Anyone here familiar with industrial DC forklift motors?

Taking a shot here. Working on a forklift that someone else gave up on. No clue why it was ever parked but previous guy that bought it not running indicated he put test batteries in and the hydro pump motor would not lite. First thing I did was make sure motor was free, which it is. Then put meter across the two terminals and rotated it slowly. most places it is around .5ohms, but there are some spots where the meter goes OL. It has been sitting for many yrs, and some outside, but I am wondering if something more could be going on?

The brushes and commutator look decent! Nothing obviously burned up. This motor would be a real pain to remove so I am hoping for some other tests to figure out what I have going on.

I have not yet put power to the machine for testing. I am a little more careful than some about that stuff. I want to study the equipment and inspect the wiring before we try that.

With a motor that's not been used for a long time, the dead spots could just be due to slight tarnish on the commutator.

If it turns smoothly, I'd try powering the machine up and see if it's ever getting voltage at the motor?

I was able to get things going today. I do believe the dead spots in motor rotation were due to poor contact. However, it seems pretty obvious that the motor still needs to come out because the arcing on the commutator is quite impressive. It did get better as it ran but start ups are pretty "sparky", with both blue and yellow sparks.

I live in the machining world so a kiss cut on the commutator is no prob, but I am curious if there is a specific procedure here? I had considered filling the slots with epoxy before turning. And/or chamfering the slots with a file after.

I really think if I keep running it like this, it would cause serious damage to the motor. I did my testing and confirmed I have full functionality. Now I need to look at making it right.

If the commutator is not chewed up, jut a clean up with a fine file or some fine emery cloth may be adequate.
If the slots are undercut, scrape them out first, so any burrs are removed by the sanding.

I've done that in the past by running a motor and holding a file with emery strip pulled over the end against the commutator.

And get some new brushes for it, unless they are absolutely immaculate.
If they are old and have any oil contamination, that will cause arcing and clog the commutator slots, adding to the problems.

I'd keep turning the commutator as a last resort, as if a segment is disturbed the motor is pretty much wrecked..
If you decide that is necessary, I'd suggest getting it fully tested and cleaned while it is out.

Is it a wound field or permanent magnet type motor? Excess current and arcing can be caused by field winding faults or mis-connections etc., as well as armature problems.

If it's an old permanent magnet type one (pre-Neodymium etc. magnets), it's also possible the field magnet has faded or been weakened by someone removing the armature without fitting a keeper as they did so.
That causes high current and low torque. And another reason to avoid disassembly if it is not essential..

I don't think that there is any specific procedure apart from taking off as little metal as possible to get the commutator bright copper everywhere. The commutator may have worn slightly eccentric, or thicker at the ends where the brushes don't touch it.

There may be connections to the windings that are proud of the brush surface, but not in line with the brushes. Don't machine them off.

I guess that it is a cylindrical commutator. Some motors have face commutators. With cylindrical commutators, you can usually machine from the end that is away from the windings, to all the way past where the brushes touch, but that's all. That may leave a step in the commutator surface, but if that isn't where the brushes touch, that's fine.

You don't need to chamfer the slots, but cleaning out any swarf is good. I wouldn't put epoxy in the slots as that would be difficult to remove afterwards and might take insulation with it as you remove it. It is not a good idea to have anything in the slots, as it will tend to lift the brushes as the segments wear away.

http://www.imajeenyus.com/workshop/20160529_hoover_commutator/index.shtml is where someone has cleaned up a commutator.

Put jumper cables on electric motor then connect to a 12v battery. You might need to turn motor by hand to get it started let it run about 1 or 2 minutes contacts will clean them self.

I had a fork lift motor on a mini bike wow instant full power the bike does a back flip if tire has too much traction. Fun to ride on, gravel & dirt, but grass is like ice, no speed control 25 mph or 0. I moved motor to a go-kart it spins the tires on take off every time. 0 to 25 mph very quick about 4 seconds on asphalt.

All good points guys! I am headed over shortly to do some work on it. I think I was back pedaling on turning the motor. It will be a serious challenge to get it out unless I get access to the bottom of the lift.

The motor sounds reasonable, and has all the power it should have. I just feel the sparks it is creating are excessive.

For this reason, I might like to at least 'try' to improve the motor without removal. I mostly have the bird cage around the brushes removed. It would be super handy to just spin the motor and scrub the commutator a bit. I probably should inspect all the brushes as well.

Any quick/easy solutions for com cleaning? Is it even worth it? I do see some pitting and damaged areas on the com, but nothing extreme.

Scrape the slots with eg. the end of a broken hacksaw blade, then lightly sand with fine paper or emery cloth, finishing with some blunted fine emery (rub it against itself until it feels evenly smooth).

Well, seems we have us a runner! Gotta say it is a surprise to me based on how it looked. I decided to just get the brushes out to take a closer look and realize most of the brushes were somewhat seized in their holders. It is just graphite pretty much a natural lube anyway. I had one brush that took quite a bit to free it. I pulled them all but I knew having to fight to remove them meant they were not free to ride the spring pressure on the commutator.

Got them all free, stuck em back in, and we have basically no sparkage at all. I was expecting something but was really happy. Happy enough I just called it fixed. they are technically pretty worn height wise, but this machine won't get that many hours anyway. I'd be surprised to see 100hrs/yr with it. But if it gets more use, I will just plan a brush replacement.

It does have sensors on each brush. I will have to see if they are hooked up but appears the temp sensors on motors were bypassed. The sensors probably failed so.....ya know, don't replace the sensor, just cut the wires.....lol