Intermittent Starter Engagement Issue

[Dad's RV-10]

My RV-7 has some kind of intermittent electrical/starter issue. It first manifested as a "click" with no starter engagement when moving the ACS key to the "start" position. I released the key and immediately tried again. The starter engaged.

I think this happened on a couple of flights on separate days (both cold starts). The third time (also a cold start), attempts to engage the starter repeatedly resulted in "click" with no starter engagement (I had flown the day prior).

The PC680 battery is about three months old. Indicated voltage on the EFIS was about 12.4v but past testing showed actual battery voltage to be 13v or better, when checked directly at the battery. In other words, EFIS indicated battery voltage is lower than the actual resting battery voltage. If memory serves, I saw the EFIS indicated battery voltage dropping while I was holding the key in the start position when the starter did not engage. After holding the key in the starter position for several seconds, the starter engaged.

It's a Skytec 149-NL starter, so there is no mechanical solenoid on the starter.

Today, I checked the battery voltage at the battery. It's 13.05v (indicates 12.3v/12.4v on the EFIS). It looks like the starter contactor is the commonly used Littelfuse ES-24021. The coil resistance is supposed to be 3.8 ohms plus/minus 5%. I checked it today (with the solenoid still installed) and saw 3.4 to 3.5 ohms. This is just outside the specification but would that be enough to cause an issue?

All of the cables and connections between the battery, master contactor, starter contactor and starter seem tight, with good integrity.

I had a friend attempt to listen for the "click" to verify if it was the starter contactor I'm hearing but the first attempt to engage the starter resulted in starter engagement just a fraction of a second after hearing the "click." Subsequent attempts resulted in immediate starter engagement.

I'm thinking it has to be either the ACS switch, the starter contactor or the starter itself.

I'm not sure what other diagnosis I can do before I start guessing and replacing parts.

Thoughts?

 

[harleyl]

We run into this from time to time on the Gulf Coast. I would try cleaning
up your ground connections really good before you start changing parts.
Also check your solenoid connections. It's cheap at twice the price...

 

[D-Dubya]

Sounds like you've done a pretty good job troubleshooting so far. Did you check the engine case ground? A loose or corroded connection between the engine and the system ground can cause symptoms similar to what you're seeing.

 

[Dad's RV-10]

Sounds like you've done a pretty good job troubleshooting so far. Did you check the engine case ground? A loose or corroded connection between the engine and the system ground can cause symptoms similar to what you're seeing.

I didn't check that specifically. I'll check that next. Thanks.

 

[lr172]

A solid, audible click with no starter spinning is about a 90% probability of a failing contactor. If it were a switch or wiring issue, there would be no clicking. An NL starter has no solenoid, so as long as it is not spinning it is not likely the problem, though there is a small chance it could be. If the bendix drive failed, you Would hear the starter spin, but not the engine. With these symptoms, and especially the intermittent nature, the universal recommendation is to replace the contactor.

Larry

 

[lr172]

Sounds like you've done a pretty good job troubleshooting so far. Did you check the engine case ground? A loose or corroded connection between the engine and the system ground can cause symptoms similar to what you're seeing.

Assuming the sensors worked on the last flight, a poor engine ground would likely result in a slow spinning starter. Though there are installations where the only device using an engine ground is the starter and in these cases a failing engine ground can go unnoticed.

 

[Richard Connell]

I like the ground suggestion.
Something else to look at.. I had an intermittent starter solenoid many years ago on my RV7. Ordered a new one, having checked all the connections etc.

When I came to replace it, it turned out that one of the nuts had actually backed off, but had arc welded itself in place. So the nut was tight, but the lug was loose.

 

[Dad's RV-10]

Thanks for the feedback. I'll replace the starter contactor and go from there.

 

[BillL]

Thanks for the feedback. I'll replace the starter contactor and go from there.

At about 40 hrs I had the same issue and connected some test wires to various places to measure voltage and get a definitive solution. At 40 hrs it was the starter contactor on the firewall. I remember holding the start position and reaching over with the other hand and connecting the volt meter - - I was sure of it at the time but, it happened again 150 hrs later and it was the starter (not your model).

https://vansairforce.net/community/showpost.php?p=1550502&postcount=16

Please take the solenoid apart and see what you find.

 

[Tim Lewis]

Sky-tec's step-by-step troubeshooting procedures are a good starting point.

https://skytec.aero/aircraft-starter-performance-issues/

I agree with Larry. Your situation sounds like a failed starter relay to me. I had a fairly new starter relay intermittently fail after a few hours. The starter relay would mechanically pull its plunger (giving the "click" noise) when I turned the key, but there was a bunch of internal corrosion on the relay's internal copper high current contacts that prevented full voltage from reaching the starter.

In my case, starter relay output voltage (as I recall) was under 2 volts in the failed condition.

