Drilled Crank Thoughts...
03-20-2008, 03:11 PM
#376
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It was a Friday afternoon ,after the beer break, just before the summer holiday shut down. The tour group passing through happened to include one especially good looking young woman,Heidi ,wearing high heels and a rather short skirt. Hans could not help but take notice. He already had his rod in his hand when the thought hit him ....drop the rod cap and he would have to bend down to get it . That would improve his vantage point when he looked at young lady. But Hans was not the only one with a rod in his hand. Suitably distracted Frederik and Ali (foriegn guest worker) also dropped their rod caps on the floor as Heidi passed by ....
03-20-2008, 03:22 PM
#377
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Must . . . resist . . . commenting on Heidi's Skirt and Hans' Rod. Must Resist.
Mention on the Sebring thread about meeting someone involved in the pseudo factory campaign of a 928 was there were problems with air entrainment in the lubrication.
The crank must make a very good swizzle stick when it whips through hot oil.
Kibort's engine is, urm I'm not sure what his engine is. Not sure how it relates to factory 928 motors. His was a one-off for a high speed record attempt if I didn't follow it's lineage wrong.
Haven't followed this thread but has anyone knife edged a 928 crank?
Just a thought.
Frappacino yummm. Not so yumm when it's on the dipstick.
Mention on the Sebring thread about meeting someone involved in the pseudo factory campaign of a 928 was there were problems with air entrainment in the lubrication.
The crank must make a very good swizzle stick when it whips through hot oil.
Kibort's engine is, urm I'm not sure what his engine is. Not sure how it relates to factory 928 motors. His was a one-off for a high speed record attempt if I didn't follow it's lineage wrong.
Haven't followed this thread but has anyone knife edged a 928 crank?
Just a thought.
Frappacino yummm. Not so yumm when it's on the dipstick.
It was a Friday afternoon ,after the beer break, just before the summer holiday shut down. The tour group passing through happened to include one especially good looking young woman,Heidi ,wearing high heels and a rather short skirt. Hans could not help but take notice. He already had his rod in his hand when the thought hit him ....drop the rod cap and he would have to bend down to get it . That would improve his vantage point when he looked at young lady. But Hans was not the only one with a rod in his hand. Suitably distracted Frederik and Ali (foriegn guest worker) also dropped their rod caps on the floor as Heidi passed by ....
03-20-2008, 03:44 PM
#378
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Kevin, the problem with your theory is it relies on a string of unlikely events.
First there was the dropped cap which just happen to be the same number as a different rod on the engine being assembled. Could happen.
Next the mixed rod and cap have to be near identical to even allow the engine to run without immediately destroying the bearing, never mind last 100,000 miles of, I'm sure "spirited" driving (it is a 928 after all) . Also could happen. Problem is, the odds of all three events happening simultaneously are probably astronomical, especially on a limited production vehicle.
If you want to bolster your theory, measure the mismatch on the inside of the big end using mismatched caps and rods, then see how these numbers compare to the max allowable mismatch to allow long engine life. I think that hundreds if not thousands of mismatched caps and rods would have to be tried before you got one that was close.
I have forgotten all my stats courses, but you could probably work up a rough range of odds. For example, dropped cap, once a week x 20 engines a day x 8 caps = 1/800 caps x the odds it would match numbers in the numbering system (0-999) x the odds of the cap actually being a perfect match. (unknown but likely quite low otherwise the factory wouldn't even bother numbering the caps?) Seems like a stretch at best.
First there was the dropped cap which just happen to be the same number as a different rod on the engine being assembled. Could happen.
Next the mixed rod and cap have to be near identical to even allow the engine to run without immediately destroying the bearing, never mind last 100,000 miles of, I'm sure "spirited" driving (it is a 928 after all) . Also could happen. Problem is, the odds of all three events happening simultaneously are probably astronomical, especially on a limited production vehicle.
If you want to bolster your theory, measure the mismatch on the inside of the big end using mismatched caps and rods, then see how these numbers compare to the max allowable mismatch to allow long engine life. I think that hundreds if not thousands of mismatched caps and rods would have to be tried before you got one that was close.
