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Prop moves but engine won't turn over

Robert M

Robert M

Well Known Member
I bought a Odyssey PC680 battery. Installed it into the plane. Powered up the system and turned the engine over without the top plugs in and ignition off. The engine rotated in the proper direction with no worries. Put plugs in, powered up ignition for engine start, tried to start again and almost nothing happened. The prop moved but only an inch and then a loud clicking. Released start button and press again - same thing over and over - 3 - 4 attempts.

The battery has been on charge for the last 2 weeks.

I replaced the starter solenoid thinking it was the culprit - same results as above.

Engine (Lycoming O320-A2B, newly rebuilt with new cylinders pistons and rings, new crank, everything else 0 time, assembled by an A&P.

Any ideas? Suggestions?
 
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The very first thing to check is all connections. A loose of dirty connection will do just that. Also make sure that your ground wire to the engine is the same size as the wire to the starter.
Under minimum load conditions, as with the plugs removed, it takes little current to spin the engine. But with plugs in, compression greatly increases the load, requiring much more current.
 
If there is a loose or poor connection to the starter, it will get quite warm or hot when you attempt to start (high resistance).
 
Mel said:
The very first thing to check is all connections. A loose of dirty connection will do just that. Also make sure that your ground wire to the engine is the same size as the wire to the starter.
Under minimum load conditions, as with the plugs removed, it takes little current to spin the engine. But with plugs in, compression greatly increases the load, requiring much more current.
Click to expand...

I will go back through ALL of the wiring but I am pretty sure it is all snugged up and tight.

Raymo said:
If there is a loose or poor connection to the starter, it will get quite warm or hot when you attempt to start (high resistance).
Click to expand...

I did not touch the starter after the start attempts. If I find no loose connections, I will try again and then check the temp on the starter.


Thank you.
 
To clarify what Raymo said, it is the faulty connection that will get hot. Not necessarily the starter.
 
Robert M said:
I will go back through ALL of the wiring but I am pretty sure it is all snugged up and tight.
Click to expand...

I assume you verified a good ground to the starter - like a #2 or #4 wire on the starter ground lug to the main firewall ground?

While not likely but possible - you may have a bad starter solenoid (solenoid may work but may have high resistance contacts). They are cheap enough to replace.

Carl
 
Did the engine turn over fine with the previous battery?

The skytec troubleshooting guide that az_gila linked to is excellent. It helped me figure out I had a bad ground between the engine and the starter. I had to clean the interface between the starter and engine and the troubles all went away. I'll add a ground strap between the two at the next oil change.
 
Fully charged battery doesn't mean anything, it can be at 12.6 and have no capacity. You can put a volt meter on the battery + post while cranking for a poor mans load test. It should stay north of 10 volts or so. Do it again at the starter post. Now if it's down you know you have a problem between the battery and the starter.
And don't forget the ground path.
A simple test here is put the volt meter between the neg post and the engine case, while cranking you should see less than 1~1.5volts.
Tim Andres
 
Carl Froehlich said:
I'd guess this killed the battery. Borrow/buy a new battery and try again.
Carl
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The battery is new and was left on a trickle charge during the last 2 weeks prior to start attempt. I don't understand how this would kill the battery, could you please explain?

az_gila said:
This troubleshooting guide may help, even if it's not a SkyTec starter -

http://skytec.aero/starter-performance-issues/
Click to expand...
Thanks, I will use all means available to figure out what's going on.

Carl Froehlich said:
I assume you verified a good ground to the starter - like a #2 or #4 wire on the starter ground lug to the main firewall ground?

While not likely but possible - you may have a bad starter solenoid (solenoid may work but may have high resistance contacts). They are cheap enough to replace.
Carl
Click to expand...
The starter solenoid was replaced after the first failed attempt. I can't honestly confirm the starter ground situation, I just can't remember right this minute and I'm not at the hangar. Will check this weekend.

Bubblehead said:
Did the engine turn over fine with the previous battery?

The skytec troubleshooting guide that az_gila linked to is excellent. It helped me figure out I had a bad ground between the engine and the starter. I had to clean the interface between the starter and engine and the troubles all went away. I'll add a ground strap between the two at the next oil change.
Click to expand...

