Leyland Marathon...The "Nearly" Truck of The 1970s?

UK PROFESSIONAL DRIVERS FORUMS OLD TIME LORRIES, COMPANIES AND DRIVERS (INTERACT
501

railstaff:

Carryfast:
Paccar states 1,850 lb/ft for the MX 13.Which just leaves the absolute mathematical certainty that using a longer lever at the crank to get it means less stress required through the piston to crank component chain.

How do you know what strain the components are under?Please enlighten me.Nearly every manufacturer has adopted steel pistons due to fuel pressure and cylinder pressure.Nearly every manufacture has adopted fractured conrods.Nearly every manufacturer is using grafite steel for the blocks.Scania must still have confidence as their offering 500hp with single cylinder heads.

It’s not rocket science using a longer lever has to mean less stress being applied through the piston,con rod,small and big ends for the equivalent torque output on the basis of force x distance.Which either means less expense in manufacture or a stronger engine or possibly a combination of both in the case of using more leverage to get the same result if not more.

502

railstaff:

Carryfast:

railstaff:
The D13 Volvo makes more torque than the MX for comparable power and with a shorter stroke.

MX 1800 lbsft 510hp

D13 1850 lbsft 500hp

Paccar states 1,850 lb/ft for the MX 13.Which just leaves the absolute mathematical certainty that using a longer lever at the crank to get it means less stress required through the piston to crank component chain.

How do you know what strain the components are under?Please enlighten me.Nearly every manufacturer has adopted steel pistons due to fuel pressure and cylinder pressure.Nearly every manufacture has adopted fractured conrods.Nearly every manufacturer is using grafite steel for the blocks.Scania must still have confidence as their offering 500hp with single cylinder heads.

To add to the absolute mathematical certainty of Railstaff’s post, a longer stroke causes higher centrifugal force in the con rod and higher acceleration loads in the little end at TDC. The failure mode in the crank and con rod is fatigue due to tensile stress. The second mathematical certainty is that CF is, once again, completely wrong.

503

[zb]
anorak:

railstaff:

Carryfast:

railstaff:
The D13 Volvo makes more torque than the MX for comparable power and with a shorter stroke.

MX 1800 lbsft 510hp

D13 1850 lbsft 500hp

Paccar states 1,850 lb/ft for the MX 13.Which just leaves the absolute mathematical certainty that using a longer lever at the crank to get it means less stress required through the piston to crank component chain.

How do you know what strain the components are under?Please enlighten me.Nearly every manufacturer has adopted steel pistons due to fuel pressure and cylinder pressure.Nearly every manufacture has adopted fractured conrods.Nearly every manufacturer is using grafite steel for the blocks.Scania must still have confidence as their offering 500hp with single cylinder heads.

To add to the absolute mathematical certainty of Railstaff’s post, a longer stroke causes higher centrifugal force in the con rod and higher acceleration loads in the little end at TDC. The failure mode in the crank and con rod is fatigue due to tensile stress. The second mathematical certainty is that CF is, once again, completely wrong.

The con rod is mostly tramsitting a downward vertical force from the piston to the crank during a power stroke with resulting compressive,inertial and shear loads not tension ?.The problem usually then being getting the rod length right to minimise those compressive,inertial and shear loads being applied especially between the piston and conrod relative to the crank when it’s halfway between TDC and BDC and during all the relevant changes of direction during a revolution ?.

Exactly what proportion of that overall loading would put the rod assembly under ‘tension’ and exactly when other than during the change in direction from exhaust to inlet stroke and compression to power stroke ?.

In either case that being far outweighed by compression and shear forces during the power stroke surely reduction of which being what increasing the leverage at the crank is all about.Or have I missed something. :confused:

504

[zb]
anorak:

railstaff:

Carryfast:

railstaff:
The D13 Volvo makes more torque than the MX for comparable power and with a shorter stroke.

MX 1800 lbsft 510hp

D13 1850 lbsft 500hp

Paccar states 1,850 lb/ft for the MX 13.Which just leaves the absolute mathematical certainty that using a longer lever at the crank to get it means less stress required through the piston to crank component chain.

How do you know what strain the components are under?Please enlighten me.Nearly every manufacturer has adopted steel pistons due to fuel pressure and cylinder pressure.Nearly every manufacture has adopted fractured conrods.Nearly every manufacturer is using grafite steel for the blocks.Scania must still have confidence as their offering 500hp with single cylinder heads.

