Trouble with a Federal Type 5

[steamdrum1]

Hello, I am new to the board and glad to be here. I have a question about a single phase Federal Type 5 siren. My brother is on a local volunteer fire dept, and about a year and a half ago their siren started acting up. The siren would not reach full RPM and eventually would not run at all. We took the siren down and removed the cover for inspection. The brushes were obviously shot and the commutator was rough as well. I took the siren home chucked the armature up in the lathe and turned the commutator smooth, took only a few thou to bring it back in condition. I then undercut the mica between the copper bars and thoroughly cleaned all the dust out. We ordered new brushes and springs from Federal and installed them according to the manual, including matching the brushes to the commutator using fine sand paper. Installed new bearings and re assembled. The siren ran like brand new until about a month ago, it was back to its old tricks. We borrowed a bucket truck and took a look inside the siren. The brushes had some wear and the commutator was carboned up pretty bad. I took some fine sand paper and cleaned the commutator then blew the dust out. The siren ran fine for 2 weeks, and is acting up again. The siren does not see much use runs 10sec at noon and 10 sec at 9 O'clock every day, and occasionaly for fire calls. Does any one have an idea on what is going wrong? is there too much arcing on the brushes? is 1 1/2 years all the life that can be expected out of a set of brushes? Any help would be greatly appreciated. Thank You Bill

[Jim Z]

if I remember correctly, the brushes on a repulsion-induction motor have to be correctly "timed;" their position relative to the stator poles has to be correctly set or else the brushes might pass too much current and not last long. If they're seriously out of whack, the motor might not start at all.