Cherokee 140 won’t start

Patrickjmars

Filing Flight Plan
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Mars83R
I am having an issue with starting my 1966 Piper Cherokee 140. When I engage the starter the prop will turn 1/4 then stop when it hits the compression. Has anyone run into this issue? Below is a list of troubleshooting I have already tried.

- Jump started plane with external battery pack. This worked.
- Tested battery (tried new battery as well). No Start.
- Checked and cleaned all grounds/connections in starter series. Didn’t see any corrosion.
- Replaced old starter solenoid.
 
Time to get out the voltmeter?
What's the voltage at the battery when you crank?
What's the voltage at the starter when you crank?
What's the voltage drop across the solenoid?
Voltage between battery negative and starter ground?
 
cables and/or the starter itself.

I just looked at the price of a new skytec lightweight starter - ouch. But it's nice when the starter works and rotates the prop...

and, I hope you get it fixed.
 
Get someone smart with a multimeter to start testing. It will be much cheaper than just starting to replace parts until the problem goes away.

That person needs to check voltage drops, while cranking, across a whole bunch of places. Most commonly, the problem is old contactors: the master and starter both. The master often gets overlooked. Starter current runs through it, too. Their contacts get oxidized and burned. Elsewhere, corrosion and oxidation occurs between the cables themselves and the terminals crimped onto them. So the tech needs to start poking at those, too, with his voltmeter. He can't use the ohmmeter, since the resistances involved are really tiny. Ohm's Law shows us that with large currents and small resistances we get large voltage drops.

Cherokee 140. Aluminum cables, likely, and they are awful for oxidation.
 
I am having an issue with starting my 1966 Piper Cherokee 140. When I engage the starter the prop will turn 1/4 then stop when it hits the compression. Has anyone run into this issue? Below is a list of troubleshooting I have already tried.

- Jump started plane with external battery pack. This worked.
- Tested battery (tried new battery as well). No Start.
- Checked and cleaned all grounds/connections in starter series. Didn’t see any corrosion.
- Replaced old starter solenoid.

My old Cherk with high-compression pistons used to do this. After chasing the problem for a while, I finally resigned myself to "catching the bounce", that is, instead of holding the starter button against the compression, releasing it and pressing it again using the momentum of the prop as it bounced back in the direction of rotation. Lots cheaper than replacing all the cables and such. Started it that way for years without any trouble.
 
Dan's advice is spot on as usual.

When you say you jump started the plane, where was the external battery connected...at the battery box or closer to the engine at a receptacle ?
 
The old Delco/prestolite style starters draw a lot of current to function and will draw more current as they age. The permanent magnet starters such as the Sky Tec are a good choice for replacement.

However, Before replacing anything else I’d do some diagnostics on the rest of the system like has been suggested.
 
The OP said plane started OK when he used an external battery pack. I am asking what kind of battery pack and where was it connected to the electrical system.

Over and out.....
 
Had much the same issue with my 69 140b. This kit solved the problem:

https://bogertaviation.com/products/battery-box-mod-with-battery-cables-stc-sa4008nm

In short - replaced crappy high resistance ground cables, and thoroughly cleaned airframe ground locations.
The mistake here is suggesting that he replace the cables and see if the problem goes away. Those old cables may indeed be bad, but on the other hand the master contactor might be shot, or the engine-to-airframe grounding might be poor. To start replacing stuff without having a definite idea of where the major fault lies is just a good way to get rid of money.

If you go to your doctor with a complaint, he sends you for blood tests or an x-ray or MRI or some other diagnostic procedure. That's to avoid prescribing 27 different pills in the hope that one of them will fix you. Or instead of cutting you open several times for transplants in the hope that he gets lucky.

A mechanic with 20 minutes and a $20 multimeter can pinpoint all of the bad spots if he knows what he's doing. It sure can save a bundle and a whole lot of visits to the shop.
 
