Slightly chewed ring gear?

3567 Views 12 Replies 6 Participants Last post by DragonProof, Feb 19, 2019

DragonProof

Discussion Starter · Jan 18, 2019

I just picked up a '73 ford 3550 that wouldn't start. Got her home and pulled the starter and found she had a relatively new starter and a slightly (?) chewed up gear ring. I know the usual advice is to split her and replace the gear ring, but I'm thinking this one is not that bad.

Full disclosure: the only time I've ever repaired a gear ring is when I threw out the flywheel in my M551 Sheridan tank, which coincidentally was also a '70's era machine. So I have no idea if the 3550's gear ring is still serviceable.

Ive attached some photos of the gear ring and starter motor. If you look at the gear ring it looks like the starter motor is failing to engage fully into the gear ring. I'm wondering if the burrs on the gears are causing the bendix gear to kick back and fail to fully engage? Maybe I could file down the gear ring? Or is the bendix gear spins up too high while trying to fully engage?

I bench tested the starter and saw that the bendix gear does fully deploy.

I wonder if there is a different style of starter motor that will throw the bendix gear to it's fully extended position before applying power to the motor? Seems like this should allow the gears to fully mesh before the starter starts spinning up.

Anyhow, any advice will be greatly appreciated.

Guy in Olympia

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DragonProof

Discussion Starter · #3 · Jan 18, 2019

Yes, that is exactly what happened. There is a slight grind, The motor turns just a fraction ( you can see the generator move like 1/16 inch), then the starter motor just whines like it is spinning at high speed.

Occasionally it will catch and start. When it does there is no grinding noise and it starts like a brand new tractor. I’m thinking there is maybe one good tooth that finally moves into place and allows it to catch.

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DragonProof

Discussion Starter · #5 · Jan 19, 2019

I agree the ring gear is toast, but I wonder if there is some way to keep it in service until I have the time to fix it or replace it. There is enough tooth left on the gear ring so that once the pinion engages it is a solid crank.

Here is one hack that I tried: I removed the solenoid cover and reinstalled the starter. Then I held the solenoid in the activated position with a wood dowel while I cranked the engine. It cranked over just fine but I didn't let it start. I tried several more times and it cranked solid almost every time. Occasionally it would do the grind and whine thing ... but after the starter slows down enough the pinion makes a loud clunk and slides into place, so on the next attempt it cranks just fine.

Not sure if this tells you anything. It makes me think there must be some way to recalibrate the starter motor and solenoid to match the wear on the ring gear.

Or if there was some way to modify the starter motor so it would not spin up until the pinion was fully extended.

A new ring gear is about $30. Getting to it is an entirely different story. The instructions that I found started with "build a gantry".

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DragonProof

Discussion Starter · #10 · Jan 19, 2019

Thanks folks, to everyone that replied. Lots of good ideas here! I'll start the process of dressing the gears, making sure I have the right starter motor, measuring and testing tolerances, etc. As I complete each step I will update this thread.

One question / concern: as I am dressing the ring gear teeth there will be some metal shavings falling into the housing (along with the metal from the already chewed teeth). How much of a problem is this? Maybe I can get a magnet down to the bottom of the housing, or flush the housing somehow. I'm guessing that the clutch is in the same housing, I don't want to cause damage to that.

- Guy in Olympia

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DragonProof

Discussion Starter · #13 · Feb 19, 2019

I'll get some photos and post an update. I ordered a new starter, they sent the wrong one so I had to send it back for an exchange. Took a couple of weeks, got the starter back but due recent snowstorms here in the PNW I have not had a chance to install and test it yet. If only I had a tractor to plow the knee-deep snow off my access road.

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Slightly chewed ring gear?

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