To add to the absolute mathematical certainty of Railstaff’s post, a longer stroke causes higher centrifugal force in the con rod and higher acceleration loads in the little end at TDC. The failure mode in the crank and con rod is fatigue due to tensile stress. The second mathematical certainty is that CF is, once again, completely wrong.

You beat me to it,i was going to mention piston speeds with increase stroke lenth.Does ring lands no favours either probably why the TL12 was fitted with steel inserts on the piston lands.

505

railstaff:
You beat me to it,i was going to mention piston speeds with increase stroke lenth.Does ring lands no favours either probably why the TL12 was fitted with steel inserts on the piston lands.

I’d guess that piston speeds are a moot point when you compare the power output of something like a ■■■■■■■ NTA putting out more power at 1,500 rpm than a TL12 is putting out at 2,200 rpm.

506

Think about what is happening internally.

Longer stroke,the piston and rod has to travel a further distance for the same crank rotation.The inertia increases massively.The piston speed increases massively.

507

Carryfast:
The con rod is mostly tramsitting a downward vertical force from the piston to the crank during a power stroke with resulting compressive,inertial and shear loads not tension ?.The problem usually then being getting the rod length right to minimise those compressive,inertial and shear loads being applied especially between the piston and conrod relative to the crank when it’s halfway between TDC and BDC and during all the relevant changes of direction during a revolution ?.

Exactly what proportion of that overall loading would put the rod assembly under ‘tension’ and exactly when other than during the change in direction from exhaust to inlet stroke and compression to power stroke ?.

In either case that being far outweighed by compression and shear forces during the power stroke surely reduction of which being what increasing the leverage at the crank is all about.Or have I missed something. :confused:

Complete lack of reading/comprehension^^^.

508

railstaff:
Think about what is happening internally.

Longer stroke,the piston and rod has to travel a further distance for the same crank rotation.The inertia increases massively.The piston speed increases massively.

I’ve said what’s happening internally.Massive compressive,shear and inertial forces acting on the con rod during the power stroke.So we reduce that compressive loading by increasing leverage at the crank thereby also reducing the resulting shear forces and inertial forces as the rod changes direction through the power stroke and then slows down at BDC.I’d guess there might be few mathematical squares related to loadings and kinetic energy in those calculations too ?.But that’s all way above my pay grade. :wink: :laughing:

How does an around 6% increase in the stroke distance,combined with a more than 25% decrease in overall engine speed,to get the same power output,translate as a massive increase in piston/rod assembly speed ?. :confused: When the figures out there suggest 25 Feet per second for 152 mm stroke at 1,500 rpm v 34 feet per second for 142 mm at 2200.What price that ■■■■■■■ 370 NTA let alone ISX now ?. :wink:

While the best way to settle this argument would be for someone to give us a TL12 motor then subject it to enough boost to provide 70-80 lb/ft per litre at 1,500 rpm and see what happens to it on the dyno.It’s my guess that we’ll get a catastrophic rod failure which will at least be one boat anchor less. :bulb: :open_mouth: :smiling_imp: :laughing:

509

[zb]
anorak:
Complete lack of reading/comprehension^^^.

Great feel free to describe all the points when a con rod is under tension. :confused:

510

Carryfast:
the figures out there suggest 25 Feet per second for 152 mm stroke at 1,500 rpm v 34 feet per second for 142 mm at 2200.

Edit to add even the old small cam 335 is putting out the TL12’s peak power output at just 1,600 rpm which is still only 26.6 feet per second.

511

Carryfast:

[zb]
anorak:
Complete lack of reading/comprehension^^^.

Great feel free to describe all the points when a con rod is under tension. :confused:

Oh boy that ■■■■■.

512

Carryfast:

railstaff:

Carryfast:
Paccar states 1,850 lb/ft for the MX 13.Which just leaves the absolute mathematical certainty that using a longer lever at the crank to get it means less stress required through the piston to crank component chain.

How do you know what strain the components are under?Please enlighten me.Nearly every manufacturer has adopted steel pistons due to fuel pressure and cylinder pressure.Nearly every manufacture has adopted fractured conrods.Nearly every manufacturer is using grafite steel for the blocks.Scania must still have confidence as their offering 500hp with single cylinder heads.

It’s not rocket science using a longer lever has to mean less stress being applied through the piston,con rod,small and big ends for the equivalent torque output on the basis of force x distance.Which either means less expense in manufacture or a stronger engine or possibly a combination of both in the case of using more leverage to get the same result if not more.

