Slowish crankage

455 Bravo Uniform

455 Bravo Uniform

Final Approach
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Aug 18, 2015
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455 Bravo Uniform
Background:
-For months, engine cranked one stroke, pauses, then resumes spinning, and fires up within 1-2 revolutions, when cold.
-Last month, engine won’t turn when hot/ already flown.
-This month, only cranked when cold AFTER being on the battery minder.

-Ammeter showed 2/3rd to 3/4 scale deflection after start, then calms down after long idle and in flight.
-Voltage showed 14.1 while running.

-The one part I “threw” at it was a new battery this month for Oshkosh.
-Same symptoms when cold (one stroke, pause, resumes cranking); Hot start is good now.

So trying to diagnose, here is the data:
-Master off 13.10v at battery
-Master on 12.38 at battery
-After a few rounds of cranking and 10 minute rest, master off, 12.82 at battery

-Battery side of solenoid 12.23
-Battery side of solenoid when cranking:
-momentary 6.5-7.0 at the very beginning of the crank
-then 9.3-9.7 through the rest of the revolutions

-Supply from solenoid to starter was hot to the touch (about 30 seconds of crank-stop-crank-stop-crank for data gathering).
-Connections were tight

-Starter side of solenoid while cranking 8.6-9.25

-Didn’t think about checking voltage on the starter end of the cable.

So what do you guys think of these voltage drops along the path? I’m thinking in the following order from cheap to expensive:
-Replace supply line from solenoid to starter with heavier gauge.
-New starter solenoid if symptoms persist.
-Rebuild starter if symptoms still persist.
 
First thing is to clean the ground from the engine case to the airframe, and then the battery ground. After that, clean the connections between the battery and the starter itself. Verify that all of those cables ohm out at less than .5 ohms before anything else. If you don't have a ground wire from the engine case to the fuselage, that may be the culprit.
 
Troubleshooting it yourself is cheap and can isolate the problem. Take voltage drop measurements across the cables, the contactors, the ground straps at the engine and battery. With the master on, you clamp the voltmeter leads on each side of a cable or contactor, for instance, with the red lead on the battery side and the black on the engine side, and crank. Before cranking you will see battery voltage. That should drop to zero during cranking. If the meter says a volt or two, you have a bad contactor or cable. If you're checking the engine ground strap, the red lead goes toward the engine side and the black to the airframe side. Battery strap, red goes to airframe and black to battery.

You will likely find a series of smallish voltage drops that add up to a serious drop. Contactors especially suffer from contact oxidation and burning. Ohm's Law always applies: If the contactor is carrying 250 amps to the starter, and its contacts present a resistance of 0.02 Ohms, a tiny resistance, you get a 5-volt drop. That's serious stuff, from a small resistance. It means that the starter gets 7 volts instead of 12, and it gets lazy.

A lot of money is thrown at new batteries and starters for no good reason. Often it's just a $40 contactor. Remember that starter current travels through both the master and starter contactors. When they're both old? Trouble. Cables are often made with crimp terminals that oxidize inside the terminal. Ground straps are just crimped and get contaminated with oil and crud. Grounding points get corroded and dirty.
 
On a Conti? Starter adapter? Hope not, for your sake.
 
Don’t replace your starter immediately, but mine was worn out after 60 years of use and required an overhaul. Same symptoms, so I took off the starter and replaced brushes (totally worn out) and bushings and it all worked great after.
 
I’ve had excellent results in cranking speed after installing bogart cables. Done this on three airplanes now. All with noted improvement. The Cessna kit adds a ground cable to the starter as part of the STC, similar to piper. This way you don’t have to worry about the ground trying to make it from the engine mount all the way up to the starter. Excellent improvement.
 
I had exact same symptoms. Cleaned all cables/connections and was marginally better. Replaced starter and it's never started better in my three years of ownership.
 
Brushes in starter. Replace them. I know, it's an airplane, not a ford tractor. But the starter works the same way. Take the starter to your local rebuilder, and get it fixed. In the meantime, make certian all cable connections are clean.
 
bluerooster said:
Brushes in starter. Replace them. I know, it's an airplane, not a ford tractor. But the starter works the same way. Take the starter to your local rebuilder, and get it fixed. In the meantime, make certian all cable connections are clean.
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Yep, tell them it is a tractor starter if they ask and have strict policies. My old Delco starter is one part number away from a common tractor starter motor.
 
