# Aro Pneumatic Drill Doesn't Spin



## ericc (Sep 26, 2015)

Hi.  I bought an ARO pneumatic right angle drill at a garage sale in a bucket of rusty stuff.  There was a needle scaler in there which worked great.  But, this drill will not turn.  The chuck turned freely.  So, I decided to see if the drill could be repaired.  After disassembling it partially, the planetary gear reduction socket was exposed.  This is as far as it would disassemble while still being capable of being tested.  I tried turning the regulator screw and removing the exhaust port, and it still would not spin.  I then removed the planetary gear and then the air motor.  The motor spun freely.  When the valve was pressed, air flowed strongly out the motor input hole.  It also freely flows out the exhaust, but the motor does not turn.  I spun the motor shaft, and it turns freely in the bearings.  I checked all the passages for obstructions and did not find any.  It seems that the rotor is just not spinning.  Do the air vanes have to come out a little bit to catch the air flow?  Web searches did not seem to turn up any clue.  Otherwise, the vanes tuck right into the rotor body, and it seems that there is nothing to get the thing started.  Once it starts spinning a little bit, it seems that centrifugal force would bring them out more and the spinning would pick up.  Can the motor be tested by putting toothpicks in the bottom of the vane slots to push the vanes out a little bit to test whether new vanes are needed.  I am not really familiar with the internal workings of this kind of tool so am a little lost.

Also, it seems that there a lot of "needs repair" pneumatic drills on Ebay, but they don't seem to be selling.  Could this be because they are difficult to repair?  I saw one that sold for 0.99.  Their new prices are pretty high, in the $100 plus range.  They seem to be useful for making aircraft out of aluminum.  Aren't web searches great?  All kinds of information just waiting to be grabbed, but apparently not the useful ones.


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## JimDawson (Sep 26, 2015)

The vanes should be relatively loose in the rotor, not sloppy, but should move freely.  They are probably just gummed up.  I would pull them out one at a time, so you can put them back in the same slot, and clean them. Then oil with some light oil, and try it again.


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## kvt (Sep 26, 2015)

agree with JimDawson.   Need to take the vanes out one at a time and cleans them.   They have to move freely in the rotor, as they should contact the wall and move in and out as they spin around this way they make contact all the time.   It is the centrifugal force that seals them to the wall normally.   try a little alcohol or other cleaner.   But be careful  some time they do not like some things and it will cause them to start coming apart.   Some times even a small amount of WD40 will loosen them up.  If you use the wrong type of oil to do the daily oil on Air tools they have a tendency to gum up.   but without the oil they start to seize up and if moisture gets to them it is even worse.   I have rebuilt and cleaned up many air tools that others thought were dead.   Use to you could order all the parts to rebuild most of the good brands like Ingersoll, Chicago Pneumatics, and others.   Have not tried to do it in many years.


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## kd4gij (Sep 26, 2015)

I have an IR 3/8 air ratchet that some one gave me because it wouldn't run. I filled it with pb blaster let it sit over night and tried it the next day and it ran some marvel mystery air tool oil through it. 5 years later it still runs great.


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## davidh (Sep 27, 2015)

if the drills reversible, the motor cylinder and end plate need to be indexed to the air inlet port deep down in the motor cavity.  or someone has taken it apart and not indexed the motor end plate with the motor cylinder.  they are designed for incoming air to "lift" the vanes so all the porting must be aligned.  not a big deal once you get it all apart.. heat is your friend in removing the whole motor, heat the housing hot, use a propane torch if you have one. . .  honest.
the main reason for all the air tools on eBay, i think, is due to the efficiency of the newer battery powered tools. . .


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## brino (Sep 27, 2015)

I bought one NOS (New Old Stock) Craftsman 3/4" drive air tool, for fairly cheap with no returns. I got it home and was sad to see it not spin with a good air supply. With nothing to lose I dis-assembled down to rotor and vanes and found it so full of old oil it could NOT spin. With a good solvent clean-up and very light re-oiling on re-assembly it's still working strong ~2 years later. In fact I used it to remove the nut on the end of the crank-shaft of my '99 Dodge Ram last week.....still going strong.
-brino


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## ericc (Sep 27, 2015)

Hi. Thanks for the suggestions. The motor spins very freely. Lubrication is very good. The vanes are all loose in the slots. If I give the shaft a spin the vanes will fly out. The point about the vanes lifting in the air flow is very interesting but I am not sure that I understand it. Does that mean that the curved sides are facing out.


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## ericc (Sep 27, 2015)

I was just thinking that there is no way to get the end plate wrong since there is a roll pin indexing it. There is no way to get it wrong with the pin in there.


