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1949 Chevy 3/4 Ton spark problem


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tinkering
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Sep 10, 2013, 5:10 AM

Post #1 of 25 (395 views)
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The motor in my 49 3/4 ton is a 235 CID out of a 54 Chevy. The motor won't fire. I have strong spark from the coil lead to ground when I open the points. It is blue and it snaps a strong 1/2 inch plus but when I turn the engine over with the starter, the spark from the coil lead to ground is 1/6 inch weak. What the heck am I missing here? I have tried a different (used) coil and condenser but it does exactly the same thing. Why would we have such a strong spark when opening the points by hand and then nearly nothing when turning the engine over with the starter?


Hammer Time
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Sep 10, 2013, 5:41 AM

Post #2 of 25 (386 views)
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Is this thing running a 12v battery?
If so, just for test purposes, try running a jumper wire directly from the battery the the + side of the coil and see if that changes anything.




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tinkering
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Sep 10, 2013, 6:03 AM

Post #3 of 25 (383 views)
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That is a heck of an idea. Thanks
It is still 6 volt. Yes I will run a jumper to the + side of coil. Should I undo the feed wire from the ignition switch first? If I do that it will isolate potential problems in that part of the circuit. Could the starter be drawing too much and robbing the ignition?
It is still 6 volt but I have jumped it with a 12 volt boost; I know that is not a good idea but I have done it.
I will get back to you when the sun comes up and I have tried the 6 volt jumper.


Hammer Time
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Sep 10, 2013, 6:10 AM

Post #4 of 25 (380 views)
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Are you sure it has a 6 volt coil? The 235 is a 12v engine.

I know the 12 volt systems are designed to start on 12v but run on 8v through using a resister wire from the ignition switch. I'm not sure about the 6v systems. That is the idea behind the jumper wire though, testing that resister wire.




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We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.



tinkering
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Sep 10, 2013, 6:32 AM

Post #5 of 25 (378 views)
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In Reply To
Are you sure it has a 6 volt coil? The 235 is a 12v engine.

I know the 12 volt systems are designed to start on 12v but run on 8v through using a resister wire from the ignition switch. I'm not sure about the 6v systems. That is the idea behind the jumper wire though, testing that resister wire.



tinkering
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Sep 10, 2013, 6:35 AM

Post #6 of 25 (377 views)
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In Reply To
Are you sure it has a 6 volt coil? The 235 is a 12v engine.

I know the 12 volt systems are designed to start on 12v but run on 8v through using a resister wire from the ignition switch. I'm not sure about the 6v systems. That is the idea behind the jumper wire though, testing that resister wire.



The original engine was a 216; it is a 6 volt engine. I ran the 235 in there successfully for a bunch of years with the original 6 volt ignition wiring and components. That makes me think there is no resistor wire; that the system runs and starts on 6 volts. Maybe I'm wrong there; did they use a resistor wire with 6 volt systems too? The funny thing is that there is a super strong 1/2 spark from the coil lead to ground when I static spark it by opening the points manually (with the ignition switch on) but when I turn it over with the starter, the spark is extremely weak (1/16" with no snap).


(This post was edited by tinkering on Sep 10, 2013, 6:37 AM)


Hammer Time
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Sep 10, 2013, 6:37 AM

Post #7 of 25 (375 views)
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Again, is it a 6v coil or a 12v coil?




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tinkering
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Sep 10, 2013, 6:40 AM

Post #8 of 25 (373 views)
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In Reply To
Again, is it a 6v coil or a 12v coil?



It is a 6 volt coil.



Hammer Time
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Sep 10, 2013, 6:42 AM

Post #9 of 25 (369 views)
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Run the jumper wire test.




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We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.



tinkering
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Sep 10, 2013, 6:43 AM

Post #10 of 25 (367 views)
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In Reply To
Run the jumper wire test.



Right on! I'll let you know.



Tom Greenleaf
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Sep 10, 2013, 3:37 PM

Post #11 of 25 (340 views)
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It can or might not matter. 12v is ballasted down to 6v if a 12v system. All were till the end of that. Vehicles were 6v ignitions till about 1969.

If you have spark at all this will run. Not a game - own stuff older than this w pos ground that is a mind bender,

T
_________________________________________
Long retired now


Hammer Time
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Sep 10, 2013, 3:51 PM

Post #12 of 25 (334 views)
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The voltage is reduced down to about 8 volts, not 6 and Chevy went to 12 volt in 1955.




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Discretesignals
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Sep 10, 2013, 4:50 PM

Post #13 of 25 (329 views)
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You could always use a mechanic's stethoscope to check the dwell angle.





Since we volunteer our time and knowledge, we ask for you to please follow up when a problem is resolved.

(This post was edited by Discretesignals on Sep 10, 2013, 4:50 PM)


Hammer Time
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Sep 10, 2013, 5:29 PM

Post #14 of 25 (324 views)
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LOL




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tinkering
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Sep 10, 2013, 10:00 PM

Post #15 of 25 (316 views)
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I guess I was mistaken about the system being a positive ground. My 23 Model T is the positive ground. Sorry for the misinformation.
I don't think there is a resistor wire or block in the 6 volt system. The auto parts store hasn't got a listing for anything. I think it is start with 6V and run with 6V. I have found that the spark problem is intermittent, so I have purchased new ignition parts to install one at a time. I will be checking and cleaning up all of the connections at the same time. When I ran the jumper wire test to the coil, I removed the feed from the ignition switch to the coil. I achieved a good strong spark from the coil lead to ground but then it disappeared again, so I am going to start by replacing the points and condenser, and other major things. When I get it going with the jumper wire, I am going to clean and tighten up the wires and connections working towards the ignition switch and ammeter etc. There must be a major voltage drop or more in the system.