Hang 4 said:
I had exact same symptoms. Cleaned all cables/connections and was marginally better. Replaced starter and it's never started better in my three years of ownership.
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And I bet that with new contactors it would start even better.
 
Matthew Rogers said:
Yep, tell them it is a tractor starter if they ask and have strict policies. My old Delco starter is one part number away from a common tractor starter motor.
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Yep, your starter is not a tractor starter, but a 6 cylinder Chevy starter. Matters not, they all work the same way.
 
Alternators as well. Mine was OH'd by a local shop that I'd been doing business with for 25 years. When my alternator went south, the A&P/I told me to take it to xxx shop, and while I was there pick up the one for another of his customers. It turns out that it was the same shop that I'd been using for many years, for various starter/alternator repairs. (I got a discount by using my shop name :D)
 
@455 Bravo Uniform - is yours a Continental?

If its a O470 I would really limit any hours flown while troubleshooting the electrical and starter in case its the adapter. Your symptoms almost exactly match ours.

My mechanic just finished our adapter repair. $2k for adapters parts and labor alone. I don't even have the bill for needing to move motor to get at it.. Would have been about half that had I know what was happening.

For possible starter adapter problem I would augment:

1. Drop oil right away and look for metals. No metal doesn't mean it hasn't went out, but its not in the motor yet.

2. When the starter is off make sure the little adapter coupling turns like it should.

3. Take all tension off the alternator belt and verify the drive pulley isn't wobbling or can push in our out. Also make sure the seal isn't starting to push out.

4. Only turn the prop forward when trying things. The adapter doesn't like being turned backwards.

5. If you have the new style adapter the spring is designed to fail right away which saves you lots in other parts.

6. You want to catch this issue early as the adapter shaft alone is probsbly pushing $2k. Ours was so bad we needed a new adapter cover but somehow the shaft was still within spec.

Hope its something simple instead!
 
Yours sounds a lot newer so probably the newer adapter and much easier to pull out if needed. Sorry, hopefully worried yiu for nothing. Just trying to save from bigger problems if you can catch it sooner. Its probably something dumb like a cable
 
Dan Thomas said:
And I bet that with new contactors it would start even better.
Click to expand...

Yep, in addition to the new cable kit, I put new contactors on also. The old ones were working but looked horrible. Everything helped.
 
When your prop pauses do you still hear the starter spinning? If not I'd guess it's not the adapter.

I recently had the joy of replacing my starter adapter on my io-520. It actually wasn't bad at all. Took me 2 hours start to finish and I bout an overhauled unit from Niagara so under a grand I was all in. My mechanic sat there and watched me. Luckily in my bonanza I have lots of room back there so no need to pull anything to get it out, just the starter.
 
Sinistar said:
@455 Bravo Uniform
4. Only turn the prop forward when trying things. The adapter doesn't like being turned backwards.
Click to expand...
If the starter drive is working properly it disengages and the prop can be turned freely backward. It's a curious setup that uses a big, tightly coiled, square-wire spring that fits tightly in a sleeve and closely over the shaft. The starter turns one end of the spring, which doesn't want to turn because it's in that sleeve, so it tightens inward and grabs the shaft and turns a gear that spins the crank. The usual trouble with those is a worn shaft or spring so the starter spins but the prop hesitates.
 
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simtech said:
When your prop pauses do you still hear the starter spinning? If not I'd guess it's not the adapter.

I recently had the joy of replacing my starter adapter on my io-520. It actually wasn't bad at all. Took me 2 hours start to finish and I bout an overhauled unit from Niagara so under a grand I was all in. My mechanic sat there and watched me. Luckily in my bonanza I have lots of room back there so no need to pull anything to get it out, just the starter.
Click to expand...

No, it just pauses
 
455 Bravo Uniform said:
No, it just pauses
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What kind of starter is it and when was the last time it was overhauled? I just went down this path...slow cranking and hard hot starts. New to me plane, I sent my starter (energizer) out to modified aircraft accessories and came back like new. Slow starting was gone but my lack of hot start led me to ruin my adapter. I got a rebuilt adapter, a solid hot start procedure, and everything is working great now.

Not saying that's your problem just laying out what mine was. For me it's always the more expensive route. Hahaha ugh
 
simtech said:
What kind of starter is it and when was the last time it was overhauled? I just went down this path...slow cranking and hard hot starts. New to me plane, I sent my starter (energizer) out to modified aircraft accessories and came back like new. Slow starting was gone but my lack of hot start led me to ruin my adapter. I got a rebuilt adapter, a solid hot start procedure, and everything is working great now.

