A different kind of hot start issue - help !

[Piper_Six]

Hello folks,

1959 Bonanza, K-35, IO470C, about ~ 68 hours SMOH.

Has a Concord battery that is about a year old.

So, here is the situation. When started cold, as in after say a week or two or three, it starts up just fine, the voltage is held well, and no issues whatsoever. Fly about 45 minutes to an hour, stop and go into town, run errands and what have you, come back say 3 to 4 hours later, engine is still warm to the touch, but not very hot. This time, while attempting to start, using the standard practice, the engine goes CLICK, and doesn't crank, try a couple times, and then it cranks but won't just move the blade may be one or half a turn, or even less. Trying this a few times, now the battery voltage is lower than 12.3 V (which is what it was at start).....

I thought it was hot so went to my hot-start procedure, which for me, is mixture cut-off, throttle in, crank and when it fires, slowly put mixture in and pull throttle out... BUT it wouldn't even crank/turn over, just makes either a whining sound or a click and nothing. I have just replaced the starter adapter only a month ago ! So it can't be the adapter (?).

So, I get a power cart, and jump the battery and it cranks right up, normal procedure and starts just fine. One thing I do notice is that the AMPS draw on start-up is rather high, 30-45 AMPS for the first few minutes during taxi, and run up but stabilizes to normal at take off and normal during flight.

My question is : Can the battery be the issue ? Why only when HOT, after leaving it all night in the hangar, next morning or even a few days/weeks later it starts just fine when cold. (No trickle charger either!)

Any thoughts on what could be going ? Is the engine that much harder to crank/turnover when hot ? and repeated attempts drains the battery down ?

What could be going on here ? Thanks in advance for any insight/guidance.

 

[Jmcmanna]

Did this happen just once, or every time? If this just happened for the first time, I am wondering if your alternator wasn’t charging your battery during the flight.

 

[Piper_Six]

Did this happen just once, or every time? If this just happened for the first time, I am wondering if your alternator wasn’t charging your battery during the flight.

This is the second time it had happened, in a span of two days - hmm... but the AMPS shows positive.... meaning, not discharging, but yes you could be right, may be it wasn't charging the battery .... I'll need to check it... interesting possibility... I probably wrongly assumed that just because the amps was positive, it is charging...

 

[Piper_Six]

This is the second time it had happened, in a span of two days - hmm... but the AMPS shows positive.... meaning, not discharging, but yes you could be right, may be it wasn't charging the battery .... I'll need to check it... interesting possibility... I probably wrongly assumed that just because the amps was positive, it is charging...

The pictures shows a +ve 0.6A, which I assumed meant - battery is charging...

 

[hindsight2020]

The whining sound isn't good. Something's slipping. And you just replaced the adapter ($$$)? Ruh roh. For your sake let's hope it's just the starter that's worn out/solenoid sticking, and not the adapter already spun from it. Certain starters are known to chew up adapters in a short amount of time, also multi-grade oils make these things slip easier.

Lightweight starters seem to be no no for bigger Conti engine adapters. They wear and slip the eff out of the adapters. If you're running a lightweight starter, especially if you run low winter weight multi-grades in the engine on top of it, get rid of it and go with the clunker heavy starter (TCM Energizer). Starters are much cheaper than adapters.

 

[Piper_Six]

The whining sound isn't good. Something's slipping. And you just replaced the adapter ($$$)? Ruh roh. For your sake let's hope it's just the starter that's worn out/solenoid sticking, and not the adapter already spun from it. Certain starters are known to chew up adapters in a short amount of time, also multi-grade oils make these things slip easier.

Lightweight starters seem to be no no for bigger Conti engine adapters. They wear and slip the eff out of the adapters. If you're running a lightweight starter, especially if you run low winter weight multi-grades in the engine on top of it, get rid of it and go with the clunker heavy starter (TCM Energizer). Starters are much cheaper than adapters.

