After 6 years and about 250 hours, the starter on my Yanmar 4JH4AE engine began misbehaving. It would occasionally do nothing when I turned the key, but would usually start without doing anything else on the second try. Recently it gave up turning at all so it was (past) time to do something about it. While other posts in this thread discuss this (and related) engines' problem of insufficient current
to pull in the starter solenoid, I was reasonably sure this wasn't the case here since the starter battery
voltage dropped when the key was turned, and continued to drop if the key was held in the start position for a few seconds. According to the parts catalog, the starter has 2 positive and 2 negative brushes
so I decided to check those first, thinking that perhaps one of them was hung up in its holder.
Removing the starter was pretty easy. I have a dual-circuit battery
switch that simultaneously connects the starting battery to the engine and the house bank to the electrical
panel. As I wanted to leave the house on, I disconnected the starting battery positive cable. However, as we'd just finished motoring, the system voltage was still slightly above nominal and so the automatic combining relay was still pulled in. This meant that the engine was still being powered from the house bank. Disabling the relay removed power from the engine. Despite this I still disconnected the negative cable from the engine first. On my installation
the negative battery cable is connected to one of the starter mounting bolts, so this came out first. I then removed the nut holding the positive cable on the solenoid, and the 5 or so wires that feed +12 to various engine circuits. There was also a single
wire with a faston connector that I removed from the solenoid. The 2nd mounting bolt was a little harder to reach, but an extension on the socket wrench took care of it.
Once out the starter and solenoid were a lot smaller than they looked installed! The rear cap of the motor is held on with 2 through bolts and 2 small screws. The small screws hold the brush holder to the cap, and the through bolts hold the cap on and the entire motor assembly together. When all 4 fasteners are removed you can remove the cap, sliding the positive wire insulator out of the cap. Note that with the through bolts removed, the motor wants to push itself apart due to the various internal springs. I basically held the parts together for this first inspection
. I found a fair amount of metallic particles in the cap, so I expected to see worn brushes
. Instead it appeared that there wasn't much wear, and by pushing the brush springs aside and moving the brushes up and down it looked like they were fine in their holders and were making good contact with the commutator. However the commutator had a lot of gray residue so I decided to burnish it.
Getting at the commutator was a bit difficult since there are 4 brushes and their holders. 2 are negative and have copper braid that's riveted to the brush holder. Note that this means that if the negative brushes are worn you need to replace the entire holder assembly. There are 2 positive brushes that are wired together to the lead that exits the cap and connects to the solenoid, so removing these from their holders made room to get to the commutator. Removing the brushes is as simple as pushing their springs out of the way and sliding the brushes out of their holders. However the entire starter still wants to push itself apart, and getting at the commutator is still difficult.
The motor separates from the gearbox
almost by itself, with a spline shaft on the armature that simply slides out of the gearbox
section. However the gearbox still wants to push itself apart, probably from the spring that retracts the bendix gear
. Rather than let it fly apart, I used a long nose vise grips to hold the gearbox together. Once the gearbox is taken care of, the outer sleeve of the motor (which holds permanent magnets) can be slid off the armature, leaving the commutator pretty accessible. While removing the brush holder from the armature would make the job go easier, there's a large clip (sort of like a c-clip) that keeps it in place, and I didn't see a good way of replacing it without buggering the shaft so I left it in place. I burnished the commutator using the space between the 2 positive brush holders, and even with restricted access it only took a few minutes. Reassembly was in reverse order, although it was easy to get the motor and gearbox misaligned, making putting the through bolts in difficult. There are several parts in the gearbox that need to be aligned, and then the end cap needs to be aligned with those. Making sure that all is aligned before engaging the motor in the gearbox and putting the end cap on makes this relatively easy though. Also, the brush holder has to be aligned with the end cap so that the 2 small screws engage in their holes. The screws aren't that long, so the brush holder has to be back far enough on the motor shaft so that it's close enough to the cap.
Installation is the reverse of removal
, albeit with a small issue: you really want to connect the negative cable last, however (at least on my engine) as this is one of two mounting bolts you're tempted to do it first. I screwed both mounting bolts in first but left them untightened. I reconnected the positive wires and the positive battery cable. The torque spec for the positive terminal is 65-87 in-lb, which was below the range of my torque wrench, so I just guessed. Once this was on I removed one of the mounting bolts, connected the negative battery cable, and tightened both mounting bolts to 65 N-m (78.2 to 98.2 N-m derated 80% when tightening to aluminum
After reconnecting the starter battery the engine failed to start! Then I realized I'd forgotten to reconnect the black wire from the ignition switch and relay to the solenoid! Once that was reconnected the engine started on the first turn of the key, and has started first time since.
My apologies for not taking photos of this small project
, but I hope this narrative helps someone out.