Actually it is rocket science, at least on a basic level… percussive force , rapid acceleration, high temperatures. not melting … avoiding catastrophic failure, fulcrums, leavers, stress… and stopping. Most rockets have to go through all that sort of thing…even force times distance Of course rockets aren’t usually constrained in engine bores… I believe that most rocket scientists involved with propulsion would have to negotiate those sort of dilemmas…may be a bit different if you were on the navigation end of things …

I know a guy that worked for NASA… by his own admission he wasn’t smart enough to get into Formula 1…

Jeff…

513

cav551:

Carryfast:

[zb]
anorak:
Complete lack of reading/comprehension^^^.

Great feel free to describe all the points when a con rod is under tension. :confused:

Oh boy that ■■■■■.

At a certain advantageous engine speed, it probably would, a little bit, at least on a NA engine. :smiley:

514

Carryfast:

railstaff:
Think about what is happening internally.

Longer stroke,the piston and rod has to travel a further distance for the same crank rotation.The inertia increases massively.The piston speed increases massively.

I’ve said what’s happening internally.Massive compressive,shear and inertial forces acting on the con rod during the power stroke.So we reduce that compressive loading by increasing leverage at the crank thereby also reducing the resulting shear forces and inertial forces as the rod changes direction through the power stroke and then slows down at BDC.I’d guess there might be few mathematical squares related to loadings and kinetic energy in those calculations too ?.But that’s all way above my pay grade. :wink: :laughing:

How does an around 6% increase in the stroke distance,combined with a more than 25% decrease in overall engine speed,to get the same power output,translate as a massive increase in piston/rod assembly speed ?. :confused: When the figures out there suggest 25 Feet per second for 152 mm stroke at 1,500 rpm v 34 feet per second for 142 mm at 2200.What price that ■■■■■■■ 370 NTA let alone ISX now ?. :wink:

While the best way to settle this argument would be for someone to give us a TL12 motor then subject it to enough boost to provide 70-80 lb/ft per litre at 1,500 rpm and see what happens to it on the dyno.It’s my guess that we’ll get a catastrophic rod failure which will at least be one boat anchor less. :bulb: :open_mouth: :smiling_imp: :laughing:

Knowbody mention engine speed,we are now talking piston speed due to the stroke lenth.An example below,a single cylinder engine to keep it simple and short.This is theretical.

Both engines on a fast idle at 1500rpm.

Engine A-stroke lenth 6 inch.

Engine B-stroke length 5 inch.

The piston on engine A will travel faster in the bore,it has to because it has to cover more distance for the same amount of crank rotation.FACT.Due to this the small end gets a harder life,as does rings,piston,excessive bore wear,clearences need to be larger for heat transfer,piston protrusion needs to be larger for stretch,this effects starting in extreme conditions.It goes on and on,you fix one design issue only to create another.Its whats known as a compromise.By your conclusion British Leyland engineers didn’t know this,honestly?

515

ramone:

railstaff:

Carryfast:

railstaff:
Thank god you didn’t work for British Leyland then.

To be fair that probably wasn’t the best reference to have on a CV if I’d have wanted to stay in the industry. :smiling_imp: :laughing:

While the DK and the MX obviously follow my logic.

On that note remind us what were the bore stroke dimensions which ■■■■■■■ chose for the ISX v N14.If I’ve read it right they chose to reduce the bore and increase the stroke ?.While I can obviously see the reasoning for that while the TL12 admirers would obviously have gone for vice versa.So what’s your view on that were ■■■■■■■ right or wrong. :unamused:

Again like shown in history manufactures draw greater power from smaller engines,but when they reach their limit you then see the return of the larger engine,volvo,scania,MAN have just released a 15 litre(D38),Iveco have a Cursor 16 in the wait.■■■■■■■ naturally progressed to ISX,but do we want to go back to the days of 8LXB,s were the back cylinders hang out of the cab.Sometimes its much easier and yes diserable to adjust the stroke instead of distrupting cylinder spacing.Things have to be made compact,additional coolers,these things are not toys anymore.

Off subject but Ive just bought a Volvo ex demo car and the biggest engine they now do is a 2.0 l 4 cyclinder 190 bhp .For the size of the car its quite fast they also do a 4 wheel drive version that rates at 235 bhp . The salesman said it was down to 2 young whizz kids that have come up with some new idea , I cant remember what it was though , all I know is its doing over 40 mpg and it`s no slouch

I’ve had one of these for 18 months now ramone; good luck.

My understanding is that there is nothing unique just turbo compound, lots of boost and high fuel pressures. The new 235 version however has a compressor which blows air into the turbo at low revs to virtually eliminate lag, so that is new and clever but only on the 235.

