need help with MF50 starter bendix

[rothmans]

Hi
I have MF50 Gas tractor.
Starter motor spins but bendix does not engage.
Starter is a Wilson rebuild Delco 1107226.

I took the starter out and dont see anything broken but havent pulled it apart yet.
If I hold the starter vertically with the bendix end of it downward the gear slides to the engage position, when I hold the starter upward the bendix slides back to the disengaged position, is that normal?
Does this starter have a solenoid driven bendix or not?
Can you tell me what might be wrong with the bendix and how to fix it?

This starter costs $400 so I want to fix it not buy one.

thanks

 

[irvingj]

If it has widely spaced, 1/8" or so tall, protruding, spiral cut "splines/threads" on the business end of the shaft, it may be the type where the drive gear slides forward due to the shaft spinning rapidly inside it when initially engaged. When it reaches its outermost position (contacting the flywheel), it locks on to the starter motor shaft and begins to turn the flywheel. (Seems like my old Chevy used that system, but it's been so long I don't remember for sure. Chevy uses Delco....) This type doesn't use an external solenoid at all. Shaft & splines do, however, need to be clean & lubricated.

This is kinda what yours sounds like. (When it falls to the lower position, does it also rotate slightly due to the spiral splines?)

You might check to be sure flywheel teeth aren't worn off too much for it to engage, and that the starter is positoned properly- you might need shims to align it properly.

It's also possible to bench test these things by connecting it to a 12V source and observing; just be darn sure starter is securely held in place so it doesn't jump off the bench! (Don't ask how I know this....)

Hope this helps some.

 

[irvingj]

rothmans-- this is what I was thinking of-- from Wikipedia:

"This overrunning-clutch pinion arrangement was phased into use beginning in the early 1960s; before that time, a Bendix drive was used. The Bendix system places the starter drive pinion on a helically-cut driveshaft. When the starter motor begins turning, the inertia of the drive pinion assembly causes it to ride forward on the helix and thus engage with the ring gear. When the engine starts, backdrive from the ring gear causes the drive pinion to exceed the rotative speed of the starter, at which point the drive pinion is forced back down the helical shaft and thus out of mesh with the ring gear."

No pics, but this may be what you have.

 

[rothmans]

There is a cylindrical thingy that covers helically-cut driveshaft so I cant see it, but I think it must be the type you described.
Everything you said to look for is fine.
There is some grime on the bendix maybe that stopped the gear from flying into place. I will clean up the bendix and then bench test the starter.

thanks

 

[rothmans]

I fixed the starter.
Turned out there was a compression pin that goes thru the drive shaft to hold the bendix in place, it was sheared off. I replaced the pin and the starter passed the bench test.

 

[radioman]

don't you love it when its a simple little thing?! I know I do! congrats on getting it fixed.

 

[irvingj]

Ah, another success story. Love it!

 

[nbruno]

Rothmans, if you're still on here I was hoping I could get some advice. I have a TO-30 with the same starter and same issue. I pulled the starter and in my case the pin just fell out, so obviously the same problem as yours. I've never pulled a starter apart and was curious if you had any pointers before doing so. Also, where were you able to find a replacement pin?

Thank you.

 

[irvingj]

Here's my 2 cents' worth:

Most likely it's a standard roll pin; they're held in place by spring tension, as the pin is made up of thin, wound spring steel, or it might also be the type that just has a single open slot in it. Operation/installation is the same.

You could take the one that came out to a parts store that sells such things (NAPA comes to mind) and match it up. Any pieces still inside can be removed with a drift punch of an appropriate diameter-- just small enough to easily fit in the hole. Installing the new one is just by tapping it in, but be sure to get it straight as it enters the hole. It sometimes helps to put a thinner pin, nail, or drift punch into one side of the hole to keep things lined up as you tap in the new pin from the other side; the keeper will be pushed out as the new pin goes in.

As far as taking the starter apart, guess I'd have to see it.