Cranks hard when hot.... - Team Camaro Tech
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post #1 of 14 (permalink) Old Sep 26th, 08, 07:12 PM Thread Starter
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Cranks hard when hot....

My 69 468 with an MSD ignition is hard to start when hot is it the starter or the timing.Please let me know if anyone has input on this......Thanks in addvance....

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post #2 of 14 (permalink) Old Sep 26th, 08, 07:25 PM
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Cool Re: Cranks hard when hot....

it is usually the starter(if the timming is ok) if your compression is high, they make a gear drive starter that would turn over a mac truck. can't give you the name or parts number but advance auto was telling me that one is available. simple bushings/brushes usually solved it in the old school days and never had one that that would not fix.
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post #3 of 14 (permalink) Old Sep 26th, 08, 07:30 PM
 
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Re: Cranks hard when hot....

Tilton starters
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post #4 of 14 (permalink) Old Sep 26th, 08, 07:30 PM
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Re: Cranks hard when hot....

How much initial timing are you running?
Much over 22 degrees or so, she'll be very hard to crank when hot.





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post #5 of 14 (permalink) Old Sep 26th, 08, 09:52 PM
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Re: Cranks hard when hot....

I'd check that you have enough available amperage to the starter if you are only having a problem with a hot engine. You could be having a hot soak problem with the starter also. Her is a good check list. The first check is "available battery voltage." For the starter to crank at normal speed, the battery must be at least 75% charged (12.4 volts or higher). Low battery voltage can not only affect the starter but every other electrical system in the vehicle.

A. Set your DVM to the 20 volt scale, then connect meter positive (+) lead to battery positive (+) post (not the clamp or cable), and the meter negative (-) lead to battery negative (-) post.

B. Disable the engine so it will not start when it is cranked. (Ground the ignition coil wire, or disable the ignition circuit or fuel pump relay.) Limit cranking time to 15 seconds or less.

C. While cranking the engine, record the volt reading on the DVM. D. Next, connect your meter positive (+) lead to the battery terminal stud on the starter, and the meter negative (-) lead to the starter housing.

E. While cranking the engine, record the volt reading.

F. Compare the two voltage readings. If both are the same, there are no excessive voltage drops on the positive feed side.

G. If available voltage at the starter is not within one (1) volt of battery voltage, there is excessive voltage drop in the circuit.

The next test is for voltage drop on the positive side of the starter circuit.

A. Make sure the battery is fully charged.

B. Disable ignition.

C. Set DVM on 2 volt scale.

D. Connect meter positive (+) lead to positive (+) battery post, and the meter negative (-) lead to the battery terminal stud on the starter. While cranking the engine, record the voltage reading.

The maximum allowable voltage drop including the solenoid or external relay in the starter circuit should be 0.6 volts or less.

If you find more than a 0.6 volt drop in the starter circuit, you can isolate the bad connection by using the following voltage drop tests.

* Check the positive battery post and cable connection by measuring the voltage drop between the two while cranking the engine. Connect the meter positive lead to the battery post and the meter negative lead to the cable clamp. A good post/cable connection should have zero voltage drop.

* Check the positive battery cable by measuring the voltage drop end to end while cranking the engine. Connect the meter positive lead to the clamp on the positive battery cable, and the meter negative lead to the end of the cable at the starter. Crank the engine and note the voltage reading. A good cable should have a voltage drop of 0.2 volts or less.

* To check the starter solenoid or relay connections, connect the meter positive lead to positive battery terminal on the solenoid or relay, and the meter negative lead to the starter motor terminal. Crank the engine and note the reading. A good connection should have a voltage drop of 0.2 volts or less.

Next, you need to check the negative side of the starter circuit. To check the entire circuit, connect the meter positive lead to a clean spot on the starter motor case and the meter negative lead to the negative battery post. Crank the engine and note the reading. The voltage drop on the negative side should be 0.3 volts or less.

If the voltage drop is too high, set your DVM to the 2 volt scale and start checking each connection on the negative side to find the bad connection or cable. Use the DVM leads to check across each connection while cranking the engine as before.

Check the negative battery post/ground cable connection (should be zero voltage drop).

Check the negative ground cable from the battery to the engine (should be 0.2 volts or less).

Check between the negative battery post and starter housing (should be 0.3 volts or less).

Check between the engine block and starter housing (should be 0.10 volts or less).
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post #6 of 14 (permalink) Old Sep 26th, 08, 11:29 PM
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Re: Cranks hard when hot....