A very impressive engine when it works, I never get less than 50mpg even on a trip from Lancashire to Bavaria in 13 hours including tunnel time in other words nailed it dud 50.3 mpg, on the other hand it is currently booked in for it’s fifth unscheduled visit to the dealers.

516

Worried now im only getting 40mpg but then again its only done 7000 miles hopefully it will improve

517

railstaff:

Carryfast:

railstaff:
Think about what is happening internally.

Longer stroke,the piston and rod has to travel a further distance for the same crank rotation.The inertia increases massively.The piston speed increases massively.

I’ve said what’s happening internally.Massive compressive,shear and inertial forces acting on the con rod during the power stroke.So we reduce that compressive loading by increasing leverage at the crank thereby also reducing the resulting shear forces and inertial forces as the rod changes direction through the power stroke and then slows down at BDC.I’d guess there might be few mathematical squares related to loadings and kinetic energy in those calculations too ?.But that’s all way above my pay grade. :wink: :laughing:

How does an around 6% increase in the stroke distance,combined with a more than 25% decrease in overall engine speed,to get the same power output,translate as a massive increase in piston/rod assembly speed ?. :confused: When the figures out there suggest 25 Feet per second for 152 mm stroke at 1,500 rpm v 34 feet per second for 142 mm at 2200.What price that ■■■■■■■ 370 NTA let alone ISX now ?. :wink:

While the best way to settle this argument would be for someone to give us a TL12 motor then subject it to enough boost to provide 70-80 lb/ft per litre at 1,500 rpm and see what happens to it on the dyno.It’s my guess that we’ll get a catastrophic rod failure which will at least be one boat anchor less. :bulb: :open_mouth: :smiling_imp: :laughing:

Knowbody mention engine speed,we are now talking piston speed due to the stroke lenth.An example below,a single cylinder engine to keep it simple and short.This is theretical.

Both engines on a fast idle at 1500rpm.

Engine A-stroke lenth 6 inch.

Engine B-stroke length 5 inch.

The piston on engine A will travel faster in the bore,it has to because it has to cover more distance for the same amount of crank rotation.FACT.Due to this the small end gets a harder life,as does rings,piston,excessive bore wear,clearences need to be larger for heat transfer,piston protrusion needs to be larger for stretch,this effects starting in extreme conditions.It goes on and on,you fix one design issue only to create another.Its whats known as a compromise.By your conclusion British Leyland engineers didn’t know this,honestly?

Did you read my previous posts.

Piston speed is related to the length of stroke ‘and’ engine speed.If you reduce the engine speed, for a given power output,by more than the increase in stroke,you get a ‘reduction’ in piston speed not an increase.While the increased leverage at the crank allows for more torque with less stress.More torque = more power for less engine speed.Usually to the point where the reduction in engine speed is greater than the increase in stroke.So I’ll do the figures again.

Engine A - ■■■■■■■ 335 280 hp at 1,600 rpm.Piston speed = 26.6 feet per second.

Engine B TL12 280 HP at 2200 rpm.Piston speed = 34 feet per second.

Let alone the same comparison with a 350 or a 320 Big Cam.

IE the ■■■■■■■ produces more ‘power’ for ‘less’,not more,piston speed. That being a function of its higher torque output at any given engine speed.Which is itself in large part a function of its longer stroke providing more leverage at the crank so more torque for a given force through the con rod. :unamused:

As I said it’s not rocket science.

Why would anyone want to fast idle the ■■■■■■■ at 1,500 rpm ?. :confused: Oh wait that’s the only selective example which would show any advantage for the TL12’s shorter stroke.However engines generally aren’t designed on the basis of a selective comparison of piston speeds at silly unrealistic idle speeds.They are designed for optimum efficiency and to stay together under load.The definition of ‘efficiency’ and ‘staying together’ in this case being which can produce the most power for the least engine speed.

518

Jelliot:
I know a guy that worked for NASA… by his own admission he wasn’t smart enough to get into Formula 1…

Jeff…

And the TL12 ( and AEC V8 ) is the result of what happens when F1 design practice is transferred to heavy truck engines.When both are designed on a totally opposing basis.

The former being the most power from a small capacity engine created by multiplying a low amount of torque by the highest possible engine speed.

The latter being vice versa.

519

cav551:

Carryfast:

[zb]
anorak:
Complete lack of reading/comprehension^^^.

Great feel free to describe all the points when a con rod is under tension. :confused:

Oh boy that ■■■■■.

