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I agree.. which makes me wonder why Greg , having installed the A-rods why were they not just pulled to be replaced with another same set with the correct offset. why the change and why not use the rods that had been used successfully? seems those were the most robust. (the non tapered H beam) . maybe it was in the interest in weight savings of the rotating assembly
Mark,
The rods with the 65 thou offset were those originally intended for a Chevvy or whatever but as I can read, that was not the case with the rods in the Mark A and Joe F cars unless you are aware of something that I am not.
I agree.. which makes me wonder why Greg , having installed the A-rods why were they not just pulled to be replaced with another same set with the correct offset. why the change and why not use the rods that had been used successfully? seems those were the most robust. (the non tapered H beam) . maybe it was in the interest in weight savings of the rotating assembly
One more time:
Carrillo (Gerhard) designed the correct offset rod, without any input, from me. The tapered beam rod is extremely robust and isn't remotely an issue with the given rpms and power output in an engine thst is run properly....huge safety margins are present.
The loads imparted onto a connecting rod in an engine that detonates is extremely high (the rod is "met" with a huge force trying to push it backwards in the opposite direction It is traveling....very similar to a hydrolocked condition, except the "explosion" is actively expanding....in the "reverse" direction.)
As it turns out, Carrillo did not design the rod to endure the force of detonation. In checking with them, they also do not believe that their regular "H" beam rod would survive this abuse.
As you endlessly go on and on, trying to find fault with the connecting rod, you might find it interesting that absolutely none of their connecting rods are designed to endure the extreme forces of detonation....these forces are not included in their design criteria!
That makes sense. The only reason ive brought up the connecting rod is that it is different vs other engines that have not failed . if it is detonation, and we all are aware of the extreme forces present in detonation, then why does the bearing not show signs of detonation forces. every force meets an equal and opposing force, so you would think , if detonation damages the rod, in that spectacular fashion, the bearing should show signs of damage as well. however, this force and direction could be different if the piston was damaged due to detonation , which stopped it in a bore, (maybe cracks at TDC, and then travels down, and jams on the way up, at a high rod angle, causing more of a shearing force. again, this is just a discussion. we are all interested in the cause of death here.
if the piston is not showing signs of detonation, then what else could have caused the failure? why would the rod break near the big end and not the small end where it is weaker? again, just questions that come to mind. it would all make sense if the rod offsets were wrong, but im sure , as you said, that is not the case.
Originally Posted by GregBBRD
One more time:
Carrillo (Gerhard) designed the correct offset rod, without any input, from me. The tapered beam rod is extremely robust and isn't remotely an issue with the given rpms and power output in an engine thst is run properly....huge safety margins are present.
The loads imparted onto a connecting rod in an engine that detonates is extremely high (the rod is "met" with a huge force trying to push it backwards in the opposite direction It is traveling....very similar to a hydrolocked condition, except the "explosion" is actively expanding....in the "reverse" direction.)
As it turns out, Carrillo did not design the rod to endure the force of detonation. In checking with them, they also do not believe that their regular "H" beam rod would survive this abuse.
As you endlessly go on and on, trying to find fault with the connecting rod, you might find it interesting that absolutely none of their connecting rods are designed to endure the extreme forces of detonation....these forces are not included in their design criteria!
That makes sense. The only reason ive brought up the connecting rod is that it is different vs other engines that have not failed . if it is detonation, and we all are aware of the extreme forces present in detonation, then why does the bearing not show signs of detonation forces. every force meets an equal and opposing force, so you would think , if detonation damages the rod, in that spectacular fashion, the bearing should show signs of damage as well. however, this force and direction could be different if the piston was damaged due to detonation , which stopped it in a bore, (maybe cracks at TDC, and then travels down, and jams on the way up, at a high rod angle, causing more of a shearing force. again, this is just a discussion. we are all interested in the cause of death here.
if the piston is not showing signs of detonation, then what else could have caused the failure? why would the rod break near the big end and not the small end where it is weaker? again, just questions that come to mind. it would all make sense if the rod offsets were wrong, but im sure , as you said, that is not the case.
Quite frankly, I think people (especially you) have been putting the horse before the cart....just for the sake of stiring ****.
Rob Edwards has a picture of the hole in the engine with the piston in clear view (maybe he will post it.) The piston does not have the wrist pin or the top piece of the connecting present. The bottom half of the piston bosses are gone.....broken off the piston.
If a connecting rod fails, in the middle from any sort of defect or excessive rpms, this will 99.9% of the time happen on the exhaust stroke. The piston slams into the cylinder head and stops....out of range of the remaining broken chunk of connecting rod that remains on the crankshaft. It will generally sit there, only gathering further damage from flying debris.....the pin does not get ripped out.....the "flailing" piece of connecting rod on the crankshaft can no longer "reach" this piston assembly.