Quote:
Originally Posted by Oldrocker View Post
C. Set DVM on 2 volt scale.

D. Connect meter positive (+) lead to positive (+) battery post, and the meter negative (-) lead to the battery terminal stud on the starter. While cranking the engine, record the voltage reading.

The maximum allowable voltage drop including the solenoid or external relay in the starter circuit should be 0.6 volts or less.

If you find more than a 0.6 volt drop in the starter circuit, you can isolate the bad connection by using the following voltage drop tests.

* Check the positive battery post and cable connection by measuring the voltage drop between the two while cranking the engine. Connect the meter positive lead to the battery post and the meter negative lead to the cable clamp. A good post/cable connection should have zero voltage drop.

* Check the positive battery cable by measuring the voltage drop end to end while cranking the engine. Connect the meter positive lead to the clamp on the positive battery cable, and the meter negative lead to the end of the cable at the starter. Crank the engine and note the voltage reading. A good cable should have a voltage drop of 0.2 volts or less.

* To check the starter solenoid or relay connections, connect the meter positive lead to positive battery terminal on the solenoid or relay, and the meter negative lead to the starter motor terminal. Crank the engine and note the reading. A good connection should have a voltage drop of 0.2 volts or less.

Next, you need to check the negative side of the starter circuit. To check the entire circuit, connect the meter positive lead to a clean spot on the starter motor case and the meter negative lead to the negative battery post. Crank the engine and note the reading. The voltage drop on the negative side should be 0.3 volts or less.

If the voltage drop is too high, set your DVM to the 2 volt scale and start checking each connection on the negative side to find the bad connection or cable. Use the DVM leads to check across each connection while cranking the engine as before.

Check the negative battery post/ground cable connection (should be zero voltage drop).

Check the negative ground cable from the battery to the engine (should be 0.2 volts or less).

Check between the negative battery post and starter housing (should be 0.3 volts or less).

Check between the engine block and starter housing (should be 0.10 volts or less).

You can't measure voltage drops this way.
I think you are confusing volts with ohms.
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post #7 of 14 (permalink) Old Sep 27th, 08, 04:39 AM Thread Starter
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Re: Cranks hard when hot....

Jim,I think it might be the timing but not sure.

Tom, this is way above my head.

James,I hope your right about the ohms verses volts because I wouldn't know how to do any of what Tom is talking about and I dont think I have a meter to do it with...

OK,I had a buddy of mine tell me to take the coil wire off when its the car is hot and see how it cranks then.Also when its hot if I put a battery charger on it it seems to crank ok.What do you think will be easiest for a plumber to try I'm no rocket scientist so I need some thing easy.

Thanks again....

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post #8 of 14 (permalink) Old Sep 27th, 08, 06:57 AM
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Re: Cranks hard when hot....

Quote:
Originally Posted by 68 Ragtop View Post
You can't measure voltage drops this way.
I think you are confusing volts with ohms.
You CAN and SHOULD measure voltage drops exactly that way.

Anyone who doesn't think so should start reading my articles in the electrical basics sticky, you have a bit to learn.

Particularly in a system that passes high current at low voltage, the method he described is the only thing that works.
You can't measure resistance, because the actual resistance that will cause an excessive voltage drop is extrememly small, tenths of ohms here.





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post #9 of 14 (permalink) Old Sep 27th, 08, 07:52 AM
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Re: Crank's hard when hot....

Mine's that way, too...

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post #10 of 14 (permalink) Old Sep 27th, 08, 09:41 AM
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Re: Cranks hard when hot....

Quote:
Originally Posted by JimM View Post
You CAN and SHOULD measure voltage drops exactly that way.

Anyone who doesn't think so should start reading my articles in the electrical basics sticky, you have a bit to learn.
I was wrong, you can measure voltage drops using that method. I stand corrected.

"D. Connect meter positive (+) lead to positive (+) battery post, and the meter negative (-) lead to the battery terminal stud on the starter. While cranking the engine, record the voltage reading."


Go try it Jim. Put one meter lead (+) on the positive battery post and the other meter lead (-) on the positive battery terminal stud on the starter and see what you get. A big fat zero volts is what I predict, because there is no reference to ground.
(Edit: you will get zero if you have a perfect conductor or the circuit is not under load, you will get a voltage reading if there is a drop)

I am not questioning your knowledge, as I read your basics part three and think it's pretty good material. Your measuring electricity section does not cover this method of measuring voltage drops, perhaps you could add it.

