The GMC CCKW

Having trouble starting my cckw after it has been running a while. If I pull up and stop/turn off ignition after any more than a 20 minute drive I have to wait several minutes to half an hour before the engine will turn over.
any ideas?

Does the engine even try to crank? Or does it do absolutely nothing when you hit the button?

Assuming the latter, I would start by doing a quick “wiggle” test – shaking all of the starter and ground connections, checking them to make sure they are clean and tight.

If nothing obvious turns up, you will need to check the voltage at the starter while trying to crank the engine with the no-start condition present. To do this, connect a voltmeter between the battery cable post on the starter and the starter case, and try to crank the engine. Make sure you have a good connection at each voltmeter lead. If the voltmeter shows battery voltage (with a tenth or two), then the problem lies within the starter.

If the reading is very low, then you will need to check the battery and ground circuits.

Best Regards,

Bob

I had the same problem, Maybe it's time to give the motor an oil change, even if it still looks good !
Regards,Anthony.

Remember you cannot use those small 12 volt battery cables on 6 volts. The current s twice as much and the diameter of h wire determines how much it can carry.

Also feel the cables, ground and hot to see if either of them is getting hot anywhere

hi all thanks for the tips
yes the engine turns over when hot but will not fire
DR D - will check that out thanks for the suggestion
I was actually wondering if it might be a "coil" issue?

Another thing to try is to run a wire from the battery to the ammeter and disconnect the ammeter feed from the starter. You get quite a voltage drop at the starter. Back at the battery, the voltage I greater.

I think everyone knows my feelings about converting to 12 volts and the advantages...

Just to clarify, does the engine seem to be turning over at normal speed? Or does it seem to crank slowly when hot?

Assuming cranking speed is OK, a quick test of coil output is a pretty easy check. Just remove the coil wire from the distributor, and hold it so that the end is about an 1/8" or 3/16" away from the block or an accessory bracket.

Have someone turn on the ignition and try cranking the engine. If you don't have spark, time to start checking the basics: points, condenser, primary wiring, coil voltage, etc. If all checks OK, then the coil would probably be the next thing to try replacing.

If a good spark is present at the coil wire, reinstall it and repeat the above at one of the plug wires to verify the rest of the secondary ignition system (cap, rotor, plug wires, etc.).

If no spark is present, I would start looking at the fuel system.

Best Regards...

another quick test is to give it a shot of starting fluid prior to trying to start it. If that does not help, hold the throttle wide open with the choke off. If tat does not help either, it is most likely ignition.

Which carb do you have? Is it the later cast iron one?

Hi thanks for more suggestions
... yes it is slow to crank over when hot ... in fact I when it 1st happened I "jump started" it on 12 volts no problem but the 6 volts wouldn't do it. ( now I just wait until it cools down)
not sure which carby (it is a zenith) it is Dr D ... but it isn't cast iron ..... and it has the early style air filtration system if that a helps.

... yes it is slow to crank over when hot ... in fact I when it 1st happened I "jump started" it on 12 volts no problem but the 6 volts wouldn't do it

OK... This seems to bring us back to the starter circuit. As mentioned in the previous posts, check the battery charge, as well as all of the starter ground and battery connections, along with the cable and ground strap size and condition.

You could check the voltage drop across the starter battery cable when cranking, as well as the ground circuit. TM9-1802A, Chapter 7, Paragraph 159 describes this procedure in detail, and specifies a maximum drop of 0.1 volts across either the battery cable or the ground circuit. A reading greater than 0.1 volt indicates excessive resistance in the circuit.

Or, you could just pull the starter and take it to a shop that specializes in starter repair and/or rebuilds. They can test it to see if it is working correctly. Make sure to mention that the problem only occurs when hot.

Personally, my money is on the starter. Most of the hot crank issues that I have seen seem to be related to the starter (armature rubbing on the field coil shoes, internal short in the field coils, dry bearings, etc. ) In this case, I'm thinking the added load is pulling down the 6 volt system enough to prevent the ignition system from supplying sufficient spark to start the engine (this theory can be easily tested as well - see above posts)

Best Regards..

you could be right mudflap ... but it is a new (NOS) starter that's been in only a couple of months ......

No mention has been made of the battery other than it being 6volt. It's necessary to have a battery with sufficient cold cranking amps that voltage drop on start is not significant. This goes along with using heavy enough cables. With only 6 volts to begin with you cannot afford to lose even a small amount.

David

May not solve the problem, but seeing as you are in Australia I would recommend you call up your closest Westrac dealer. We get our 6 volt batteries from them made by CAT. 6 volt used to be problematic for us and the batteries didn't have good cold cranking amps. These start the old vehicles up like a 12 volt, hold charge whilst not being used for say 6 months and they last!!

Like I say, this may not solve your particular problem but it's certainly worth looking into!

Kind Regards.

How is the situation of your carburetor?Can it be high float bowl fuel leavel?Can it be idle misadjusting screw?

battery in good order
starts the vehicle up like a 12 volt ... at least when its freshly charged ... seems my generator not working properly
This is not the probl;em though ... the problem is after the vehicle is running for half an hour or more the wont start ... but then let it cool down for a while and it starts no problem