 

[Dad's RV-10]

Sky-tec's step-by-step troubeshooting procedures are a good starting point.

https://skytec.aero/aircraft-starter-performance-issues/

I agree with Larry. Your situation sounds like a failed starter relay to me. I had a fairly new starter relay intermittently fail after a few hours. The starter relay would mechanically pull its plunger (giving the "click" noise) when I turned the key, but there was a bunch of internal corrosion on the relay's internal copper high current contacts that prevented full voltage from reaching the starter.

In my case, starter relay output voltage (as I recall) was under 2 volts in the failed condition.

Thanks for the link. Very helpful.

If I can get another set of hands, maybe I'll try disconnecting the starter cable from the output of the contactor and comparing the voltage across the battery to the voltage across the contactor whth the key in the start position.

But with the intermittent nature of the problem, I'm not sure that will tell me much.

 

[gasman]

Today, I checked the battery voltage at the battery. It's 13.05v (indicates 12.3v/12.4v on the EFIS). It looks like the starter contactor is the commonly used Littelfuse ES-24021. The coil resistance is supposed to be 3.8 ohms plus/minus 5%. I checked it today (with the solenoid still installed) and saw 3.4 to 3.5 ohms. This is just outside the specification but would that be enough to cause an issue?

All of the cables and connections between the battery, master contactor, starter contactor and starter seem tight, with good integrity.

I'm thinking it has to be either the ACS switch, the starter contactor or the starter itself.

I'm not sure what other diagnosis I can do before I start guessing and replacing parts.

Thoughts?

You noted a one volt drop on your EFIS..... Don't discount a bad master solenoid.

The contact paddles in a solenoid must stay parallel to the contact disc. There are two nuts on each lug. The one near the case is there to hold the lug in position. When installing a cable on the lug, you must hold that nut with a wrench so it does not move as you tighten the other nut to hold the cable.

If the lug gets turned any amount, you have degraded the capacity of the solenoid.

I use DE-OX on all of my big contact locations... including grounds.

BTW, you should have two ground cables from the airframe to the engine case.

 

[Dad's RV-10]

You noted a one volt drop on your EFIS..... Don't discount a bad master solenoid....

It's not quite a 1 volt drop. Voltage at the battery is 13.05, not 13.5. So more like .6v-.7v drop.

But thanks for the information. I'll keep it in mind.

 

[John Tierney]

I had an intermittent starter on the ACS key switch in my second year of ownership. I finally figured out it was the screw on the start wire at the ACS switch.

The screw had fallen out, but the ring terminal was still mostly making contact with the ACS switch tab, because all of the wires on the back of the ACS switch were strain relieved/bundled together. Found the screw under the carpet and reinstalled same. All better.

 

[Dad's RV-10]

I had an intermittent starter on the ACS key switch in my second year of ownership. I finally figured out it was the screw on the start wire at the ACS switch.

The screw had fallen out, but the ring terminal was still mostly making contact with the ACS switch tab, because all of the wires on the back of the ACS switch were strain relieved/bundled together. Found the screw under the carpet and reinstalled same. All better.

I would think with your situation, you'd either get starter engagement or nothing at all (no click).

Is that what you experienced, or did you hear the contactor click, with no starter engagement?

 

[kkmarshall]

Actually, the 149NL does have an integral starter solenoid. Look at Skytec manuals online for instructions on replacing the shear pin and you will see it in the exploded parts diagram. It can definitely fail to make contact from burned or eroded contacts, and can fail to actuate if the coil is open or shorted.

 

[lr172]

Actually, the 149NL does have an integral starter solenoid. Look at Skytec manuals online for instructions on replacing the shear pin and you will see it in the exploded parts diagram. It can definitely fail to make contact from burned or eroded contacts, and can fail to actuate if the coil is open or shorted.

Are you sure that solenoid provides the electrical path to the motor or just activates the plunger to move the drive? I thought it was the latter. In all my years here, I have never seen a post about a failed solenoid in the NL series. LS versions have a traditional solenoid/contactor and fail all the time. To my eye, there is not enough room in there for a traditional solenoid with large copper contacts and assumed it was a traditional solenoid to move the gear and not a combo solenoid / contactor.

 

[Dad's RV-10]

I replaced the starter contactor today with a TWD 24021BX from Napa. It's literally the same Cole Hersee/Littelfuse part as the original (now made in Mexico).

The sample size is small but I engaged the starter three times and all three attempts resulted in instantaneous starter engagement.

Hopefully, it's fixed!

 

[kkmarshall]

149NL solenoid

Yes, it has a traditional solenoid built in. If you look at Skytec’s exploded view under instructions for replacing the shear pin, you can see the contacts and the round disc that connects them when the solenoid is activated to push out the drive gear. That’s how the power from the “B” terminal gets to the external grey wire going to the starter motor. This type of solenoid uses “L” shaped copper contacts under the two studs you see externally, and the copper disc contacts them when it is pulled down to extend the gear.

