CCKW; OK to use 8 volt battery

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Hammerhead
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CCKW; OK to use 8 volt battery

Post by Hammerhead » Sun Feb 18, 2018 1:49 pm

I wanted to throw this out to you guys to get your opinions. My CCKW is still wired 6 volts. I've had a couple of the guys in our Affiliate recommend I get an 8 volt battery for better cranking power. Will that cause any problems and actually help in colder weather. Thanks.
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Re: CCKW; OK to use 8 volt battery

Post by Joe Gopan » Sun Feb 18, 2018 3:36 pm

I wouldn't do it. They start real good on the original rated battery listed in the parts books. The key is a Starter that has been professionally serviced by an auto electric shop, same goes for the generator. If the Starter, Generator, Regulator are well maintained as well as wiring being in specification, it should start up just fine.
I guess I am spoiled as I had NOS Starter, Generator, Regulator and Wiring available when I restored my CCKW and have no issues.
8 Volts gives a shorter life to bulbs and requires monkeying with perfectly good regulators which are best left alone.
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Re: CCKW; OK to use 8 volt battery

Post by johnseidts » Sun Feb 18, 2018 4:02 pm

8 volts won't give you much more, and you need to adjust your regulator accordingly. My CCKW tipper had an annoying issue with a brand new battery running down. I went through everything, and it still cranked slower than my jeep with a battery twice the size. Finally, after re-charging the battery and cleaning the contacts on the terminals for one last time, we had a light rain followed by a freeze. Same problem. But when I got under the truck, I noticed that the starter cable was the original cloth-covered cable with all the shellac/waterproof gone. I had my electric guy make me a new cable that day, and the starter has spun like a Ferrari ever since. Mack used 6 volts on their trucks until the early 1980's, and nobody complained about them. 6 Volts works if done right. No need for more.
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Re: CCKW; OK to use 8 volt battery

Post by Hammerhead » Wed Feb 21, 2018 4:19 pm

Thanks for the input. John, I'm having the same problem you had. I put the rebuilt starter on, new cables, new battery, new belts, rebuilt Generator, new plugs, new points and still weak starting. I'll go thru everything again with a fine tooth comb. Thanks again John and Joel.
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Re: CCKW; OK to use 8 volt battery

Post by artificer » Wed Feb 21, 2018 6:06 pm

Use this Jeep flow chart [basically the same] & always make sure that the engine to frame to battery ground leads are fine.
http://jeepdraw.com/images/Starter-Diag ... 8.3.15.pdf
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Re: CCKW; OK to use 8 volt battery

Post by johnseidts » Wed Feb 21, 2018 6:48 pm

I know artificer knows his stuff- good advice. One other thought to keep in your mental "tool bag;" when things get overhauled, they get painted (at least good shops still do that). I had a Farmall Cub with a slow start issue (6 volt positive ground). I pulled the starter to take back to the overhaul shop and there was a perfect paint ring around the mating surface with the flywheel housing. We are only talking about a 1/8-1/4" wide surface ring-shaped and about 5" in diameter but this was how the starter housing grounded to the tractor. I scraped that paint off the mating surface, re-installed the starter, and she spun like a top. It doesn't take much to stop low-amperage electric.
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Re: CCKW; OK to use 8 volt battery

Post by Joe Gopan » Thu Feb 22, 2018 5:06 am

Wouldn't hurt to use External Tooth Lockwashers on Starter to Bell Housing Bolts.
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Re: CCKW; OK to use 8 volt battery

Post by mudflap » Sat Feb 24, 2018 10:00 pm

Interesting stuff.

John, I like your troubleshooting chart. Very informative.

With regards to checking for excess voltage drops, paragraph 120 of TM9-801 ('44) also has some very nice diagrams showing how to make voltage drop measurements across the starter battery cable and the ground system. The specification given is 0.1 volts max for each. I know that 0.3 volts doesn't sound like much, but when you only have 6 volts to start with, every little bit helps.

As mentioned above, removing these components, cleaning any paint or corrosion from the mating surfaces is very important. The use of star washers, as Ben mentions, can also be very helpful to ensure a good electrical connection. For the ground connections, after sanding and cleaning the attachment points, I usually put a small dab of lithium grease on the surface before reassembly, to help keep moisture out of the connection. Don't worry about it adding resistance, it will displace as the connection is tightened up.

I also wonder about the type of engine oil used. Some guys swear by running 50w for "added protection". I can easily see how this could cause issues cranking at colder temperatures.