I’ll word it better then maybe you can answer the question.In what way would increasing the stroke and therefore leverage at the crank have any major downside on any tensile loads.As opposed to beneficial effects of the increased leverage at the crank reducing compressive and shear loads,through the con rod,during the power stroke,for a given torque output.Bearing in mind that an increase in specific torque also generally means a net reduction in engine speed/piston speed for a given power output.

520

Carryfast:

railstaff:

Carryfast:

railstaff:
Think about what is happening internally.

Longer stroke,the piston and rod has to travel a further distance for the same crank rotation.The inertia increases massively.The piston speed increases massively.

I’ve said what’s happening internally.Massive compressive,shear and inertial forces acting on the con rod during the power stroke.So we reduce that compressive loading by increasing leverage at the crank thereby also reducing the resulting shear forces and inertial forces as the rod changes direction through the power stroke and then slows down at BDC.I’d guess there might be few mathematical squares related to loadings and kinetic energy in those calculations too ?.But that’s all way above my pay grade. :wink: :laughing:

How does an around 6% increase in the stroke distance,combined with a more than 25% decrease in overall engine speed,to get the same power output,translate as a massive increase in piston/rod assembly speed ?. :confused: When the figures out there suggest 25 Feet per second for 152 mm stroke at 1,500 rpm v 34 feet per second for 142 mm at 2200.What price that ■■■■■■■ 370 NTA let alone ISX now ?. :wink:

While the best way to settle this argument would be for someone to give us a TL12 motor then subject it to enough boost to provide 70-80 lb/ft per litre at 1,500 rpm and see what happens to it on the dyno.It’s my guess that we’ll get a catastrophic rod failure which will at least be one boat anchor less. :bulb: :open_mouth: :smiling_imp: :laughing:

Knowbody mention engine speed,we are now talking piston speed due to the stroke lenth.An example below,a single cylinder engine to keep it simple and short.This is theretical.

Both engines on a fast idle at 1500rpm.

Engine A-stroke lenth 6 inch.

Engine B-stroke length 5 inch.

The piston on engine A will travel faster in the bore,it has to because it has to cover more distance for the same amount of crank rotation.FACT.Due to this the small end gets a harder life,as does rings,piston,excessive bore wear,clearences need to be larger for heat transfer,piston protrusion needs to be larger for stretch,this effects starting in extreme conditions.It goes on and on,you fix one design issue only to create another.Its whats known as a compromise.By your conclusion British Leyland engineers didn’t know this,honestly?

Did you read my previous posts.

Piston speed is related to the length of stroke ‘and’ engine speed.If you reduce the engine speed, for a given power output,by more than the increase in stroke,you get a ‘reduction’ in piston speed not an increase.While the increased leverage at the crank allows for more torque with less stress.More torque = more power for less engine speed.Usually to the point where the reduction in engine speed is greater than the increase in stroke.So I’ll do the figures again.

Engine A - ■■■■■■■ 335 280 hp at 1,600 rpm.Piston speed = 26.6 feet per second.

Engine B TL12 280 HP at 2200 rpm.Piston speed = 34 feet per second.

Let alone the same comparison with a 350 or a 320 Big Cam.

IE the ■■■■■■■ produces more ‘power’ for ‘less’,not more,piston speed. That being a function of its higher torque output at any given engine speed.Which is itself in large part a function of its longer stroke providing more leverage at the crank so more torque for a given force through the con rod. :unamused:

As I said it’s not rocket science.

Why would anyone want to fast idle the ■■■■■■■ at 1,500 rpm ?. :confused: Oh wait that’s the only selective example which would show any advantage for the TL12’s shorter stroke.However engines generally aren’t designed on the basis of a selective comparison of piston speeds at silly unrealistic idle speeds.They are designed for optimum efficiency and to stay together under load.The definition of ‘efficiency’ and ‘staying together’ in this case being which can produce the most power for the least engine speed.

Can you read for starters?

If you can try reading a basic book on engine design and principles.

It was a theretical example which is FACT,ive not made it up.

I choose to keep the engine speeds the same for comparison reasons.Knowbody else as yet has questioned it but you,the majority seem to be happy with the theory.It is FACT.

Anybody who has any serious engine experience will understand what a fast idle refers to,if you care to look at ■■■■■■■ product care you will see it refered to quite often,mainly during the warm up procedures.Any engine speed over idle is refered to as a fast idle.

Just to clear up any misconceptions of a PT fuel pump running at 1500rpm steady and not running on to the governor,that is made possible by the VS and top throttle portion of the fuel pump.

Why do you continue to move the goal posts?