Hi Dan. I mostly agree with you. Mostly. ;) The troubleshooting steps as reported suggest a voltage drop getting to the starter. A booster masks that, somewhat, and gives enough kick to turn things over (and as stated above, it'd be good to know where that was connected). New battery did not help (again, suggesting voltage drop/high resistance). OP says they cleaned the grounds, sort-of ruling that out. I could fault the starter, but since a booster allowed it to turn over, that suggests the starter isn't totally bad. This leaves the cables, which may or may not be the original aluminum.

To the OP: Are the battery cables 'original'? There's a service bulletin regarding replacing the aluminum cables with copper. Note that this isn't the same as the Bogert kit I referenced in my other post.

https://www.barteltaviation.com/pdf/Piper/Piper SB 836A - Aluminum Wire Inspection.pdf

In my case, the decision was easy, as the braided positive cable in the battery box was frayed. Resistance measured OK, but voltage drop under load was too much. I elected to use the Bogert kit, as sourcing the original braided cable, with all of its connections (Stud through the battery box, etc), was not significantly less expensive than the bogert kit, and the Bogert kit simplified and modernized the connections to the battery. Between the new positive cable modification, new ground cables, cleaning all ground to airframe connections, the difference was dramatic.


The mistake here is suggesting that he replace the cables and see if the problem goes away. Those old cables may indeed be bad, but on the other hand the master contactor might be shot, or the engine-to-airframe grounding might be poor. To start replacing stuff without having a definite idea of where the major fault lies is just a good way to get rid of money.

If you go to your doctor with a complaint, he sends you for blood tests or an x-ray or MRI or some other diagnostic procedure. That's to avoid prescribing 27 different pills in the hope that one of them will fix you. Or instead of cutting you open several times for transplants in the hope that he gets lucky.

A mechanic with 20 minutes and a $20 multimeter can pinpoint all of the bad spots if he knows what he's doing. It sure can save a bundle and a whole lot of visits to the shop.
 
Resistance measured OK, but voltage drop under load was too much.
Yea, the resistance of a power cable is too low to get a reasonable measurement (if it's good or bad) with the typical multi-meter. A 4 wire Ohm meter would get you closer, but still probably not close enough to get a meaningful result. Better to measure voltage drop under load - but then you have to compare to something that you think might be good for comparison - one could measure the ground and + cables, or cables between the solenoid and the starter, etc. and see if one stands out from the others. If nothing jumps out, then either they are all good or all bad. :)
 
You might be able to find a bad connection by feeling each potential one for heat with your fingers immediately after cranking, but be prepared for the guilty one being very hot:eek:.
 
At one time had extra long jumper cables made from welding cable.
This would enable replicating any portion or the entire Starting Circuit.
So you could go directly Batt to Starter including the Ground Path.

Unfortunately; someone needed them more than me.
 
Could be multiple problems. Use multimeter.

For me, similar problems. My multimeter data pointed to starter solenoid. The solenoid-to-starter cable was also a secondary culprit (looked bad, got hot, marginal multimeter data but not convincing due to my cheap meter). New solenoid, better but not totally fixed. Replaced the 9” cable, all great.

Multimeters are inexpensive and indispensable diagnostic tools. Instructions for troubleshooting are simple. Some mechanics are guessers and parts replacers, just like us mere mortals/civilians.
 
Hi Dan. I mostly agree with you. Mostly. ;) The troubleshooting steps as reported suggest a voltage drop getting to the starter. A booster masks that, somewhat, and gives enough kick to turn things over (and as stated above, it'd be good to know where that was connected). New battery did not help (again, suggesting voltage drop/high resistance). OP says they cleaned the grounds, sort-of ruling that out. I could fault the starter, but since a booster allowed it to turn over, that suggests the starter isn't totally bad. This leaves the cables, which may or may not be the original aluminum.
In Post #10 Doug Reid asked an important question that hasn't been answered: Where was the system boosted? At the battery? At the starter solenoid? Or at an external power socket? The external socket and starter solenoid both bypass a whole bunch of possibilities, including the master contactor. One needs to know the circuit diagram and where the boost was connected to intelligently diagnose anything.