God I hope it isn't the starter adapter ($$$) again ! Yikes, yes I will check on the Oil and possibly look at a heavy duty starter... don't recall exactly which one is on it now... I will check.

 

[hindsight2020]

God I hope it isn't the starter adapter ($$$) again ! Yikes, yes I will check on the Oil and possibly look at a heavy duty starter... don't recall exactly which one is on it now... I will check.

Go check it, the cheap part of the system might be trashing the spendy part of the system.

The reason why a power cart will help you start when warm is because it will spin you faster than battery, creating the necessary additional torque on the suspect spring to still grab the engine and turn it. On battery on a warm start, the thin hot oil is exacerbating the slipping problem and the battery is not capable of compensating by turning the starter faster the way the power cart can, and make the worn spring tighten down the clearance to make it grab. At the beginning of the day the oil was cold and more viscous, not as much RPM was required to make the worn spring grab and catch the engine side, so the battery sufficed in that instance. It's basically masking the underlying damage when cold, but it rears its head when warm. That's merely a symptom, the problem would be the spring was already trashed by the lightweight starter not allowing the spring to release on starter de-energize, which shaves the spring when the engine fires (aka trashes your adapter).

The consensus on the Beech site seems to be if you had an Iskra and other lightweight type starters, and it trashed your adapter, then you put the new one back on that same starter? Even one start can damage your spring again, and here comes slipping city all over again. It's that bad for your adapter.

The recommendation of going with the clunky heavy starters is based on the ability of that starter to allow the spring to unwind backwards and disengage when the starter is de energized, due to no back-travel resistance of the armature on the clunky type starters. And I quote from BT site:

"The old-school heavyweight Delco, Teledyne, and Prestolite starters use a conventional rotating armature and fixed field winding. The armature is a set of coils wound around a central shaft. The field is constructed of a tightly wound set of coils that are fitted inside the starter motor case. The armature is connected to the field through a pair of spring loaded brushes, whose faces ride on a section of the armature called the commutator. Aircraft battery voltage is applied via the starting switch, which closes the starter relay contacts, which then carry the big in-rush of current from the battery to the brushes and onward into the armature. This current flow in the presence of the field windings produces torque causing the armature shaft to rotate rather enthusiastically, thus turning the input shaft and worm gear of the starter adapter."

The Prestolite unit falls into the category of what I call "old-school/heavyweight" starters and as such, the armature has no resistance to turning when de-energized. This design allows the old-school starter adapter spring to UNWIND freely without any undue resistance coming from the starter armature.

The wear/clearance between the adapter shaft and the grabbing spring is a critical parameter in getting a good enough grab on the shaft to swing the prop around. When this dimension/clearance grows, so does adapter slipping. It would reason that very lubricious oils with slip additives can exacerbate a spring to shaft clearance/wear issue.

Good luck man. Bos are great airplanes, it's a shame about the engine choices.

 

[Piper_Six]

Go check it, the cheap part of the system might be trashing the spendy part of the system.

The reason why a power cart will help you start when warm is because it will spin you faster than battery, creating the necessary additional torque on the suspect spring to still grab the engine and turn it. On battery on a warm start, the thin hot oil is exacerbating the slipping problem and the battery is not capable of compensating by turning the starter faster the way the power cart can, and make the worn spring tighten down the clearance to make it grab. At the beginning of the day the oil was cold and more viscous, not as much RPM was required to make the worn spring grab and catch the engine side, so the battery sufficed in that instance. It's basically masking the underlying damage when cold, but it rears its head when warm. That's merely a symptom, the problem would be the spring was already trashed by the lightweight starter not allowing the spring to release on starter de-energize, which shaves the spring when the engine fires (aka trashes your adapter).

The consensus on the Beech site seems to be if you had an Iskra and other lightweight type starters, and it trashed your adapter, then you put the new one back on that same starter? Even one start can damage your spring again, and here comes slipping city all over again. It's that bad for your adapter.