This is the first and only battery I have used for starting the engine. I have used other batteries (i.e. old motorcycle batteries) to power up the system for light and flap operations checks.

maniago said:
Load test the battery. Maybe someone around you has one of these. Kinda an esoteric piece of equipment, but Ive used mine a bunch over the years. $20.

https://www.harborfreight.com/100-amp-612v-battery-load-tester-61747.html

Any time I've had a clicking starter in a car, it was the battery. Bad connections typically show up as slow or labored cranking.
Click to expand...
Harbor Freight is one of my favorite places to shop for all things - tool related.

Thanks again to all the replies, looks like I gots me some investigatin' to do.
 
Robert M said:
The battery is new and was left on a trickle charge during the last 2 weeks prior to start attempt. I don't understand how this would kill the battery, could you please explain?
Click to expand...

There are multiple threads in the VAF archives about how trickle chargers kill the PC680 battery. There is no need to trickle charge, the battey will hold its charge on the shelf for many months. That is one of the advantages of AGM battery technology.

But this issue is easily investigated by attempting an engine start with a known strong battery. If you do need to purchase a new PC680, be sure you do the homework on proper care and feeding of the little guy.
 
What Sam said.

And the quick and dirty way to check the 'system' is a pair of *quality* jumper cables.

If you jump it from a known-good source (car, golf cart, UTV, etc) and it still doesn't turn over, you have wiring issues.

If it does start, then you either have issues with the terminals at the battery, or the battery itself.
 
If it is a poor connection it can be easily pinpointed by voltage drop test. Example would be put the voltmeter leads positive batt to positive starter. Crank engine. Voltage drop should not be more than around .5 volts so volt the meter should not show more than .5 volts. If the meter shows high volage move the leads closer together along that circuit example would be from starter
to start solenoid... The poor connection can be pinpointed by moving the leads along the positive, or, negative circuit. My guess is if the battery is good you're going to have a 12 volt drop somewhere along the positive or negative circuit.
 
Do you have a ground wire from the engine case to the firewall? Preferably the same bolt as you used for the battery ground.......assuming you have a firewall mounted battery.

The engine mount is NOT a reliable ground path.
 
Dumb question Robert, but can yo turn the prop over by hand? (With the mags off.)

I know when I was out there last we were turning it over but I wonder if one of the cylinders may have filled with oil for some odd reason.
 
Robert M said:
...ut plugs in, powered up ignition for engine start, tried to start again and almost nothing happened. The prop moved but only an inch and then a loud clicking. Released start button and press again - same thing over and over - 3 - 4 attempts.

The battery has been on charge for the last 2 weeks.
Click to expand...

The repeated loud clicking sounds like a starter solenoid that isn't getting enough voltage to fully extend. This is a common symptom of low voltage at the starter. Could be a battery problem, or a problem with connections in the circuit feeding the starter.

Definitely do a capacity test on the battery. I found that taking about 300 feet of 14 gauge copper wire and short circuiting the battery works for this. I took a 100 foot roll of 2-conductor-plus-ground household 14 gauge wire and wired the three conductors in series with wire nuts (300 feet total length) and then put clamps on the two loose ends. This presents a resistance of about 0.75 ohms, so at 12 volts, you would get about 16A. I'm going off my memory here, but I think a standard battery capacity test is to load the battery at a current that should deplete its nominal full charge in one hour. So, for the battery I was testing, at about 16 Ampere-hours of capacity, the resistance was just about right. I took my clamp current meter and verified the current. You have to watch the voltage and stop the discharge when it gets to the "discharged" voltage specified by the manufacturer. Do not allow the battery to continue discharging below this minimum voltage or you will damage it permanently.

You probably ought to look up the proper procedure for your battery, and certainly should do the calculations for yourself, but this is the basic way I did my battery capacity test. Note, I did this test on a lead acid AGM battery after talking with the manufacturer (Gill) about the procedure.
 
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Borrow a fresh battery from someone. Sounds like how my original PC-680 went. Trickle charging with the approved unit wouldn't get it charged enough to spin the prop after a while. Just clicking from the solenoid.
 
