Slow cranking-not battery or starter

[Montana71-F100]

My 1971 F 100 with a 360 was turning over slowly and then stopped like the battery was dead. I put a charger on it and after a couple of hours it started. That was a couple of weeks ago and it happened again today. I've had the battery for several years so I thought it needed replacing. With the new battery installed, it was still cranking slowly but started. Since it cranked slowly with the new battery I had the old battery tested. It tested good. The machine also tested the starter and alternator, both of which tested good. Does anyone have any ideas of what to look for since the battery and starter are testing good? I replaced the starter within the last couple of years.

[pcmdub]

Starter Solenoid??

[cep62]

clean every connection on all the cables .
oil , paint and corrosion all can weaken the power. how big are your cables ?
small cables with the bolt on terminals will cause issues.
I like run a ground cable to the solenoid base from the battery negative.

[Montana71-F100]

clean every connection on all the cables .
oil , paint and corrosion all can weaken the power. how big are your cables ?
small cables with the bolt on terminals will cause issues.
I like run a ground cable to the solenoid base from the battery negative.

Thanks. I checked the connections under the hood but will go underneath and check the starter. The cables have never been changed so size isn't the issue.

[Montana71-F100]

Starter Solenoid??

Thanks, I changed the starter within the last couple of years. How would I check the solenoid?

[cep62]

The cables have never been changed so size isn't the issue.

Check the voltage at the starter while it's cranking .
BE CAREFUL ! make sure it Can't roll.
I've heard of corrosion under the insulation of cables that looked good.
The starter grounds to the block where it mounts. , make sure there's not grease or paint that is interfering.
Also make sure you have a good ground to the block .
I've seen "not much" cause starting problems.

How would I check the solenoid?

with a voltmeter , make sure you get close to 12 volts when cranking.

[zgerbic]

Ground connections play a big part in getting enough current to the starter to turn over an engine. You might take a jumper cable, negative side, and connect it to the negative post of the battery and to the starter housing itself. This eliminates any problems from poor ground where the battery cable meets the engine block or in the battery post connector.

Another possibility for slow cranking with strong battery and good cable connections is the bushing at the tip of the starter. I have seen this myself on my truck with what looks like an almost new starter. What happens is after a lot of hard starts, such as just after rebuilding a new engine, the brass bushing wears out of round. This causes the armature of the starter to bind inside the starter housing under load. Taking out the starter and testing it might show there is nothing wrong with the starter as it spins just fine. Put it back and it is really hard to crank the engine even with two fully charged batteries.

It can be a solenoid problem if the contacts are really burned up badly. Generally this is not the case. You can test a lot of the wiring and solenoid problems with a simple voltmeter.

It is best to make sure you don't have any bad connections at the battery, solenoid or starter, and that the battery is properly charged and in good shape.

Hook a voltmeter across the battery. It should read 12V or higher. Crank the engine. If the voltmeter is dropping down to a low voltage like 8V or less, the starter is pulling way too much current. This can be caused by binding in the starter, too high engine compression,or timing too far advanced.

If the voltage stays up near 11V or more, there is probably too much resistance in the cables or solenoid contacts. You can hook a voltmeter across the solenoid. Crank the engine and look for a voltage reading on the voltmeter. It should be under 1V if the solenoid contacts are good. If the reading is higher than 1.5V to 2V, I would suspect the solenoid contacts are burned up pretty bad. Swap the solenoid and test again. If the solenoid is ok, hook the voltmeter from the positive post of the battery to the power connection on the starter. Crank the engine. The voltage drop should be 1V or less. This should be true for the negative cable from the battery to the engine block/starter housing.
Keep in mind there may be 200A to 300A flowing through the cables while cranking so a poor connection (a little resistance) will drop one or more volts at each spot. What I am saying is that you start with 12V and pull down 200As and the battery voltage may drop to 9 or 10V. Then subtract all the voltage drops and what is left is what the starter sees. If the cabling, connectors and grounds end up dropping 3V or 4V, the starter may only be getting 6V or 7V, and struggling.

[Montana71-F100]

It was the starter. I checked all connections and sanded them until there was no more black on them and tried it. Then and replaced the solenoid and it still cranked slowly so I decided to replace the starter. The electric tester showed it was good but it must have been mechanical. One reason I dismissed the starter, besides testing good, was that I replaced it a little over a year ago. Fortunately it had a lifetime warranty on it so that took some of the sting away form the fact that I bought a battery that I didn't need. Thanks everyone for your responses. I learned a lot!

[fastEdsel]

There was a very gifted and fantastic guy who lived in our town and he always had something to say or add to a conversation. He had every model of flathead Ford V8 restored and running from 1932-1953. When the discussion turned to circuits and batteries he said "50% of the world's problems are caused by women, the other 50% are caused by dirty battery posts." Glad you got your Ford going again!

[basketcase0302]

My money is on the timing, (as your description of it starting once it sat for awhile is typical of timing being too far advanced).