Top Stud Starter Solenoid Autopsy

[Save Old Iron 1,566]

Welcome to another session of SOI University

a recognized institute of higher learning, experimentation, investigation and serious shenanigans are the norm for the day.

An old friend called me up to help him work on his lawn tractor - how could I refuse.

We tried to get his non wheel horse 11Hp tractor started the other day. I was rewarded with this - a top terminal starter solenoid with symptoms of a good click but no power to the starter.

We substituted a good solenoid and the tractor worked fine. I put this one in my pocket and had something to take apart and play with over the rainy weekend. Around here, rain means something comes apart ...

A quick trip to the drill press to drill off the heads of the rivets securing the metal frame / base to the housing gets us this far

removal of the nuts holding the copper studs and the trigger lead and pressing the studs out from the housing

label a few interesting items on the back side of the coil assembly

a closer look at the spot welding of the negative coil lead to the grounded body of the solenoid coil

closer inspection of the problem area of this solenoid - vaporized contactor studs and contactor disc

one contactor stud was really blown away in the area touched by the contactor disc

the edges of the studs are vaporized because the disc only touches the studs in a limited area - this tractor also sat for years and the engine had seized - and many attempts were made to start the engine before it was free to turn over.

so I cleaned up the contactor studs

rotated both studs 180 degrees in the housing to provide a fresh area for the disc to contact

flipped the disc over in the plunger mechanism to provide a clean non-pitted surface for the studs to contact

and reassembled the parts back to original

a few small bolts to attach the bottom ground plate to the body and the solenoid is now fully functional again.

So if you have that one off type solenoid or just have to keep stuff original at all costs - this may work out for you. For me, its just a cheap date on a rainy weekend.

[Coadster32 793]

Cool! Thanks for doing this. Question though. I understand the spring returns the disc off the stud terminals disengaging the starter and battery stud. Can you explain how the coil "throws" the disc there in the first place? (The clicking noise I would assume to be the disc getting thrown to the studs.)

[Kelly 1,030]

I just a few weeks ago swapped a solenoid on a cousins tractor, was doing the same thing, before calling me he put a new bat. and starter on it thinking it was clicking it must be good, so after swapping in a new one, to show him what was wrong ground the rivets off and showed him the burnt contacts, he was bummed he spent $150 before and it was a $17 fix.

[rmaynard 15,737]

Coadster32. Not to step on the professors toes, but here is the answer to your question.

The solenoid coil is an electro-magnet. The plunger attached to the disc, which goes into the hole in the middle of the coil is steel. When you apply 12 volts to the coil, the electro-magnet quickly pulls the plunger into the coil, thus making contact electrical contact with the studs, (and the clicking sound). When the 12 volts from the starter switch is released (after the engine starts), the spring pushes the disc and plunger back away from the coil and studs.

Bob

[Save Old Iron 1,566]

Class participation - doesn't get any better than this - and Bob is right on the money.

I think I have a pic of the coil inside the housing of the solenoid. I'll post that later today.

@ Kelly, that's why I hate guessing so much - once you start to truly understand how this stuff works, a whole new world opens up - a much less expensive, less painful, less frustrating world.

In this case, there was $0 cost - Ok - maybe a few cents for 4/40 bolts and nuts to reseal the housing to the mounting bracket.

So if your in the business of refurbishing low budget tractors, a few of these tricks can easily save you a few $$ in profit.

[300zx 7]

Chuck, looks good. The Kohler relays are very similar, but the studs are on the side with square heads. They are just as easy to service, especially when you are in a hurry and don't want to run to get a new one. Has any one tried to repair the Onan starter relay? I have a candidate, but I was waiting on someone else to go first!!

[VinsRJ 723]

Very Cool! I'll need to file card this in the brain....... :)

[racinfool40 202]

:) love this site I learn something new everyday Thanks for the lesson and sharing !!!!!

[horsefeathers 15]

Save_Old_Iron, I love your collage of higher knowlage!

You should publish one of those "tractors electrical" for dummys books!

SOI University Rules!

I'am a member of the Shade tree, back yard, grass roots

Fix it for nothing with nothing! Use your McGiver skills club!

Sometimes I think I'am in over my head!

