<VV> Maybe the starter.

[Hugo Miller]

Some years ago I began fitting Odyssey batteries to my coaches, at 
great expense, as the one thing I need abve all else is reliability. You 
can tell they are good quality batteries, because when you go to pick 
them up, the feel like they are glued to the ground.
The way I described these batteries to friends and colleagues was to 
say they spun the engine over (Cummins 10 litre diesel) from cold in the 
middle of an English winter just as if it were a hot engine on a 
summer's day.
And yet some on this group are trying to tell me that it takes more 
energey to turn an engine over at normal running teperature than it does 
when cold?
Are we living in some sort of parallel universe or what?


On 2020-08-09 03:46, FrankDuVal via VirtualVairs wrote:
> You are confusing several comments.
>
> 1. A cold engine does turn easier than a hot engine. Now, a frozen
> engine, as in low temperature frozen, does turn harder! Cold for this
> discussion is 70 °F or 21 °C. For our California members! This frozen
> slow crank is mostly oil viscosity related for frictional loss.  Even
> the oil in he starter bushings, and anything else turned by the
> engine, like transmission input gears. Add to that the harder to move
> fuel, and harder to atomize fuel at frozen temperatures. Diesel fuel
> gets hard to move at 16 °F   (-8° C). BTDT. :)   And then if there is
> water in the fuel.....It doesn't move at all!  BTDT also....:)
>
> 2. A hot starter also turns harder than a cold starter (again, cold
> as in not yet running today, not winter time in Minnesota).
>
> 3. Worn parts like bushings in starters allow the armature to be out
> of position due to magnetic forces acting upon it. Hence the pole
> piece marks on armatures with worn bushings.
>
> 4. Worn bushings + drag of armature on pole pieces makes it harder to 
> turn.
>
> 5. A mechanical piece of equipment that works OK when cold but not OK
> when warm is a temperature related problem. Worn parts change shape
> due to heat (as do perfectly fine parts), so a marginally OK starter
> suddenly becomes a not good starter because of heat. And as soon as 
> it
> and the engine cool down, works fine again. But of course, it is not
> working fine, but does start the engine so it does not yet get
> replaced, even though it is worn out.
>
> 6. No one said the engine alone got so hot the perfectly fine starter
> could not turn it over. The starter is bad, the engine is not, just
> operating normally as a warm engine, needs more umph to turnover when
> warm.
>
> 7. Not mentioned yet, but related to worn bushings, is starter drive
> to flywheel clearance. It might be possible the magnetic forces on 
> the
> armature cause it to shift enough in worn bushings to close the gear
> gap, causing more frictional loss. When cold, maybe that force is 
> less
> due to the engine turning over easier. Starters are series wound
> motors, the more the load, the more current they draw, the more
> magnetic force increases inside on the armature.
>
> 8. The only proof is that just changing the starter fixes the
> problem. So, the proof of what is wrong with the starter is change a
> part at a time and retest! Who has the time and energy, so just put
> bushings and brushes in and call it a day! Ha!
>
> I like having discussions.
>
> Frank DuVal
>
> On 8/8/2020 3:51 PM, Hugo Miller via VirtualVairs wrote:
>> And the notion that a heavy diesel engine with over a million miles 
>> on the clock would be so tight at normal running temperature that a 
>> massive 24 volt starter cannot even turn it over - well that is 
>> frankly laughable. I am equally certain that an engine at normal 
>> running temperature will take less effort to crank than a cold engine. 
>> I thought that was universal knowledge, so obvious that it wouldn't 
>> need stating. The Wehrmacht found that out to their cost at 
>> Stalingrad. _______________________________________________
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