Trouble starting on low compression

[Cooper40]

I have a '49 Plymouth thats been sitting for 30+ years. Low compression. We got it running yesterday for about 3 seconds. We ended up putting oil in the cylinders and that got it to pop off. Then tried it again right after and no luck. Tried it again today doing the same thing, oil in the cylinders right before start. No go. Made sure the battery was charged but it is loosing its charge quickly when we crank on it. 

The plugs were also wet today when we tried it so how did it work yesterday? Would putting too much oil in soak them down too much to get spark fast enough? 

[Sniper]

How low compression? I've had 50 psi per hole for the last 4 years and it runs fine. I think you've wetted your plugs and killed the spark either get a new set of plugs or clean your old ones really good

Edited October 27, 2023 by Sniper

[Cooper40]

@Sniper The readings are:

1 - 55

2 - 60

3 - 80

4 - 70

5 - 50

6 -60

Yeah I'm using new plugs. I was thinking that and a combination of not enough cranking speed. We'll try again tomorrow with a charged up battery. 

Edited October 27, 2023 by Cooper40

[Sniper]

I don't think that compression readings are bad enough to keep it from running. Let us know how it goes with the charged up battery

[Los_Control]

Sounds like you have enough compression to run.

Nothing wrong with adding oil to the cylinders, it will be good for the engine ...... but bad for the plugs.

 

The wet plugs you pulled out need to be cleaned & dry really well for them to work again ..... If any oil left around the electrodes, they will not fire properly.

 

So it makes sense, it ran once but the plugs got so oiled fouled it did not run again.

 

Cranking speed will always help it start, just need to work with what you have.

[Cooper40]

@Sniper Will do.

 

@Los_Control Yeah ok that does make sense. I will try again tomorrow with a charged up battery and let you know the results. 

 

[Ivan_B]

Dry the plugs with an open flame, that should help.

[TodFitch]

2 hours ago, Cooper40 said:

@Sniper The readings are:

1 - 55

2 - 60

3 - 80

4 - 70

5 - 50

6 -60

Yeah I'm using new plugs. I was thinking that and a combination of not enough cranking speed. We'll try again tomorrow with a charged up battery. 

 

2 hours ago, Sniper said:

I don't think that compression readings are bad enough to keep it from running. Let us know how it goes with the charged up battery

 

Way back when I first got my '33 Plymouth it was hard to start and missing some power but I drove it a few thousand, yes thousand, miles that way. When I finally learned enough to to a compression test I found it had 50 to 60 psi on the three “good cylinders” and zero on other three cylinder. So yes, I would expect an engine with the lowest compression a 50 to run. Probably pretty hard to start, but it should start and run. 

 

26 minutes ago, Ivan_B said:

Dry the plugs with an open flame, that should help.

That sounds like an excellent idea. I haven’t heard of it before but it make sense.

[Cooper40]

@TodFitch Wow ok. How did you first get it to run?? Did you have to use 12 volts or pull start it?

@Ivan_B I was thinking about that. I'll try the open flame on the plugs if they get wet again. 

Edited October 27, 2023 by Cooper40

[vintage6t]

Also make sure your battery connections are good and fuel delivery/carb is working properly.

 

As for battery connections, clean all connections well and make sure you have a 6v cable, at least 00 in size, and not a 12v cable. A 12v cable won't deliver the current you need to start.

[Cooper40]

@vintage6t Cables are 2/0 (00) size. However, we didnt change the cable going from the solenoid to the starter. That one looks rough. Ordered a cable yesterday (same size as the main neg and pos battery cables) so waiting for that to come. 

 

We didn't even touch the carb lol. I hear fuel squirting when I pump the throttle and since it did fire off for a few seconds it only stopped when I stopped giving it fuel. Then wouldn't fire up after because I think it lost compression? 

[TodFitch]

5 hours ago, Cooper40 said:

@TodFitch Wow ok. How did you first get it to run?? Did you have to use 12 volts or pull start it?

In warm weather it would generally start pretty quickly. In winter I sometimes resorted to jump starting the 6v system from a 12v car something I would not recommend nowadays since I am a bit more cautious. That was when I first got the car 50 years ago. I was in college in Upstate New York and it was my “daily driver” but since I lived on campus I didn’t actually have to drive every day.

[Veemoney]

3 hours ago, Cooper40 said:

We didn't even touch the carb lol. I hear fuel squirting when I pump the throttle and since it did fire off for a few seconds it only stopped when I stopped giving it fuel. Then wouldn't fire up after because I think it lost compression? 

A few things to add to info you have so far.

1. Compression readings are good enough to start as others have said. They normally would improve on an engine that has sat for a while with additional running. Not sure if you had the choke and throttle open when taking them but if not they are likely better than posted.
2. Choke, if it has an automatic choke is it operating correctly and if manual choke are you setting it for starting?
3. If you have a helper that can give a quick spray of starter fluid to the carb as you crank it that will help to get it fired off initially. Just a quick 1 second blast is all I'm talking about so don't go ape shlt with it if it doesn't pop off right away. 
4. Once it fires off keep it running with the gas pedal above idle for a bit and gradually ease down on it as it warms up. Remember to check the choke.

[Ivan_B]

3 hours ago, Veemoney said:

Once it fires off keep it running with the gas pedal above idle for a bit

I would normally use the manual throttle control for that.