Hammer Time
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Sep 11, 2013, 6:05 AM

Post #16 of 25 (309 views)
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Before you just start throwing parts at it, you first need to determine whether it's the power supply side that is dropping out or the ground pulse from the other side of the coil. You may be having an issue with the coil itself.




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We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.



(This post was edited by Hammer Time on Sep 11, 2013, 6:06 AM)


tinkering
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Sep 11, 2013, 10:18 AM

Post #17 of 25 (305 views)
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In Reply To
Before you just start throwing parts at it, you first need to determine whether it's the power supply side that is dropping out or the ground pulse from the other side of the coil. You may be having an issue with the coil itself.


The points look well worn so I will change them out, and the condenser at the same time; I have this feeling about them. While I do that, I will be checking the wire, insulator, and connections on the ground side. If that does it, I will return the coil to the store. Otherwise, the new coil will be the next thing I put in. Coils may be a less common cause but in the past I have had a no start situation solved by installing a new coil. I have disconnected the power supply side at the -neg terminal of the coil, and I have run a jumper from a separate battery; so when I get it running in this configuration, I will work my way back up the power supply side; in case it is a compound thing. I would like to give it new cap, rotor, and plugs but they are not causing this poor spark condition at the coil lead.

Thanks



Hammer Time
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Sep 11, 2013, 10:34 AM

Post #18 of 25 (300 views)
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Throwing parts at it is not testing.




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We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.



Tom Greenleaf
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Sep 11, 2013, 10:35 AM

Post #19 of 25 (299 views)
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Hammer - Try replying to things you know about which isn't much!

!!


Tom
_________________________________________
Long retired now


Hammer Time
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Sep 11, 2013, 10:41 AM

Post #20 of 25 (295 views)
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Off your meds again huh Tom?




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tinkering
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Sep 11, 2013, 11:11 AM

Post #21 of 25 (290 views)
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In Reply To
Throwing parts at it is not testing.

That is true. I think the points should be replaced because of the visual inspection, and I have always had the tendency to change the condenser at the same time as the points. Because of the intermittent nature of this, I feel that the best thing to do now is check, clean, and secure all of the conductors, insulators, and connections. Then a test light or meter reading indicating a voltage drop can be trusted. The resistance between the primary posts on the coils is about 1.2 ohms (close to the value of an old coil I have here). The resistance values of both of these coils are very close to one another. I will compare them to the resistance of the new coil I have. Sometimes I get lazy and just change out a part so I can hopefully get on with other tasks (I am hoping to get a garage pad poured before the snow flies here. I am trying to get this truck started so I can jockey it out of the way. I trust I can remain patient Crazy




Hammer Time
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Sep 11, 2013, 11:17 AM

Post #22 of 25 (287 views)
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It won't hurt to replace the points and condenser but you really need to figure out which side of the circuit is dropping out if any.




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We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.



tinkering
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Sep 11, 2013, 11:31 AM

Post #23 of 25 (285 views)
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In Reply To
It won't hurt to replace the points and condenser but you really need to figure out which side of the circuit is dropping out if any.

That is great advice. I will check everything from the +post of the coil, through the points and condenser, all the way to ground. I will post any voltage drops, and readings while cranking, if I have to get the meter out again.



tinkering
User

Sep 11, 2013, 5:06 PM

Post #24 of 25 (279 views)
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CoolI made up a new primary ignition feed wire from the +coil post to the distributor. The the primary ignition wire insulated connector that goes into the side of distributor (the points and condenser wire connect to it in there)was loose and dirty (not any more). I installed the new points and condenser. I have a good 3/4 inch blue snapping spark from the coil wire to ground when turning it over with the starter (hooray!). Because I installed the new wire, beefed up the insulated connector; installed points and condenser, all at the same time, I am not sure what the main instigator was, so I will venture to say that there was a voltage drop over that primary ignition insulated connector; I also suspect the points just because they were quite burned, and the condenser could have been adding to it.

The motor fired. I got it to run but had to keep priming it through the carb. The fuel pump is not delivering to the float bowl. Rot and mice have consumed major portions of both oil lines; I need to replace those before I can run the motor for any length of time. The water pump is leaking (not enough to stop me from moving the truck across the yard when I get the oil lines on.)

I still have the separate battery and jumper wire feeding the coil. I need to work my way back up the positive feed side of the power supply through the ignition switch and ammeter, to the main connection on the starter; making sure the connections are all cleaned and tightened, and that there is no missing wire insulation.

Unfortunately I didn't get any of those voltage measurements taken at the coil etc. while cranking the starter. I would have liked to have seen what the reading were too. Maybe we can get those after we get the second battery and the ignition jumper wire out of there.

I did not replace the coil, rotor, cap, or plugs.

IT'S RUNNING!


Hammer Time
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Sep 11, 2013, 5:33 PM

Post #25 of 25 (275 views)
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Glad to hear you got it resolved.

Closing this question as solved now to keep the spammers out.




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We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.





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