448 Onan starter and more

[Spike188]

With all of the fear mongering about winter coming and hearing of frost close by, it is time to do today, that which could be done tomorrow.

The 448 starter failed shortly after this picture was taken last March. I dreaded the thought of pulling the tins to remove the starter. So today was the day and less than an hour after beginning the starter is out.

Rambling and photos to follow.

[Spike188]

There was nothing obviously wrong with the starter. The brushes have a lot of life in them and there is no wear on the bearings. After reassembling it, I dropped it off at a starter shop for analysis today. The battery is 350 cold cranking amp but once the engine is hot the starter gets sluggish to the point of no crank. That has been going on for 3 seasons and getting progressively worse. The last number of start attempts, the gear would not sling hard enough to engage.

[MattA]

How much voltage drop do you get while cranking? Poor connection somewhere? Issue with the starter solenoid? Dirty starter commutator? Just throwing ideas out there.

[Spike188]

@MattA Unfortunately a voltage drop test was never thought of until the starter was removed. Bypassing the solenoid never worked or connecting jumper cables at the starter. The negative cable was tight at the block connection point.

Years ago an a machine with a pancake motor and printed disc armature we would see the field magnets degrade. The very first it it happened I separated the motor halves, not knowing that it cause catastrophic lose of magnetism. The motor had to be sent to a motor shop in Wisconsin for rebuild every couple of years. That experience makes me wander if this starter has weak field magnets.

[DavidBarkey]

What I have run into a lot over the years in automotive and the GTs is the connection where the cable goes into the tab end goes bad . If the starter comes back good , change all your cables . Cold , connections are "good enough" . But when hot the tab can loose connection with the cable wires. What starter does yours have ? remote or on starter solenoid ?

[Spike188]

Dave, it is a remote solenoid. The starter is a Bosch. The cables are all less than 5 years old. The batteries are 350 cold cranking amp.

[JSinMO]

If I read this right the starter works when cold but not when hot. I don’t have experience with weak field magnets and I never really thought about it before so I have to ask a possibility dumb question. Are magnetic fields affected by heat?

Just thinking while I’m typing I’m kinda leaning toward Mr. Dave’s thought. It sounds like something is going open when hot. Ive seen a lot of 6V systems act this way. But it much more critical for them to have very good connections and heavier cables.

I’m interested in what you find out.

[JSinMO]

@Spike188 I hope it’s ok if I update my post inside of your topic. You inadvertently gave me some homework to do and down the rabbit hole I went!

I never realized how heat can effect magnets but 10 websites and a couple of videos later I learned a some things!
Here’s a handy guide from one of the pages I was on.

Here’s quick reference chart of basic materials and peak operating temperatures:

Neodymium magnets: 120-160 C.
Samarium Cobalt magnets : 200 C.
Flexible magnets: 80-160 C.
Ceramic ferrite: 450 C.
Alnico magnets: 525C.

I couldn’t come up with what type are in a Bosch starter.

[DavidBarkey]

@JSinMO Good to know info.
My experience has been that the heat causing size changes / tolerances with in the starter . Different materials and masses grow at different rates . changing the "gap" between parts .
Example
The aluminum end housings and bronze bushings grow faster and sooner but less than the steel armature shaft . So the depending on the temp you could have loose or tight on the shaft .
The outer housing is a much thicker steel tube and greater mass then the steel plates of the armature . So when heated will grow larger in diameter pulling the magnetic fields away from each other .
Copper when heated looses some of its ability to flow current . This resistance causes a drop in the magnetic field .
Steel when heated starts loosing its magnetic properties as well .
Same goes for the steel ends on copper cables .
Soldered on ends can fail to as the solder today is not as forgiving to vibration and corrosion as it use to be due to the lack of lead in it .
I do not remember the numbers for all this nor care to , but knowing that these things are effected by heat in this manner helps with diagnosis .
This is why most starter motors are made with ceramic type magnets . Smaller , lighter, less material , more stable at higher temperatures. But that dues not make them fool proof . Magnets can break , come unglued ect.

My 2 cents . You may keep the change .

[Seabee]

I have a point here! Years ago I cleaned up the block on my Studebaker Avanti and painted it so it looked nice. A few years later the engine would start well when Cold, but it was a real challenge when hot. I finally pulled the starter and hauled it to an electronics rebuilder. He said nothing wrong with it! I bought new cables and came home and installed them. Not real wonderful! I pulled the starter and polished the flanges on the starter with a wire wheel and I polished the engine bosses where the starter met the engine block.

Problem solved! I was proud of that Black paint when I did it, but when I wire wheeled it off of the contact areas, the engine started fine and still does! It was all due to bad grounds! Good wires on your 448 is a good starting place, but be sure the grounds on the engine block and battery are clean.

Bill Moyer