I'm not an electrical guru--

But back in the automotive days, when we had a Ford style solenoid system and got that rapid clicking, there wasnt enough voltage to close the solenoid contacts. Thus, the solenoid coils are sitting there chattering. Battery voltage below 10 volts can produce that. WE used to call it service voltage.

Put a volt meter on the battery and try to energize the starter and see what the voltage drop is. If it stays above 9.5 volts---hopefully alot higher, then looks for a contact or ground issue. If below, load test the battery to see if it stays above the voltage draw requirements.

Occam's razor---if the engine was turning over fine previously, and nothing changed with the engine, then back up and see what the difference is in the entire system. Battery, batter cables, grounds. Like Raymo said, even alittle bit of corrosion can create this issue.

AGAIN----not my line of expertise, but remembering from the old days.

Tom
 
There are two solenoids in the system. The starter relay (solenoid) and the starter solenoid that is housed on the starter to pull the bendix gear in.
There are two ways to wire the system if you have the "light weight" starter. In the day, it was recommended that the jumper be removed from the main starter power stud to the solenoid and the auxiliary output terminal of the starter relay should be used to energize the starter solenoid. More recent plans show the jumper left in place with a note that states if the starter doesn't seem to disengage properly, run the extra wire and energize it off the auxiliary output terminal.
I mention this for two reasons. If you have removed the jumper and have a separate wire to the starter solenoid, that is one more thing to check. I had a starter relay fail in such a way that the aux. output was making intermittent and/or partial contact. My symptoms where similar to the OP's. I changed the starter relay to a part number crossed over at the auto parts store. Wrong relay! It wouldn't work (the aux. terminal can be used as an exciter for a coil in some auto applications and operates in cycles)
I then ordered new from Vans and all was good again. Turns out all I would have needed to do was put the jumper back in and elliminate the separate solenoid wire. Poor troubleshooting on my end.

If you have the jumper in, all of the above is moot.
 
Mike S said:
Do you have a ground wire from the engine case to the firewall? Preferably the same bolt as you used for the battery ground.......assuming you have a firewall mounted battery.

The engine mount is NOT a reliable ground path.
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I have the starter bolted directly to the bare aluminum of the engine block. I see no way to attach another lead for grounding the starter with a separate wire. The engine block in grounded to the firewall at the same location that the negative side of the battery is attached.

N941WR said:
Dumb question Robert, but can yo turn the prop over by hand? (With the mags off.)

I know when I was out there last we were turning it over but I wonder if one of the cylinders may have filled with oil for some odd reason.
Click to expand...

I have hand propped the engine with the mags off. It is stiff but it can be turned. That was a thought that went through my mind.

I will stop the trickle charging of the battery. I don't remember reading anything about that being bad but I will do it. I will also try the "other battery" idea to see if my PC680 is the problem. Then on to checking the voltage drops and such.

THIS PLANE WILL FLY, just not today.

Thanks again.
 
I suggest that you confirm that it is the contactor/primary solenoid that is chattering. This is mostly typically caused due to the battery voltage dropping too low (9-10 volts) to hold the solenoid closed. However, it can also be caused by a failing solenoid or due to inadequate current in the solenoid activation circuit. That solenoid draws about 4 amps on the coil for activation and a bad ground or connector problem can cause resistance and inadequate current to hold the solenoid open (chatter) even when the battery has plenty of capacity.

chattering is all about the activation portion of the solenoid and is not related to the primary power path or it's ability to flow current. They chatter only if there is inadequate wattage applied to the coil to hold it open.

As mentioned by others, your starter may also have a solenoid. It is critical that you find out which one is chattering so that you can properly troubleshoot.

Larry
 
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After doing all sorts of checks on amps and volts, I found out that the starter was not grounded. I figured that the starter would be ground to the crankcase - not in this case. I ran a #2 "Van's" cable from the starter case mount to the firewall. The engine turned over like a champ.

Problem solved and thanks to everyone and all of the advice I received.

Robert
 
Does the firewall have a battery cable going to the (-) battery post? and is there a (-) battery cable going from the battery to the case? unless you have sever corrosion in the starter fasteners, the case would have provided a sufficient current path..... :rolleyes:
 
Robert M said:
After doing all sorts of checks on amps and volts, I found out that the starter was not grounded. I figured that the starter would be ground to the crankcase - not in this case. I ran a #2 "Van's" cable from the starter case mount to the firewall. The engine turned over like a champ.

