[zb]
anorak:Carryfast:
It’s obvious that there were loads of caveats and qualifications attached to that statement nor is it saying that no tensile ( inertial ) load exists.
It was intended to make anyone think.0
I’ll remind you that it isn’t me who’s trying to suggest that AEC couldn’t have held a 130 x 154 motor together at 1,900 rpm because the bs ‘centrifugal forces’ contained in a skipping rope would defeat them. 
Carryfast:
[zb]
anorak:Carryfast:
It’s obvious that there were loads of caveats and qualifications attached to that statement nor is it saying that no tensile ( inertial ) load exists.
It was intended to make anyone think.
I’ll remind you that it isn’t me who’s trying to suggest that AEC couldn’t have held a 130 x 154 motor together at 1,900 rpm because the bs ‘centrifugal forces’ contained in a skipping rope would defeat them.
It isn’t me either, or anyone else.
Franglais:
.
A con rod isn’t subject to just tensile and compressive forces. When at an angle there are shear forces involved. Look at the cross section? It often bears a resemblance to an “H” section beam.
Failure isn’t just a catastrophic failure through fracture, it can also be a plastic distortion.
.
As an aside, look too at reinforced concrete beams: especially pre-stressed one, the metal reinforcement is not symmetrical.
.
Tell us which ’ forces at an angle’ could possibly exceed those caused by compressive loads on the rod between TDC and 90 degrees after TDC on the power stroke ?.Why wouldn’t reducing those compressive loads, by multiplying them with more leverage, for a given torque output, help to alleviate that.
[zb]
anorak:Carryfast:
[zb]
anorak:Carryfast:
It’s obvious that there were loads of caveats and qualifications attached to that statement nor is it saying that no tensile ( inertial ) load exists.
It was intended to make anyone think.
I’ll remind you that it isn’t me who’s trying to suggest that AEC couldn’t have held a 130 x 154 motor together at 1,900 rpm because the bs ‘centrifugal forces’ contained in a skipping rope would defeat them.
It isn’t me either, or anyone else.
Feel free to explain what this is all about in the context of TL12 v RR Eagle.Or even the TL12 made to the 590’s bore stroke ratio.What are you actually arguing about by referring to ‘‘load on the big end caused by centrifugal acceleration’’ and and why.
How could such a load on the big end possibly exceed the tensile strength of the big end bearing cap fastenings.Since when did big end cap bolts need to be stronger than head bolts and main bearing cap bolts and why aren’t they.
Carryfast:
Feel free to explain what this is all about in the context of TL12 v RR Eagle.Or even the TL12 made to the 590’s bore stroke ratio.What are you actually arguing about by referring to ‘‘load on the big end caused by centrifugal acceleration’’ and and why.
Centrifugal acceleration is one of the factors which influence engine design. You used to to think it did not exist, as evidenced by the quote above, which is rapidly disappearing over the horizon in the mirror LOL. Now you appear to be enraged by the very existence of tensile loads- how can they possibly exist, inside a thing full of fire■■? Grrrr!!!
[zb]
anorak:Carryfast:
Feel free to explain what this is all about in the context of TL12 v RR Eagle.Or even the TL12 made to the 590’s bore stroke ratio.What are you actually arguing about by referring to ‘‘load on the big end caused by centrifugal acceleration’’ and and why.Centrifugal acceleration is one of the factors which influence engine design. You used to to think it did not exist, as evidenced by the quote above, which is rapidly disappearing over the horizon in the mirror LOL. Now you appear to be enraged by the very existence of tensile loads- how can they possibly exist, inside a thing full of fire■■? Grrrr!!!
I’ve clearly said they are negligible v the compressive loads at the required type of specific torque outputs and engine speeds.
So tell us why would your bs tensile loads have possibly influenced the design of the 760/TL12 v the RR Eagle or even a 130 x 154 design knowing that a 183 mm stroke at an 0.79 bore stroke ratio can work happily at 2,300 rpm and the fact that the ‘tensile’ loads can’t possibly exceed the tensile strength of the big end bearing cap fastenings.
As opposed to the main bearing cap and head fastenings containing the compressive forces.
What caused the failures pictured in the above link?
Tension?
Compression?
Shear?
All the above?
Carryfast:
[zb]
anorak:Carryfast:
Feel free to explain what this is all about in the context of TL12 v RR Eagle.Or even the TL12 made to the 590’s bore stroke ratio.What are you actually arguing about by referring to ‘‘load on the big end caused by centrifugal acceleration’’ and and why.Centrifugal acceleration is one of the factors which influence engine design. You used to to think it did not exist, as evidenced by the quote above, which is rapidly disappearing over the horizon in the mirror LOL. Now you appear to be enraged by the very existence of tensile loads- how can they possibly exist, inside a thing full of fire■■? Grrrr!!!
