A 16 horsepower Kohler single cylinder K341 starter was not quickly spinning through compression strokes. Each compression event slowed the spin rate close to zero. So the engine couldn't start. Thoughts of inoperative Automatic Compression Releases, voltage drops exceeding 0.1 volt at various high-load starting-circuit connection points, weak battery, bad ground (that's redundant as it is covered by usual loaded-voltage-drop tests at connections, but for some silly reason I thought of it separately) went through my head. As a quick and dirty way to indicate whether the starter was was able to deliver good starting torque, I connected jumper cables from my dual battery diesel truck to the engine ground and the starter's +12V connection. It behaved the same way.
Two bolts and one electrical connection nut removal later the starter was off and in hand. Then removing two long through-bolts allowed the ends to be removed from the case. First observation was even more black dust than usual. I first thought that probably indicated worn out brushes, but they're still pretty good. Using an old recycled toothbrush so many of us keep in our tool boxes for a couple minutes outside where releasing that dust wouldn't bother me revealed that one of the two magnets bonded to the case interior is broken into at least four large pieces. A distinct step could be seen on the inner magnetic surface that should be held a few thousandths of an inch from the spinning armature's electromagnetic poles. At least one section of the soft broken magnet had been rubbing against those steel armature poles, which must have become that black dust. The armature is undamaged, the bearing clearances typical, and the Bendix mechanism only needed cleaning and lubrication. A short blast of PB Blaster to help disperse bearing lubrication was applied, reducing bearing drag. Air hose blast and it's ready to go back into service except for that rubbing magnet.
How in the world could that magnet have become broken while it was on the engine? I assume that it was not installed in that condition.
I looked at my donor parts but I don't have another compatible Kohler starter. I may try epoxying that magnet back together even though I know the previous single magnetic field would be stronger than the bonded pieces could produce, but it might get this starter running well enough to serve until I encounter another donor.
Anyone ever encountered broken field magnets inside a starter motor?
Any thoughts about how it could have occurred?
![]()
In another discussion thread, I mentioned that some of Kohler's starters ran 4 brushes with 16 electromagnetic armature magnets, whereas their later-production longer-length starters use the cheaper-to-build 2-brush configuration with only 10 electromagnetic armature magnets. Has anyone ever tested their comparative spinning torque? More poles = more torque, but shorter-length = less torque. I just don't know how those opposing predictors worked out in comparing these Kohler starters. I'm VERY sure that it cost more to make the 4-brush 16-pole version, even though it's shorter and uses less material. Also, bush wear rate on the 2-brush configuration is probably higher because the contact surface circumference travel per rotation is much longer than the end-loading 4-brush configuration. It just appears like the more compact 4-brush configuration was designed to be Lexus quality whereas the slightly-longer 2-brush configuration was designed to be Toyota Tercel quality. Both good, but the former even better. But that's just my take as a designer of many devices.
John
Two bolts and one electrical connection nut removal later the starter was off and in hand. Then removing two long through-bolts allowed the ends to be removed from the case. First observation was even more black dust than usual. I first thought that probably indicated worn out brushes, but they're still pretty good. Using an old recycled toothbrush so many of us keep in our tool boxes for a couple minutes outside where releasing that dust wouldn't bother me revealed that one of the two magnets bonded to the case interior is broken into at least four large pieces. A distinct step could be seen on the inner magnetic surface that should be held a few thousandths of an inch from the spinning armature's electromagnetic poles. At least one section of the soft broken magnet had been rubbing against those steel armature poles, which must have become that black dust. The armature is undamaged, the bearing clearances typical, and the Bendix mechanism only needed cleaning and lubrication. A short blast of PB Blaster to help disperse bearing lubrication was applied, reducing bearing drag. Air hose blast and it's ready to go back into service except for that rubbing magnet.
How in the world could that magnet have become broken while it was on the engine? I assume that it was not installed in that condition.
I looked at my donor parts but I don't have another compatible Kohler starter. I may try epoxying that magnet back together even though I know the previous single magnetic field would be stronger than the bonded pieces could produce, but it might get this starter running well enough to serve until I encounter another donor.
Anyone ever encountered broken field magnets inside a starter motor?
Any thoughts about how it could have occurred?
In another discussion thread, I mentioned that some of Kohler's starters ran 4 brushes with 16 electromagnetic armature magnets, whereas their later-production longer-length starters use the cheaper-to-build 2-brush configuration with only 10 electromagnetic armature magnets. Has anyone ever tested their comparative spinning torque? More poles = more torque, but shorter-length = less torque. I just don't know how those opposing predictors worked out in comparing these Kohler starters. I'm VERY sure that it cost more to make the 4-brush 16-pole version, even though it's shorter and uses less material. Also, bush wear rate on the 2-brush configuration is probably higher because the contact surface circumference travel per rotation is much longer than the end-loading 4-brush configuration. It just appears like the more compact 4-brush configuration was designed to be Lexus quality whereas the slightly-longer 2-brush configuration was designed to be Toyota Tercel quality. Both good, but the former even better. But that's just my take as a designer of many devices.
John
