disconnect battery when changing oil?

NoHeat

NoHeat

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Is it a common practice to disconnect the negative terminal of the battery when changing oil?

My shop did this, and I'm wondering if that is part of the usual routine.
 
brian];1652443 said:
Whatcha flying? Might make a difference.
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:yeahthat:

I'd ask the shop why they did that. Might be something as simple as the battery cable's in the way of getting to the oil filter. In other cases, it might be a shop safety rule to disconnect the battery whenever anyone is working inside the engine compartment. But I personally don't do that on my Tiger when I change the oil and filter.
 
Are there any service manuals that include that particular instruction?
 
It's not common practice. I'm pretty sure they did that so the engine could not be started while the oil was out, and/or while the mech was working around the prop.

I don't like working forward of the wing with two people, so I might disconnect the batt terminal if someone is going to be up there a lot.
 
not common practice....but, I like it.

No one can start it until that lead is connected.....hopefully oil is added too. :D
 
Checkout_my_Six said:
not common practice....but, I like it.

No one can start it until that lead is connected.....hopefully oil is added too. :D
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Um... swing the prop and find out how the battery doesn't matter in most GA airplanes. I wouldn't let a disconnected battery lull me into any feeling of safety around the prop. Pull the mags or the plugs and I'm happier.

That said, however, disconnecting the battery is pretty much a standard item in auto maintenance; just about every shop manual since the early nineties starts off each maintenance activity under the hood or anywhere on the electrical system with "Disconnect the battery ground" or something similar.

Might just be becoming a standard practice in aviation shops too.
 
care to tell the class how SOS works? :D

BTW...I don't think anyone was advocating that this improved safety....just inadvertant running the engine with no oil.
TMetzinger said:
Um... swing the prop and find out how the battery doesn't matter in most GA airplanes. I wouldn't let a disconnected battery lull me into any feeling of safety around the prop. Pull the mags or the plugs and I'm happier.

That said, however, disconnecting the battery is pretty much a standard item in auto maintenance; just about every shop manual since the early nineties starts off each maintenance activity under the hood or anywhere on the electrical system with "Disconnect the battery ground" or something similar.

Might just be becoming a standard practice in aviation shops too.
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Checkout_my_Six said:
BTW...I don't think anyone was advocating that this improved safety....just inadvertant running the engine with no oil.
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No, I was advocating the safety aspect as well as the protection of the engine. Pretty much no one would swing a prop with another worker in the arc. Well - some people are completely stupid, and I can see where it could happen, but the probability in comparison to an accidental bump of the key or start button is so low as to be incalculable. Of course, the counter to that is all the reports of people getting hit by a prop while someone ELSE is swinging it.

Beuller?
 
docmirror said:
No, I was advocating the safety aspect as well as the protection of the engine. Pretty much no one would swing a prop with another worker in the arc. Well - some people are completely stupid, and I can see where it could happen, but the probability in comparison to an accidental bump of the key or start button is so low as to be incalculable. Of course, the counter to that is all the reports of people getting hit by a prop while someone ELSE is swinging it.

Beuller?
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If you're after added safety....for ground handling the prop....better add more ground straps to the P-leads of each mag....to insure they're both well grounded.

or....removing a plug from each cylinder would have that same affect. :yes:
 
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Checkout_my_Six said:
If you're after added safety....for ground handling the prop....better add more ground straps to the P-leads of each mag....to insure they're both well grounded.

or....removing a the plug from each cylinder would have that same affect. :yes:
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Actually, except for one outlier, we're not handling the prop. We're changing oil. There's no reason I can think of for anyone to swing the prop except at the start of the job to get it out of the way. Like I said, there are no bounds to stupidity, so what about the time needed to remove a plug, or take a P lead off? Surely, someone could swing the prop during that time.

Reducto ad absurdem is always fun. Stay in bed, under the covers and your chances of getting hit by a prop are reduced significantly. I was just trying to answer the OP question with a modicum of everyday logic.
 
I don't believe disconnecting the minus cable of the battery is unrealistic, (safety wise) but it is one more thing that can be screwed up by the one doing it.
 
Is it not a remote, but real, possibility that a dropped tool could short out the starter solenoid and start the prop turning at an inopportune moment?

I thought that was the main reason to disconnect the battery.

Was there not an incident not too long ago of a plane accidentally starting during maintenance and causing a lot of damage?
 
Sounds like a good practice even if not required.

Our A&P fired a Cherokee up after replacing some jugs. Yep. No oil. Start over. That one cost him.

Stuff happens.
 
There was an incident a several years ago (in Idaho?) where a tech was working on the ramp w seats out under the panel of a majored 182 which also had a new propeller installed.

He touched the wrong two terminals together & it started full throttle, charging into the shop thru an open door, hitting a big bucket of scrap bolts, throwing shrapnel everywhere. It finally stopped after chewing into another parked airplane in the shop.

The tech was not injured as he rode thru this..........
 
nrpetersen said:
There was an incident a several years ago (in Idaho?) where a tech was working on the ramp w seats out under the panel of a majored 182 which also had a new propeller installed.

He touched the wrong two terminals together & it started full throttle, charging into the shop thru an open door, hitting a big bucket of scrap bolts, throwing shrapnel everywhere. It finally stopped after chewing into another parked airplane in the shop.

The tech was not injured as he rode thru this..........
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I'm sure that buffed right out. :D
 
docmirror said:
...so what about the time needed to remove a plug, or take a P lead off? ...
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Disconnecting a p-lead will make the magneto hot so, as regards to safety, it's not something you'd want to do.
 
