lift pump to avoid the churning over and over. If you're worried about the engine starting before everything is fully lubricated, note it will still have to rotate a few times before starting to actually draw fuel into the carb and you can always spin it with the ignition off if it's been sitting for a while.

- MG