I have forgotten all my stats courses, but you could probably work up a rough range of odds. For example, dropped cap, once a week x 20 engines a day x 8 caps = 1/800 caps x the odds it would match numbers in the numbering system (0-999) x the odds of the cap actually being a perfect match. (unknown but likely quite low otherwise the factory wouldn't even bother numbering the caps?) Seems like a stretch at best.
Of the four rod and cap pairs I pulled out of just one core (390, 447, 542, 548), one pair gave a mismatch of about .005" to .001" at the parting line in the bore. Measuring the inner bore diameter gave a value of 2.170". The matched cap gave a value of 2.168" -- so .002" difference. Also remember the crush would not be equivalent (less) so that additional clearance would be even smaller because the shell would not completely seat.
I think the odds of such a mismatch resulting in a viable initially babied motor are proportional to finding just such a combination in only four rods from one motor.
Originally Posted by Kevin W
I think that hundreds if not thousands of mismatched caps and rods would have to be tried before you got one that was close.
Consider it bolstered.
03-20-2008, 04:03 PM
#379
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Brendan,
There was a hi-res photograph of the rod in question pre-failure taken by the engine builder. There are hi-res pictures of other rods in the same engine bracketing its manufacturing time that do not show the same morphology shift. There are hi-res photographs of rods from another engine that also do not show this morphology shift. There are hi-res photographs that do not show these morphology shifts even when the components are deliberately mismatched. The manufacturing process is now a hard fact and it does not support such a morphology shift -- in fact, it is a clear indicator of a problem. These are hard facts.
Edit: It's Easter Sunday
There was a hi-res photograph of the rod in question pre-failure taken by the engine builder. There are hi-res pictures of other rods in the same engine bracketing its manufacturing time that do not show the same morphology shift. There are hi-res photographs of rods from another engine that also do not show this morphology shift. There are hi-res photographs that do not show these morphology shifts even when the components are deliberately mismatched. The manufacturing process is now a hard fact and it does not support such a morphology shift -- in fact, it is a clear indicator of a problem. These are hard facts.
Edit: It's Easter Sunday
Last edited by Kevin Johnson; 03-23-2008 at 10:01 AM.
03-20-2008, 04:03 PM
#380
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OK so the last multiplier is 1 in 4. So we have 1 in 800 x 1 in thousand x 1 in 4. Around 1 in 3.2 million. Pretty slim odds. Of course the only number that is solid is the 1 in a thousand due to the numbering system, the other number are more speculative. Edit: Oh I forgot to add the odds of the engine being babied, let's use 1 in 4 again, now we are at 1 in 12.8 million. Of course we could just measure the suspected big end and see if it is in spec. And of course the odds of it being on the 1/6 journal, x 4 again > 50 million to 1.
Last edited by Kevin Q; 03-20-2008 at 04:53 PM. Reason: more odds
03-20-2008, 04:11 PM
#381
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I dunno Jim, I think I've seen some photo's of the 928 assembly line that would indicate that the tech's didn't necessarily take a break to have their beer.
Rumour has it that Heidi's real name was Gina, and that she was the niece of some famous Italian sports car maker. Industrial espionage at its best.
03-20-2008, 04:22 PM
#382
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kevin, im not sure what failure you analyse but years of treating psychosis has taught me there is no arguing with insanity
put an end to the speculation and bolt your deliberately mismatched rods and caps together in that engine youve got and see if it runs. according to you that combo will be good for 100 thousand miles of street driving right?
put an end to the speculation and bolt your deliberately mismatched rods and caps together in that engine youve got and see if it runs. according to you that combo will be good for 100 thousand miles of street driving right?
03-20-2008, 04:36 PM
#383
Brendan,
There was a hi-res photograph of the rod in question pre-failure taken by the engine builder. There are hi-res pictures of other rods in the same engine bracketing its manufacturing time that do not show the same morphology shift. There are hi-res photographs of rods from another engine that also do not show this morphology shift. There are hi-res photographs that do not show these morphology shifts even when the components are
There was a hi-res photograph of the rod in question pre-failure taken by the engine builder. There are hi-res pictures of other rods in the same engine bracketing its manufacturing time that do not show the same morphology shift. There are hi-res photographs of rods from another engine that also do not show this morphology shift. There are hi-res photographs that do not show these morphology shifts even when the components are
But I think that a point that may have been missed is that the photo shows the very edge of the rod and cap, which has nothing to do with the actual ID location of the combined piece.