The recommendation of going with the clunky heavy starters is based on the ability of that starter to allow the spring to unwind backwards and disengage when the starter is de energized, due to no back-travel resistance of the armature on the clunky type starters. And I quote from BT site:



Good luck man. Bos are great airplanes, it's a shame about the engine choices.

Thank you... that's some very good insight and thank you for the reference from Beechtalk as well... very informative, what you describe is probably highly likely, I will share the message with my A&P right away ! Thank you.

 

[Pilot Steve]

I have no magic answer for you but I did just recently replace both an alternator and a starter. I removed a lightweight SkyTec starter and replaced it with a beefy Hartzell starter and it has changed my starting world. No more struggling to start.

I'm sure your A&P will get you fixed up but if your battery is easy to access and you have a cheap voltmeter it would be interesting to see what the battery voltage is before you attempt to start. That would rule out potentially half your problem.

 

[Piper_Six]

I have no magic answer for you but I did just recently replace both an alternator and a starter. I removed a lightweight SkyTec starter and replaced it with a beefy Hartzell starter and it has changed my starting world. No more struggling to start.

I'm sure your A&P will get you fixed up but if your battery is easy to access and you have a cheap voltmeter it would be interesting to see what the battery voltage is before you attempt to start. That would rule out potentially half your problem.

Thanks... will do.

 

[charlie]

The only scenario not discussed here is inadequate main bearing clearances. If for whatever reason the case was assembled with fretting in the bearing saddles. This could happen if the case was not overhauled in spite of existing fretting or developed the fretted condition after assembly. When hot the crank is pinched by the bearings and the starter does not have the power to provide the necessary breakaway torque. Once the engine is running having started cold the additional drag is not enough to slow the engine. It will lead to a spun bearing. I would do a comparative check or breakawaway torque hot vs cold. Withe 6 plugs removed to eliminate compression from the equation pick a blade and compare the force necessary to start the blade moving hot vs cold. Once the blade is moving the difference in the torque needed to continue rotation will be much less. Your symptoms fit the profile for this EXCEPT for the intermittant whirring noise which would be starter or clutch problems.

 

[Piper_Six]

The only scenario not discussed here is inadequate main bearing clearances. If for whatever reason the case was assembled with fretting in the bearing saddles. This could happen if the case was not overhauled in spite of existing fretting or developed the fretted condition after assembly. When hot the crank is pinched by the bearings and the starter does not have the power to provide the necessary breakaway torque. Once the engine is running having started cold the additional drag is not enough to slow the engine. It will lead to a spun bearing. I would do a comparative check or breakawaway torque hot vs cold. Withe 6 plugs removed to eliminate compression from the equation pick a blade and compare the force necessary to start the blade moving hot vs cold. Once the blade is moving the difference in the torque needed to continue rotation will be much less. Your symptoms fit the profile for this EXCEPT for the intermittant whirring noise which would be starter or clutch problems.

Certainly, this is something that has not been talked about, I will pass this along and see what he says. Thank you !

 

[flyingcheesehead]

What kind of oil are you using?

I've seen Aeroshell eat up a brand new starter adapter in less than six months. Not just any Aeroshell, but the 15-50 and the "Plus" oils (like W100 Plus) will do this due to the anti-scuff additive that is in their additive packages.

If you have a Continental, don't run oils with the anti-scuff - I believe that's down to just the Aeroshell 15-50 and Plus oils now that Exxon Elite is no more. What you want is Phillips XC 20W-50, with Camguard added (which makes up for Phillips' additive package otherwise not being as good as Aeroshell's). I've been running that combo for nearly a decade now, no starter adapters or other oil-related issues whatsoever.

 

[Piper_Six]

Folks, thank you for all the comments and suggestions. Here is an update....

