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Old 23-04-2013, 17:51   #1
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Starter Motor Fails When Hot

Hi, I have now been hung up several times by the starter motor failing to crank when the engine is hot. (Lister HRW6. Bosch starter) Starting from cold Aok, batteries Aok. When the problem has occurred the starter gives a puny whirry sound but fails to crank engine. When its had time to cool it cranks like an excited puppy. Any advice even the obvious would be most welcome.
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Old 23-04-2013, 17:55   #2
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It is probably the bendix or solenoid associated with the bendix. If you tap it lightly it may throw the gear out and mate up with the flywheel. Probably best to replace or have the starter serviced.
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Old 23-04-2013, 17:58   #3
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Re: Starter motor fails when hot

replace/rebuild it before it screws you over at a bad time
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Old 23-04-2013, 18:00   #4
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Sounds like the Bendex spring not allowing engagement of gear to turn over engine. Try inspecting if visible (rust) and lite lube. Best to pull starter and have inspected by rebuild shop... Starter does turn when start is attempted?
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Old 23-04-2013, 18:15   #5
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The obvious, take it to the repair shop and before it hangs me up in a bad place rings true. Still interested in thoughts as to why its a hot not cold problem. Thanks guys.
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Old 23-04-2013, 18:33   #6
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Re: Starter motor fails when hot

Starter motors are "high impulse" motors, designed to sacrifice everything in order to put out large amounts of power for very short periods. Part of this design is to have very tight tolerance between the windings and the rotor, and if the starter is used too long, it overheats from the high power going through the wiring, the rotor coils expand, and they scrape against the windings. Then they short out, too.

If you use a typical starter for more than 15-20 seconds at a time, it overheats and takes permanent damage and the symptoms are exactly what you've got. It can take 10-20 minutes to cool back down after one hard start. Odds are you need to have it pulled and rewound before it totally slags down.
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Old 23-04-2013, 19:29   #7
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Hello Hellosailer Accepting that the solution remains the same, take to repair shop but to clarify, the problem occurred when the engine is hot not after a hard start on the starter motor.
To set the scene, I get on the boat, start motor, no problem, motor to fuel bowser (5min) stop engine, fuel up, start motor, no problem. Motor to fishing mark about 1 hour,, stop engine. No fish, after 20 minutes i decide to move. Now the problem occurs. Not happy, make a cup of tea and curse thought of having to get down bilge and check all connections. Give it another try still just a half baked whirr but no crank of the engine. Finish cup of tea. Avoid job by having my sandwich and seeing if fish are on the bite. It's a lovely day on the water. So about an hour + after I have stopped engine and half an hour after last start attempt, I give it another try before I resort to trying to find fault. WHOO HOO it cranks like a new one. Relieved, but lingering doubt. Run boat here and there over next few weeks, no problems. However, the next time I did a longer run the problem reoccurred. Hopes of a one off aboration dashed. Experienced as I now am I reached for the kettle and repeated former problem solving process. whoo hoo it worked again.
So it's when the whole engine is hot that the problem occurred. This is not to suggest seized engine, its the starter that fails to properly crank.
Do I take from your post that if the starter had been hard cranked in the past and damage has occurred that this is the resultant problem or were you saying that if I had hard cranked for 10 -20 seconds that it would then take the starter motor 20 minutes to cool down and permanent damage could have been done in the process?
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Old 23-04-2013, 19:55   #8
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Re: Starter motor fails when hot

15 seconds cranking then 1 minute cooling period is accepted by most manufacturers and is specified in service manuals.

There are two components of the starter solenoid. One part "pulls in" the plunger to engage the starter gear to the flywheel. The other part "holds in" the plunger to keep the starter gear engaged. In your case, it sounds like the "pull in" windings are intermittently going open when the engine is hot. You may need to replace the starter as an assembly in order to fix your problem as the solenoid might not be available separately.
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Old 23-04-2013, 20:00   #9
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Re: Starter motor fails when hot

I would ck the battery conections first, they can be the biggest reason for starters not working properly when the engine room heats up! just a thought ! and ya probley cked them allready ! but it's a thought !
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Old 23-04-2013, 20:09   #10
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My understanding is that this starter motor spins and throws in the cog down a sort of worm gear. It's and older design and doesn't have the solenoid on the side of the motor, its at the head of the motor. Thanks for the reply. Good info of crank and rest periods. Have never heard the specifics, just knew not to continuously crank.
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Old 23-04-2013, 20:38   #11
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Re: Starter motor fails when hot

