Bearing overload

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  • #26
Baluncore
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As you appear to be more convinced by marketing rhetoric than by pragmatic reality, any attempt to correct your misconceptions would clearly be a waste of my time.
 
  • #27
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Usually marketing rhetoric is used to over state the merits of a product, not to depreciate the integrity of a product, but none the less, I found a third manufacturer (King Engine Bearings) that uses terminology that may be more to your liking. They describe fatigue of the overlay (due to among other things, advanced ignition timing);
The fatigue of a copper based lining starts with fatigue of the overlay. The overlay flakes off from the underlying layer, disturbs the oil film, and changes the lubrication regime from hydrodynamic to boundary. The load localizes at the contact area causing the formation of small cracks on the lining surface.​
So whether the bearing overlay is displaced, extruded, abraded, or flaked, the point is the bearing is damaged. As to the cause of damage, if ignition timing is advanced enough while the starter is cranking the engine, eventually a point is reached where the ignited burning expanding gases push down with enough force to stall the starter motor. We have already calculated the forces involved- and sure, the rods can be damaged, but that doesn't prevent the rod bearings from being damaged also. If you ever seen rod bearings with copper showing only on the top bearing shell, one of the causes of this is what I am talking about.
 
  • #28
Baluncore
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351tom said:
If you ever seen rod bearings with copper showing only on the top bearing shell, one of the causes of this is what I am talking about.
What you appear to be saying is that; advanced timing during starting has the same effect as operating an overheating engine, with advanced timing, under full power, at high RPM, for more than an hour. That is simply not the case.

I have rebuilt hundreds of broken engines and seen many different modes of failure.
I have seen plenty of bent and broken connecting rods.
I have never ever seen an extruded low friction film.

You are clearly living in a different universe or reality to me.
This Physics Forum must be a wormhole between our different universes.
 
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  • #29
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I think the different types of engines we are considering may account for the "different universes". Your earlier comments;
During starting, the ignition timing should prevent an advanced spark occurring, so we can ignore pre-ignition.
indicate you have in mind either stock production engines made since electronic ignitions have been used, or engines that have been upgraded in this regard. This leaves out precisely the engines I am referring to. Take the chevy 350 for example, by far the most widely used small block engine of all time across many forms of racing , vintage vehicles, custom builds, etc. When these engines are built for performance, the stock electronic ignitions (if there were any as in pre early 1970's versions) no longer apply because the characteristics of the engine change so greatly. For example the HEI module may have had only 6 degrees retard at start. That was perfect for the engine it was designed for, but is just about useless for the racing engine with a 42 degree locked out distributor. Many times aftermarket ignition products that facilitate ignition retard at cranking are utilized, but for various reasons, many times they are not. There are a lot of variables involved, but depending on the specifics of the engine in question, you may not need to go anywhere near as far as 42 degrees to completely stall a starter motor. What I was trying to do is quantify the forces involved when this happens.
Now as far as comparing bearing loads of an engine at full power vs at cranking, consider this; the load on the engine at full power is determined by the combustion gases expanding into chamber that is increasing in size as the piston goes down the bore, whereas, the load on the cranking engine is determined by the combustion gases expanding (no, make that trying to expand) into a chamber that is decreasing in size as the piston is being forced up the bore.
You indicate that in your wealth of experience you have never seen the top rod bearing damage I mentioned. I don't doubt you at all, in the realm of the types of engines you deal with, it may be likely you never will. But take the comparative novice speedfreek who went through 2 engine rebuilds in 5000 miles with rod bearings failing showing copper (locked distributor at 36 degrees) then went to a mechanical advance with 18 degrees initial & had no problems. He is just dealing with a different kind of an engine.
 
  • #30
Baluncore
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A “comparative novice speedfreek†or a computer chip “over-clocker†is NOT an engineer.

They are individuals abusing the technology.
They have no concept of reliability engineering.
They are pushing beyond the SOE to destruction.

Economics and reliability are critical to engineering.
This is supposed to be an engineering forum.
 
  • #31
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A “comparative novice speedfreek†or a computer chip “over-clocker†is NOT an engineer.

They are individuals abusing the technology.
They have no concept of reliability engineering.
They are pushing beyond the SOE to destruction.

Economics and reliability are critical to engineering.
I agree with you 100%
My aim here is to quantify the possible bearing loads in the aforementioned scenario to point out the folly of such engine modifications. Knowing the torque of the starter motor, I suspect it will depend on on 3 more things; location of spark BTC, cranking speed, & the time interval from spark to combustion. If anyone has insight into that last item, (or the characteristics of the combustion process with regard to this) please contribute.
 

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