This morning, after 4-5 days, it started right away, just fine, not an issue. And flew about an hour to go see my Son at KMDQ, (from KEKY). It was rather unusually cold (early) morning, about 45 degrees, and it started just fine, the voltage was full at 12.4V on startup. On hooking up a trickle charger it showed 98% full, and by the time I got some preflight items and doors done, it was at 100%. At KMDQ, after landing, went away to run errands and came back to the airport at around 2:30 PM, engine felt very cool, it had cooled off, and again started just fine.

Flew back to home base KEKY, and parked in front of my A&P's shop, shut down and tried restarting in 20 minutes... no joy ! Again that whining sound and click, blade did move a little but then not much after a couple tries. With the cowl open, and A&P looking at the starter, tried engaging the starter, and interestingly, he noted that the whining sound seems to originate at the starter relay(s), there are two. (Incidentally, the cables are all brand new bogart cables that I replaced not too long ago. Also, it is a 1 year old concord battery and a beefy energizer starter, with a month old starter adapter.)

I had him hold a phone and recorded the sound... I will try and upload the short video clip and also some pictures. He seems to think it is these starter relays that may be the issue. It is a m4v file, not sure if it will upload.

Would appreciate your thoughts and comments.

 

[Piper_Six]

Trying to upload a few pictures... video won't load. The relay on top is where the A&P suspects the whining noise is coming from.

 

[Dan Thomas]

Those are tired old contactors. Get the mechanic to take voltage drop readings across the master and starter contactors. Voltage DROP, not straight voltage readings. The voltmeter gets connected to the big terminals on the contactor, with the negative lead on the terminal that feeds the aircraft system or starter, as applicable. Master contactor first: with the master off, the voltmeter should show battery voltage; the ground path will be through the turn coordinator. If it reads nothing, turn a landing light on. With the master on, the voltage should drop to zero as the contactor's contacts close, forming a short across the voltmeter leads. If you see voltage with the master on, the contactor is shot. I would replace it if the voltage was more than 0.1 volt with all the landing lights on.
Next, the starter contactor. With the master on, the voltmeter should show battery voltage. When cranking, it should drop to zero. If you see any voltage, replace the contactor. Whatever voltage you see across the contactor is voltage the starter isn't getting. Go back and see what the voltage drop at the master is when cranking.

Contactor contacts get burned every time they open. They're copper, which means they oxidize over time. Both factors introduce resistance, and with large current flows, like starter current, it takes only a tiny fraction of an ohm to cause starter problems. Many batteries, and many starters, have been replaced just because an comparatively inexpensive contactor was shot.

Ohm's Law: E=IxR. Voltage equals current times resistance. That starter draws hunderds of amps. Let's say it draws 300 amps at 12 volts. If we see a three-volt drop across the contactor, which is VERY bad, it means that the contactor has an internal reistance of 0.01 ohms. Like I said, a tiny fraction of an ohm can cause lots of grief.

For some reason, this sort of stuff isn't covered nearly well enough in mechanic training.

 

[Piper_Six]

Thank you Dan,

I checked the drop across the main (master) relay, and it does exactly as you say - shows full battery voltage with master switch OFF, and drops to Zero with the master ON.

I couldn't access the starter relay, and kick the starter switch (was alone)... BUT I noticed something - with the master switch OFF, I measure between the hot end (meaning, where the battery is hooked up) of the main master relay and the starter cable at the starter.. it showed full battery voltage (12.6V) ... Does this mean the +ve is always ON at the starter ? Somehow this seems odd ?

 

[Let'sgoflying!]

Contactor contacts get burned every time they open.

I see no diodes

 

[Snowmass]

I have not had time to go through all the replies but if your engine is similar to my IO-520 than your starter drive uses a coil of spring wire that grabs a drum in order to crank the engine. Kind of like a Chinese finger vise. When this assembly becomes worn it sips and the starter spins but the engine does not crank. This is a common problem; I had it. Cold oil has more friction than hot oil so a warm engine may experience more slipping.