I would hope that after putting the two pieces together for stamping, and then putting the rod bolts in, that the rods are properly sized. After that it doesn't matter what the outside of the rod casting looks like.
03-20-2008, 04:58 PM
#384
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Dr Nick, true. This "chain of events" is the reason Airliner crashes are so rare. A chain of events has to happen just right. The odds of it happening are so low that it almost never occurs twice the same way. This is good news, but it also means that fixing the cause of a crash is kind of like closing the barn door after the horses have left.
03-20-2008, 05:08 PM
#385
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Gina still disguised as Heidi was covertly taking photos for her Uncle he was particularily interested in the secret process of using mismatched rod caps which assured that the engine would run well for 100,000 miles since none of her Uncle's exotic Italian engines had ever lasted anywhere near than long... Hoping to get her hands on one of the rods she had slipped Ali a note with her room number at the hotel where the tour group was staying it read " Meet me at the hotel at 10 this evening room 928 (happenstance ,fate,chance) bring the rod and especially a cap, we need to be very careful ". Ali not being all that familiar with western culture was needless to say much looking forward to the planned meeting. Frederik and Hans became increasingly disturbed by Ali's behavior so much so that they reported to their supervisor that ....
03-20-2008, 06:16 PM
#386
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There is a nice model online drawn from the common birthday problem.
The formula for a 50:50 chance of a match is the square root of the number of categories times 1.2.
In this case the number of categories is 1000, subsuming 000 is valid.
The square root of 1000 is 31.622
31.622 X 1.2 = 37.622
So, if 38 rods were selected from a mixed bin of rods with serial numbers ranging from 000 to 999, the odds would be 50:50 that two would match. Of course there are a lot of assumptions in the distribution of serial numbers in a mixed bin of rods used on an ongoing basis. Good thesis project there.
So, what's that? Every 5 engines? Four times a day? By the odds, it would happen twice a day.
Dropping, size, etc. all on top of that, of course. Still hardly rare.
Kinda counter-intuitive, eh? That's the normal reaction in a stats class.
The formula for a 50:50 chance of a match is the square root of the number of categories times 1.2.
In this case the number of categories is 1000, subsuming 000 is valid.
The square root of 1000 is 31.622
31.622 X 1.2 = 37.622
So, if 38 rods were selected from a mixed bin of rods with serial numbers ranging from 000 to 999, the odds would be 50:50 that two would match. Of course there are a lot of assumptions in the distribution of serial numbers in a mixed bin of rods used on an ongoing basis. Good thesis project there.
So, what's that? Every 5 engines? Four times a day?
By the odds, it would happen twice a day. Dropping, size, etc. all on top of that, of course. Still hardly rare.
Kinda counter-intuitive, eh? That's the normal reaction in a stats class.
OK so the last multiplier is 1 in 4. So we have 1 in 800 x 1 in thousand x 1 in 4. Around 1 in 3.2 million. Pretty slim odds. Of course the only number that is solid is the 1 in a thousand due to the numbering system, the other number are more speculative. Edit: Oh I forgot to add the odds of the engine being babied, let's use 1 in 4 again, now we are at 1 in 12.8 million. Of course we could just measure the suspected big end and see if it is in spec. And of course the odds of it being on the 1/6 journal, x 4 again > 50 million to 1.
03-20-2008, 06:27 PM
#387
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After carefully weighing all the evidence, hypotheses, conjectures, statistical estimates, and WAGs, I declare this contest a draw. 
Let's move on to "Does God exist?"
Let's move on to "Does God exist?"
03-20-2008, 06:30 PM
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kevin, im not sure what failure you analyse but years of treating psychosis has taught me there is no arguing with insanity
put an end to the speculation and bolt your deliberately mismatched rods and caps together in that engine youve got and see if it runs. according to you that combo will be good for 100 thousand miles of street driving right?
put an end to the speculation and bolt your deliberately mismatched rods and caps together in that engine youve got and see if it runs. according to you that combo will be good for 100 thousand miles of street driving right?
God has whispered in my ear to stop being so mean to drnick. 
Last edited by Kevin Johnson; 03-23-2008 at 10:06 AM.
03-20-2008, 06:36 PM
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