One year ago, I had the ford dealer replace my starter on my 97 F250 7.3L diesel. It started dragging, and they tested it, and replaced it. I live 200 mi. away from the dealership, so it is not easy to return.

About 3 weeks later, the starter didn't engage the flywheel on the first try. In the next several Months, it did this a few more times. Then the starter went out completely, so I took it to my local mechanic. He replaced it and all was fine. A few weeks later it did the not engaging thing again. Sometimes it would engage on the second attempt, sometimes it took 4 or 5 tries.

Shortly thereafter, my transmission went out, so I opted for a factory rebuilt one. The same local mechanic replaced it. A week later, the starter thing again, so I talked to the mechanic, and he agreed to replace the starter at no cost to me. He said he inspected the flywheel, and felt it was OK. He tested my fairly new batteries, and they are OK. Said he found no other issues.

The new starter is doing the same thing!

I am scheduled to take it back to him in the AM. I would like some opinions as to what could be going on. He is a very good mechanic, and has a great reputation. I have 180,000 mi., and he has worked on it since new.

Another mechanic friend told me that there could be a batch of bad starters, but over the course of one year?

Please help...
Eric

 

I guess what I'm looking for, is a list of possible things that cause a starter to not fully engage into the flywheel.
1. Bad solonoid
2. Low voltage
3. Bad flywheel teeth
4. Misalignment
5. Loose bolts
6. Bad connection

Anything else?

 

You've pretty much got the list right there. Intermittent engagement issues and clearing on 2nd or later attempt sure sounds like low voltage at the starter solenoid or ring gear damage. Both issues make it difficult for the starter to clear a tooth abutment and will appear intermittently until the problem is so severe that it happens continuously.

A tooth abutment between the engine ring gear and starter pinion gear is normal. The starter is supposed to rotate a bit to clear the abutment and find the next gap. Once in the gap is will get full mesh into the ring gear and crank. If the voltage is too low at the starter solenoid then the pull-in force of the starter will not be sufficient to overcome friction and clear tooth abutment. Likewise, gear damage can form ridges and burrs that cause the starter gear to hang up and not be able to pass. The starter solenoid has a momentary pull-in coil that provides the extra force needed to actuate the pinion gear into the ring gear. That coil could overheat if left on for 5 - 10 seconds and cause further degradation of solenoid performance and even failure.

Low voltage could be the result of a discharged or weak battery, or excessive voltage drop in the wiring harness due to loose and/or corroded terminal connections. It is also possible that the wiring harness is simply undersized and creating excessive voltage drop. There should be no more than 1V drop between the battery and starter when the starter is cranking at full rated current in the coldest of winter days. That probably means no more than 0.5V right now in warmer weather.

Gear damage is caused by the starter and ring gear meeting on "undesirable terms".... basically one is moving and the other is not. You have to change out the ring gear to fix. After shutdown the engine will tend to come to rest in one of four quadrants due to cylinder compression. Unless the mechanic rotated the engine over, he only inspected one of those quadrants and not all four. Too bad they didn't start fresh when the transmission was removed.

As for the sluggish cranking, I'm not sure. The cranking motor shouldn't be damaged from the difficult engagement. It might be a sign that you have low voltage at both the solenoid and cranking motor (large battery cable to starter) resulting in long and labored start attempts that overheat the cranking motor.