Not saying that's your problem just laying out what mine was. For me it's always the more expensive route. Hahaha ugh
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It’s a “stock” starter. I’ll need to check the log book to see when it was last changed/rebuilt.

You guys have all given me some good input, thanks. Will post back with each iteration.

The short cable from the contactor to the starter being hot to the touch, but not the cable at the battery/hot end is interesting. Gonna look at that next, as it’s least intrusive, costly, and quickest.
 
Maybe I missed it, what type of airplane?
 
Ok, if the wiring is anything like a 172, the extra (starter direct) ground STC from Bogart will do wonders. I’ll see if I can find a pic of one that I installed.
 
455 Bravo Uniform said:
The short cable from the contactor to the starter being hot to the touch, but not the cable at the battery/hot end is interesting. Gonna look at that next, as it’s least intrusive, costly, and quickest.
Click to expand...
Take a voltage drop reading across that cable. Probably see something significant. You might try to see which end it is by putting the test leads on the cable wire itself and the crimped terminal; could be oxidation between the wire and terminal offering resistance. Cutting that terminal off and crimping a new one onto a fresh section of cable can fix it. Running solder into the joint makes it a lot more permanent by keeping oxygen and oil and water out.

The interface between the terminal nuts and cable ends at the contactor and starter can get corroded as well.
 
I was troubleshooting a slow starting Seneca. Looking at the cable between the solenoid and starter, it just looked odd. Metered it and it showed a big voltage drop. Removed it and it was 'crunchy' and had a small bump in the middle. Opened up the insulation and it was powdery inside. The bump was the worst bit. Aluminum wire rearing it's ugly head!
 
Dan Thomas said:
If the starter drive is working properly it disengages and the prop can be turned freely backward. It's a curious setup that uses a big, tightly coiled, square-wire spring that fits tightly in a sleeve and closely over the shaft. The starter turns one end of the spring, which doesn't want to turn because it's in that sleeve, so it tightens inward and grabs the shaft and turns a gear that spins the crank. The usual trouble with those is a worn shaft or spring so the starter spins but the prop hesitates.
Click to expand...

newer adapters will turn the starter motor if the propellor is turned backwards. Ours does this. The Standard Practices Manual says to remove the starter motor if desired when timing magnetos.
 
I promised I’d get back to you all. Here is what I ended up with:

5371F57C-2392-4BFE-BF84-84A277716FE9.jpeg

In addition, with the starter end of the starter contactor cable disconnected and turning the starter key, I get a 0.2v drop from the input side to the output side of the starter contactor and another 0.03 loss from the output side to the end of the cable.

Talked to my local avionics guy and a trusted A&P. They think it’s probably a starter issue drawing so many amps. They are going to put a meter on it to check the amp draw through the line at my annual next month. In the meantime, replacing the cable is a quick and cheap option.
 
A .2V drop with essentially no amperage draw (you said the power lead to starter was disconnected) across the starter contactor seems pretty significant to me. If you just measure the resistance across the contactor with nothing connected at input or output side (with key in start position), what are you seeing (and repeat across several cycles of the key as the contactor disc turns each time it’s cycled). As Dan mentioned earlier, relatively small resistance compounds to large voltage drops at the amperage levels of a starter.
 
Ryan Klems said:
A .2V drop with essentially no amperage draw (you said the power lead to starter was disconnected) across the starter contactor seems pretty significant to me. If you just measure the resistance across the contactor with nothing connected at input or output side (with key in start position), what are you seeing (and repeat across several cycles of the key as the contactor disc turns each time it’s cycled). As Dan mentioned earlier, relatively small resistance compounds to large voltage drops at the amperage levels of a starter.
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Exactly. The voltmeter should show NO voltage drop with no load on the system. It takes current flow to make a voltage drop. Ohm's Law. That voltmeter doesn't draw enough to create a measurable drop across a contactor with no current flowing through it, unless the contactor is really, really bad. It shouldn't even run the starter.

The diagram shows a 0.6 volt drop across the starter contactor when cranking. That's not good at all.

The 0.8 volt drop across the starter cable does not match up with 0.3 ohms resistance. 0.8 volts divided by 0.3 ohms is only 2.7 amps. A starter draws a hundred times that.
 
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