Of all the subjects a mechanic studies and needs to know, electrical theory is easily the weakest for most. When it comes to owners, the same thing applies. That's why we see suggestions to replace this or that "because that's what my problem was" or something. The circuitry here is a lot more complex than that, and without understanding it, and the effects of tiny resistances, all suggestions are useless.

Ohm's Law: E = I x R. Voltage equals current times resistance. We have a starter that can draw as many as 250 amperes. We might have a bad contactor or cable that presents a resistance of 0.05 ohms, a figure your typical multimeter will never measure accurately. Its test leads might even have that much resistance. But that 0.05 ohms times 250 amps equals a 12.5 volt drop. In a 12-volt system, that means you get nothing at all. And that's with one-twentieth of an ohm. Of course, the resistance causes a massive voltage drop, which reduces the amperage, which also reduces the voltage drop, and you can see that it gets a bit complex. In any case, measuring the voltage across suspect components is the way to find the fault. If you turn the master on, and connect the multimeter (set to volts) across the starter contactor, you will see 12 volts. Battery voltage. This is because the meter is drawing a tiny bit of current to get its reading, and it is grounding through the starter. That doesn't make much difference to the microamps drawn by the meter, so we get an accurate reading. Now you hit the starter, and the voltage should drop all the way to zero as the contacts short the multimeter. If the voltage drops to one or two volts, you have a bad contactor. Across the master contactor you should see zero volts when the master is on, engine not cranking. Crank it and see if the voltage rises above zero. If it does, the contactor is bad. It has resistance that diverts a few microamps into the voltmeter.

These small voltages add up throughout the system, since they're all in series. You might replace a cable and get rid of a two-volt drop, but there are a bunch of other resistances in that circuit that are giving a total of three volts drop, and the starter's performance is still not so good. You've got to find them all. If you don't, one or more will just get worse and strand you somewhere someday, a situation that instantly gets a lot more expensive than just doing the job right in the first place.
 
Someday the forum software will have a bot to post this troubleshooting guide for every starting issue thread
Try this: Performance Issues (skytec.aero)
That's a good resource, but it involves measuring voltages directly. Depending on the resolution of the analog scale, or the stability of the digital readout, you might get something useful and might not. We're talking about measuring over a fairly brief cranking period.

I used an analog meter for this. My digitals jumped around too much as the starter load changes with compression strokes. And I didn't measure the voltages across the stuff and to ground; I did as #3 in that thing shows: measure voltage drops across the various places. Even in #4 it should be voltage drop measurements, not resistance measurements, since even tiny resistances will make large voltage drops. Small resistances are difficult or impossible to measure with the typical affordable meters.

With an analog meter, bad stuff shows up instantly as the meter needle fails to drop to zero when the cranking starts.
 
For the record; my “ Copper Cables?” comment was not a suggestion to automatically replace the originals to address the issue.
Always troubleshoot first.
 
The OP appears to have skipped.
 
1966 Piper. Old and worn wiring and parts. Possible aluminum wiring.

What could possibly go wrong? Lol

Got to love old airplanes.

Dan is spot on.
 
Time to get out the voltmeter?
What's the voltage at the battery when you crank?
What's the voltage at the starter when you crank?
What's the voltage drop across the solenoid?
Voltage between battery negative and starter ground?
Have to take off the cowling to get to starter. Going to do this next week with a mechanic.
 
Current update. I was able to get the plane started after replacing the master solenoid. I’m not sure if that was the actual fix though.

I am planning on getting the front cowling of next week and test the starter when cranking since there still seems to be a weaker start than I would like.
 
Funny how you run across something out of the blue that is relevant elsewhere in your life. I'm not saying it is 'the tool to use', but could help. Use at your own risk.
 

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Thanks everyone. After replacing the Starter solenoid the aircraft initially did not start, but I only tried once. 1 day later I came out to move the aircraft to a hangar to work on it and it magically started. The plane has continued to start with no issue for the last 25 hours and 10 starts. I will update if anything further continues.

Thank you everyone for the advice.
 
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