The solution is cheap is airplane stuff goes. Contact Niagra Air Parts for the solution. The're experts.

 

[Dan Thomas]

Thank you Dan,

I checked the drop across the main (master) relay, and it does exactly as you say - shows full battery voltage with master switch OFF, and drops to Zero with the master ON.

I couldn't access the starter relay, and kick the starter switch (was alone)... BUT I noticed something - with the master switch OFF, I measure between the hot end (meaning, where the battery is hooked up) of the main master relay and the starter cable at the starter.. it showed full battery voltage (12.6V) ... Does this mean the +ve is always ON at the starter ? Somehow this seems odd ?

That's normal. You're energizing the meter by connecting to the hot line, which is battery +, and the starter terminal, which is much less than one ohm to ground. That starter draws a lot of current, and to do that its resistance has to be very low, so the meter sees it as pretty much no resistance at all.

The starter's tiny resistance lets the tiny current required to make the meter read without any discernible voltage drop. This is how mechanics get fooled sometimes, like I did once, many years ago. The strobe on a 172 wasn't working. No flash. I disconnected the power lead at the strobe and measured the voltage between it and ground, and saw battery voltage. All is well with the power line, right? Ha. I installed a new strobe power supply ($300) and still no flash. Now I had to start thinking. Still saw battery voltage if I pulled the plug off the strobe supply box and measured it, but I stuck a pin through the insulation on the power wire and plugged it back in and measured the voltage at that pin. Nothing. The real problem was a worn-out circuit breaker, with badly oxidized contacts. It would pass enough current, a few microamps, to satisfy the meter, but not enough to get the strobe to work. The strobe's power supply resistance was low enough to drop the voltage at the input to practically nothing when it was plugged in..

 

[Dan Thomas]

I see no diodes

If the airplane's schematic shows it, there should be a diode at the master terminals. Not all airplanes had it. Solid-state diodes in 1959 were massive, high-resistance selenium things with big square cooling fins, not the compact tiny silion diodes we're used to seeing now. I ran into those old diodes when fixing
old TVs and radios in the late '60s/early 70s.

If the airplane has an ACS ignition switch with a Start position, it should have a diode at the starter contactor. If it has a Bendix switch, that diode is not required. AD 93-05-06:
https://rgl.faa.gov/Regulatory_and_...B8ABD56539B4684886256A3E00759DBF?OpenDocument


The diodes didn't protect the the big contacts in the contactor. The master diode suppressed the voltage spike from the contactor coil when the master was turned off to prevent it getting into the bus and maybe some expensive electronics as the contactor was much slower to open than the spike was to zip through the system. The starter contact diode was to prevent that same coil spike from burning the contacts in the ACS switch, which shared a contact plate with one of the magneto circuits.

 

[Piper_Six]

Thanks, that is good to know ! So as for the master relay, based on that test, it is functioning okay, but still better to replace it I think since it is worn and old....

 

[Piper_Six]

Hmm... vaguely recall a concept I think was called "back EMF" from relay coils, and needed a diode to prevent this back current...something similar in concept I think. I used to "dabble" with electronics way way wayyyy back but then "life" got in the way, and I got left behind when digital circuits came around.... I am talking building with vacuum tubes, RF oscillators with EL-84 and 2-807s in final with 600VDC on the plate ! for amateur radio... those were the days... I can't figure out the simplest darn thing anymore !

 

[Doug Reid]

Go back and read your first post again. You jumped the battery and it started like normal...what would be the lesson you learned here ?

 

[Piper_Six]

Yes, I hear you, but my thoughts were that, because I kept trying a few times to start, the battery by then had drained substantially, and by now, the engine / oil had also cooled down substantially ? Just thinking out loud. What is intriguing is that if it is just the battery (being weak), it starts just fine after a few days of not flying. The issue seems to be when it is a hot start after landing and trying to start up again in say 20 minutes to an hour or so...

 

[PaulMillner]

multi-grade oils make these things slip easier.