[Cooper40]

We've got it to pop off for a second but it doesn't catch and the battery starts cranking very slow. It's like the battery is loosing its charge very quickly. We'd charge it up for a couple hours, try again and the same thing. It would fire but then as soon as it doesn't catch and keeps cranking it gets slower and slower. We've tested the battery with a multimeter on the DC volts setting and are getting 6.3 when it's not charging and when it's charging it's at 6.4. We're not really sure what to do. We're thinking it's the battery and not the starter because it would gradually slow down as we were cranking. 

 

 

Edit: We've only been charging the battery for a couple hours at a time and its never been fully charged. We're going to charge it overnight until it shows that it's fully charged and then try again. 

Edited October 27, 2023 by Cooper40

[TodFitch]

1 hour ago, Cooper40 said:

We've only been charging the battery for a couple hours at a time and its never been fully charged. We're going to charge it overnight until it shows that it's fully charged and then try again. 

A battery hydrometer is a useful tool to have if you are dealing with non-sealed lead-acid batteries. It will tell you the state of charge for each cell (should be the same or there is an issue) and let you know if the battery is fully charged or not.

 

A quick check shows at least one 6v lead-acid car battery to have a 65 amp-hour rating. On my 1970s vintage charger with a max output of 6 amps it would take 11 hours to fully charge one.

 

However lead-acid batteries are damaged if they are taken below 50% charge. And it sounds like you may have been doing that.

 

Anyway, put your battery on a charger and while you wait visit your local auto supply store and pick up a hydrometer. I am assuming, of course, that they still sell such things in this age of sealed batteries. They used to be pretty cheap as there is not much to them. But they can tell you if a cell is bad, etc. and thus let you know if the battery simply needs charging or if it is due for replacement.

[Sniper]

If you are checking a battery state of charge with a voltmeter you would expect to see 2.1 volts per cell on a fully charged battery. For a 6-volt battery you have three cells those are the caps. So 6.3 volts is about what I would expect to see for a fully charged battery that does not have a surface charge. If your charger is only putting out 6.4 volts to charge the battery with then you've got a problem with your charger. Because it should be well above that most likely above seven volts when it's charging.

[Tired iron]

in my experience, you can't really tell the health of the battery with a voltmeter.  You need a load tester. Reasonably priced at Harbor Fright, or take the battery to an auto parts store and theyll test it for you.  Sounds like you may need a new battery.

[Sniper]

I test batteries for a living, last week I tested almost 650 identical 12v batteries.  Had 5 bad ones and as soon as I hooked up the tester and saw the fully charged voltage I knew they were bad.  The tester just confirmed it. 

 

A good battery's voltage will drop down with a steady load on it then start to climb back up.  A bad battery will not come back up with a load on it, some will drop to a very low level quickly.  Turning on head lights can simulate enough of a load most times.  Typically, the fully charged voltage of a 12v battery is in excess of 13v.  If it's about 12.6 or less it will fail a load test.  I would expect to see a 6v battery somewhere near v, but I don't test those for a living.

 

You can tell just by measuring the voltage of a fully charged battery, of course it helps if you have 650 of the same exact battery to used as a data sample, lol.

[9 foot box]

   I agree with the load test. Voltage is a false determination of cranking power. When starting any of my engines cold, they need an application of choke to stay running. Your 49 probably has a Sisson automatic choke. The majority of my vehicles have choke and throttle cables, and I use them both at cold startup.   Rick D.

[Sniper]

1 hour ago, 9 foot box said:

I agree with the load test.

 

What are you measuring during a load test?

 

Voltage

 

But what do I know, I've only tested thousands of batteries for the last 10 year.

 

 

[9 foot box]

   I only have a cheap box tester that I got from my dear old friend, Louie. When I hook a battery to it, it shows a voltage and color scheme of the condition of a 6 or 12 volt battery. When I switch to load the gauge reads the availability of voltage or if it’s discharged. If the gauge drops off, the battery is bad and won’t take a full charge. Rick D.

[Tired iron]

11 hours ago, Sniper said:

 

What are you measuring during a load test?

 

Voltage

 

But what do I know, I've only tested thousands of batteries for the last 10 year.

 

 

 

Hi Sniper.  I wasn't meaning to challenge your skills or experience (though I can see how my post might read that way!).  Just to point out that I've had the experience of a car battery reading 12 or so volts on a voltmeter, but then, under a load demand, not being able to deliver enough ooomf.  I didn't want the OP to think that his battery is good and not the problem just because he gets a reading in the vicinity of 12 volts on a voltmeter and without any load on it.  Or is this not correct?  Ready to learn something here!

[Sniper]

I think you are missing that I have very carefully stated "fully charged battery".  If your fully charged battery, less any surface charge effect is below 12.8v, on a 12v battery, then it is weak and failing, get much below 12.4 and it is not long for life. 

 

Load testing will confirm this, but without a baseline load test you really can't do much interpreting.  IOW, tested when new to establish what new performance is, only then can you make more specific opinions about it's health in use.  Frankly, the best load tester you can get you already have, your starter.  A starter draws hundreds of amps, a hand held load tester maybe 100?

 

It can take up to 14 hours to fully charge a lead acid battery.  So odds are the battery in your car isn't fully charged in regards to this discussion.

 

Anyway, if you really want to go down the battery rabbit hole this place has a lot of info.  https://batteryuniversity.com/articles

[Cooper40]

@Sniper @Tired iron @9 foot box @TodFitch

We ended up bringing the battery to O'Reillys, they tested it and said it was good. Turns out we were using a battery maintainer not a charger to charge the battery! Got a charger and charged it up overnight and got a full charge. The car started this morning for the first time! Refer to my most recent post for details. 

Edited October 29, 2023 by Cooper40