The way I measure the drop is to check it from battery ground to battery positive underload, then battery ground to positive terminal on the starter under load. The difference between the two is the voltage drop across the conductor (battery cable).
The method Tom (Oldrocker) described is new to me and the website he linked (below in post #11)explains it very well and is a much simpler and more accurate method.

Thanks guys for lesson!

Last edited by 68 Ragtop; Sep 27th, 08 at 07:19 PM. Reason: I was wrong, and learned something new today!
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post #11 of 14 (permalink) Old Sep 27th, 08, 02:36 PM
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Re: Cranks hard when hot....

68 Ragtop, you are wrong. If you study up on electrical theory, you will see that my method is how you measure voltage drop. I took electrical theory and have a sound understanding on the subject. If you disagree, that's fine, but you will be disagreeing with everyone that has ever written a text book on the subject along with every scientist in the field. You can read up on it here, http://www.engine-light-help.com/voltage-drop.html and there are many other sources. "Go try it Jim. Put one meter lead (+) on the positive battery post and the other meter lead (-) on the positive battery terminal stud on the starter and see what you get. A big fat zero volts is what I predict, because there is no reference to ground." On a good circuit you should get zero, but on one with high resistence you will get a voltage reading simply because the voltage takes the path of least resistance and if there is high resistance in the circuit, say too small of a cable to carry the needed amps, your meter will be the path of least resistance and will measure a voltage reading.

This guy has it explained in an easy to understand way http://www.vernco.com/sparks/id606.htm

Last edited by Oldrocker; Sep 27th, 08 at 03:03 PM. Reason: addition
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post #12 of 14 (permalink) Old Sep 27th, 08, 05:13 PM
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Re: Cranks hard when hot....

If your timing is on and all your connections are ok the 1st thing I would look at is to make sure you have enough cranking amps in your battery, usually 700+, under that can give you a hot-hard start condition. Been there, done that, checked the battery last, now I check it 1st!

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post #13 of 14 (permalink) Old Sep 27th, 08, 06:39 PM
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Re: Cranks hard when hot....

Quote:
Originally Posted by david calligan View Post
Jim,I think it might be the timing but not sure.

Tom, this is way above my head.

James,I hope your right about the ohms verses volts because I wouldn't know how to do any of what Tom is talking about and I dont think I have a meter to do it with...

OK,I had a buddy of mine tell me to take the coil wire off when its the car is hot and see how it cranks then.Also when its hot if I put a battery charger on it it seems to crank ok.What do you think will be easiest for a plumber to try I'm no rocket scientist so I need some thing easy.

Thanks again....
The test I am talking about is fairly easy to do. All you need is a DC voltmeter set to the 20 volt scale. Hook one lead to the positive battery terminal, the other lead to the post on the starter that the battery cable connects to. Crank the engine with the engine at the temperature that it acts up, with the coil wire off so it wont start, while observing the volt meter. Anything over .6 volts will cause the problem you are having. You may need bigger battery cables especially if you are using anything under 2 gauge wire, positive and negative. If it is trunk mounted, you should use 00 gauge for the best amp deliverance. Another easy way to test if it is battery cable size related is to add a cable from your battery to the starter with jumper cables. Also go from the battery negative to ground. If it cranks normal then, you need bigger battery cables.The fact that it does better when you are using a battery charger tells that it is suffering from a lack of amp supply. Yellow69RSZ is right also, if you don't have enough cranking amps from the battery, it will cause sluggish starting.
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post #14 of 14 (permalink) Old Sep 27th, 08, 07:25 PM
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Re: Cranks hard when hot....

Quote:
Originally Posted by Oldrocker View Post
68 Ragtop, you are wrong. If you study up on electrical theory, you will see that my method is how you measure voltage drop. I took electrical theory and have a sound understanding on the subject. If you disagree, that's fine, but you will be disagreeing with everyone that has ever written a text book on the subject along with every scientist in the field. You can read up on it here, http://www.engine-light-help.com/voltage-drop.html and there are many other sources. "Go try it Jim. Put one meter lead (+) on the positive battery post and the other meter lead (-) on the positive battery terminal stud on the starter and see what you get. A big fat zero volts is what I predict, because there is no reference to ground." On a good circuit you should get zero, but on one with high resistence you will get a voltage reading simply because the voltage takes the path of least resistance and if there is high resistance in the circuit, say too small of a cable to carry the needed amps, your meter will be the path of least resistance and will measure a voltage reading.

This guy has it explained in an easy to understand way http://www.vernco.com/sparks/id606.htm
Tom, thanks for the link, it explains it very well.
I learned something new today!
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