Problem solved and thanks to everyone and all of the advice I received.

Robert
Click to expand...

The infamous grounding gremilin strikes again! Glad it turned out a simple fix. Pass it on to the next guy!
 
Robert M said:
After doing all sorts of checks on amps and volts, I found out that the starter was not grounded. I figured that the starter would be ground to the crankcase - not in this case. I ran a #2 "Van's" cable from the starter case mount to the firewall. The engine turned over like a champ.

Problem solved and thanks to everyone and all of the advice I received.

Robert
Click to expand...

Robert, just to clarify, you had a ground from the battery to the engine case and that was not sufficient for the starter? If so, I will need to do some checkin'. :eek:
 
Grounds and things

Electrons are negatively charged and seek the positive. The "ground wire" to the starter is where the electricity comes from to the starter. That wire and the positive wire should be the same size. The "ground wire" must be 300 mil ohms or less.
 
An OHM test of a conductor with starter current loads will not be as efficient as a voltage drop test under load, if he is saying he is loosing more than .5 VDC through the case, somewhere he is loosing conductivity through the threads of the starter or where he has a cable attached on the rear of the case to the battery?
 
BillL said:
Robert, just to clarify, you had a ground from the battery to the engine case and that was not sufficient for the starter? If so, I will need to do some checkin'. :eek:
Click to expand...

bret said:
An OHM test of a conductor with starter current loads will not be as efficient as a voltage drop test under load, if he is saying he is loosing more than .5 VDC through the case, somewhere he is loosing conductivity through the threads of the starter or where he has a cable attached on the rear of the case to the battery?
Click to expand...

Yeah, that is my question. That does not seem right unless the case/cable interface was not electrically clean. That big hunk of aluminum seems to be a pretty solid electrical unit.
 
The ground cable attaches to the crankcase at one of the sump bolts. I'm thinking that I did not remove enough paint from the contact point for a solid connection. I am planning to look at that first.

The cable from the starter relay to the starter is the same size (#2 AWG) as the cable from the crankcase to the firewall. It came in several lengths from van's in the Wiring Harness Kit.

The battery (Odyssey) negative side attaches to the firewall, the crankcase ground wire attaches at the same point. The ground wire now running from the starter case attaches to the firewall at the firewall ground tabs.

Robert
 
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Grounds are one of the most overlooked items when troubleshooting any electrical problem, with most mechanics having no idea how to properly test the circuit using the voltage drop method.

We had a Cessna185 with a 550 on our field with a persistent cranking problem. Fresh engine, new battery, new cables, new starter, etc.

Asked the owner to pull any associated panels plus the cowl and I would find the problem in 15 minutes. First we load tested the battery for its ability to supply current, then voltage drop tested the positive and negative circuits. We found a large drop on the negative circuit which was, like Roberts problem, isolated to a poor case ground. The cause was a powder coated engine mount not making contact to an engine mount isolator jumper strap. Instead of removing the isolator to clean off the coating we added an additional ground cable from the fire wall to the case solving the problem.

There was one clue that he mentioned later. The engine control cables under the panel would get hot when he would start the engine. These cables had become the ground path.

A voltage drop test would had found Roberts problem and isolated it in minutes.

Is the battery good, what is the voltage across the battery when cranking, what is the voltage across the starter when cranking, voltage difference is total lose. If excessive lose then test the positive and negative circuits, isolate area to a cause. Easy

George Meketa
RV8
 
Final findings.....

The engine ground cable connects to the crankcase at one of the bolts holding the sump. I disconnected the cable at that point, and, using my super, delux, special, way-cool, Walmart inspection mirror, I looked at that connection point. Wow, painted with virtually no bare aluminum at all. Sanded off all of the paint from the aluminum and reconnected the cable. Then I disconnected the other cable running from the starter to the firewall. The engine spun like there were NO spark plugs at all.

Mission accomplished and a very grateful THANK YOU to all of those contributors to the thread.

First engine start should happen Sunday, 10/1.

Robert
 
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