Not multigrades... multigrade oils are fine. But the TCP/TPP additive in Shell's 15/50 or plus branded single grades, or Phillips new Victory oils, are bad news for Continentals.

 

[Piper_Six]

Finally managed to get a video clip uploaded .... listen with the sound turned up. My A&P says the sound seemed to be coming from the master/starter relay and not the starter ....

 

[PaulS]

Weak battery, bad connection, bad relay or bad starter. Start with the battery, have it load tested. Repeatedly cranking it when it is in that state really isn't good for anything.

I agree that when you jump start it cranks right up is a big clue pointing to the battery, start there. It's been two weeks..... time to do something, start simple, battery.

 

[Dan Thomas]

Go back and read your first post again. You jumped the battery and it started like normal...what would be the lesson you learned here ?

Even that idea should be tested before spending money. A voltage reading taken at the battery to see how much the voltage falls during cranking. It could drop to 8 or 9 volts, maybe, but a bad battery will fall further than that.

Us old guys used to diagnose car startin g problems with the headlights. Turn the headlights on and crank the engine. If the headlights dimmed way down, the battery was bad or the battery connections were bad. If the headlights didn't dim much and the engine didn't crank properly, there was a problem with the starter or its contactor or related connections.

Like I've said before, too many starters and batteries are replaced based on quick assumptions. And then, with the new battery and/or starter, money still has to be spent to find the real problem. Better to spend that up front.

 

[Dan Thomas]

Not multigrades... multigrade oils are fine. But the TCP/TPP additive in Shell's 15/50 or plus branded single grades, or Phillips new Victory oils, are bad news for Continentals.

Only sometimes. We never had any issues with it, in numerous airplanes. I agree, though, that it can reduce friction enough to allow slippage, even in the small Continentals. They have a friction overrunning clutch.

 

[Dan Thomas]

Finally managed to get a video clip uploaded .... listen with the sound turned up. My A&P says the sound seemed to be coming from the master/starter relay and not the starter ....

Falling voltage will cause a buzz like that, or often a chatter. The voltage falls far enough that the coil starts losing its pull, the contacts open, the voltage rises, the contacts close, the voltage falls, the contacts open, the voltage rises......repeat endlessly many times per second. Either the battery or maybe the master contactor. Some educated probing with the voltmeter will find it.

 

[Dan Thomas]

Hmm... vaguely recall a concept I think was called "back EMF" from relay coils, and needed a diode to prevent this back current...something similar in concept I think. I used to "dabble" with electronics way way wayyyy back but then "life" got in the way, and I got left behind when digital circuits came around.... I am talking building with vacuum tubes, RF oscillators with EL-84 and 2-807s in final with 600VDC on the plate ! for amateur radio... those were the days... I can't figure out the simplest darn thing anymore !

The voltage spike from the coil is caused by the rapidly collapsing magnetic field in the coil when the current is cut off. The collapse generates a big voltage spike. It's the same principle a magneto or ignition coil uses to generate the spark voltage in the secondary winding.

I'm with ya on the modern digital stuff. Except that it's NOT simple at all, or we would be able to fix it. It's unbelievably complicated, unbelievably miniaturized. I was impressed in high school with the size reduction between a vacuum pentode and a transistor. Now my laptop has millions of transistors in it.
Maybe our inabilities to understand the modern stuff is due to the many plate voltage jolts we got when fixing stuff. I was hammered more than once by TV flyback voltage. Everything hurts for a long time.

 

[Snowmass]

I am having trouble following all the paths this discussion is taking. To eliminate all relay stuff simply disconnect the starter wire from the relay and connect directly to jumper cables connected to your auto battery. If the starter turns the prop then trace the wiring. But, a whining sound means that the starter is turning but the engine is not so this can only mean a slipping starter clutch. A bad relay might click or arc but this is not whining. The starter clutch/spring may not have been to new specs, I.e. bad rebuilds, I replaced the spring on my clutch but it started slipping again so I got a rebuilt one from Niagra. No problems regardless of oil, temperatures or additives since.