I’ve clearly said they are negligible v the compressive loads at the required type of specific torque outputs and engine speeds.
So tell us why would your bs tensile loads have possibly influenced the design of the 760/TL12 v the RR Eagle or even a 130 x 154 design knowing that a 183 mm stroke at an 0.79 bore stroke ratio can work happily at 2,300 rpm and the fact that the ‘tensile’ loads can’t possibly exceed the tensile strength of the big end bearing cap fastenings.
As opposed to the main bearing cap and head fastenings containing the compressive forces.
Tensile loads are not “negligible”. You have actually stated the truth, while denying it:
Carryfast:
…the fact that the ‘tensile’ loads can’t possibly exceed the tensile strength of the big end bearing cap fastenings.
Now, twist that last sentence round, and you will have a design criterion.
Franglais:
Link to pictures of con-rodsWhat caused the failures pictured in the above link?
Tension?
Compression?
Shear?
All the above?
All of the bent rods are hydraulic locks, therefore compressive buckling, nowt to do with the design of the rod. The bent and broken ones may or may not be seized bearings, at either end. The “7.3 vs 6.0” one is a tensile fatigue failure of the rod, either where it is waisted above the big end, or just above the bolt. Difficult to say where. The “Piston broke in half” one is a tensile failure, either the piston or the big end bolts.
In-service failures are not usually good representations of design limitations. They are usually extraordinary events, like the driver tries to ford a stream, and gets a cylinder of water in his engine, or over-revs his engine, or his fitter is a farmer. The only design ■■■■-up in the above list is the tensile failure of the rod one. It seems, from the text, that the manufacturer selected a material with too short a fatigue life, with the cyclic tensile loads present.
[zb]
anorak:Franglais:
Link to pictures of con-rodsWhat caused the failures pictured in the above link?
Tension?
Compression?
Shear?
All the above?All of the bent rods are hydraulic locks, therefore compressive buckling, nowt to do with the design of the rod. The bent and broken ones may or may not be seized bearings, at either end. The “7.3 vs 6.0” one is a tensile fatigue failure of the rod, either where it is waisted above the big end, or just above the bolt. Difficult to say where. The “Piston broke in half” one is a tensile failure, either the piston or the big end bolts.
In-service failures are not usually good representations of design limitations. They are usually extraordinary events, like the driver tries to ford a stream, and gets a cylinder of water in his engine, or over-revs his engine, or his fitter is a farmer. The only design ■■■■-up in the above list is the tensile failure of the rod one. It seems, from the text, that the manufacturer selected a material with too short a fatigue life, with the cyclic tensile loads present.
‘‘Fitter is a farmer’’ Cheeky [zb] 
[zb]
anorak:Franglais:
Link to pictures of con-rodsWhat caused the failures pictured in the above link?
Tension?
Compression?
Shear?
All the above?All of the bent rods are hydraulic locks, therefore compressive buckling, nowt to do with the design of the rod. The bent and broken ones may or may not be seized bearings, at either end. The “7.3 vs 6.0” one is a tensile fatigue failure of the rod, either where it is waisted above the big end, or just above the bolt. Difficult to say where. The “Piston broke in half” one is a tensile failure, either the piston or the big end bolts.
In-service failures are not usually good representations of design limitations. They are usually extraordinary events, like the driver tries to ford a stream, and gets a cylinder of water in his engine, or over-revs his engine, or his fitter is a farmer. The only design ■■■■-up in the above list is the tensile failure of the rod one. It seems, from the text, that the manufacturer selected a material with too short a fatigue life, with the cyclic tensile loads present.
Over revving an engine and getting the conrod to fail under tension is an example of your contention, denied by some, that tension is a significant force in design.
It also shows, I suggest, the limits of a design. Not a design failure.
If an engine is designed to run at a specific max RPM and somebody runs it higher, that isn`t a design failure. It is a failure in service due to misuse.
It is maybe a good marker for a design limitation: an engine designed to run at say 2,000rpm that runs for years at that speed, but immediately lets go at 2,100rpm could be proof of using adequate but not excessive materials?
Franglais:
It is maybe a good marker for a design limitation: an engine designed to run at say 2,000rpm that runs for years at that speed, but immediately lets go at 2,100rpm could be proof of using adequate but not excessive materials?