There are some things that can't be easily explained. It sounds like something in your starter is expanding causing ether the worm gear to not engage when hot or the motor itself is not producing enough power when it is warm or hot. If you take the starter off, you may be able to see the problem. Inspect the worm drive and spring. It should be clean, rust free and well greased. there is a bearing or a bushing at the end that my be worn. A quick trip to a starter rebuild shop should be able to fix the problem without to much expence.
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Old 23-04-2013, 20:43   #12
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Re: Starter motor fails when hot

Quote:
Originally Posted by Avayak View Post
My understanding is that this starter motor spins and throws in the cog down a sort of worm gear. It's and older design and doesn't have the solenoid on the side of the motor, its at the head of the motor. Thanks for the reply. Good info of crank and rest periods. Have never heard the specifics, just knew not to continuously crank.
By 'worm gear' I take it you mean what's usually referred to as the worm (the wormgear is the wheel that the worm meshes with in a worm gearbox)?

If that's what you mean, your supposition is correct: the end of the starter motor shaft is like a multi-start, high helix angle worm, or looking at it another way, it's like a helical spline.

The self-actuating Bendix drives (and similar designs by others), which were not pulled into mesh with the ring gear by a solenoid, were relying solely on inertia.

The pinion's rotational inertial resistance means it does not want to spin up quickly enough to revolve with the motor shaft, so the only alternative is to screw itself along the helical spline and into mesh with the ring-gear. There is a heavy spring to take the severe shock of engagement.

There's a problem here which resulted in such starters being phased out (from the automotive scene) in about the 1980s: if an engine fires before getting to proper cranking speed, it may fire once or twice, but not start properly.

If the flywheel is relatively light, so that even one firing impulse can momentarily accelerate the crankshaft rotation past cranking speed, an inertia-engaged starter can demonstrate a problem whose technical name is "premature ejection":

(not to be confused with a condition which is generally regarded - especially by women - as a grave dysfunction, but some prefer to think of as a demonstration of exuberance and vitality ...)

Even if the ignition switch is held in the cranking position, the pinion will have been kicked along the helix in the reverse direction, taking it out of mesh, the moment the engine overruns, and without the inertia impulse from the initial acceleration of the starter motor, there's nothing to cause it to find its way back, hence the whirring noise.

From your description it's not clear whether the motor turns over at all: if not, then it's not a premature ejection problem, but if it does, it's a possible diagnosis.

The reason I see it being a possible explanation in the conditions you describe is this: If the engine's prewarmed, it's more likely to fire prematurely, and if it's no longer in the first flush of youth, it's unlikely to pick up and start properly at the first suggestion of firing.
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Old 23-04-2013, 20:49   #13
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Thanks Rocketman, good comment, hard to figure but solution is clear. No more cups of tea and hat fulls of hope just a healthy dose of arthritis pills, make like a pretzel and get ornery thing out and down to the repair shop. Nothing is expensive when put against being at risk in a boat.
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Old 23-04-2013, 21:30   #14
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Re: Starter motor fails when hot

This is a long shot but I had a heat related problem with the starter on my hot rod. I had switched to an aluminum flywheel and due to a greater expansion rate over steel, when hot its thickness was enough that when the solenoid pushed the straight cut starter gear towards the flywheel teeth if it caught tooth to tooth the outward travel wasn't far enough to engage the starter motor, so no motor spin, just clunk. Used shims on the block's starter flange to add a few mm of starter to flywheel distance, problem over. If your problem is the same and only happens with heat soak from the crank to the flywheel, if flywheel as some exposed area, mist it with some water for the evaporative cooling effect and see if that doesn't speed up the recovery time. If it does, buy some starter shims and find out how many needed.
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Old 23-04-2013, 21:33   #15
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Re: Starter motor fails when hot

There is a solenoid on the bendix type starter, but all it does it act as an electrical switch, that is a small current from the start switch, maybe 20 amps, causes an electromagnet to pull contacts closed so that a large amount of current, say 200 amps, can flow to the starter. This solenoid is located remotely from the starter and connected to it are heavy battery cables, one to the battery and the other to the starter. A third much lighter in wire goes to the ignition switch. If the solenoid is in the engine compartment, it can get hot and not carry the current it should. Put a hair dryer on it and see if the problem occurs.

It also might be that the brushes are worn down and do not make contact against the commutator when the engine is hot because of expansion of metal in the starter. In this case, run the boat at the dock until the engine is hot and the starter does not work and them pour cold water on it to see if it works, or our could just pull the metal band off the back of the starter and inspect the brushes to see if brushes are worn out. Here is an explodes view of this kind of starter with a bendix. If you do not have a hair dryer handy, you could also pour cold water on the solenoid after the engine compartment is hot.

http://search.yahoo.com/search;_ylt=...arts%20diagram

Click on the upper right picture in the link above
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