If you look at this picture that Rob has, there is very "wide" damage to the block, the cradle, and the oil pan...like the wrist pin was still in the connecting rod for several (many) revolutions, before the rod broke again....slinging those pieces out of the engine.
From this picture, alone, I'm questioning if the rod was even the first point of failure.
Semi-retired, as of Feb 1, 2023.
The days of free technical advice are over.
Free consultations will no longer be available.
Will still be in the shop, isolated and exclusively working on project cars, developmental work and products, engines and transmissions.
Have fun with your 928's people!
I've seen several destroyed 928 engines......but damn that pic is possibly the WORST I have seen....when casper blew and broke the stock rod in 4 pieces it didn't vent the block or oil pan at all....it just dented and bent the oil pan
I've seen several destroyed 928 engines......but damn that pic is possibly the WORST I have seen....when casper blew and broke the stock rod in 4 pieces it didn't vent the block or oil pan at all....it just dented and bent the oil pan
Yeah, this picture was taken though the hole in the oil pan....
These pistons would either have double Spirolox or Kramm-Lox....no "circlips" allowed, here.
Doubtfully, either is going to come out...although the piston pin "hammering" on the pin retainers gets really severe with detonation (that's one of the first signs of detonation.)
Here's the shot looking up the bore of cylinder #7:
Originally Posted by GregBBRD
Quite frankly, I think people (especially you) have been putting the horse before the cart....just for the sake of stiring ****.
Rob Edwards has a picture of the hole in the engine with the piston in clear view (maybe he will post it.) The piston does not have the wrist pin or the top piece of the connecting present. The bottom half of the piston bosses are gone.....broken off the piston.
If a connecting rod fails, in the middle from any sort of defect or excessive rpms, this will 99.9% of the time happen on the exhaust stroke. The piston slams into the cylinder head and stops....out of range of the remaining broken chunk of connecting rod that remains on the crankshaft. It will generally sit there, only gathering further damage from flying debris.....the pin does not get ripped out.....the "flailing" piece of connecting rod on the crankshaft can no longer "reach" this piston assembly.
If you look at this picture that Rob has, there is very "wide" damage to the block, the cradle, and the oil pan...like the wrist pin was still in the connecting rod for several (many) revolutions, before the rod broke again....slinging those pieces out of the engine.
From this picture, alone, I'm questioning if the rod was even the first point of failure.
thats what i was thinking..........the piston failed first then, all heck broke loose.
Originally Posted by FredR
Mark,
The rods with the 65 thou offset were those originally intended for a Chevvy or whatever but as I can read, that was not the case with the rods in the Mark A and Joe F cars unless you are aware of something that I am not.
Fred, you misread, or i mis-wrote my message. i was saying.. why not use the previous rods that were sucessful, rather than the new A-rods... (even with the correct offset) . i shouldn't have brought that up.. i was just curious as to the change.
thats what i was thinking..........the piston failed first then, all heck broke loose.
Fred, you misread, or i mis-wrote my message. i was saying.. why not use the previous rods that were sucessful, rather than the new A-rods... (even with the correct offset) . i shouldn't have brought that up.. i was just curious as to the change.
The crankshaft design changed, requiring the use of different dimension rods.
The rods with the 65 thou offset were those originally intended for a Chevvy or whatever but as I can read, that was not the case with the rods in the Mark A and Joe F cars unless you are aware of something that I am not.
Both of these engines had the correct offset rods.
Both of these engines had the correct offset rods.
yes, i think he mistook what i said.. it wasnt clear. what was the cause of the A -Rod failure that led you to change those rods in marks engine to the "Tapered H" design.
Originally Posted by GregBBRD
The crankshaft design changed, requiring the use of different dimension rods.
can you tell us , at the high level, what had changed on the new crankshaft? was this your design even though it was built by someone like moldex?
yes, i think he mistook what i said.. it wasnt clear. what was the cause of the A -Rod failure that led you to change those rods in marks engine to the "Tapered H" design.
Mark,
My post was querying why anyone would install a 65 thou rod offset into any 928 motor and nothing whatsoever to do with the recently failed motors. Your response seemed to intimate I was somehow relating this to the failed motors- just not the case.
My perception is that there is very little side clearance between the con rod and the piston bosses and that crank end float is specified by Porsche to ensure that what happened in the failure scenario depicted by the Carillo finite element analysis [using Chevvy spec rods at 65 thou offset] cannot happen. From what Greg said it would seem that motors in those "early days" were being built with rods creating this 65 thou offset, that being the case either there was quite some clearance between the rod and piston bosses creating an overturning moment or the rod had a built in bending stress with the rod small end side face in hard contact with the piston boss on one side and either way the poor thing was ultimately doomed to failure before the motor had been cranked.
05-17-2018, 01:57 PM