It might have stayed together at 2200rpm earlier in its life. Restricted to 2000rpm, it might have enjoyed three lives.
Franglais:
What caused the failures pictured in the above link?
Tension?
Compression?
Shear?
All the above?
Firstly tell us when and where the piston and rod assembly is under any greater stress than between a few degrees before TDC on the compression stroke to 90 degrees after TDC on the power stroke.
Try to substitute leverage at the crank with more cylinder pressures and/or more piston area that’s your most likely failure point.Or the head to block joint in the case of using higher cylinder pressures as a substitute for leverage at the crankshaft.
Question for Anorak if torque is only equal to ‘bore squared x stroke’ how does he explain the principle of the triple expansion engine regards the equivalent output of the smallest cylinder bore and piston v the largest.A bigger bore just means more torque for the equivalent cylinder pressure like more leverage ‘but’ still at the expense of more load on the con rod assembly.
The fact is the TL12’s leverage deficit v the Eagle or TD120 was greater than its piston area advantage and that’s why they didn’t dare sign the TL12 off for production with an inter cooler and increased boost in an attempt to match them.It would have been the worst of all worlds of more stress on both the piston and rod assembly and the head to block joint.
None of which having anything to do with holding the piston and rod to the crankshaft against supposed ‘centrifugal’ forces.But quite possibly what happens when excessive compressive forces on ignition meet the intertial load on the rod assembly between the compression stroke and the power stroke.Bearing in mind an around equivalent piston speed with a 152 mm stroke at 1,900 rpm as 142 mm stroke at 2,000 rpm and we know that a 183 mm stroke can manage fine at 2,300 rpm without the rod flying away from the crankshaft.
So assuming that tension was the main cause of your examples how is it that the big end bearing cap fasteners were obviously stronger in tension than the con rod.I don’t buy it.
[zb]
anorak:
Tensile loads are not “negligible”. You have actually stated the truth, while denying it:Carryfast:
…the fact that the ‘tensile’ loads can’t possibly exceed the tensile strength of the big end bearing cap fastenings.Now, twist that last sentence round, and you will have a design criterion.
Tensile loads are negligible compared to compressive ones at truck type engine speeds.Which part of a 183 mm stroke happily managing at 2,300 rpm didn’t you understand.
Are you for real.Feel free to explain how the tensile load on the con rod can exceed the tensile strength of the big end bearing cap fastenings and yet those fastenings will still hold.You do know what holds the con rod to the crankshaft in that regard.
You still don’t seem to want to answer the question why are main bearing cap and head fastenings stronger than big end bearing cap fastenings.Now awaits you telling us that the big end bearing cap fastenings are actually stronger.
The two things that many so-called fitters ignore are: ‘big end bolts are single use only’ and ‘never punch mark con rods and big end caps’.
And this was the result of a machine shop welding an 80 year old con rod which had failed a crack test. IIRC I was told this let go at virtually tickover speed as traffic moved off downhill.
cav551:
The two things that many so-called fitters ignore are: ‘big end bolts are single use only’ and ‘never punch mark con rods and big end caps’.And this was the result of a machine shop welding an 80 year old con rod which had failed a crack test. IIRC I was told this let go at virtually tickover speed as traffic moved off downhill.
FFS. It’s a sad fact that 90% of welders reckon their welds are just as strong as parent material (and 100% of farmers know someone at least as good. Hi Pete LOL). The truth is that the fatigue life of any welded joint is an order of magnitude lower than that of parent material, even if done with the most fancy process, by a trained person. The only way to repair that conn rod would have been to smash it with the hammer, before it could find its way into an engine, and replace it with a new one.
Calling ZB Anorak…
A PM is on the way shortly about the last post.
Franglais:
Over revving an engine and getting the conrod to fail under tension is an example of your contention, denied by some, that tension is a significant force in design.
Let’s just say that the world’s scrap yards aren’t littered with blown up C18’s.
High engine speeds aren’t an issue in the case of an engine designed to produce as much power as possible at as low rpm as possible.
It’s the exact opposite in designing an engine which can withstand massive compressive loads to create torque at low engine speeds.Which means maximising leverage at the crankshaft.It’s a truck engine not an F1 engine.
I really dont know what this means but the last TL12s ran at 2000rpm and produced 860lbft , the Flexitorque
So would I be correct in assuming that most con rod failures are a result of tensile loads rather than compressive loads, at least the ones that fail at high rpm?
As to the question of why are head bolts and main bearing fastenings stronger, well logic tells me that like big and little end fastenings, size matters, to create the same clamping force on a larger area you either need more fastenings or stronger ones. Right or wrong?