Then I look up at the sky at night!

WOW there's a lot hanging over our heads!

Grease the lightning and keep our Wheel Horses turning!

Thanks for all your help!

HORSEFEATHERS!

[Save Old Iron 1,566]

Coadster,

here are a few pics of the coil windings inside the solenoid case. As was mentioned, the magnetic force is created within the coil by applying 12volts thru the ignition switch lug to the coil. The magnetic force then causes the solenoid plunger to move the copper contactor disk into the contactor lugs. There is your first big "click". When the coil de-energizes, the return spring smacks the plunger back down into the stops located in the steel base-plate - there's click #2.

Enjoy

[rickv1957 72]

Nice thread Chuck,great info! Rick

[Coadster32 793]

I get the mechanical part of it. (12v to coil, magnetism throws pin and disc, contact between studs, spring released after 12v). It seems obvious that the coil directs the magnetism in such a way that it throws the pin and disc to the plates. I guess that's the technical part I don't quite get. I do understand that when current flowsdown a wire, a magnetic field is created around a wire.

[YNOT 0]

To determine the direction of plunger travel, apply the right hand rule of motion.

With right hand, Fingers indicate direction of winding, Thumb indicates direction of plunger travel.

Tony

[Save Old Iron 1,566]

Thanks Tony,

check out this website

http://www.physics.sjsu.edu/becker/physics51/mag_field.htm

especially Fig. 27.34

it describes how to determine the direction of the solenoid core will travel

and

mentions a torque effect that actually spins the plunger slightly while the plunger is moving. This would explain why the entire rim of the contactor disk is pitted. Every time the starter solenoid is engaged, the area on the contactor disk spins slightly, exposing a different area of the contactor disk to the contactor studs.

It's starting to make sense.

[FarmerJim 5]

Thanks Chuck! because of your valiant efforts I'm starting to understand a lot more about electrical parts on these old machines. Do I get extra credit for noticing the pictures on our classroom wall? HorseFeathers should be proud! :)

[Coadster32 793]

Ask and you shall receive. Thanks Chuck! :)

[Save Old Iron 1,566]

Do I get extra credit for noticing the pictures on our classroom wall? HorseFeathers should be proud!

If you want to get your picture put up on SOI's "refrigerator" for all to admire, just say so. All worthy submissions will be put on the wall!

[horsefeathers 15]

You got me.... Horsefeathers and Pink Floyd on the "refrigerator"At SOI University!

Thats right, I'am on the "Dark side of the moon"! When it comes to electricity!

(is there electric on the dark side?) SOI has a formula for that question!

So there are unknown "gassers" in the university ERRRR...I mean...

Unknown gasses in the universe!!!!

I enjoy a good electrical storm it's relaxing!!!

Remeber in an electrical storm don't run for the trees (there's squirrels up there!)

Hide in a ditch and cover yer Azz or head! If ya' know wich is wich?

HORSEFEATHERS!

Great advice on how to get something started!!!

Thanks Chuck!!!

[Save Old Iron 1,566]

Hide in a ditch and cover yer Azz or head! If ya' know wich is wich?

HORSEFEATHERS!

whichever you do your best thinking with

always worked for me !

[horsefeathers 15]

When I have a perplexing question (most offten electrical)

I find myself scratching my head and azz and I do forget which is which!!!

I guess I do my best thinking when I don't think!

Or I'am in the execuitive wash room!!! Gold key you know!

I try not to think too much... Whats that smell?

HORSEFATHERS!

If I can get past the smell I have a new topic!

Early starter /generators how do they work?

can they run CW or CCW

I rember something about polerizing a generator!

[Save Old Iron 1,566]

Vince, here is the link I was directing you to for a better understanding on starter solenoid (relay) internals

[rick 237]

Very good lesson for the "uninitiated"! We used to do the same thing with the old Mopar gear reduction starters, to get them going again, on the cheap so to speak.

[specialwheelhorse 174]

Just reworked one and thanks a bunch now I'm ready for the next thirty years.

I won't last that long !! Only snag ,took a little while to round up four little 4-40 bolts

But I got enough for two more rebuilds for $ 1.36 Wooo Hooo !!