 

[F1R]

Check your paint

A new engine has new paint on the cases and accessory case, where the ground is normally attached. I witnessed a new IO 390 that would crank fine on land but would not crank when the seaplane was sitting in the water.

The paint under the ground strap on the case was acting as an insulator. All it had for a ground conductor was the cross section of a 1/4" steel bolt. Scraping the paint off the case so the ground strap had face contact with the aluminum case resolved the problem totally.

 

[lr172]

Yes, it has a traditional solenoid built in. If you look at Skytec’s exploded view under instructions for replacing the shear pin, you can see the contacts and the round disc that connects them when the solenoid is activated to push out the drive gear. That’s how the power from the “B” terminal gets to the external grey wire going to the starter motor. This type of solenoid uses “L” shaped copper contacts under the two studs you see externally, and the copper disc contacts them when it is pulled down to extend the gear.

Thanks. Never knew it had one.

 

[bjdecker]

Yes, it has a traditional solenoid built in. If you look at Skytec’s exploded view under instructions for replacing the shear pin, you can see the contacts and the round disc that connects them when the solenoid is activated to push out the drive gear. That’s how the power from the “B” terminal gets to the external grey wire going to the starter motor. This type of solenoid uses “L” shaped copper contacts under the two studs you see externally, and the copper disc contacts them when it is pulled down to extend the gear.

I think you're referring to the BWD S5613 solenoid that rides "shotgun" on the starter assembly... No?

(pic)

 

[Dad's RV-10]

I think you're referring to the BWD S5613 solenoid that rides "shotgun" on the starter assembly... No?

(pic)

The 149-NL doesn't have an external solenoid as pictured above. It has an internal solenoid.

 

[Dad's RV-10]

I replaced the starter contactor today with a TWD 24021BX from Napa. It's literally the same Cole Hersee/Littelfuse part as the original (now made in Mexico).

The sample size is small but I engaged the starter three times and all three attempts resulted in instantaneous starter engagement.

Hopefully, it's fixed!

View attachment 47858 View attachment 47859

Quoting myself but I've flown the plane numerous times since replacing the contactor and all starter engagement attempts have been instantaneous.

 

[[email protected]]

If you have to replace the starter then get a B&C. They will go the life of an engine with no problems. Overhaul the starter with engine overhaul and your good for another 2,000 hours.

 

[jakej]

If you have to replace the starter then get a B&C. They will go the life of an engine with no problems. Overhaul the starter with engine overhaul and you’re good for another 2,000 hours.

I contacted B&C several years ago to get an RMA# for my B&C starter to be refurbished (@ 2038hrs) Bill (bless his soul) asked for a picture of the starter gear - after he received the picture he advised that it’s good to go & I should just keep flying it - now with 2854 hrs it’s still trucking along. Gotta love that sort of faith in a product.

 

[lr172]

The 149-NL doesn't have an external solenoid as pictured above. It has an internal solenoid.

View attachment 47931

Just for historical benefit. Only a week or two after my post questioning the presence of an internal solenoid, the one on my 6 began to intermittently fail. I posted in another thread about finding replacement parts and then replaced the the worn copper contacts and the solenoid winding module. They use Denso parts.

 

[JonJay]

Quoting myself but I've flown the plane numerous times since replacing the contactor and all starter engagement attempts have been instantaneous.

If you still have the old contractor, and want to invest a few minutes time, drill out the rivets and check out the interior. What you should find is a copper disk that makes the high amperage contact. This disk is designed to randomly rotate. If the disk gets “stuck”, it will pit and form a high resistance area on the disk.
Your symptoms were exactly this. The solenoid clicks as the disk is bought into contact, and sometimes it passes enough current, and sometimes not.

 

[Dad's RV-10]

If you still have the old contractor, and want to invest a few minutes time, drill out the rivets and check out the interior. What you should find is a copper disk that makes the high amperage contact. This disk is designed to randomly rotate. If the disk gets “stuck”, it will pit and form a high resistance area on the disk.
Your symptoms were exactly this. The solenoid clicks as the disk is bought into contact, and sometimes it passes enough current, and sometimes not.

I actually did open the contactor several weeks ago. The disk seems to rotate freely. But testing with a strong car battery, I have a repeatable failure on the bench.

When I put power to it, it activates. When I immediately put power to it a second or third time, it fails to activate. This happened when testing the contactor three days in a row.

I can see a little black discoloration on one of the pass-through lugs. Other than that, I don't see any glaring faults. But it's certainly not functioning properly, in the airplane or on the bench.

 

[lr172]

I

When I put power to it, it activates. When I immediately put power to it a second or third time, it fails to activate. T

That usually means there is a burr or wear or some other issue inside the coil area where the piston slides up and down a sleeve inside the windings. Problems in the contacts can be intermittent and often are, but rarely with this kind of regularity. It could also be a failing wire in the winding. First pull is cold and it works. After the first attempt it warms up and the break spreads apart, preventing more use until it cools down. That explains the repeatibility of your experiment.