Hammerhead, you mentioned replacing plugs and points. Do you think the problem is mainly due to slow cranking, or just a general difficulty in starting? If the latter, do you have a good hot spark? What is the condition of the ignition coil? Is the distributor grounded properly? Perhaps if you are not already running them, you may want to install non-resistor plugs and solid core plug wires. Other obvious things are choke operation, and one of the most often overlooked contributors to poor starting - stale fuel.

On a somewhat more technical (read: geeky) note, does anyone know if there is an actual specification for CCKW engine cranking speed? (Ben, did they ever cover this in Army Tech School, perhaps?) This thread got me thinking about my truck. I have never had any problem starting, however the engine does seem to crank a little on the slow side although I'm not sure if it's just me unconsciously comparing it to modern day vehicles.

So.... remaining true to my lab-rat heritage, I scrounged a digital oscilloscope and measured my engine's cranking speed. The image below shows the battery voltage (at the battery) during crank. This battery is approximately one year old and was fully charged. The temp in my garage was 50 deg F.

CCKW Cranking Waveform 01.jpg
CCKW Cranking Waveform 01.jpg (130.13 KiB) Viewed 646 times
CCKW Cranking Waveform 01 calculations.jpg
CCKW Cranking Waveform 01 calculations.jpg (16.49 KiB) Viewed 646 times

The fluctuations in the battery voltage waveform are due to the increase in starter current as each piston moves up on the compression stroke. Since the CCKW engine has 6 cylinders, every three pulses is equivalent to one complete engine revolution. The scope measured the time for three pulses as 744 msec (0.744 sec). A little conversion math shows that the cranking speed is approx 80 RPM.

By modern standards this seems pretty low for a six cylinder engine (I would have expected at least 100). However, it may be correct for a vehicle from this era. If there are any other nerdy-type CCKW owners out there like me who can make a similar measurement, I would be interested in hearing from you.

One other item of interest. Note the minimum and maximum voltage readings on the right side of the display. This is saying that during cranking, the battery voltage is fluctuating between 5.7 and 5.4 volts (I know that's not a big difference. My engine is pretty tired). If you add to this the voltage drop across the system, you can bet your last k-ration can that the ignition coil is seeing even less. To make matters worse, the lowest voltage is at TDC compression, right in the neighborhood when the plug fires.

So, unlike their 12 volt descendants, who have much more voltage to spare, it's easy to see why it's important to keep the battery and associated wiring on 6 volt systems in tip top shape, in order to keep things starting reliably.

Best Regards......

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Re: CCKW; OK to use 8 volt battery

Post by artificer » Sun Feb 25, 2018 1:04 am

Bad connections are next to always an issue to do with poor starting performance....first being dirty/corroded battery terminals.
All connection issues including these battery terminals can be felt immediately after trying to start.
Evidence of a bad connection will be very obvious.
Then one needs to see why the connection @ that point is bad & rectify.
John GIBBINS Member Institute of Automotive Mechanical Engineers [Ret], ASE Master Medium/Heavy Truck & Auto Technician USA -2002 Licensed Motor Mech NSW MVIC 49593 Current 2015
TO DIAGNOSE, TROUBLESHOOT OR FAULT FIND ANY AUTO SYSTEM....
Understand how system parts interact with one another. GOOD parts can then be established & the NOT GOOD problem/s part/s isolated for repair or replacement.

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Re: CCKW; OK to use 8 volt battery

Post by Joe Gopan » Sun Feb 25, 2018 4:31 am

Only CCKW starter specs I know of are done during bench testing. There are no load RPM requirement (6000RPM) and a torque test. If bench testing goes well, it is assumed that trouble is elsewhere.
2011 MVPA PIONEER AWARD - MVPA #1064
HONOR GRAD-WHEELED VEHICLE MECHANIC SCHOOL 1960 - US ARMY ORDNANCE SCHOOL(MACHINIST) ABERDEEN PG 1962 - O-1 BIRD DOG CREWCHIEF - 300,000+TROUBLE FREE M-38A1 MILES
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Re: CCKW; OK to use 8 volt battery

Post by Marty, SoCal » Sat Mar 03, 2018 4:12 pm

A word on 8V batteries, seems that the Group 2 size 8V is about unobtainable, only the smaller Group 1 size is fairly easy to get anymore, which might not have the cold cranking amps needed for a larger engine. Group 1's are what were used in 6V CJ's and old VWs
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