My battery is live when I stop my motor either by pulling the mixture or turning off the mags. I have no reason to believe a momentary inadvertent arcing of the solenoid will start my engine. My battery's on the firewall and I don't disconnect it during service.
 
Maybe a oddly placed firewall mounted battery :dunno:
 
FastEddieB said:
Is it not a remote, but real, possibility that a dropped tool could short out the starter solenoid and start the prop turning at an inopportune moment?
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If the master is off there shouldn't be any juice to the starter/solenoid, yes?
 
Bill Jennings said:
If the master is off there shouldn't be any juice to the starter/solenoid, yes?
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Well, yes & no. :lol: There is more than one solenoid. A large wire is still hot from the battery to one side of the "main" solenoid. The master switch controls the solenoid which send power to the rest of the system. A seperate "starter" solenoid is activated by a ket or momentary push button.

It is not a bad idea to disconnect the battery when working on any vehicle.
 
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Silvaire said:
Disconnecting a p-lead will make the magneto hot so, as regards to safety, it's not something you'd want to do.
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Right. I got it reversed.

BTW, my A&P was sliced pretty well a few months ago by a prop that was just bumped by the starter running. The prop arc has a fair amount of inertia even when the engine isn't 'running'. Not my plane luckily.
 
some guys probably shouldn't work on airplanes, I guess. Instead they can imagine statistically unimportant scenarios and stir folks up on the Internet!
 
Stewartb said:
some guys probably shouldn't work on airplanes, I guess. Instead they can imagine statistically unimportant scenarios and stir folks up on the Internet!
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you're right....they should stick to flight instructing.....:goofy::D
 
It's something I was taught back in the 1970's, but it wasn't really because of the chance of accidentally starting the airplane. It was more because of the chance of dropping tools. They could damage the aircraft in various ways if they shorted out against something hot.

It's also the first line of the instructions for practically every conceivable procedure when working on cars, including those for which the chances of a short are remote such as changing a cabin air filter or a taillight bulb. I suspect that has to do with liability more than anything else.

Rich
 
I'm not a fan of making changes to systems unrelated to the maintenance being performed. On anything. Airplanes, vehicles, whatever.

Good way to create a problem that wasn't there to begin with.
 
As far as the airplane and mechanical concerns go, there is no reason to disconnect the cable. There are some potential destructive acts that may be prevented though. Your shop is the first I have heard of doing this and is likely the result of having an employee start a plane with no oil in it and having to buy an engine.
 
denverpilot said:
I'm not a fan of making changes to systems unrelated to the maintenance being performed. On anything. Airplanes, vehicles, whatever.

Good way to create a problem that wasn't there to begin with.
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In general I agree with this sentiment, I try not to pull any bolt I don't need to in the process of a repair or service, however in this case I'm rather ambivilant since battery terminals cleaned and serviced at oil changes is not an altogether bad idea.
 
Bill Jennings said:
If the master is off there shouldn't be any juice to the starter/solenoid, yes?
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My airplane was built with the power to the starter full time (actually, to the mechanical switch mounted to the starter). The engine would crank if the switch engaged, even with the Master off. Once was handling a longish piece of safety wire and it slipped under the rubber boot and touched the terminal. Jerked it away by hand...
tach_owie.jpg


I added a solenoid a few years ago to take care of that problem....

Ron Wanttaja
 
denverpilot said:
I'm not a fan of making changes to systems unrelated to the maintenance being performed. On anything. Airplanes, vehicles, whatever.

Good way to create a problem that wasn't there to begin with.
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Disagree, on a vehicle the only problem it creates is the loss of the clock on my stereo. Let me tell you about the fuses I accidentally blew BEFORE I changed my ways.

Now if i'm working on the suspension or the brakes, I don't bother. But if I'm doing electrical or working under the hood, I want the car's electrical system DEAD.
 
As a single data point, my Sky Arrow AMM calls for disconnecting the battery when working in the engine compartment:

16125164306_7b631b52bf.jpg


I wonder how many others do the same?

It's a good practice, but one I often have not followed. Probably going to try to do a better job doing it going forward.
 
wanttaja said:
...I added a solenoid a few years ago to take care of that problem....
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I'm curious, prior to adding the solenoid what exactly was the function of your master switch? :dunno:
 
Silvaire said:
I'm curious, prior to adding the solenoid what exactly was the function of your master switch? :dunno:
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Many designs have a large gauge cable running directly from the battery to the starter solenoid. Shorting that WILL start the engine turning regardless of other switch positions.

Will stipulate there may be other designs.
 
Silvaire said:
I'm curious, prior to adding the solenoid what exactly was the function of your master switch? :dunno:
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Power to the nav lights, strobe, and avionics Motel 6 (It wasn't much of a suite).

Ron Wanttaja
 
Were I work we disconnect the battery when doing almost anything.

Some years ago I was working on a Beaver on floats, the plane was on a trailer and I was working on a ladder. Had to change a vacuum pump. Well I disconnected a primer line to get pump out. The wrench I was using arced on the bus bar on the firewall. Everything went up in flames, I fell off ladder then fell off the trailer.

The quick actions of a fellow mechanic climbed into the Beaver grabbed the extinguisher and put fire out.

No real damage except my pride!!!!
 
We disconnect the batteries at the end of every day. But it only takes the turn of one knob for each battery.
 
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