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## davidh (Sep 28, 2015)

does that pin go thru the end plate and index to a hole deep down in the housing bore ? or is there a pin on the side of the "front" end plate that indexes with a little slot in the side of the housing ?  
the vanes go "flat side out"  the "rear end plate"  (thats the one thats closest to the air supply into the tool) has slots or groves in it to allow a small amount of air to get under the vanes. 
if you take it totally apart and study all the parts over a beer or something, it will suddenly just make sense.
i have a bunch of little motors apart in my shop and would be more that happy to take some photos with some notations on them.  let me know.  its fun to share things a fella knows about. . . . . the tool repair business kept my family fed and clothed for 30 plus years.  actually it still kinda does.


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## Bill C. (Sep 28, 2015)

The last large shop I worked in used air power drill motors for field work.  They use a oil designed for air tools. Little cans look like Liquid Wrench style with a pointed top.  Put a few drops in the bottom of your air motor before connecting the air hose


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## ericc (Sep 28, 2015)

Hi Davidh.  It is the first one.  There is a roll pin going all the way through the air motor.  It indexes both the top and bottom end cap.  I'll have to look for the air channels that lift the vanes.


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## davidh (Sep 28, 2015)

Bill C. said:


> The last large shop I worked in used air power drill motors for field work.  They use a oil designed for air tools. Little cans look like Liquid Wrench style with a pointed top.  Put a few drops in the bottom of your air motor before connecting the air hose




thats is a good idea too, however, if you remember to oil the hell out of the tool BEFORE you put it away, it will retain  OIL and not moisture, for however long it sits before you use it again.  that has been my suggestion since my conversation with the chief engineer from Ingersoll Rand, many years ago.
i recommended Marvel Mystery Oil, with a tad amount of automatic transmission oil added to it.  in my opinion it was superior to "air tool oil".
jist sayin'


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## ericc (Sep 29, 2015)

I think I get it now. The front end piece has a groove which directs air to an inner arc which will cause the air to push the vanes out. 

The picture shows the air path as well as the hole for the indexing pin. Air flows up two axial holes in the motor shell into the outer groove. 

I still don't know why it doesn't work. Maybe the vanes are too worn. They are below the surface of the rotor.


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## davidh (Sep 29, 2015)

nice picture.  is this the front or rear end plate ? (the rear is the end toward the air inlet )  take pictures of both end plates and both ends of the motor cylinder.  there are a few other things that need to be verified.  also a photo of the outer end of the housing, aim the camera toward the bore of the housing.  there is no magic, i promise.


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## davidh (Sep 29, 2015)

here is a snapshot of a motor from a die grinder.  taken with the "rear" end plate removed and flipped over along side the cylinder assembly.  notice the oblong hole in the end plate, thats where the incoming air comes thru and notice the funny looking mating part of the cylinder.  most all cylinders are like this in some form or other and often when diy's take the motor apart, the cylinder gets reversed (end for end) and this "air inlet " section on the end of the cylinder is on the wrong end. 
if push comes to shove, send it to me and i will make it run, probably have new vanes for it here also. . . . .


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## kd4gij (Sep 29, 2015)

davidh said:


> thats is a good idea too, however, if you remember to oil the hell out of the tool BEFORE you put it away, it will retain  OIL and not moisture, for however long it sits before you use it again.  that has been my suggestion since my conversation with the chief engineer from Ingersoll Rand, many years ago.
> i recommended Marvel Mystery Oil, with a tad amount of automatic transmission oil added to it.  in my opinion it was superior to "air tool oil".
> jist sayin'




 I like Marvel Mystery air tool oil.


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## davidh (Sep 29, 2015)

i do the regular Mystery oil like i said but i mix it in bulk for resale. . . .   i think its cheaper.


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## ericc (Sep 30, 2015)

Here are more pictures.


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## ericc (Sep 30, 2015)

The first is the back end where the air enters. The second is the rotor. The third and fourth is the back and front of the cylinder. the front has the short roll pin. It can't be flipped because the front cap won't fit due to the blind hole.


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## davidh (Sep 30, 2015)

is the rotor removable from the rotor shaft ?   some of the more expensive ones are built that way  
do you have a model number of the tool ?  probably not.
wanna to send it ?  no charge, no guarantee ?
should fit in a "usps small flat rate box" for less than $6


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## ericc (Oct 1, 2015)

Hi davidh.  There are some things written on the tool.  The rotor seems to be fixed on the spindle.  Although there is no way of telling without trying to press it.  I think that ARO is a middle of the line brand.  Thank you for the offer.  I will get to it after some blacksmithing.


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