.

 

[Dan Thomas]

I am having trouble following all the paths this discussion is taking. To eliminate all relay stuff simply disconnect the starter wire from the relay and connect directly to jumper cables connected to your auto battery. If the starter turns the prop then trace the wiring. But, a whining sound means that the starter is turning but the engine is not so this can only mean a slipping starter clutch. A bad relay might click or arc but this is not whining. The starter clutch/spring may not have been to new specs, I.e. bad rebuilds, I replaced the spring on my clutch but it started slipping again so I got a rebuilt one from Niagra. No problems regardless of oil, temperatures or additives since.

.

The A&P traced the whine to the starter contactor, not the starter itself or the starter drive. I've heard contactors chatter and whine (buzz) before.

Using jumper cables confirms that the starter is OK. It doesn't tell you where, in the entire circuit, the trouble is. A voltmeter does that.

 

[Snowmass]

Buzz yes, but I would not call this a whine. if the voltage is too low and also chatter. Contactors should be cheap especially if you use automotive. You are lucky. Of course this does not explain why only a hot start problem.

 

[Dan Thomas]

Buzz yes, but I would not call this a whine. if the voltage is too low and also chatter. Contactors should be cheap especially if you use automotive. You are lucky. Of course this does not explain why only a hot start problem.

Hot start issues can occur with contactors. The master has been carrying alternator current and can heat up some, especially if its contacts are burned or corroded and there is some resistance. The starter contactor is always located near the starter, so is in the engine compartment and gets plenty warm.

The contacts in a common contactor consist of copper bolts with square heads, and square shoulders. The bolts go into the contactor case from the inside, through insulators. The square shoulder goes through a square hole in the insulator, and the insulator has a square shoulder that goes into square holes in the case. All this to prevent rotation of the bolt. The battery or starter cables go onto the bolts. The top sides of the bolt heads (inside the case) are contact faces, and a round disc of copper, attached to a steel slug, makes contact when the steel slug is pulled into the coil. When all of this burns and wears, the surfaces on the bolt heads get eroded so that the disc ends up fitting into a depression, and its sides can either get hung up on the edge of one of the depressions on the bolt, or it can stick in the depression. The disc heats up and expands, either from ambient heat or by carrying large currents, and will hang up on an edge (poor contact) or stick between the ledges on the two bolts (hung starter). When a mechanic removes or installs the battery or starter cables he can inadvertently rotate a bolt a little bit, leaving the disc contacting only a corner of the bolt head More poor contact, more heat and burning.

 

[Nathan Miller]

Mike Busch addresses this very issue in his AOG webinar. Eerily similar. Check it out below - start at the 24 min mark and watch until at least the 28 min mark.

Watch "AOG! Dealing With Breakdowns Away From Home" on YouTube

 

[Piper_Six]

Many thanks y'all, I have a set of Master Relay and Starter Relay ordered, plus a new Concord battery - expected to arrive this week, will replace them all and report the results. Thank you all for some very enlightening suggestions.

 

[Dan Thomas]

Many thanks y'all, I have a set of Master Relay and Starter Relay ordered, plus a new Concord battery - expected to arrive this week, will replace them all and report the results. Thank you all for some very enlightening suggestions.

While you're at it, check all the ground connections, the engine/mount/firewall being especially critical. I prefer to do this with the volmeter, since it involves less dirty work based on speculation and guessing. Positve lead on the starter case (not terminal), negative on the firewall, and crank. Any voltage at all indicates a resistance in the grounding.

Old airplanes are fun. Age takes its toll. Just ask any old guy here. I just wish a couple new contactors and a new battery would make me 25 again.

 

[PaulS]

Yup, and check means look for loose connections, then white and green crusties (corrosion). Clean and tighten if you find any.