A question about starter motors...

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Hi all, this isn't actually about a car - it's a starter on a generator.

My symptom is this (and it's intermittent):

sometimes - the starter turns, but the pinion is very slow against the resistance of the engine and doesn't turn it over. I can hear the starter spinning internally... also high heat at the positive terminal of starter (visible smoke). Other times, it turns over fine.

I always assumed the armature and pinion were all one piece, but apparently there are three different designs, one of which seems to have a kind of clutch mechanism... so presumably this "clutch" part is slipping.

I'll know more when I've stripped it down.

This genny is over 12 years old and has done a hell of a lot of work as I live off-grid -- in the winter it's often run every other day for 4 - 8 hours, and this is the first bit of trouble Ive had with the starter... it's a Hitachi and came with the machine when new. Quite impressive really, I think the genny has over 6000 hours (last time I looked).

Anyway... chances are I may have to at least replace the armature assembly (I do have a spare lying around), but just wondering if anyone here has had this kind of problem before and whether there's any outside chance of an easy fix to the existing starter?

Cheers.
 
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Well... I have the starter stripped down... everything is clean as a whistle and looks good. I've tried gripping the pinion in vice grips and attempting to turn the armature by hand to simulate the "slipping" but presumably I'm not able to produce the kind of torque needed... plus it was an intermittent problem anyway. pinion spins back the other way like it's meant to.
Seems this is a pretty rare but not unheard of problem: https://www.quora.com/Pre-engaged-s...r-slipping-But-only-sometimes-Anyone-know-why

So I guess i'll try the spare armature I have and see how that goes. Other than that, I'll have to see if the armature is available as a spare for that make of Hitachi starter.. or else buy another starter.
 
At a guess, one of the two field windings of the dynastarter is starting to feel its age, and is occasionally shorting out - hence the heat and smoke.
These devices also often incorporate a sprag clutch that disengages when the engine starts - it’s worth looking at that too.
For such an important machine I’d consider getting the dynastart rewound, if a new replacement isn’t available.
John :)
 
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The report seems to fit what was called a lazy starter, what was actually wrong was worn bearings, so the armature was closer than normal to the field coil shoes, if the engine was easy to turn over starter worked fine, but if the oil was thick and it needed more effort the armature would bend slightly, only a few thous, but enough so armature touched the field coil shoes, so would really slow down the starter.

Normally you can see where the armature has touched the field coil shoes, and new bearings fixes the problem.
 
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